MARYLAND DEPARTMENT OF THE ENVIRONMENT " '..".;,;..;:"··~><":,:;;=;;~.:o:2: - 1800 Washington Boulevard. Baltimore MD 21230 MDE 410-537-3000. 1-800-633-6101

Martin O'Malley Shari T. Wilson Governor Secretary

Anthony G. Brown Robert M. Summers, Ph.D. Lieutenant Governor Deputy Secretary

July 7, 2009

Commander US Army Garrison, Aberdeen Proving Ground ATTN: IMNE-APG-SHE-R/ Ms. Cindy Powels Building E5771 Magnolia Road Aberdeen Proving Ground, MD 21010-5401

RE: Final Record of Decision for the New O-Field Site, U.S. Army Garrison, Aberdeen Proving Ground, Maryland, June 2009

Dear Ms. Powels:

The Federal Facilities Division (FFD) of the Maryland Department of the Environment's Hazardous Waste Program has reviewed the referenced document. The FFD's review also included historical records, the administrative record for the New O-Field site, including the 2009 Proposed Plan and the appropriateness of the conditional variance per COMAR 26.04.07.26 as discussed in our letter dated July 15,2008.

Based on this review the FFD finds that the New O-Field site presents unique conditions which justify the use of the variance provision in COMAR 26.04.07.26. Further the FFD finds that conditions i, ii, and iii of our letter dated July 15, 2008 are adequately addressed in the referenced document. Consequently, the FFD supports the Army's remedial decision.

The FFD encourages both the U.S. Army and the U.S. Environmental Protection Agency to move forward expeditiously on this project once all parties have signed this Record of Decision. If you have any questions, please contact me at (410) 537-3475.

i erely

-z# Jo FairbanK, Chief ~ Federal Facilities Division

JF:jf

cc: Mr. Ken Stachiw Mr. Frank Vavra Mr. Horacio Tablada Mr. Harold L. Dye, Jr.

-, Recycled Papcc www.mde.state.md.us TTY Users 1-800-735-2258 Via Maryland Relay Service

`

EA Engineering, Science and Technology Mid-Atlantic Region 15 Loveton Circle Sparks, Maryland 21152 Telephone: (410) 771-4950 Fax: (410) 771-4204

10 August 2009

Cindy Powels Installation Restoration Program ATTN: STEAP-SH-ER Aberdeen Proving Ground, Maryland 21010

Re: Record of Decision for Army Environmental Database-Restoration (AEDB-R) Site EAOF04: O-Field Study Area Operable Unit 4: New O-Field Groundwater and Source Area and Other O-Field Areas (OOA)

Dear Ms. Powels:

Please find enclosed for your records the final document “Record of Decision for Army Environmental Database-Restoration (AEDB-R) Site EAOF04: O-Field Study Area Operable Unit 4: New O-Field Groundwater and Source Area and Other O-Field Areas (OOA).” The subject document has been signed by EPA and AEC and has received concurrence from MDE and the APG Garrison.

Per our discussion, copies are being sent to the individuals below for final review and signature. Should you have any questions or comments regarding this document, please do not hesitate to call me at (410) 771-4950.

Sincerely,

Michael C. Ciarlo Project Manager

Enclosure

cc: Frank Vavra, EPA (3 copies and 1 disk with PDF) Douglas Scarborough, AEC (1 copy and 1 disk with PDF) John Fairbank, MDE (1 copy) Cindy Powels (2 copies and 1 disk with PDF)

O-FIELD STUDY AREA

Record of Decision for Army Environmental Database­Restoration (AEDB-R) Site EAOF04: O-Field Study Area Operable Unit 4: New O-Field Groundwater and Source Area and Other O-Field Areas (OOA)

Final July 2009

u.s. Army Garrison Aberdeen Proving Ground, Maryland

DISTRIBUTION RESTRICTION STATEMENT APPROVED FOR PUBUC RELEASE: DISTRIBUTION IS UNUMITED. #9752-A-l

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CONTENTS

LIST OF FIGURES iii LIST OF TABLES iv LIST OF ACRONYMS AND ABBREVIATIONS v

I. DECLARATION 1

1.1 SITE NAME AND LOCATION 1

1.2 STATEMENT OF BASIS AND PURPOSE I

1.3 ASSESSMENT OF THE NEW O-FIELD AND OTHER O-FIELD AREAS SITE I

1.4 DESCRIPTION OF THE SELECTED REMEDIES 2

1.5 STATUTORY DETERMINATIONS 3

1.6 DATA CEIlTIFICATION CHECKLIST 4

1.7 AUTHORIZING SIGNATURES 4

2. THE DECISION SUMMARY 5

2.1 SITE NAME, LOCATION, AND DESCRiPTION 5

2.1.1 NEW O-FIELD SOURCE AREA AND GROUNDWATER 5

2.1.2 OTHER O-FIELD AREAS 7

2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES 7

2.3 COMMUNITY PARTICIPATlON 8

2.4 SCOPE AND ROLE OF RESPONSE ACTION 9

2.5 SITE CHARACTERiSTICS 10

2.5.1 NEW O-FIELD GROUNDWATER AND SOURCE AREA 11 2.5.2 OTHER O-FIELD AREAS 14

2.6 CURRENT AND POTENTIAL FUTURE SITE AND RESOURCE USES 14

2.7 SUMMARY OF SITE RiSKS 15

2.7.1 HUMAN HEALTH RISK ASSESSMENT 16

2.7.2 ECOLOGICAL RISK ASSESSMENT 23

2.7.3 BASIS FOR ACTION 26

2.8 REMEDIAL ACTION OB,JECTIVES 28

2.9 DESCRIPTION OF ALTERNATIVES 30

2.9.1 NEW O-FIELD 30

2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES 42

2.10.1 NEW O-FIELD GROUNDWATER AND SOURCE AREA 43

2.11 PRINCIPAL THREAT WASTES 49

2.12 SELECTED REMEDIES 49

2.12.1 NEW O-FIELD GROUNDWATER AND SOURCE AREA 49

2.12.2 OTHER O-FIELD AREAS 57

2.13 STATUTORY DETERMINATIONS 62

2.13.1 PROTECTION OF HUMAN HEALTII AND THE ENVIRONMENT 62

2.13.2 COMPLIANCE WITH ApPLICABLE OR RELEVANT AND ApPROPRIATE

REQUIREMENTS 63

2.13.3 COST EFFECTIVENESS 69

2.13.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE

TREATMENT TECHNOLOGIES (OR RESOURCE RECOVERY

TECHNOLOGIES) TO THE MAXIMUM EXTENT PRACTICABLE 70

2.13.5 PREFEnENcE Fon TnEATMENT AS A PnINCII'AL ELEMENT 70

2.13.6 FIVE-YEAR REVIEW REQUIREMENTS 70 2.14 DOCUMENTATION OF SIGNIFICA T CHANGES FROM PREFERRED ALTER ATIVE IN

THE PROPOSED PLAN 70 3. RESPONSIVENESS SUMMARy 71

3.1 OVERViEW 71 3.2 BACKGROUND AND COMMUNITY I 'VOLVEMENT 71 3.3 SUMMARY OF COMMENTS RECEIVED DURING THE P DUC COMMENT PERIOD AND

AGENCY RESPONSES 72 3.3.1 COMMENTS mOM THE P DUC MEETING 72 3.3.2 COMMENTS mOM THE QUESTIONNAIRE 1 CLUDED WITH THE FACT

SHEET 74 4. REFERENCES 77

APPENDIX A: SAMPLE NEWSPAPER NOTICE ANNOUNCING THE PUBLIC COMMENT PERIOD AND PUBLIC MEETlNG

APPENDIX B: MARYLAND DEPARTMENT OF THE ENVIRONMENT RESPONSE TO VARIANCE I~EQUEST FOR NEW O-FIELD REMEDY

II

Number

2

3

4

5

6

7

LIST OF FIGURES

Title

Aberdeen Proving Ground and vicinity

O-Field location map

O-Field Study Area Operable Units

New O-Ficld disposal features

Other O-Field OU4 sample locations

New O-Field Remedial Design

New O-Field and the OOA Land Use Control boundaries

III

LIST OF TABLES

Number

Conceptual Site Model- New O-Field

2 Risk Summary for Primary COCs Contributing to Cancer and Non-Cancer Hazards for the New O-Field

3 Chemicals of Concem for Ecological Receptors

4 Comparative Analysis Summary of Remedial Alternatives, New O-Field

5 Temporary Criteria Used to Evaluate Establishment of Site-Speci fic Criteria

Remedy Effectivencss Prior to

6 Cost Summary for Alternative 8: Pel111eable Cover, Bio-Beneficial Sediment Cover, and Groundwater Bio-Enhancement with Wetland Buffer

7 New O-Field Action Specific/Location Specific Federal and State ARARs

IV

AA APG APGSCC ARAR AWQC

BERA BTAG

CERCLA CFR cm/sec COC COMAR CSF CWM DCE DNT

EA EPC ERA

FFA FS ft ft'

HEAST HHRA HI HQ

111.

IRIS

LDR LUC

MCL MDE mg/kg mglkg-bw/day

LIST OF ACRONYMS AND ABBREVIATIONS

Aberdeen Area Aberdeen Proving Ground APG Superflmd Citizens Coalition Applicable or Relevant and Appropriate Requirement Ambient Water Quality Criteria

Baseline Ecological Risk Assessment Biological Technical Assistance Group

Comprehensive Environmental Response, Compensation, and Liability Act Code of Federal Regulations Centimeter(s) Per Second Contaminant of Concern Code of Maryland Regulations Cancer Slope Factor Chemical Warfare Material Dichloroethene Dinitrotoluene

EA Engineering, Science, and Technology, Inc. Exposure Point Concentration Ecological Risk Assessment

Federal Facility Agreement Feasibility Study Foot or Feet Square Foot or Square Feet

Health Effects Assessment Summary Table Human Health Risk Assessment Hazard Index Hazard Quotient

Inch(es) Integrated Risk Infonnation System

Land Disposal Restriction Land Use Control

Maximum Contaminant Level Maryland Department of the Environment Milligram(s) Per Kilogram Milligram(s) Per Kilogram Body Weight Per Day

v

NCEA NCP NOAEL

O&M OAA OSHA

PAH PCB PJU ppm

RAB RBC RCRA RFA RID RG RAO RI RME ROD

SARA SEP SVOC

TAL TBC TCE TCl TRV

UE flg/dL UPL U.S. USEPA UU UXO

VOC WP XRF

LIST OF ACRONYMS AND ABBREVIATIONS (continued)

National Center for Environmental Assessment National Oil and Hazardous Substances Pollution Contingency Plan No Observed Adverse Effects level

Operation and Maintenance Other Aberdeen Areas Occupational Safety and Health Administration

Polycycl ic Aromatic Hydrocarbon Polychlorinated Biphenyl Permeable Infiltration Unit Partes) Per Million

Restoration Advisory Board Risk-Based Concentration Resource Conservation and Recovery Act RCRA Facility Assessment Reference Dose Remediation Goal Remedial Action Objective Remedial Investigation Reasonable Maximum Exposure Record of Decision

Superfund Amendments and Reauthorization Act Sequential Extraction Proccdure Semivolatile Organic Compound

Target Analyte List To Be Considered Trichloroethene Target Compound list Toxicity Reference Value

Unrestricted Exposure Microgram(s) Per Deciliter Upper Prediction limit United States U.S. Environmental Protection Agency Unlimited Use Unexploded Ordnance

Volatile Organic Compound White Phosphorus X-Ray Fluorescence

VI

I. DECLARATION

1.1 SITE NAME AND LOCATION

O-Field Snldy Area Operable Unit (OU) 4 (EPA OU-38), located in the Edgewood Area of Aberdeen Proving Ground (APG), Maryland, requires remedial action under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) to address contaminated soil, sediment, surface water, and groundwater. OU4 is comprised of the New O-Field Source Area and Groundwater (New a-Field) and Other a-Field Areas (OOA). a-Field Study Area OU4 is Anny Environmental Database-Restoration (AEDB-R) Site EAOF04.

1.2 STATEME T OF BASIS AND PURPOSE

This Record of Decision (ROD) prescnts the Selected Remedy addressing a-Field Operable Unit (aU) 4: New a-Field and the OOA. New a-Field requires remedial action and the OOA site requires Land Use Controls (LUCs), preventing funlre residential land usc, elemcntary and secondary schools, child care facilities, and playgrounds. The remedial action sclected for New a-Field was chosen in accordance with CERCLA, as amended by the Superfund Amendments and Reauthorization Act (SARA), and to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). The infonnation supporting thc decisions on the Selected Remedy is contained in the administrative record for APG.

The OOA site does not require further response action based on a reasonably anticipated industrial/military exposure scenario; however, to SUpp0l1 the reasonably anticipated future use of the site for industrial/military purposes, and to reduce the potential for future risks, a use restriction will be implementcd by the Installation at this site to prohibit future residential land use, elementary and secondary schools, child care facilities, and playgrounds.

The United States (U.S.) Department of the Anny (site owner) is thc lead agency for New a­Field and the OOA. The Army and the U.S. Environmental Protection Agency (USEPA) are issuing this ROD selecting the remedial actions for New a-Field and the OOA. These actions have been coordinated with the Statc of Maryland, represented by the Maryland Department of the Environment (MOE), who concurs with the Selectcd Remedies. USEPA and MOE support the Selected Remedics as nccessary to adequately and cost effectively protect human health and the environment.

1.3 ASSESS 1ENT OF THE lEW O-fIELD A 'D OTHER a-fIELD AREAS SITE

The response actions selected in this ROD are necessary to protect the public health or welfare or the cnvironment from actual or threatened releases of hazardous substances into the environment.

1.4 DESCRIPTION OF THE SELECTED REMEDIES

New O-Field The soil, sediment, surfacc water and groundwater at New O-Field have been impacted by site­specific contaminants, which resulted from buried materials and chemical agents. ln conjunction with previous characterization efforts, tlle results of the Data Evaluation and Risk Characterization (EA 2007), Rl Report for the O-Field Study Area (IT 2002), Addendum to the RI Report for the O-Field Study Area (GP 2007), New O-Field Groundwater Evaluation: Assessment of Natural Attenuation (Shaw 2004), and ecological risk management presented in the Feasibility Study (GP/EA, 2008) were used to delineate areas impacted by the contaminants of conceJ11 (COCs). The COCs identified are as follows:

• New O-Field Soil: Arsenic, cadmium, cluomium, copper, lead, mercury, silver, zinc and dioxins for terrestrial wildlife.

• New O-Field Sediment: White phosphorus hazard for waterfowl and cationic metals for benthos.

• New O-Field Groundwater in Seeps/Surface Water: Chlorinated VOCs and cationic metals (primarily zinc) for aquatic organisms.

These COCs are considered to be a threat to the environment. There are principal threats at the site to human health and the environment from direct exposure to shallow buried chemical warfare material (CWM) and other waste materials. A Feasibility Study was developed to evaluate the remedial alternatives as discussed in this document in order to address the impacted soil, sediment, surface water and groundwater at the site.

The selected remedy presented in the FS and proposed plan for New O-Field Source Area and Groundwater was Alternative 8 - Permeable Cover, Bio-Beneficia] Sediment Cover, and Groundwater Bio-Enhancement Barrier with Wetland Buffer, which is intended to prevent unacceptable human or ecological exposure to contaminants and to prevent migration of contaminants in soils and from waste at New O-Field by:

• Installation ofa 1.6 acre 2 foot (ft) thick permeable soil/sand cover over the trenches and the WP-contaminated soil generated during the Pushout Area Removal Actions (to include permeable geotextile fabric, a minimum of 18 inches (in.) of clean soil, 6 in. of topsoil, and vegetation);

• Placement of a vegetated bio-beneficial sediment cover over the bottom of the open water of thc pond composed of sand or soil amended with a carbon source such as topsoil, chitin (shrimp or crab shell), or compost placed in lifts to minimize mixing with underlying scdiment (may also include a surface layer of gravel or stone to armor against erosion, or an underlying layer of permeable geotextile to prevent mixing);

• Installation of an in-situ bio-enhancement barrier system to address VOC contamination in groundwater by using wells in the area for injection of nutrients and microbes directly downgradient from the trenches and potentially along the entire depth of the aquifer to the underlying clay layer;

• As part of the in-situ bioenhancement ban·ier, filling of a groundwater-filled depression

2

in the treatment area with limestone to aid in controlling pH and provide a centralized point for extraction;

• Construction of a vegetated wetland buffer composed of sand or soil amended WitJl organic carbon would include installation of a 25 ft barrier 400 ft along tJle shoreline of the open water of the pond, encompassing approximately v.. acre;

• As needed, coir fiber logs will be placed between the wetland buffer and the open water to help armor and stabilize the wetland;

• Implementation of Land Use Controls (LUCs) for New O-Field that, to reduce the potential for future risks, maintain the future land use as military/industrial and prevent future residential land use (i.e. housing, elementary and sccondary schools, child care facilities, and playgrounds) as long as chemical concentrations remain elevated above levels that allow for unlimited use (UU) and unrestricted exposure (UE);

• Implementation of additional LUCs for New O-Field that would prevent digging, groundwater use or other activities in the area of the covers, buffer or groundwater treatment area that are incompatible with remedy effectiveness as long as chemical concentrations rcmain elevated above levels that allow for UU and UE;

• Long-tenn groundwater monitoring (4 monitoring wells would be installed for performance monitoring with 2 sampling events in the first year) and surface water monitoring;

• Long-term O&M of the permeable cover, wetland buffer, bio-beneficial scdiment cover, and groundwater treatment systems; and,

• Five-year reviews for 30 years.

OOA In conjunction with previous characterization effons, the results of the Data Evaluation and Risk Characterization (EA 2007), R1 Report for the O-Field Study Area (IT 2002), Addendum to the RI Rcport for the O-Field Study Area (GP 2007), New O-Field Groundwater Evaluation: Assessment of Natural Attenuation (Shaw 2004) reports were used to delineate areas impacted by the contaminants of concern (COCs). The R1 addendum concluded that there were no potential risks to humans or ecological receptors. However, the area may contain scattered UXO and CWM and is in close proximity to both the Old O-Field and New O-Field sites.

The selected remedy presented in the FS and the proposed plan for the OOAs was LUCs. To reduce the potential for future risks, LUCs will be implemented to maintain the future land use as military/industrial and prevent future residential land usc (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds), including utilization of groundwater as drinking water, as long as chemical concentrations remain elevated above levels that allow for unlimited use and unrestricted exposure.

1.5 STATUTORY DETERMINATIONS

The remedies mect the rcquirements of CERCLA Section 121 and, to the extent practicable, the NCP. The Selected Remedy is protective of human health and the environment, complies with Federal and State requircments that are legally applicable or relevant and appropriate to the remedial action, is cost effective, and utilizes permanent solutions to the maximum extent practicable. The Selected Remedy employs treatment as one component of the overall remedy to

3

//..

reduce tOXICIty, mobility, or volume of hazardous substances, pollutants, or contaminants. Therefore, the Selected Remedy satisfies the statutory preference for remedies that employ treatment as a principal el~ment.

Since the primary source of contamination at the New O-Field and the OOA will remain in place with the activities conducted under the Selected Remedy, the site will still have residential use restrictions based on potential unacceptable residual risk for such use. Therefore, a CERCLA 121(0) 5-year review will be conducted for the New O-Field and the OOA in accordance with CERCLA to ensure that the remedies remain protective of human health and the environment.

1.6 DATA CERTIFICATION CHECKLIST

The following information is included in the Decision Summary section of this ROD. Additional information can be found in the Administrative Record file for OU 4: New O-Field Groundwater and Source Area and OAA.

• COCs and their respective concentrations (Section 2.5); • Baseline risk represented by the COCs (Section 2.7); • Remedial goals established for COCs and the basis for these goals (Section 2.8); • Principal threat presented by waste in the trenches (Section 2.11); • Current and reasonably anticipated future land use assumptions and current and

potential future beneficial uses of groundwater used in the baseline risk assessment (BRA) and ROD (section 2.6);

• Potential land and groundwater use available at the site as a result of the Selected Remedies (Section 2.12);

• Estimated capital, annual operation and maintenance (O&M), and total present worth costs, discount rate, and the number of years over which the remedy cost estimates are projected (Section 2.9 and Section 2.12); and

• Key factors that led to selecting the remedy (i.e., a description of how the Selected Remedy provides the best balance of tradeoffs with respect to the balancing and modifying criteria, highlighting criteria key to the decision) (Section 2.10, Section 2.12, and Section 2.13).

1.7 AUTHORIZING SIGNATURES

Maria R. Gervais Colonel, US Army Commanding, U.S. Army Environmental Command

a n Hodgkiss cting Director

Hazardous Site Cleanup Division U.S. Environmental Protection Agency, Region III

4

2. THE DECISION SUMMARY

2.1 SITE NAME, LOCATION, AND DESCRIPTION

The Army is the lead agency for OU4 (EPA OU-38): New O-Field and the OOA (EPA Site LD M02210020036), which is located in the Edgewood Area of APG. APG is located on the Chesapeake Bay, approximately 15 miles northeast of Baltimore, Maryland. APG covers approximately 72,000 acres (including water) of Harford and Baltimore counties (Figure 1). It is bordered to the east and south by the Chesapeake Bay; to the west by Gunpowder Falls State Park and residential areas; and to the nOlth by the towns of Edgewood, Magnolia, Aberdeen, and Perryman. The land surrounding APG is used for farming and industry, but also includes residential areas. Residential areas are predominantly new town houses and developments located in Harford County. The Bush River divides the Installation into two separate areas, the northern Aberdeen Area and the southern Edgewood Area. The Edgewood Area has been utilized by the Army as a center for research, development, testing, and manufacture of militaJy­related chemicals and chemical warfare agents since 19 J7 (U .S. ArnlY Toxic and Hazardous Materials Agency, 1983).

O-Field is located approximately 4 miles south of the Edgewood cantonment in a restricted access area of the Installation on the Gunpowder Neck Peninsula and occupies approximately 260 acres in the Edgewood Area of APG. The location of the O-Field Study Area is shown on Figure 2. O-Field is located in a restricted portion of the Installation. Access to the restricted aJ'ea is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical security counternleasures to include ban'ier systems, sensors and random patrols by law enforcement personnel are in place to prevent unauthorized access. For purposes of environmental investigation and restoration, O-Field was divided into the following four areas referred to as OUs:

• OU I: Old a-Field Groundwater; • OU2: Old a-Field Source Area; • OU3: Watson Creek; and • OU4: New O-Field Source Area and Groundwater and the OOA.

The scope of this ROD is OU4: New O-Field Source Area and Groundwater and the OOA. This site requires remedial action under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) to reduce risks to human health and the environment (GP 2008).

2.1.1 NEW O-FIELD SOURCE AREA AND GROUNDWATER

New a-Field occupies approximately 57 acres located east of Watson Creek Road between the road and Watson Creek (Figure 3). This area consists of an open field sun'ounded to the south, west and east by forest and to the north by a pond and the Watson Creek marsh. Previous disposal activities have impacted soil, sediment, surface water, and groundwater. The New 0­Field site was active from the 1950's through the late 1970's as a destruction, demilitarization, disposal, and training area. Burning operations were conducted in trenches in the notthern portion of the open field, and the burned material was pushed out into the marsh. Two burn

5

trenches remain uncovered. Disposal operations were conducted in 12 covered trenches now buried below a thin cover of soil (approximate locations shown in Figure 4). Ten of the covered trenches are located in the northem portion of the open field and were approximately 20 to 25 ft wide and ranged from 40 to 220 ft long (GP, 2008). Two other covercd trenches are located in the southem portion and were approximately 20 ft wide and 100 ft long (GP, 2008). The trenches are expected to be approximately 6 to 10 ft deep (GP 2008). Historical records indicate the possible presence of additional disposal activities in the northwest portion of the site; however, test pits and sampling have determined that this area does not contain a source of contamination (GP, 2008). Sample locations are presented on Figure 5. The wastes disposed at New O-Field were reported to include acids; research laboratory samples of CWM, including nerve agents; munitions and munition-related items; military clothing impregnated with hazardous compounds; animal carcasses; explosive material from the National Bureau of Standards; and shells filled with white phosphorus (WP), and incendiary compounds (GP, 2008).

As stated above, the trenches are expected to be approximately 6 to lOft deep. The depth to groundwater in much of the area of the trenches is approximately 5 ft but varies due to seasonal tluctuation. Also, liquid wastes that may leak out from any containers or munitions that con-ode and breach may sink and enter the water table. Therefore, the lower portion of the waste is expected to be in direct contact with the water table or buried below the water table, although it is not feasible to confirm this directly through excavation. This has resulted in elevated dissolved concentrations of chlorinated solvents, chemical agent degradation products, and sevcral metals in groundwater emanating !i·om the area of the buried trenches. The vast majority of this contamination is located in the top ten feet of the upper water-bearing unit and directly beneath or northeast of the trench area.

In 1997, an incidental fire in the New O-Field marsh revealed the presence of a large volume of debris in the push out area north and east of the trenches. This debris was identified as consisting of matcrial that had been pushed out of the burn trenches after burning/demilitarization. This material was identified as another potential source of chemicals. Based on preliminary surveys, history of disposal practices, and the fact that this material was largely burned or demilitarizcd, it was considered feasiblc to sample and excavate the debris in the pushout area, unlike the material buried in the trenchcs. A series of removal actions were conducted between 200 I and 2004 to remove the debris that had been pushed out into the marsh. The removal actions produced approximately 14,425 individual, non-reportable ordnance and explosive (OE) related items, 6,500 cubic yards (cy) of non-OE class waste such as ash, soil, glass, metal, concrete, and miscellaneous waste; 1,500 tons concrete; 75 tons bulk steel; and, 526 reportable items (i.e. potential UXO). As paIl of the removal action, the material removed from the marsh was screened repeatedly to separate soil from debris and subsequently resulted in burn-off of particles of WP. This soil was stockpiled on-site and contains marginally elevated concentrations of metals; it may also contain minor residual amounts of WP, although this has not been detected in analytical samples. The removal actions also created a large excavated area of 3.6 acres, 2.2 acres of which is a man-made pond (Figure 4), and the remainder of which is a densely vegetated intermittently tlooded wetland. This pond intercepts groundwater from the upper unconfined water bearing unit in the form of visible groundwater seeps along the pond shoreline and in the form of cross-sectional advection along the remaining pond bottom. These

6

seeps likely contribute chemicals to surface water and residual chemical concenrrations have been detected in pond and marsh sediment.

2.1.2 OTHER O-FIELD AREAS

The Other O-Field Areas occupy approximately 67 acres west of Watson Creek Road between the road and the Gunpowder River (Figure 3). This area consists primarily of forest. Historical records indicated possible historic disposal activities in the portion of the site near the entrance to New O-Field; however, surveys and sampling have identified that this area does not contain significant contamination of environmental media (GP 2007; 2008). Historical environmental investigations at the OOA have included collection of soil, sediment, surface water, and ground water samples and performance of a geophysical survey (GP, 2007). Sample locations are presented on Figure 5. No significant sources of chemicals have been identified.

2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES

The New O-Field site was established as a demilitarization and disposal area for ordnance, equipment, and chemical warfare materiel which included chemical warfare agents, white phosphorus, chlorinated solvents and metals. New O-Field contains open and covered rrenches where waste was bumed and/or buried. This waste and past disposal practices have contributed chemicals to soil, groundwater, sediment, and surface water. The OOA site was included in the review and analysis because of its close proximity to the New O-Field site. These areas are expected to remain under military authority with long term monitoring being conducted onsite.

Historical environmental investigations at New O-Field and the OOA have included an initial remedial investigation and risk assessment conducted before 1997 (IT 2002); additional remedial investigation and risk assessment conducted after the marsh fire in 1997 (IT 2002); studies of the natural attenuation of chemicals in groundwater (Shaw 2004); risk assessment investigations (EA 2007) during which soil, sediment, surface water, seep water, and groundwater samples were collected (Figure 5); and a remedial investigation addendum and risk assessment and risk assessmeJ1l screening providing more specific focus on the OOA in 2007 (GP 2007). It should be noted that samples of sub urface soil, buried waste, and groundwater samples could not be collected directly from the area of the open and covered trenches at New O-Field due to the risks of explosion and chemical ageJ1l release associated with disturbing buried UXO or CWM. Information regarding the contents of these trenches is drawn from historical records, geophysical surveys, and the composition of chemical contamination and waste found in the areas immediately adjacent.

Nineteen RODs have been issued for the Edgewood Area, and specifically three have been issued for the O-Field Study Area. The first ROD issued for the O-Field Study Area was signed in 1991 for remedial action at OU I: Old O-Field Groundwater. The first interim ROD addressed groundwater at Old O-Field through downgradient extraction, rreatment, and discharge to surface water with the purpose of mitigating environmeJ1lal impacts associated with direct discharge of contaminated groundwater to Watson Creek. The second interim ROD issued for the O-Field Study Area was signed in 1994 for remedial action at OU2: Old O-Field Source Area. Thc second interim ROD addressed waste material in Old O-Field through constmction of a

7

Permeable Infiltration Unit (PJU). The PIU controls risks associated with unplanned detonations of UXO and exposure to CWM and other chemicals by covering the waste and allowing infiltration of rainwater. This infiltration of rainwater allows natural degradation processes to break down waste and decreases long term risks. Together, the PIU and O-Field Groundwater Treatment Facility (GWTF) address risks associated with Old O-Field. Pumping and treatment from the downgradient extraction system began in 1995, while construction of the PIU was completed in 1998. A third ROD for the O-Field Study Area was signed in I997for OU 3: Watson Creek. The third ROD provides for long-term monitoring in Watson Creek which began in 1998.

The following sections briefly describe historical operations and impacts to site media as a result of these operations at New O-Field and the OOA. The information presented for this site represents a compilation of previous site investigations. Detailed descriptions of site history, characteristics, and land use at New O-Field and the OOA are presented in the Data Evaluation and Risk Characterization for New O-Field (EA 2007), Addendum to the Remedial Investigation (GP 2007), the FS (GP 2008), Remedial Investigation (RI) Report (IT 2002), and the New 0­Field Groundwater Evaluation (Shaw 2004).

2.3 COMMUNITY PARTICIPATION

Community relations activities that have taken place at APG to date include monthly Restoration Advisory Board (RAB) meetings, APG Superfund Citizens Coalition (APGSCC) meetings, public meetings and site tours, as well as press releases, and public access to the APG website.

Administrative Record - Consistent with requirements of CERCLA Section 113(k), an Administrative Record containing information associated with CERCLA cleanup activities at APG is available to the public. The locations, contact information, and hours of operation for the Administrative Record file are as follows:

Harford County Library - Aberdeen Branch 21 Franklin Street Aberdeen, MD 2100 I (410) 273-5608 Hours: Monday, Tuesday, and Thursday lOam to 8 pm

Wednesday I pm to 8 pm Friday and Saturday lOam to 5 pm Sunday Closed (May - September only) Sunday I pm to 5 pm (October - April)

Harford County Library - Edgewood Branch 2205 Hanson Road Edgewood, MD 21040 (410) 612-1600 Hours: Monday, Tuesday, and Thursday lOam to 8 pm

Wednesday I pm to 8 pm Friday and Saturday lOam to 5 pm Sunday Closed

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Washington College Clifton M. Miller Library Kent County ChesteI1own, MD 21620 (410) 778-7280 Hours: Monday through Friday 8:30 am to 4:30 pm

Saturday Closed Sunday Closed

Mailing List - A mailing list of all interested parties in the community is maintained by APG and updated regularly.

Proposed Plan - The Proposed Plan (EA 2009) regarding the remedial actions for New O-Field was made available to the public for comments.

The Proposed Plan for the New O-Field and the OOA was made available to the public from 20 Febmary 2009 to 23 March 2009. It can be found in the Administrative Record file and the infollllation repository maintained at the USEPA Docket Room Region III and the libraries of Harford County and Kent County listed above. The notice of availability of the Proposed Plan was published in the newspaper, The Aegis, on 20 February 2009. Follow-up notices were also published in The Avenue on 25 February 2009, the Kent County News on 26 February 2009, the East County Times on 26 February 2009, and The Cecil County Whig on 20 February 2009.

A public meeting was held on 26 Febmary 2009 at 6:30 pm at Vitali's Restaurant and Banquets located at 1705 Edgewood Road and Route 24 in Edgewood, Maryland to present the Proposed Plan. At this meeting, representatives from the Army, USEPA, and MDE answered questions about problems at the site and the remedial alternatives. The Army and USEPA also used this meeting to solicit a wider cross-section of community input. Responses to comments received during this period are included in the Responsiveness Summary, which is included in Chapter 3 of this ROD.

2.4 SCOPE AND ROLE OF RESPONSE ACTION

The O-Field Study Area has been divided into four OUs to facilitate investigation under CERCLA. OU I: Old O-Field Groundwater consists of contaminated groundwater in the area of Old O-Field. For this OU, downgradient extraction of groundwater, treatment, and discharge to surface water is being conducted in accordance with an interim ROD signed in 1991 to mitigate environmental impacts associated with direct discharge of contaminated groundwater to Watson Creek. OU2: Old O-Field Source Area consists of the buried waste and munitions in the Old 0­Field landfill. Risks associated with these wastes were addressed through construction of the Permeable Infiltration Unit (PIU) in accordance with an interim ROD issued in 1994. The PIU controls risks associated with unplanned detonations of UXO and exposure to CWM and other chemicals by covering the waste and allowing infiltration of rainwater. This infiltration of rainwater allows natural degradation processes to break down waste and decreases long term risks. Together, the PIU addressing OU2 and groundwater treatment addressing OU 1 provide

9

complementary remedies for Old O-Field. These remedies involvc LUCs for the Old O-Field Area. A third ROD was signed in 1997; it was issued for the O-Field Study Area for OU 3: Watson Creek. The third ROD provides for long-term monitoring in Watson Creek which began in 1998.

This ROD describes the final remedy for OU4: New O-Field Groundwater and Source Area and the OOA; the extent of this OU and these sites are shown in Figure 3. The New O-Field portion of OU4 warrants remediation to address risks from chemicals of concern (COCs) and risks associated with buricd waste. The Selected Remedy for the New O-Field portion of OU4 includes installation of a pernleable cover, a bio-beneficial sediment cover, and a groundwater bio-enhancement barrier with wetland buffer. It also includes LUCs and long term monitoring and maintenance. This remedy protects human health and the environment by restricting and reducing exposure to COCs in soil, sediment, and surface water provided by the remedial components and LUCs. The remedy components also reduce contaminant migration. The remedy for New O-Field is compatible with the remedies for the other OUs of the O-Field Study Area. The components of the Selected Remedy for New O-Field prcvent migration of contaminants to the other OUs, and LUCs maintain land use consistent with that required by existing LUCs in the surrounding OUs.

OOA portion of OU4 does not wan·ant remedial action, because the RI addendum concluded that there were no potential risks to humans under industrial land use scenarios or ecological receptors. However, the area may contain scattered UXO and CWM and is in close proximity to both the Old O-Field and New O-Field sites. Residential land use would be incompatible with sun·ounding land use and it has been determined that LUCs will be employed at the OOA site. Adjacent sites such as Old O-Field and New O-Field will maintain military industrial land use controls due to elevated soil and groundwater concentrations and risk of chemical release. LUCs maintaining current land use/exposure conditions and preventing future residential land use (i.e., housing, elementary and secondary schools, child care facilities, and playgrounds) will be included as a component of the final remedy for the OOA site.

2.5 SITE CHARACTERISTICS

Ncw O-Field Groundwaler and Source Area and the OOA are located in restricted access areas of APG on the Gunpowder Neck Peninsula. Current and expccted future land use in these areas is military/industrial. The nearest residential land use is over 2 miles away across the Gunpowder River. The site characteristics are described separately below for the New O-Field Groundwater and Source Area and for the OOA.

Based on previous site investigations that havc becn performed at. the New O-Field and t.he OOA, it has been detennined that surface soil at. bot.h of t.he sites is impacted with site-specific COCs. The following discussion includes characteristics specific to each sit.e. Table I presents a concept.ual site model illust.rat.ing contaminant sources, release mechanisms, exposurc pathways, migration rout.es, and pot.ential human and ecological receptors at each sit.e.

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2.5.1 EW O-FIELD GROUNDWATER AND SO RCE AREA

The covered trench areas at New O-Field are relativcly flat and slope downward gradually from the southwest towards the pond and marsh (Figure 4). The area is periodically mowed and supports sparse grassy vegetation with several bare areas above the trenches. The open trenches range from approximately 6 to 8 ft deep and also slope towards the pond; they are unmowed and therefore overgrown with small trees. There is a 4 to 6 ft deep triangular depression between the covered trenches and the pond left from the removal action that contains water approximately I ft deep. The stockpiled soil remaining from the pushout area removal actions is staged in a large pile west of the trenches; the pile is approximately 135 ft x 155 ft with an average height of 12 ft (G P 2008).

The New O-Field pond covers approximately 2.2 acres of the 3.6 acre area that was excavated for the removal action. The primary source of water to the pond is expected to be groundwater discharge; however, it is also likely to share an interminent connection with Watson Creek and is therefore subject to tidal influence. The additional 1.4 acres of the former pushout area excavation southeast of the field are too shallow to support permanent standing water and have overgrown with reeds as a periodically flooded wetland. The marsh beyond the pond is a tidal marsh associated with Watson Creek that is also overgrown with reeds.

Groundwater at the site flows primarily to the north and the water table is very close to the surface. Its depth ranges from 5 ft below ground surface (bgs) in the southeast of the site to expression at the surface as groundwater seeps into the pond. Groundwater is expected to be in contact with the waste in the bonom of the trenches, although this cannot be confirmed directly due 10 hazards associated with excavation. Groundwater is present in both an upper water­bearing unit that ranges from 10 to 20 ft in thickness and a lower water bearing unit that ranges from I to 14 ft in thickness. At New O-Field, these units are separated by a layer of silty clay that is as thick as 5 ft in some areas but appears to be discontinuous in some areas. The confining layer below the lower water bearing unit is a continuous clay layer 43 to 55.5 ft thick (USGS 1991; IT 2002). The surficial aquifer is considered a Class liB aquifer by USEPA and a Type I aquifer by the State of Maryland. In accordance with EPA's assessment of the site hydrology, there is no useable aquifer at New O-Field. At New O-Field, shallow groundwater which contains elevated concentrations of volatile organic compounds (VOCs), CWM degradation products, and metals and which may receive inputs of other chemicals o'om buried waste flows a velY short distance from the trenches to the adjacent pond and the pond water flows a short distance through the marsh to Watson's Creek. Consequently, there is no land where a residential or production well could realistically be placed downgradient of the trenches due to their proximity to the adjoining pond, marsh, and Watson Creek. The groundwater requires treatment 10 ensure that discharge does not pose a risk to the ecological community through seeps.

II

S' -~~--- -- C- -- -- ----- - -- N O-Fiel -- ------ Other O-Field - -- - --­~- ~-- ~

Human Receptor and PlIthways Ecological Receptor Primary Primary Secondary Secondary Source Release Source Release

Mechanism Mechanism Industrial Illegal Terrestrial Terrestrial Aquatic and Wildlife that Workers Trespassers Plants and Soil Wildlife Benthic Consume

(Dermal contact. (Denna! contact, Invertebrates (Ingestion of Organisms Aquatic dust/vapor dust/vapor (Direct contact) environmental (Direct contact, Organisms inhalation. inhalation, media and food ingestion) (Ingestion of incidental incidental items that have environmental ingestion) ingestion) accumulated medin and food

chemicals) items that have accumulated chemicals)

Nell' O-Field Gromu/II'(tfer alt(l Source Arca

Surface soil in the Trench Arca

and Stockpile Erosion and

runoff

Direct exposure

Sediment & Surface water

Direct Exposure

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

NONE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

Pond sedimcnt containing

residual Direct exposure

CURRENT & FUTURE

CURRENT & FUTURE

NONE NONE CURRENT &

FUTURE CURRENT &

FUTURE chemicals

Buried Waste and Subsurface

Soil

Leaching

Erosion

Groundwater

Soil/Sediment

Exposed waste on surface

Seeps to Surface Water Direct

exoosure Release of dust and

vapor to air

CURRENT & FUTURE

FUTURE

FUTURE

CURRENT & FUTURE

FUTURE

FUTURE

CURRENT & FUTURE

FUTURE

FUTURE

CURRENT & FUTURE

FUTURE

FUTURE

FUTURE

FUTURE

NONE

FUTURE

FUTURE

FUTURE

OIlier O-Field Arcas

Soil. Sediment. and Surface water (No Direct exposure

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE

CURRENT & FUTURE source

identified)

CURRENT & FUTURE" indicates that exposure pathway is potentially complete under both current use and future hypothetical use scenarios assuming no remediation. "FUTURE" indicates that exposure pathway is potentially complete under only future hypothetical use scenarios assuming no remediation. "NONE" indicates that there is no complete pathway under either current 01' future scenarios.

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Surface soil sampling was conducted in several rounds as part of the remedial investigation starting in 1992 and ending in 2004. Surface soil samples from thc open field, the trenches, and the forested areas of New O-Field confirmed the presence of elevated metals, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), polycyclic aromatic hydrocarbons (PAHs), pesticides, dioxins, and furans (GP 2008). The highest concentrations of metals, VOCs, SVOCs, PAHs, dioxins, and furans were all located in or near the area of the covered and open trenches; concentrations of several of these chemicals exceeded regulatory criteria. The highest concentrations of pesticides occurred near the marsh area; these concentrations are consistent with spraying and are not considered related to past disposal. There were also infrequent or sporadic detections of polychlorinated biphenyls (PCBs), the explosive pentaerythritoltetranitrate (PETN), and several CWM degradation products.

Sampling of the stockpiled soil pile revealed marginally elevated concentrations of metals and chemicals that are generally similar to or lower than those detected in the area of the disposal trenches. Analyses of these soil samples did not detect the presencc of WP, although it may bc present at minor, residual levels in the pile.

Groundwater sampling conducted from 1993 through 2002 confirmed that the groundwater at New O-Field contains elevated concentrations of VOCs, CWM degradation products, and metals. The highest concentrations occurred in the upper water-bearing unit downgradient from the area of the covered trenches in the direction of groundwater flow; there wcre a small number of sporadic, lower detections in the lower water bearing unit. The primary organic contaminants in groundwater are tetrachloroethene (PCE) and its daughter products [trichloroethene (TCE), dichloroethene (DCE), and vinyl chloride) located in the upper water bcaring unit. The highest detected PCE concentration of I000 ~lg!L is above the Maximum Contaminant Level (MCL) of 5.0 ug/L. Despite the elevated concentrations, the concentrations of VOCs appear to be decreasing over time due to natural attcnuation as documented in several snldies of New O-Ficld groundwater (Shaw 2004).

Data from sediment sampling is availablc from the marsh both before and after thc pushout area removal actions and from the pond and excavated marsh area. Sediment sampling was conducted in several rounds as part of the remedial invcstigation starting in 1992 and ending in 2004. The highest concentrations of metals and many other chemicals were detected in the marsh prior to thc removal action. After the removal action, thc highest concentrations of most metals, dioxins, pesticides, and VOCs were detected in pond sediment with sporadic additional detections found in the marsh and excavated areas. Low level concentrations of WP wcre also detected in the open water area of the pond. Toxicity tests were perfomled using pond sediment; these identificd low-sevcrity toxicity in the open water areas of the pond.

Surface watcr sampling was conducted in several rounds as part of the remedial investigation starting in 1992 and ending in 2004. Surface water sampling found elevated concentrations of VOCs, CWM degradation products, and metals. Many of the highest concentrations of VOCs and metals detected in pond water above regulatory screcning levcls were locatcd near the pond shoreline, northeast of the disposal trenches and in an area of suspected seeps. Toxicity testing using pond surface water found toxicity in the area of suspected seeps.

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2.5.2 OTHER a-FIELD AREAS

The majority of the OOA is forested land between Watson Creek Road and the Gunpowder River (Figure 3). Soil samples in the OOA contained low levels of YOCs, SVOCs, pesticides, and dioxins/furans; however, all of the detections were below industrial Risk-Based Concentrations (RBCs). Nine inorganics exceeded risk-based ecological screening levels for soil, but only one (copper) also exceeded reference background. Arsenic 5.6 mg/kg was detected above its industrial RBC (1.9 mg/kg), but it was below the Ecological Soil Screening Level (EcoSSL) for plants (18 mg/kg) and below reference background (maximum of 7.6 mg/kg). Gross alpha and gross beta were also slightly elevated in the soil samples, with maximum concentrations slightly above reference background concentrations (GP, 2008).

One surface water sample was collected from an ephemeral pond at OOA in 2004. Toluene was the only organic compound detected. This surface water sample was very turbid, requiring several filters to obtain a dissolved sample. The following total metals were detected above Biological Technical Assistance Group (BTAG) screening levels and reference background levels: aluminum, arsenic, barium, beryllium, cadmium, copper, iron, lead, vanadium, and zinc. However, all metals except copper were either non-detect, below screening levels, or within regional background reference levels in the filtered (i.e., dissolved) sample. Copper was detected at a low dissolved concentration slightly elevated above reference concentrations, and flagged as estimated below detection limits. This single exceedence was not considered indicative of a significant surface water source, especially given the small size of the pond (approximately';" acre) and the fact that it is ephemeral.

Groundwater sampling was conducted at select OOA monitoring wells in 1993, 1994, 1997, and 2004. No defined plumes were identified for the OOA, and detections of chemicals were considered sporadic isolated occurrences. Two SVOCs and two VOCs were found at low levels that were below the MCLs for those chemicals for which MCLs were available. Concentrations of several metals were detected in groundwater. Total concentrations of aluminum, cadmium, iron and manganese exceeded MCLs. However, dissolved aluminum, cadmium, and iron concentrations were within the range of regional reference concentrations in all samples. Concentrations of manganese were below regional reference concentrations in all but sample OF-81, where the concentration was 2230 Ilg/L, which exceeds the MCL of 866 'Ig/L. This single exceedence was not considered indicative of a significant groundwater source. It should be noted that groundwater discharges to a nearby surface water body. Installation of a water supply well in this area would draw surface water into the aquifer.

2.6 CURRENT AND POTENTIAL FUTURE SITE AND RESOURCE USES

Control of New O-Field Groundwater and Source Area and the OOA is expected to remain under military authority with continued land use for military training, operational range, and industrial activities for the foreseeable future; therefore, funlre residenrial development is highly unlikely for these sites.

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The current land use surrounding New O-Field and the OOA generally consists of military industrial areas which are anticipated to remain the same in the future. A restriction, which extends offshore approximately I mile into the Chesapeake Bay and thc Gunpowder River, is imposed on public recreation including, but not limited to, swimming, scuba diving, and docking or grounding a boat. The water bodies, marshes and upland areas arc also an important habitat for waterfowl, fish, and other wildlife species.

There are currently no drinking water wells at New O-Field and the OOA, and the groundwater is not in use. As discussed in Section 2.5.1 of this report, there is no useable aquifer at New 0­Field and there is no realistic placement for a well to be installed downgJ'adient of the trenches at New O-Field.

2.7 SUMMARY OF SITE RISKS

The following sections summarize the human health and ecological risk assessments perfonned for New O-Field and the OOA. The risk assessments estimate what risk the site poses and identify the contaminants and exposure pathways that need to be addressed by the response action.

The response action selected in this ROD is necessary to protect the public health or welfare or the environment from actual or threatened release of hazardous substances into the environment. Speci fic concerns for human health are future risks posed by potential release or migration of contaminants from buried waste at New O-Field. Specific concerns for wildlife are metals in soil, pond sediment, and surface water and WP in sediment.

The risk from potential releases at the site cannot be quantified because the buried waste cannot be directly characterized due to the risks of explosion or chemical agent release if the waste is disturbcd. Also, it has been estimated that the volume of impacted soil at New O-Field is approximately 20,000 ydJ and a thorough characterization of the full volume of waste would require substantial excavation and would incur costs potentially greater than the cost of remediation.

While chemical analytical data is not available for buried waste, data are available for soil, sediment, surfacc water, and groundwater in other portions of the site and were used to perform a human hcalth risk assessment (HHRA) and bascline ecological risk assessment (BERA). A baseline risk assessment was performed to characterize human health and ecological risks at New O-Field and to identify contaminants of concern. Because the remedial investigation was conducted in scveral phases, assessments were perfol1ncd in two separate rounds as updated data became available. In addition to the unquantified risks posed by the trenches, contamination already released to environmental media at New O-Field poses unacceptable and quantified risks to ecological receptors from copper, lead, and dioxins in soil; from a combination of metals and WP in pond sediments; and from chemicals in groundwater seeps.

There are no industrial use scenario human health risks for the OOA, and ecological risk screening identified no potential for unacceptable risks; LUCs will be established to ensure maintenance of current land use/exposure scenarios because of the risk posed by the potential for

15

buried UXO or CWM in the area and because residential land use would be incompatible with land use within the O-Field Smdy Area.

2.7.1 H MA HEALTH RISK ASSESSMENT

The purpose of an HHRA is to dctermine whether exposure to site-related contaminants would likely adversely affect human health. The focus of the human health risk assessment is on the potential human hcalth cffccts that could occur under current or potential funtre use scenarios in the event that contamination is not remcdiated. An HHRA is conductcd by performing a hazard assessmelll, exposure assessment, toxicity assessment, and risk characterization. Results are summarized in Table 2.

2.7.1.1 New O-Field Groulldwater alld SOl/rce Area

Two HHRAs were performed for New O-Field; thc second was performed to includc an updatcd data set after the 1997 tire and rc-sampling of the New O-Field marsh. Both asscssments were performed by evaluating potential exposure pathways, cxposure point conccntrations, and toxicity of the chemicals. Because thc rcmcdial investigation was conductcd in several phases, successive HHRAs were performed as updated data became available.

2.7.1.1.1 Identification ojCollfamilUlllts ojPotelltial COllce,."

The principal thrcat/risk to human health at Ncw O-Field is direct exposure to shallow buried CWM and other waste materials in thc trenches. The buried waste itself cannot be directly charactcrized (i.e. sampled) due to the risks of explosion or chemical agent release if the waste is disturbed; therefore, a quantitative risk evaluation is not possible. A thorough characterization of the full volume of waste would require substantial excavation, which is infcasible due to safety concerns and would entail costs that would likely exceed the cost of remediation. However, information regarding the contents of the trenches can be drawn from historical rccords, geophysical surveys, and the composition of chemical contamination and waste found in the arcas immediately adjacent to and downgradient of the trenches. Based on these data sources, thc trenches likely contain CWM, UXO, and sources of volatile organic compounds, metals, and chemical warfare agent degradation products. In the initial phases of both risk asscssments conducted for New O-Field, a screening comparison of contaminant conccntrations against USEPA Region Ill's industrial RBCs was performcd. Contaminants whosc conccntrations were above these scrcening values were maintained for further evaluation and were identi tied as COPCs. These COPCs were deternlincd to be antimony, arsenic, cadmium, chromium (III & VI), copper, lead, manganese, mcrcury, methylmercury, silver, vanadium, zinc, and dioxins.

The buried waste constinues an uncontrolled, uncharacterized sourcc of ongoing or potential rei case of chemicals to various environmental media. Such releasc poses an ongoing risk to human health and the environment in the future. Potential release of chemical agents and contamination could occur as a rcsult of inadvertent human activity, animal burrowing or natural crosion proccsses. Another potential release mcchanism is explosive relcase and dispersion of CWM. This is of greatest conccm whcn subsurface conditions arc dry. Dry conditions do not facilitate breakdown of munitions or agents, and allow the possible ignition of WP. Moist

16

conditions, caused by contact with groundwater or infiltration of precipitation, help decrease the likelihood and magnitude of a release by rusting and breaching munitions that would otherwise stay intact. Wet conditions also hydrolyze (break down) chemical warfare agents into relatively non-toxic forms, and prevent the ignition of WP, which may burn when it becomes dry.

Leaching into groundwater is also a primary release mechanism. As documented in the FS, the trenches are expected to be 6 10 lOft deep, and groundwater in the vicinity of the trenches is often present 5 ft below the ground surface. Therefore the bottom portion of buried waste is expected to be present in the water tahle, especially when it is considered that seasonal fluctuations in the groundwater table (estimated at 6.5 ft in magnitude) are high enough to cause more groundwater to enter into the bottom of the trenches. Also, liquid wastes leaking from any containers or munitions that corrode and breach may sink into the water table. However, in both assessments conducted for New O-Field, groundwater was eliminated as an exposure pathway due to i) the remoteness of the arca from residential or industrial area; ii) the fact that the surficial aquifer has a high iron and chloride content, which make it less suitable as potable water; and iii) the prescnce of UXO and the proximity to Old O-Field which would preclude development of the area. Therefore, in accordance with EPA's assessment of the site hydrology based on a review of site groundwater data, there is no useable aquifer at New O-Field. Shallow contaminated groundwater flows a very shon distance from the trenches to the adjacent pond and the pond watcr flows a short distance through the marsh to Watson's Creek. Consequently there is no land where a residential or production well could realistically be placed downgradient of the trenches due to their proximity to the adjoining pond, marsh, and Watson Creek.

2.7./.1.2 Exposure Assessmellt

In the exposurc assessment, the human population, or groups of individuals potentially exposed to site media (i.e., potential human reccptors) are characterized. Pathways applicable to potential receptors at the site are identified from thc many potential pathways of exposure. The COCs in relevant media (e.g., soi I, groundwater) are converted into systemic doses, taking into account rates of contact (e.g., ingestion rates) and absorption rates of different COCs. Thc magnitude, frequency, and duration of these exposures are then integrated to obtain estimates of daily doscs over a specified period of time (e.g., lifetime, activity-specific duration).

RcceplOrs are chosen based on current site use and on potential future use of the site. Potential receptors to be considered for the New O-Field site include a current/futurc site worker, future trespasser and future swimmer. Residential use of the site was not considered a possible scenario given the history of site use.

Thc COCs idcntified at Ncw O-Field were evaluated using modcls to calculate the amount of chemical ingcsted, inhaled, or dermally absorbed from soil, sediment, and surface water. These calculations were then used with toxicological data to estimate canccr and non-cancer risks. The first HHRA evaluated risks posed by current and future land-use exposure pathways with respect to exposure 10 contaminants at New O-Field to on-site workers, illegal trespassers, and adult swimmers in the Gunpowder River. The second HHRA evaluated current and future land­use exposure pathways to on-site workers and trespassers. Swimmers in the Gunpowder River

17

were not re-evaluated because there were no substantial changes to the data set from the first HHRA.

2.7.1.1.3 Toxicity Assessment

A human toxicity assessment was performed to evaluate whether exposure to specific contaminants may cause adverse effects, and to identitY specific numeric criteria that could be used to assess the impacts of such exposures.

For non-cancer endpoints, contaminant-specific reference doses (RIDs) were compiled fi'om the toxicity values from thc Integrated Risk inforn1ation System (IRIS) and from the Health Effects Assessment Summary Tables (HEAST). An RID is an estimate of the daily contaminant exposure to the human population (including sensitive subpopulations) that is likely to be without an appreciable risk of deleterious effects during a lifetime. The RID is used as a reference point for gauging the potential effects of site exposures. Usually, exposures that are less than the RID are not likely to be associated with adverse health effects.

For carcinogenic endpoints, cancer slope factors were derived from the results of human epidemiological studies or chJOnic animal bioassays. These slope factors relate cumulative exposures to the probability of developing cancer. Animal studies are conducted to detect possible adverse effects and used to create the 95% UCL slope of the dose-response curve. This curve is adjusted for humans using mathematical models and scaling to derive the slope factor for humans. The actual risks associated with exposures to potential carcinogens are unlikely to be higher than the risks calculated using a slope factor.

Among the selected COCs, dioxins were evaluated as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs), which are present in environmental media. Toxicity was evaluated based on the contaminant's toxicity relative to that of 2,3,7,8-TCDD, which has been shown to be the most potent member of the class of PCDDs/PCDFs. The concentration of each related chemical was multiplied by its 2,3,7,8-TCDD toxicity equivalency factor (TEF), and the sum of all the 2,3,7,8-TCDD equivalents was the 2,3,7,8-TCDD equivalent concentration, used as the PCDD/PCDF exposure point concentration in the RA.

Exposures to lead may cause adverse noncarcinogenic health effects; however, USEPA has not developed an RID for this chemical. Lead was selected as a chemical of concern in New O-Field surface soil and Gunpowder River surface water. For the evaluation of this chemical in surface soil, USEPA has developed an Uptake Biokinetic (UBK) Model to evaluate lead exposure for young children I to 6 years of age. Howevcr, because this model is not appropriate for the receptor of concern (i.e., adults) at this site, it could not be used in this RA. Instead, this assessment compares lead levels at New O-Field to regulatory guidance. USEPA (1994b) has established Soil Screening Levels (SSLs) of 400 mg/kg for residential sites, while 1,000 mg/kg is a screening level value that applies to industrial sites. These levels are used in the assessment to evaluate potential effects to workers and illegal trespassers at New O-Field.

18

In order to assess exposures to lead in surface water, lead concentrations were compared to US EPA's MCL for lead in residential and public drinking water, 15 IlgIL. The concentration 15 IlgfL has also been identified as the final cleanup level for lead in groundwater usable for drinking water at Supernll1d sites. Because this lead concentration was designed to be protcctive of individuals drinking water, it is reasonable to assume these levels would be highly protective of individuals incidentally ingesting surface water during infrequent swimming activities in the Gunpowder River.

Several carcinogenic PAHs (i.e., benzo(a)pyrene and dibenzo(a,h)anthracene) were selected for evaluation in the RA. Among the carcinogenic PAHs, only benzo(a)pyrene has a slope factor tJlat has been developed by USEPA. In order to assess exposures to the other PAHs, CSFs are derived by adjusting the toxicity criterion for benzo(a)pyrene with a TEF. The TEF used for each carcinogenic PAH is based on that compound's relative potency, as compared to the potency of bcnzo(a)pyrene. The TEF for dibenzo(a,h)anthracene (the only other carcinogenic PAH, besides benzo(a)pyrene, evaluated in the RA) of 1.0 was used to derive a slope factor for this carcinogenic PAH.

2.7././.4 Risk Characterization

A human health risk assessment was conducted to assess potential non-carcinogenic effects and cancer risks from various reccptor scenarios for surface soil, sediment, surface water and groundwater at New a-Field. These calculations were then used with toxicological data to estimate cancer and non-cancer risks. Cancer risks are expressed as an upper bound probability; for this site, I x 10.6, would mean that one in one million individuals could contract cancer due to exposure to the potential carcinogen under the specified exposure conditions. The upper-bound Iifetimc cxcess cancer risks derived in this report can be compared to USEPA's acceptable risk range for health protectiveness at Superfund sites of Ix 10-4 to I x 10.6 (USEPA, I990a). Non­cancer risks are measured as a "hazard index" (H I) in which the threshold level exists (H I = I) below which non-cancer health effects are no longer predicted. USEPA's Office of Solid Waste and Emergency Response (aSWER) (USEPA, 1991 b) issued a directive stating that where the cumulativc carcinogenic site risk to an individual based on RME for both current and future land-use is less than I x I0.4 and the non-carcinogenic hazard quotient is less than one, action generally is not warranted unless there are adverse environmental effects.

Onsite worker

The potential upper-bound Ii fetime excess canccr risk to an on-site worker who may ingest chemicals in surface soil at New a-Field is 4x I 0.6 This value is on the lower end of USEPA's acceptable risk range of Ix I 0-4 to Ix I0·6for human health protectivencss. The HI is less than one (6x I0.2) for chemicals exhibiting non-carcinogenic effects. This is bclow the tJlreshold valuc of 1.0, indicating that adverse effects associatcd with exposures to non-carcinogenic chemicals would not be expected to occur. The potential upper-bound lifetime excess cancer risk to an on­site worker who may absorb chemicals in surface soil through dermal contact at New a-Field is 3x I 0.5 This risk (primarily due to PCDDsfPCDFs) falls within US EPA's acceptable risk range of Ix I 0-4 to Ix 10·6for human health protectivencss. The Hl is less than one (4x I 0.1

) for

19

chemicals exhibiting non-carcinogenic effects, indicating that adverse non-carcinogenic effects would not be likely to occur.

An on-site worker may be exposed to chemicals in surface soil via a combination of pathways. Therefore, potential risks were evaluated for both incidental ingestion and dermal absorption exposure pathways combined. The maximum total cancer risks for an on-site worker who may ingest and be exposed to surface soil dermally is 3x I0-5 Therefore, the cumulative cancer risks to an on-site worker falls within USEPA's acceptable risk range of Ix I0-4 to Ix I0-6

Individual exposure pathways also were combined to estimate the total potential for non­carcinogenic effects to occur. The total non-cancer risks for an on-site workcr associated with the incidental ingestion and dermal absorption of soil shows that the cumulative Hl for each target organ is less than one. Therefore, adverse non-carcinogenic effects are not likely to result from the incidental ingestion and dermal absorption of surface soil.

The excess upper-bound lifetime cancer risk and HI were also calculated for an on-site worker for the incidental ingestion of and dermal contact with arsenic at Old O-Field and for arsenic and manganese in New O-Field surface soil. Although these metals were not detected above background concentrations, they were identified for evaluation based on comparison to USEPA Region III RBCs. For both incidental ingestion and dermal contact the excess upper-bound lifetime cancer risk is below USEPA's acceptable risk range of IxIO-4 to Ix10-6 Further, the I-n is less than one for non-carcinogenic effects.

Illegal Trespassers

The potential upper-bound lifetime excess cancer risks to illegal trespassers who may ingest chemicals in surface soil at New O-Field is 4x10-6 This value is on the lower end of US EPA's acceptable risk range of Ix I0-4 to Ix I0-6for human health protectiveness. The HI is less than one (5x I0-2

) for chemicals exhibiting non-carcinogenic effects. This is below the threshold value of 1.0, indicating that adverse effects associated with exposures to non-carcinogenic chemicals would not be expected to occur.

The potential upper-bound lifetime excess cancer risks to illegal trespassers who may absorb chemicals in surface soil through dermal contact at New O-Field is 4x I0-5 This risk (primarily due to PCDDsIPCDFs) falls within USEPA's acceptable risk range of Ix10-4 to Ixl0-6for human health protectiveness. The HI is less than one (5x I0. 1

) for chemicals exhibiting non-carcinogenic effects, indicating that adverse noncarcinogenic effects would not be likely to occur.

Individual exposure pathways also were combined to estimate the total potential for carcinogenic and non-carcinogenic effects to occur. The total cancer and non-cancer risks for an illegal trespasser associated with thc incidcntal ingestion and dermal absorption of chemical in soil and surface water shows that the cumulative HI for each target organ is less than one and that overall cancer risks are 4x10-5 (within USEPA's acceptable risk rangc). Therefore, adverse effects are not likely to result from the incidental ingestion and dermal absorption of surface soil from casual contact, or from incidental ingestion and dermal contact with chemicals in surfacc water while swimming.

20

The excess upper-bound lifetime cancer risk and HI for illegal trespassers were calculated for the incidental ingestion of and dermal contact with arsenic and manganese in New O-Field surface soil. Although these chemicals were not detected above background concentrations, they were selected for evaluation bascd on comparison to USEPA Region III RBCs. For both incidental ingestion and dermal contact thc excess upper-bound lifetime cancer risk is within USEPA's acceptable risk range of I x I0" to Ix 10.6 Further, the HI is less than one for noncarcinogenic effects.

Swimmer

Potential adverse noncancer effects were estimated for adults swimming in the Gunpowder River under future land-use conditions (because no carcinogens were selected for evaluation in Gunpowder River surface water, only noncancer effects were determined). The HIs for both incidental ingestion and dennal absorption of chemicals in surface were both less than one (3x I 0.2 for incidental ingestion and 7x I0.2 for dennal absorption), indicating that adverse noncarcinogenic effects associated with these pathways would not be expected to occur. An HI was also calculated for the incidental ingestion of manganese in surface water by an individual swimming in the Gunpowder River. Although not detected above background concentrations in Gunpowder River surface water, manganese was prescnt at concentrations exceeding its USEPA Region III drinking water RBC. The fact that concentrations are within background values indicates that adverse effects associated with ingestion of and delmal contact with manganese in surface water would not be associated with the site.

Exposure to Lead

Lead was detected in New O-Field surface soil at concentrations ranging from II to 993 mg!kg, with a 95% UCL concentration of 218 mg/kg. Botl1 the 95% UCL and the maximum concentration arc below the industrial soil screening Icad levels. Accordingly, it is reasonable to conelude that under the existing industrial use scenario concentrations of lead in the surface soil are unlikely to adversely affect on-site workers at the New O-Field study area. The industrial level of 1,000 mg/kg is a reasonable level to use to determine whether a potential exists for adverse effects due to lead exposures, as adult trespassers would be at the site on a very infrequent basis. It is reasonable to conelude, thereforc, that concentrations of lead in the surfacc soil are unlikely to affect illegal trcspassers at New O-Ficld. To assess the risk presented by lead in surface water, lead concentrations were compared to USEPA's MCL of 15 ~lg/L. The maximum concentration of lead in the Gunpowder River is 4 flg/L, which is much lower than USEPA's MCL, which is based on daily ingestion of water. It is, therefore, reasonable to coneludc that lead concentrations arc highly unlikely to adversely affect thc health of swimmers who incidentally ingest surfacc watcr.

Conclusions

The HHRAs concluded that for all media and cxposure pathways cvaluated in the HHRA, the total uppcr-bound exccss lifetimc cancer risk estimates were within USEPA's acceptable risk rangc for health protectivencss at CERCLA sites. The exposurc pathways evaluated did not

21

include residential use. The non-cancer His for all media and pathways were less than I, indicating that adverse effects are not likely to occur, and lead levels were within acceptable ranges. Therefore, there are no current or future risks based on the conccntrations currently present in exposure media. As discussed on Section 2.7, there are potential future risks associated with buried wastes should transport and exposure occur.

Uncertainties

As the buried waste at New O-field cannot be directly sampled, uncertainty exists as to the exact quantity of chemicals in the subsurface and how much may be transported to surface environments (EA 2007). Due to the uncertainty associated with the buried waste, there is also a level of unce'tainty with the human health risk assessment methodology. The methodology may undercstimate risks, and may result in the site having greater risks present than estimated.

2.7./.2 OIlier a-Field Areas

2.7./.2.1 Jdell/ijicalioll ofColl/amillanls ofConcern

For planning purposes, risks from exposure to soil under both a residential and industrial scenario werc evaluated. Soil data were evaluated through comparison to RBCs and risk ratio analysis. Risk ratio analysis is a precautionary screening level evaluation that evaluates whether risks require further evaluation. Based on risk ratios, the only chemical in soil that exceeded industrial soil RBCs was arsenic. The total cancer risk ratio was 2.95x I 0.6 There were no non­cancer COCs because all non-cancer COCs werc eliminated during screening; therefore, the total non-cancer risk ratio was zero. Since the total cancer risk ratio was below 5.0 x I 0.5 and total non-canccr risk ratio was below 0.5, which are the acceptable upper limits in risk ratio analysis', completion of a full HERA for industrial scenarios was unwan-anted, and no risk to human health was identified under industrial scenarios. A comparison to residential soil RBCs was also pcrformed for planning purposes. Six inorganics (aluminum, arsenic, chromium, iron, manganese, and vanadium) were sclected as COCs. Under a residential scenario, the total cancer risk ratio (assuming reasonable maximum exposure) was 1.30E-05 and the non-cancer risk ratio was 1.81. Since all six of these inorganics were within the rangc of reference background and land-use at the site is cxpected to remain industrial, completion of a full HHRA for residential use was unwarranted. It should be noted, however, that the data quality objectives for the OOA sampling and risk assessment were developed based on future military/industrial land use. The area may contain scattered UXO and CWM, and is surrounded by sites such as Old O-Field where LUCs maintaining military industrial land usc arc required due to elevated contaminant concentrations in soil and risk of chemical release.

2.7.1.2.2 Exposure Assessmenl

No complete pathways exist for exposures to groundwater in the OOA. OOA is located in a rcstricted downrangc area, and the planned fUl1tre use is designated industrial. Several metals were detected above MCLs in OOA groundwatcr samples. Aluminum, cadmium, iron, and manganesc were detected above MCLs in samples from groundwater wells; aluminum, beryl hum, chromium, iron, lead, magnesium, manganese, sodium, and thallium were detected

22

above MCLs in direct push technology groundwater samples. However, evaluation of groundwater data found that there was no plume of these metals. Also, the MCLs for aluminum and manganese are secondary MCLs affecting taste only. The closest water supply wells to the a-Field Study Area are located in H-Field, which is upgradient of OOA. Groundwater from the surficial aquifer discharges to the Gunpowder River, but sufficient mixing occurs that aquatic organisms are not impacted. Surface water west of Watson Creek Road is likely to be present only after rain events. For these reasons, groundwater and surface water were not evaluated in the OOA risk screening. Exceedence of screening level criteria for drinking water is considered in remedy selection for the OOA. In specific, LUCs will be implemented to maintain current land use/exposure conditions and prevent future residential exposure to groundwater and surface water at OOA (GP 2008).

2.7.2 ECOLOGICAL RISK ASSESS 1E T

2.7.2.1 New O-Field Source Arell lIlId Groulldwater

2.7.2.1.1 ldel/tificlItioll ofCOI/tamillllllts ofCol/cem

COCs were identified based on the results of the weight of evidence presented in the Baseline Ecological Risk Assessment (BERA). A variety of exposure point concentrations and scenarios were evaluated as part of this approach, including site maxima and site mean. The BERA identified site-wide risks from metals (arsenic and copper) and total dioxins in soil, modeled doses of which exceeded ecological benchmarks for wildlife. Table 3 presents the final list of COCs as developed in the BERA.

2.7.2.1.2 Exposure Assessmellt

As discussed above, data were not available for quantitative risk assessment for waste buried in the trenches. However, exposure to chemicals originating from the shallow buried CWM and other waste materials in the trenches is considered the principal threat/risk. Data were available for soil, sediment, surface water, and groundwater in other portions of the site and wcre used to perform the BERA.

The BERA is an eight-step process to characterize COC risks to identified receptors (EA 2007). The BERA assessed the potential for adverse effects on the survival, growth, and reproduction of a selected group of ecological receptors bascd on food web modeling and toxicological studies. Similar to the HHRA, ecological-based numeric criteria are used to identitY the ecological COCs. The focus of the BERA is on population level risks site-wide.

There is an additional threat to ecological receptors at New a-Field that was considered in the FS. This is the potential presence of particles of WP in pond sedimcnts. While concentrations of WP were relatively low and did not indicate a modeled potential for risk, there is a risk that waterfowl may consume individual particles of WP and experience acute toxicity. This risk was considered in developing remedial altematives.

23

Tablc 2 H uluan H ca t I h Risk summary or p'nmary cacs contributml! at New a-F'ICId

Tolal Contamiu::ant ConccntnlliOIlS Carcino~cnic Total Non~Cllrcinogcllic

hn!·/k Risk Risk

Total Risk

Mcdia Exposure

ROllte ConI. or Concern

Frequency

0' Detection Min. 1\Iax

Cancer Slope Factor

Across Exposure

Routes

Source (Target Or!!n'~)

Exposure Route Total

Oil-site Worker BCl1z0 (a) nvrcnc II/59 43 1900 7.3E+00 2.9E-O? NA NA Dibcnzo anthracene

(a,h) 2/59

120 610 7.3E+00 1.0E,07 NA NA J-1cxachlorobcnzc 7/49 47 7800 1.6£+00 3.9E-07 Liver 8,6[-04

Ingestion PCDDsJPCDFs 17/23 0.004 3 1.29 1.5613+05 3.2E-06 Rc lroduction 5.7E-02

Chromium 71nl 5.6 1900 NA NA CNS 2.6E-03

Copper 73/73 3.5 22.800 NA NA GIIl'ril3liOll 3.5E-03

Total Tof:llln"cstiull Risk 4£·06 Inl'l'slion I-II 6.0E-02

BCl1ZQ (a) pyrcnc II/59 43 1900 7.3£+00 1.3E-06 NA NA Soil Dibcnzo

anthracenc (a.h)

2/59 120 610 7.3E+00 4.5E-07 NA NA

Hexachlorobenze 7/49 47 7800 1.6E+00 1.7E-06 Liver 3.8E-03

Dermal PCDDslPCDFs 17/23 0.004 3 1.29 1.56E+05 2.3E-05 Renroduclioll 4.2E-OI

Chromium 7\171 5.6 1900 NA NA CNS I.IE-03

Copper 73m 3.5 22.800 NA NA Gl Irritalion 1.6£-04

Tolal TOI:l1 Dcrlllul Risk 3[-05 Dermal HI 4.01::'01

Tolul Cancer Risks Across Ex )Osurc Roule 3£.-05 Tola\ HI 4.6£.-01

IIle '(II Tres UlH'U

Bcnzo (;1) nvrcnc II/59 43 1900 7.3E+00 2.7E-07 NA NA Dibcnzo amhracene

(a.h) 2/59 120 610 7.3E+00 9.8E-08 NA NA

Hcxach[orobenzc 7/49 47 7800 1.6E+00 3.8E-07 Liver 6.8E-04

Ingestion rCDDs/PCDFs

Chromium

17/23

71/71

0.004 3

5.6

1.29

1900

1.56E+05 N

NA A

3.0E-06

NA

Reoroduelion

CNS

4.6E-02

2.0E-03

Soil Copper 73/73

3.5 22.800 NA N A NA GllrritatiOl1 2.8E-03

Toful Tolal III"cslion Risk 4[-06 In''estioll HI 5.0[-02

Benzo (a) nvrenc II/59 43 [900 7.3E+00 1.8E-06 NA NA Dibcnzo anthracene

(a,h) 2/59

120 610 7.3E+00 6.3E-07 NA NA

Dermal Hexach[orobenze

rCDDs!PCDFs

7/49

17/23

47 0.004 3

7800

1.29

1.6E+00

1.56£+05

2.4£-06

3.2E-05

Liver

Renroductioll

4.4£-03

4.9E-OI Chromium 71/71 5.6 1900 NA NA CNS I.3E-03 Contler 73/73 3.5 22.800 NA NA Gl Irritation 1.8E-04

Total Total Dermal Risk 4£-05 Dermal HI 5£-01

Tolal Cancer Risks Across Exposure

Tolal Risk 4E-05 Roule 5.5£-01

24

Table 2 (continued) ummary nmary ontributing at ew OF' IdRisk s for P COCs C N - Ie

1'013.1 Non-CllrcinogenicContaminant Concentrations (moll.: Risk

fuqul'ncy Cancer Source ":xpcuurc (Target

Media or Slope

Onl:;;n)Min.Route Cont.orCollccrn Detection MliX Factor

S",illlllwr ill GlIIlJJtJlI'der Hirer

Antimonv 4/16 Blood I 2.SE-02 2.8 I 11.2 INA Vanadium 12/13 None I 5.4E-04 3.1 60 NA

Ingestion Total

Surface Tolal In!!csliOIl Risk In!!cslion HI 3.0£.·02

WOller Antimonv I 4/16 2.8 I 11.2 NA Blood I 7.0-02 Vanadium I 12/13 None I 5.IE·033.1 I 60 INA

Dermotl Tolal

Tolal Derllllli Risk Dermal HI 7E-02

Total Risk I Oil-Site Workers. II/e ,td Tresnussers Buried Inhal:l\ion waste Risks arc unquamificd because media loc:llcd in a subsurface area thatand

Chemical warfhrc agems. cannal be s.1.mplcd due 10 the risk of explosive and chemicnl agent release: dCm1.11'nd metals. VOCs, explosives erosion could expose waste and rcsult in human health exposures.

ace soil

EPC Exposure Point Conccmralion. mglkg-bw/day Milligrams PCI' Kilogram Body Weight Per Day. USEPA United Slates Environmental Protection Agency. NC[A National CClller for EnvirOl1mcl1Ial AsseSsmelll. eNS - Celllr,!I Nervous System

subsmf

(I) LC:ld exposure is based on blood lcvclmodcling nOI HQs or I-lIs (2) Data prcscllIcd for lead found in soil includes dala from lhe original III IRA and daln collected during the additional 2006 sampling event. The olher COCs arc represented by data frollllhc HHRA only.

Exposure Roole Tolal

1'01:11 Carcinogenic

Risk Tolal Risk

Across Exposure

Routcs

INA INA

NA INA INA

I

is

2.7.2.1.3 Ecological Effects Assessmelll

The BERA identified potential risks for terrestrial plants as demonstrated by bare areas associated with high chemical concentrations of metals in the areas of the covered trenches. Risks were also identified for aquatic and benthic organisms from sediment in the open water areas of the pond and from seeps along the pond shoreline. While specific chemicals could not be associated with the toxic effects, metals and VOCs were suspected as the primmy toxicants. The BERA did not find risks 10 soil invertebrates or to wildlife (such as heron) thai use aquatic environments.

2.7.2.1.4 Risk Characterization

The BERA identified site-wide risks from metals (arsenic and copper) and total dioxins in soil, modeled doses of which exceeded ecological benchmarks for wildlife; it also identified risks from other metals in hot spots directly above the trench area. The BERA also idemified potential risks for terrestrial plams as demonstrated by bare areas associated with high chemical concentrations of metals in the areas of the covered trenches. Risks were also identified for aqumic and bemhic organisms from sedimem in the open water areas of the pond and from seeps along the pond shoreline. While specific chemicals could not be associated with the toxic effects, metals and VOCs were suspected as the primary toxicants. The BERA did not find risks to soil invertebrates or to wildlife (such as heron) that use aquatic environments. The BERA

25

identified that buried waste in trenches may also present a future risk if exposed through erosion or leaching. The ecological risk management section in the FS further documented management considerations and identified COCs and how they would be addressed by various remedial options. The list of COCs is presented in Table 3.

2.7.2.2 Other O-Field Areas

An ecological risk screening was performed for the OOA to identify COCs and associated effects to the site ecology. Site concentrations were compared to Region III BTAG screening levels (or more recently derived Ecological Soil Screening Levels (EcoSSLs) developed by the EPA, where available), to reference concentrations, and to remedial goals (RGs) developed for the soils at New a-Field as part of the extensive ERA for New a-Field that has been on-going since the mid-1990s. Based on these comparisons, no ecological risks were identified for the OOA, and further independent evaluation of risk was detel111ined to be unwan·anted.

2.7.2.3 Uncertainties

There are a number of uncertainties associated with the ecological risk assessment. In many cases, model assumptions are chosen conservatively and may overestimate risk; the use of site­specific data in the risk assessment helps to decrease this likelihood.

2.7.3 BASIS FOR ACTION

Remedial action is being taken at this site because of the future potential unacceptable risk to human receptors and the environment. The remedial action selected in this ROD is necessary to protect the public health or welfare or the environment from actual or threatened releases of hazardous substances into the environment.

Per USEPA guidance, containment is the presumptive remedy for military landfills containing buried waste that are impractical to sample or excavate (USEPA, 1996). Containment is typically accomplished through use of a landfill cap or actions to address contaminant migration in groundwater; however, military landfills may contain unique wastes or compounds that require specialized remediation. Therefore, application of the containment presumptive remedy to military landfills must include consideration of land use, sensitive environments, and special treatment or containment issues.

26

Table 3: Chemlcals of Concern for Ecological Receptors*

Chemical of Concern

New O-field

Medium Minimum Detection (m~/k~\

Maximum Detection (me/ke)

Mean (mg/kg)

Frequency of

Detection Receptors

Arsenic Soil 1.42 316 16.33 59/63

• Vennivorous Manunals • Vcnnivorous Birds • Terrestrial Plants • Herbivorous Mammals

Cadmium Soil 0.11 63.5 5.11 55/73 • Terrestrial Plants • VCn11ivorous Birds • Vennivorous Mamlllais

Chromium Soil 5.6 1900 105.41 71nt • Terrestrial Plants • Vennivorous Birds • Vennivorous Mammals

Copper Soil 3.5 22,800 590.55 73/73

• Terrestrial Plants • Vcnnivorous Mammals • Vemlivorous Birds • Herbivorous Mammals

Lead Soil 6.8 916 140 74n4 • Terrestrial Plants • VCIl11ivorous Birds

Mercury Soil 0.0342 3.7 0.34 40/50 • Terrestrial Plants • VCfmivorous Birds • VCllllivorous Mammals

Silver Soil 0.5 416 9.06 37n4 • Terrestrial Plants • Vennivorous Birds • Vermivorous Mammals

Zinc Soil 15.2 8810 698.39 74n4 • Terrestrial Plants • VCllnivorous Birds

Dioxins Soil 0.0029 1.62 0.23 23/35 • Herbivorous mammals • Vennivorous Mammals • Vennivorous Birds

Multiple contaminants -

Especially zinc, other cmionic Sediment metals, and VOCs

NA NA NA NA

• AquaticlBenthic Organism

Multiple contaminants ~ Metals, Dioxins. chemical degradation Surface products, pesticides. PAHs. \Vater SVOCs and VOCs

NA NA NA NA

• AquaticlBenthic Organism

• MlIlunum, maxImum. mean, and frequency values presented m this table represent dala from the 2002-2004 BERA sampling events that included toxicity and sequential extraction procedure (SEP) analysis. Mean concelllration calculations use one·half the detcction limit for non-delectable conccntrJtions. The values in this tnble are based 011 a subsct of the site data from thc risk assessment investigations. RJ data was used 10 detennine the hotspots. and the risk data further evaluated the hotspots using advanced chemical analyses nnd toxicity tests. For this reason, sample numbers and values in Ihis table may differ from those in olher tables.

27

Based on this infollllation, the presumptive remedy of containment at New O-Field is appropriate for the area of the trenches whcn combined with special consideration of the military specific wastes they contain. Typically, an impermeable cover would be required for a municipal landfill. However, for New O-Field, several special circumstances must be considered. As discussed above, the bottom portion of buried waste is expected to be within the water table. If an impermeable cover was installed, it would not suceed in preventing groundwater from moving through the bottom of the waste and becoming contaminated with liquids that have leaked from above or chemicals from the waste itself. Also, as waste in the water degrades, waste from above may settle into the water table over time. 1n addition, New O-Field contains buried CWM, WP, and UXO; containment of these wastes is safer under hydrated conditions. Water breaks down chemical warfare agents and decreases the risk of their transport beyond the site. Finally, wet conditions prevent ignition of WP. Based on this information, a permeable cover that allows rainwater to infiltrate into the trenches provides considerable advantages when combined with systems that provide groundwater treatment and address other risks at the site.

Although there were no industrial risks identified at the OOA, it is located close enough to the New O-Field and Old O-Field to warrant land use controls. The subsequent sections will document remedial action to be conducted on New O-Field, including LUCs for the OOA.

2.8 REMEDIAL ACTION OBJECTIVES

Remedial Action Objectives (RAOs) are goals devcloped for the protection of human health and the environment. The RAOs developed for New O-Field are as follows (GP 2008):

• Protect humans and ecological receptors from hazards associated with the buried wastes, and prevent fut1ll'e disturbance of the New O-Field source area that would cause exposure to these wastes;

• Protect ecological receptors from population-level risks due to dircct contact with contaminated soiVsediment; and,

• Protect ecological receptors from population-level risks associated with constituents in groundwater that discharge to New O-Field marsh and Watson Creek and prevent further degradation of surface water from groundwater discharge to the pond.

The remedial alternatives for New O-Field discussed below focus on containment of contaminants from buried waste and also address the COC impacted surface soil, sediment, and surface water. For each RAO, RGs w'ere developed. With respect to protection of human health and the environment from buried waste in the trenches, the remedial goals are qualitative in that they are based on elimination of exposure and tTansport pathways that may occur in the future that were not quantified due to the hazardous nature of the buried waste. This approach is consistent with use of a presumptive remedy.

It is important to note that the permeable cover design utilized in Alternative 8 differs from the specifications of a typical sanitalY landfill cap specified in the Code of Malyland Regulations (COMAR) 26.04.07.21, which is an ARAR for the site. The primary differences are due to the fact that the buried materials at New O-Field contain military-specific wastes that are best addressed by allowing infiltration of precipitation that breaks down and neutralizes risks from

28

CWM and UXO; a permeable cover, therefore, provides important risk reduction by allowing wet conditions. Also, the bottom of the buried waste is expected to be in contact with groundwater. The state of Maryland has granted approval for a variance to allow the permeable cover design, with the stipulation that impactcd groundwater will be treated using in situ bioremediation before it exits the treatment zone or area of attainmelll, which is the area being treated using emulsified oil. The variance also considers the fact that a portion of the waste is already in contact with groundwater. Therefore the RGs for buried material include treatment of groundwater, and treatment of chemicals in groundwater is considered integral to the presumptive remedy for the site.

Ecological goals or benchmarks associated with other media at New O-Field and their inherent uncertainties were assessed in the FS to detennine how risks could be addressed. The primary risk drivers for ecological receptors are chemicals in the area of the trenches and the open water pond. It was detennined that implementation of any of the evaluated altematives to provide containment of the buried waste will also address ecological risks and reduce them to acceptable levels. This is accomplished by the fact that containment measures will effectively eliminate exposures to the 1.6 acre area above the buried trenchcs, treat associated groundwater before it enters surface water, and eliminate exposures to sediment in the 2.2 acre open pond. Therefore, RG's are statcd in tenns of eliminating exposures to contaminants in specific areas in lieu of individual COC-specific numeric criteria.

To protect humans and the environment from hazards associated with the buried wastes, the qualitative RGs are: o Eliminate potential erosion that could expose material in the trenchcs.

To protect populations of ecological receptors from chemicals in soil, sedimel1l, and ground water seeps, the qualitative RGs are:

Surface Soil in the 1.6 acre Area of the Open and Covered Trenches o Reducc ecological receptor exposures to elevated metals in surface soil by placement of the

soil cover over the most contaminated surface soils.

Sedimelll in 2.2 acre Area of the Open Pond

o Eliminatc waterfowl exposures to sediment containing WP in the pond. o Reduce aquatic organism exposures to sedimcnts containing elevated metals in the pond.

Chemicals in e.round water o Reduce aquatic organism exposures to scep water cOl1laining elevated metals.

o Create conditions that degrade buried material and break down or decrcase bioavailability of cOl1lamination in groundwater, thus decreasing concentrations of VOCs, CWM, and metals and preventing further degradation of the surface water from groundwater discharge to the pond.

The process by which these goals will be achieved is discussed in the Section 2.12 detailing thc selected rcmcdy.

29

2.9 DESCRIPTION OF ALTERNATIVES

This section presents a description of the remedial alternatives that were developed for New 0­Field. The estimated present worth capital costs, the estimated present wOlth O&M costs, and the estimated total present worth costs in this section are rounded to the nearest $1,000.

2.9.1 NEW O-FIELD

The following is a description of each of the alternatives that were developed for New O-Field.

• Alternative I-No Action. • Alternative 2- Permeable Cover with Groundwater Bio-Enhancement. • Alternative 3- Low-Permeability Cover with Groundwater Rio-Enhancement. • Alternative 4- RCRA Cap with Constructed Wetland. • Alternative 5- RCRA Cap and Subsurface Barrier with Monitored Natural

Attenuation. • Alternative 6- Full-Scale Excavation, On-Site Treatment, Off-Site Disposal and

Monitored Natural Attenuation. • Alternative 7- Full-Scale Excavation, On-Site Treatment, On-Site Landfill,

and Monitored Natural Attenuation. • Alternative 8- Permeable Cover, Bio-Beneficial Sediment Cover, and

Groundwater Bio-Enhancement Barrier with Wetland Buffer.

2.9.1.1 Alterl/ative I: NoActioll

Estimated Present Worth Capital Cost: $0 Estimated Present Worth O&M Cost: $0 Estimated Total Present Worth Cost: $0 Estimated Construction Timeframe: Immediate Estimated Time to Achieve RAOs: Will not achieve RAOs

Pursuant to Section 300.430(e)(6) of the NCr, the "No Action" alternative is developcd to provide a baseline against which the other remedial alternatives are to be compared. The No Action alternative includes no remedial actions, land use controls, or five year reviews. The No Action alternativc would not be protective of human health and the environment during implememation or in the long tcrnl. Because no remedial actions would be specified for Alternative I, the alternative is not protective and therefore will not be considered.

2.9.1.2 Alte1'llative 2: Permeable Cover with Groulldwater Bio-EII/ulIIcemellf

Estimated Present Worth Capital Cost: $2,680,000 Estimated Present Worth O&M Cost: $1,907,000 Estimated Total Present Worth Cost: $4,587,000 Estimated Construction Timeframe: 12 Months Estimated Time to Achieve RAOs: Circa 2013

30

This remedial alternative involves placing a pernlcable cover, with an armored toe, over the trenches and WP-contaminated soil generated during the Pusbout Area Removal Actions. The penneable soil cover allows continued infiltration which serves to break down munitions constituents and hydrolyze any releases of chemical agents. This provides reduction of limtre hazards to site workers and prcvents potential catastrophic releases that would cause acute risks. For this alternative, hot spots would also be removed outside the footprint of the cover and the cxcavated material either placed under the cover or, if hazardous, disposed of off-site. The adjacent pond would be filled.

Treatability studies would bc conducted for this alternative. Treatability studies would be used to further evaluate the potential for biodegradation of contaminants in the groundwater at New O-Field and to examine the effect of increased elecuon donor (e.g., acetate, methanol, ferric citrate, glucose, sucrose, etc.) concentrations. After treatability studies are completed, the full­scale implementation of an in-sinl biodegradation system would take place. Long-term groundwater monitoring would be required to evaluate the effectiveness of the system. Also, to reduce the potential for funlre risks, LUCs would be implemented and maintained to prevent rcsidential land use, digging, groundwater use, or other activities incompatiblc with remedy effectiveness. O-Field is located in a restricted portion of the Installation. Access to the restricted area is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical security countermcasures to include barrier systems, sensors and random patrols by law enforcement personnel are in place to prcvent unauthorized access. LUCs would include additional fencing, signage, and notation in the post GIS. It is expcctcd that this rcmedial alternative will achieve RAOs by the first five year review for this site.

Alternative 2 would address the RAOs Ihrough the following remedial components:

• Installation of a 1.6 acrc 3 ft thick penneable soiVsand cover over the trenches and WP­contaminated soil generated during the Pushout Area Removal Action consisting of permeable geotextile, clean soil, 6 in. of topsoil, and vegetation;

• Annoring of the toe of the cap with stone, due to the proximity to the IDO-year floodplain;

• Closure of the pond (partially-filled in with sand or soil); • Installation of either passive or active in-sinl biodegradation system to address VOC

contamination in groundwater (a passive system would include only injection and monitoring wells, and an activc systcm would include added extraction wclls, to enhance mobility of the nutrients);

• Implementation of LUCs for Ncw O-Field that, to reduce the potential for future risks, maintain future land use as military/industrial and prevent future rcsidential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) as long as chemical concentrations rcmain elevated above levels that allow for UU/UE;

• Implementation of additional LUCs for New O-Field that would prevent digging, groundwater use, or other activities in the area of the covcr or groundwater treatment area that are incompatible with remedy effectiveness as long as chemical concentrations rcmain elevated above levels that allow for UU/UE;

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• Implementation of LUCs for the OOA that, to reduce the potential for future risks, maintain future land use as militarylindustrial and prevent the future residential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations remain elevated above levels that allow for UU/VE;

• Hot spot soil/sediment removal (outside the footprint of the cover); • Long-ternl O&M of cover; • Long-tcnn groundwater monitoring; and, • Five-year reviews for 30 years.

2.9.1.3 Alternative 3: Low-Permeability Cover ",itll Groulldwater Bio-Elllwllcemellt

Estimated Present Worth Capital Cost: $2,725,000 Estimated Present Worth O&M Cost: $1,624,000 Estimated Total Present Worth Cost: $4,349,000 Estimated Construction Timeframe: 12 Months Estimated Time to Achieve RAOs: Circa 2013

This remedial alternative involves placing a low permeability cover, with an arnlored toe, over the trenches and WP-contaminated soil generated during the Pushout Area Removal Actions. The low permeability provides additional protection against disturbance but would reduce infiltration from rain/snow events and reduce the breakdown of munitions constituents. For this alternative, hot spots would also be removed outside the footprint. of the cover and the excavated material either placed under the cover or disposed of off-site. The adjacent pond would be closed.

Treatability studies would be conducted for this alternative. Treatability studies would be used to further evaluate the potential for biodegradation of contaminants in the groundwater at New O-Field and to examine the cffect of increased elect.ron donor (e.g., acetate, methanol, ferric citrate, glucose, sucrose, etc.) concentrations. After treatability studies are completed, the full­scale implementation of an in-situ biodegradation systcm would take place. Long-term groundwater monitoring would be required to evaluate the effectiveness of the system. Also, to reduce the potential for future risks, LUCs would be implemented and maintained to prevent residential land use, digging, groundwater use, or other act.ivities incompatible with remedy effectiveness. O-Field is located in a restricted portion of the lnstallation. Access to the restricted area is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical security countermeasures to include barrier systems, sensors and random patrols by law enforcement personnel are in place to prevent unauthorized access. LUCs would include addit.ional fencing, signage, and notation in the post GIS. It is expected that this remedial alternative will achieve RAOs by the first five year review for this site.

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Altemative 3 would addrcss the RAOs through thc following remedial componcnts: • Installation of a 1.6 acre 3 ft thick low pcrmeability cover ovcr the trenchcs and WP­

contaminated soil gcnerated during the Pushout Area Rcmoval Actions consisting of a gcosynthctic clay layer (GCL), high density polyethylene (HOPE) geomembrane, geotextilc material, and 6 in. of gravcl;

• Annoring of thc toc of the cap with stone, due to thc proximity to thc 100-ycar floodplain;

• Closurc of the pond (filled in with sand or soil); • Installation of either passive or active in-situ biodegradation system to address VOC

contamination in groundwater (a passive system would include only injection and monitoring wells, and an active system would includc addcd cxtraction wells, to cnhance mobility of the nutrients);

• Implemcntation of LUCs for New O-Field that, to reduce the potcntial for future risks, maintain the future land use as military/industrial and prevent future residential land usc (i.e. housing, elemcntary and secondary school, child care facilities and playgrounds) as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Implemcntation of additional LUCs for New O-Ficld that would prevent digging, groundwater use, or other activities in the area of the covcr or groundwater treatmcnt area that are incompatiblc with rcmcdy effectivencss as long as chemical conccntrations remain elcvated abovc levels that allow for UUlUE;

• Implemcntation of LUCs for the OOA that, to reduce the potential for future risks, maintain thc future land use as military/industrial and prevent futurc residential land usc (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations rcmain elcvated abovc levels that allow for UU/UE;

• Hot spot soiVscdiment removal (outside the footprint of the cover); • Long-term O&M of cover;

• Long-term groundwater monitoring; and, • Five-year reviews for 30 years.

2.9.1.4 Alternative 4: RCRA Cap with COllstructed Wetllllld

Estimated Present Worth Capital Cost: $5,845,000 Estimated Present Worth O&M Cost: $1,047,000 Estimated Total Present Worth Cost: $6,892,000 Estimated Construction Timeframc: 12 Months Estimated Time to Achieve RAOs: Circa 2010

This remedial alternative involves placing a RCRA cap, with an armored toc, over the trenches and WP-contaminated soil generated during thc Pushout Area Removal Actions. Thc extremely low pel1neability providcs additional protection against disnlrbance but would limit infiltration from rain/snow events, limiting thc breakdown of munitions constitucnts. For this altemative.

33

hot spots would also be removed outside the footprint of the cover and the excavated material either placed under the cover or disposed of off-site. The adjacent pond would be closed.

This remedial alternative also includes constructing a wetland along the shoreline. The higher organic matter content found in wetlands will retard movement of the VOCs such as ethenes resulting in a much longer retention time. Sorption will give more time for biological degradation to occur and, therefore, limits the depth to which the wetland needs to be constructed for maximum effect. Metals would be removed through the combined processcs of precipitation, sorption, and plant uptake. CWM breakdown products would be addressed by biodegradation in the wetland bed, due to their low sorption potential. Long-term groundwater monitoring would be required to evaluate the effectiveness of the system. Also, to reduce the potential for future risks, LUCs would be implemented and maintained to prevent residential land use, digging, groundwater use, or other activities incompatible with remedy effectiveness. O-Field is located in a restricted portion of the Installation. Access to the restricted area is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical security countermeasures to include ban·ier systems, sensors and random patrols by law enforcement personnel are in place to prevent unauthorized access. LUCs would include additional fencing, signage, and notation in the post GIS.

Alternative 4 would address the RAOs through the following remedial components:

• Installation of a 1.6 acre RCRA Cap with GCl, HDPE geomembrane, geotextile drainage fabric, 2 ft of common fill, and vegetated topsoil over the trenches and WP­contaminated soil generated during the Pushout Area Removal Actions;

• Closure of the pond (filled in with sand or soil); • Annoring of the toe of the cap with stone, due to the proximity to the IDO-year

floodplain; • Installation of a constructed wetland consisting of a 50-ft barrier along thc shoreline

containing compost and/or peat, erosion control fabric, an 80 mil drainage filter layer, a 6-in. layer of topsoiVpeat mixture (with the remaining portions of the pond filled with sand), and planting of specific wetland species (such as cattails);

• Implementation of LUCs for New O-Field that, to reducc the potential for future risks, maintain the future land use as mililary/industrial and prevent futurc residential land usc (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Implementation of additional lUCs for New O-Field that would prevent digging, groundwater use, or other activities in the area of the cap or wetland that are incompatible with remedy effectiveness as long as chemical concentrations remain elevated above levels that allow for UUlUE;

• Implementation of LUes for the OOA that, to reduce the potential for future risks, maintain the future land use as military/industrial and prcvent future residential land use (i.e. housing, elementary and secondary schools, child care facilities and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Hot spot soil/sediment removal (outside the footprint of the cover); • Long-tenn O&M of cap and wetland;

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• Long-tellll groundwater monitoring; and, • Five-year reviews for 30 years.

2.9.1.5 AlteTllative 5: RCRA Cap al/d Sl/bsl/rface Barrier ",ith MOl/itored Natl/ral Attenl/ation

Estimated Present Worth Capital Cost: $2,765,000 Estimated Present Worth O&M Cost: $906,000 Estimated Total Present Worth Cost: $3,671,000 Estimated Construction Timeframe: 19 Months Estimated Time to Achicve RAOs: Circa 20 II

This remedial alternative involves placing a RCRA cap, with an armored toe, over the trenches and WP-conraminated soil generated during the Pushout Area Removal Actions. A subsurface barrier is included with this altemative to reduce groundwater flow through the trenches, thus reducing contaminant migration in groundwater and limiting the breakdown of munitions constituents. For this alternative, hot spots would also be removed outside thc footprint of the cover and the excavated material either placed under the cover or disposed of off-site. The adjacent pond would be closed.

This alternative involvcs allowing VOC concentrations IJ1 groundwater at Ncw O-Field to attenuate naturally. Natural attenuation processes include volatilization, evapotranspiration, biodegradation, adsorption, dispcrsion, and dilution through recharge. Gcnerally, the most important natural attenuation process for organic chemicals is biodegradation. However, the attenuation of VOCs may be inhibited due to the presence of competing terminal electron acceptors in the groundwater. A contingency plan would be developed and implemented in consultation with EPA and MDE if monitoring indicates that groundwater RAOs cannot be met. Long-teml groundwater monitoring would be required to evaluate the effectiveness of the systcm. Also, to reduce the potential for future risks, LUCs would be implemented and maintained to prevent residential land use, digging, groundwater use, or other activities incompatible with remedy effectiveness. O-Field is located in a restricted portion of the Installation. Access to the restricted area is limited to properly cleared pcrsonnel or individuals in an escorted capacity. A wide variety of physical security counternleasures to include barrier systems, sensors and random patrols by law enforcement personnel are in place to prevent unauthorized access. LUCs would include additional fencing, signage, and notation in the post GIS.

Alternative 5 would address the RAOs through the following remedial components:

• Installation of a 1.6 acrc RCRA Cap with GCL, HDPE geomembrane, geotextile drainagc fabric, 2 ft of common fill, and vegetated topsoil over the trenches and wp· contaminated soil generated during the Pushout Area Removal Action; Subsurface barrier to reduce groundwater flow through the trenches;

• Installation of an estimated 860 linear ft slurry wall (commonly bentonite) as a non­structural subsurface barrier to impcde groundwater flow through the formation of a filter cake on the trench walls that reduces the soil penneability of the wall while excavation depths key into a low permeability stratum such as clay or bcdrock to assure minimal

35

leakage under the wall; • Closure of the pond (filled in with sand or soil); • Annoring of the toe of the cap with stone, due to the proximity to the 100-year

floodplain; • Implementation of LUCs for New O-Field that, to reduce the potential for future risks,

maintain the future land lise as military/industrial and prevent future residential land use, including utilization of groundwater as drinking water, as long as chemical concentrations remain elevated;

• lmplementation of additional LUCs for New O-Field that would prevent digging, groundwater lise, or other activities in the area of the cap that are incompatible with remedy effectiveness as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Implementation of LUCs for the OOA that, to reduce the potential for future risks, maintain the land use as militarylindustrial and prevent residential land use (i.e. housing, elementalY and secondary schools, child care facilities and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations remain elevated above levels that allow for UUlUE;

• Monitored natural attenuation for groundwater (including long-term groundwater monitoring of downgradient existing wells);

• Long-term O&M of cap and subsurface barrier and monitoring of groundwater; • Hot spot soil/sediment removal (outside the footprint of the cover); and, • Five-year reviews for 30 years.

2.9.1.6 Alternative 6: FI/II-Scale Excavation, Oil-Site Treatment, Off-Site Dispasul and Manitored Natl/ral Attenl/(l/ion

Estimated Present Worth Capital Cost: $36,637,0002

Estimated Present Wonh O&M Cost: $906,000 Estimated Total Present Worth Cost: $37,543,0003

Estimated Construction Timeframe: 65 Months Estimated Time to Achieve RAOs: Circa 2015

This remedial alternative involves excavation of soil and subsurface materials from the disposal trenches and the hot spots at New O-Field and the closure of the adjacent pond. Mechanically­assisted manual excavation techniques would be used to remove the contaminated soil (i.e., mechanical removal of overburden soil, manual removal of the waste materials, and then mechanical removal of the impacted soil below). Excavated materials would be sorted and staged on-site for treatment and disposal. A treatability study would be required prior to site activities to determine the appropriate reagent for stabilization/solidification. Following treatment, the waste material would be transpOiled off-site for disposal at a solid waste landfill.

1 Capital costs for this alternative do not include additional treatment and disposal of UXO and CWM; costs would be substantial. Disposal costs also do not include disposal of stockpiled soil from the New O-Field Pushout Area Removal Actions. J Towl costs for this alternative do not include additional treatment and disposal of UXO and CWM; costs would be subSlalltial. Disposal costs also do not include disposal of stockpiled soil from the New O-Field Pushout Area Removal Actions.

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This alternative also involves allowing VOC concentrations in groundwater at New O-Field to attenuate naturally. Natural attenuation processes include volatilization, evapotranspiration, biodegradation, adsorption, dispersion, and dilution through recharge. Generally, thc most important natural attenuation process for organic chemicals is biodegradation. However, the attenuation of VOCs may be inhibited due to the presence of competing terminal electron acceptors in the groundwater. A contingency plan would be developed and implemented in consultation with EPA and MOE if monitoring indicates that groundwater RAOs CalUlot be met. LUCs including fencing, signage, and notation in the post GIS would be implemented and maintained ro prevent residential land use, digging, or other activities that are incompatible with remedy effectiveness.

Also, to reduce the potential for future risks, LUCs would be implemented and maintained to prevent residential land use, digging, groundwater use, or other activities incompatible with remedy effectiveness. O-Field is located in a restricted portion of the Installation. Access to the restricted area is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical security countermeasures to include barrier systems, sensors and random patrols by law enforcement personnel are in place to prevent unauthorized access. LUCs would include additional fencing, signage, and notation in the post GIS.

Alternative 6 would address the RAOs tlu·ough the following remedial components:

• Full-scale excavation of trenches (cstimated volume of the soil and waste to be removed is over 20,000 cy);

• Two-stage on-site treatment of hazardous waste and soil including thennal desorption for organics removal and stabilization/solidification for immobilization of heavy metals;

• Off-site disposal at a solid waste landfill; • Closure of the pond (filled in with sand or soil); • Monitored natural attenuation for groundwater (including long-term groundwater

monitoring of downgradient existing wells); • Implementation of LUCs for New O-Field that, to reduce the potential for future risks,

maintain the future land use as military/industrial and prevent future residential land lise (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Implementation of LUCs for the OOA that, to reduce the potential for future risks, maintain the future land usc as militaly/industrial and prevent future residential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) including utilization of groundwater as drinking watcr as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Hot spot soiVsediment removal; and • Five-year reviews for 30 years.

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2.9.1.7 Alternative 7: Full-Scale Excavatioll, Oil-Site Treatmellt, Oil-Site Lalldfill, alld Monitored Natural Attelluatioll

Estimated Present Worth Capital Cost: $35,119,000' Estimated Present Worth O&M Cost: $1,129,000 Estimatcd Total Present W0l1h Cost: $36,248,0005

Estimated Construction Timeframe: 77 Months Estimated Time to Achieve RAOs: Cil'ca 2016

This remedial alternative involves excavation of soil and subsurface materials from the disposal trenches and the hot spots at New O-Field and closure of the adjacent pond. It also involves allowing VOC concentrations in groundwater at New O-Field to attenuate naturally.

Mechanically-assisted manual excavation techniques would be used to remove the contaminated soil (i.e., mechanical removal of overburden soil, manual removal of the waste materials, and then mechanical removal of the impacted soil below). Excavated materials would be sorted and staged on site for treatment and disposal. A treatability study would be required prior to site activities to detemline the appropriate reagent for stabilization/solidification. Following treatment, the waste material would be moved for disposal to an on-site triple lined landfill constructed for this purpose.

This altemative also involves allowing VOC concentrations in groundwater at New O-Field to attenuate naturally. Natural attenuation processes include volatilization, evapotranspiration, biodegradation, adsorption, dispersion, and dilution through recharge. Generally, the most important natural attenuation process for organic chemicals is biodegradation. However, the attenuation of VOCs may be inhibited due to the presence of competing temlinal electron acceptors in thc groundwater.

A contingency plan would be developed and implemented in consultation with EPA and MDE if monitoring indicates that groundwater RAOs cannot be met. Also, to reduce the potential for future risks, LUCs would be implemented and maintained to prevent residential land use, digging, groundwater use, or other activities incompatible with remedy effectiveness. O-Field is located in a restrictcd portion of the Installation. Access to the restricted area is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical sccurity countermeasures to include barrier systems, scnsors and random patrols by law enforcement personnel are in place to prevent unauthorized access. LUCs would include additional fencing, signage, and notation in the post GIS.

-I Capital costs for this ahclllativc do not include additional treatment and disposal of UXO and C\VM; costs would be substantial. Disposal costs also do nol include disposal of stockpiled soil from the New O-Field Pushollt Area Removal Actions. 5 Total costs for this nltclll<llive do not include additional treatment and disposal of UXO and CWM; costs would be substantial. Disposal costs also do nol include disposal of stockpiled soil from the New O-Field Pushout Area Removal Actions.

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Alternative 7 would address the RAOs through thc following remedial components:

o Full-scale excavation of trenches (estimated volume of the soil and waste to be removed is over 20,000 cy);

o Two-stage on-site treatment of hazardous waste and soil including thermal desorption for organics removal and stabilization/solidification for immobilization of heavy metals;

o On-site disposal in triple lined landfill under a RCRA Cap with GCL, HDPE geomembrane, geotextile drainage fabric, 2 ft of common fill, and vegetated topsoil;

o Closure of the pond (filled in with sand or soil); o Monitored namral attenuation for groundwater (including long-term groundwater

monitoring of downgradient existing wells); o Implementation of LUCs for New O-Field that, to reduce the potential for fUtllre risks,

maintain the future land use as military/industrial and prevent future residential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) as long as chemical concentrations remain elevated above levels that allow for UU/UE;

o Implementation of additional LUCs for New O-Field that would prevent digging, groundwater use, or other activities in the area of the cap or monitored natural attenuation area that are incompatible with remedy effectiveness as long as chemical concentrations remain elevated above levels that allow for UU/UE;

o Implementation of LUCs for the OOA that, to reduce the potential for future risks, maintain the future land use as militmy/industrial and prevent futurc residential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations remain elevated above levels that allow for UU/UE;

o Long-tenn O&M of landfill; o Hot spot soil/sediment removal; and, o Five-year reviews for 30 years.

2.9.1.8 Altemative 8: Permeable Cover, Bio-Beneficial Sediment Cover, and Groundwater Bio-Enhancement Barrier with Wetland Buffer

Estimated Present Worth Capital Cost: $1,874,000 Estimated Present Worth O&M Cost: $1,774,000 Estimated Total Preseot Worth Cost: $3,648,000 Estimated Construction Timeframe: 12 Months Estimated Time to Achieve RAOs: Circa 2013

This remedial alternative involves placing a penllcable cover, with an armored toe, over the trenches and the WP-contaminated soil gencrated during the Pushout Area Removal Actions. Thc cover meets remedial goals by decreasing the potential for human and ecological exposures to buried waste and by decreasing ecological exposures to contaminated surface soil. An important benefit of the penlleable soil covcr is continued infiltration which serves to break down munitions constitllents, breach munitions to decrease their explosive potential, and wet WP to prevent ignition. Infiltration will also hydrolyze, or break down, any rclcases of chemical

39

agents to produce less toxic compounds. This provides reduction of fUlllre hazards to site workers and prevcnts potential catastrophic releases that would cause acute risks.

An in-situ bio-enhanccment barricr would be implemented to address YOCs in the groundwater as well as other chemicals potentially released from buried waste by providing treatment of groundwater before it leaves the zone of bioremediation. Treatability studies would be used to further evaluate the natural biodegradation of contaminants in groundwater at New O-Field and to determine the most appropriate Ilutrients and delively system for continuation of the process. Once the studies are complete, the full-scale implementation of an in-situ bio-enhancement barrier would involve the installation and operation of an active system that uses injection and extraction wells to deliver nutrients and microbes to the treatment zone located at the center of the CYOC plume immediately downgradient of the trenches. Ifnecded, passive injection may be used to fill gaps in the zone of bioremediation.

This remedial altemative also includes the construction of a wetland buffer along the shoreline of the open water of the pond downgradient of the penneable cover and bio-enhancement zone. Coir fiber logs will be placed between the wetland and the open water to help armor and stabilizc the wetland. Coir fiber logs, consist of coconut (coir) fibers compressed in a tube of mesh netting. The coir fiber logs would be cinched to the stakes, along the bank, using coir roping to keep them Ii-om rising and dropping with the tide. The wetland buffer will be vegetated with plants that contribute additional organic carbon to the system, thus providing a naturally regenerating system that continuously treats and sequesters contamination. This will address the seeps that enter the pond and help in remediation of groundwater that has already moved beyond the planned zone of bioremediation. A potential problem with constructed wetlands is reduced treatment efficiency in winter in northern latitudes. Biological processes such as microbial degradation are known to be temperature dcpendent.

For the bio-beneficial sediment cover, a I ft thick layer of cover material would be placed over the bottom of the open water area of the pond to prevent exposures to contaminated sediment. In areas where the mean water depth is lcss than one foot, the cover may be less than a foot thick to avoid complete filling of the pond and wetlands. In these areas, the cover would be placed over a permeable geotextile to limit mixing with the sediments beneath. It would stop at the mean water lcvel and be vegetated with appropriate wetland species. The cover surface would be vegetated with submerged aquatic vegetation through seeding. The addition of the carbon to the scdiment cover material will help create conditions that arc highly reducing and very anaerobic. These conditions encourage the activity of microbes that break down chlorinated compounds such as those detected in New O-Field groundwater that has already moved beyond the zone of planned bioremediation. The same conditions that encourage these microbes also serve to sequester metals in forms that are non-mobile, non-bioavailable, and non-toxic.

Long-term groundwater monitoring would be required to evaluate the effectiveness of the system. Also, to reduce the potential for future risks, LUCs would be implemented and maintained to prevent residential land use, digging, groundwater use, or othcr activities incompatible with remedy effectiveness. O-Field is located in a restricted pOilion of the Installation. Access to the restricted area is limited to properly cleared personnel or individuals in an escOiled capacity. A wide variety of physical security countermeasures to include balTier

40

systems, sensors and random patrols by law enforcement personnel are in place to prevent unauthorized access. LUCs would include additional fencing, signage, and notation in the post GIS. It is expected that this remedial alternative will achieve RAOs by the first five year review for this site.

It is important to note that Alternative 8 does not include hot spot excavation, which is included in Alternatives 2 through 7. The rationale for Alternative 8 developed in the FS includes an evaluation which demonstrates that the vegetated pernleable soil cover, wetland buffer, and biobeneficial sediment cover reduce ecological exposurcs to chemicals such that risks are within acceptable levels. Therefore, hot spot excavation is not required for this alternative. The same rationale may apply in part to other alternatives, but Alternative 8 is unique in that it prcserves as much of the current terrestrial, wetland, and aquatic habitat as possible while providing risk reduction.

Alternative 8 would address the RAOs through the following remedial components:

• Installation of a 1.6 acre 2 ft thick penneable soil/sand cover over the trenches and thc WP-contaminated soil generated during the Pushout Area Removal Actions (to include penneable geotextile fabric, a minimum of 18 in. of clean soil, 6 in. of topsoil, and vegetation);

• Placement of a vegetated bio-beneficial sediment cover over the boltom of the open water of the pond composed of sand or soil amended with a carbon source such as topsoil, chitin (shrimp or crab shell), or compost placed in lifts to minimize mixing with underlying sediment (may also include a surface layer of gravel or stone to armor against erosion, or an underlying layer ofpernlcable geotextile to prevent mixing);

• Installation of an in-sinl bio-enhancement barrier system to address VOC contamination in groundwater by using existing wells in the area for injection of nutrients and microbes directly downgradient from the trenches and potentially along the entire depth of the aquifer to the underlying clay layer while a groundwater-filled depression in this area will be filled with limestone/lime to aid in controlling pH and provide a centralized point for extraction;

• Constmction of a vegetated wetland buffer composed of sand or soil amended with organic carbon including installation of a 25 ft barrier 400 ft along the shoreline of thc open water of the pond, encompassing approximately y,. acre;

• Placemcnt of coir fiber logs between the wetland and the open water to help armor and stabilize the wetland;

• Implementation of LUCs for New O-Field that, to reduce the potential for future risks, maintain the future land use as military/industrial and prcvent future residential land use (i.e. housing, elementaty and secondary schools, child care facilities, and playgrounds) as long as chemical concentrations remain elevated above levels that allow for UUIUE;

• Implementation of additional LUCs for New O-Field that would prevent digging, groundwater usc or othcr activities in the area of the covers, buffer or groundwatcr treatment area that are incompatiblc with remedy effectiveness as long as chemical concentrations remain elevatcd above levels that allow for UU/UE;

• Implemcntation of LUCs for the OOA that, to reduce the potential for future risks. maintain the futurc land use as military/industrial and prevcnt future residential land use

41

(i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Long-term groundwater monitoring (4 monitoring wells would be installed for performance monitoring with 2 sampling events in the first year) and surface water monitoring;

• Long-tenn O&M of the permeable cover, wetland buffer, bio-beneficial sediment cover, and groundwater treatment systems; and,

• Five-year reviews for 30 years.

2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES

To evaluate the remedial alternatives for New O-Field, the potential perfornlancc of each alternative is considered in terms of the nine evaluation criteria required by the NCP. The nine criteria are categorized into one of the three following groups:

• Threshold criteria, which are requirements that each alternative must meet in order to be eligible for selection: • overall protection of human health and the environment; • compliance with ARARs;

• Pril11wy balancing criteria, which are used to weigh major trade-offs among alternatives: • long-term effectiveness; • reduction of toxicity, mobility, or volume through treatment; • short-term effectiveness; • implementability; • cost;

• Modifj1ing criteria, which are considered after receipt of comments on the preferred alternative and other alternatives presented in the proposed plan, and whieh indicate whether the State and the community support the selected alternative. In the final balancing of trade-offs between alternatives upon which the final remedy selection is based, modifying criteria are of equal importance as the balancing criteria:

• state acceptance; • community acceptance.

A summary of the comparative analysis of the remedial alternatives for New O-Field is presented in Table 4.

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2.10.1 EW O-FIELD GRO NDWATER AND SOURCE AREA

2.10././ TlIresllOld Criteria

Overall Protection of Human Health and the Environment

Alternative I, No Action, would not be effective in preventing exposure of future industrial workers or ccological receptors to lhe contaminants in wastes; therefore, A Iternative I would not be protective of human health or the environment. Thus, Alternative I will not be considered fi.lrther in this analysis since it fails this criterion.

All of the other alternatives (including waste excavation, covers, bio-enhancement, etc.) are expected to be protective of human health and the environment and effective at preventing exposure to receptors to some degree. The cover alternatives (Alternativcs 2, 3, 4, 5, and 8), in conjunction with LUCs and groundwater treatment (Alternatives 2, 3, 4, and 8) would be protective of human health and the environment and cffeetive at achieving RAOs by mitigating risks to hypothetical fi.lture industrial workers and ecological receptors, and controlling the source rclease. Even though waste and contaminated soil will remain in place for the cover alternatives, active steps would be taken by either bio-enhancement (Altematives 2, 3 and 8), constructed wetland (Alternatives 4 and 8), and/or subsurface barrier (Alternative 5) to contain and/or reduce the source area. Altemative 8 combines both wetland and bio-enhancement components. The pemleable cover alternatives (Alternatives 2 and 8) provide significant risk reduction by allowing infiltration; infiltration will allow breakdown of buried CWM and serve to suppress any releases through hydrolysis.

The waste excavation alternatives (Alternatives 6 and 7) would also achieve RAOs and are comparatively more protective over the long-tenn than the cover alternatives through the removal of waste material and contaminated soil/sediment with Alternative 6 offering the most long-term protection because waste is disposed off-site. Alternatives 6 and 7 would facilitate natural attenuation processes to cOlllinue at New O-Field at a faster rate than other alternatives. It should be noted that these alternatives involve short ternl risks associated with UXO and CWM hazards during excavation.

In terms of overall protection of human health and the environment, Altematives 6 and 7 provide the most protection in the long term but involve short teml risks. Alternatives 2, 3, and 8 provide the second most protection by eliminating exposures, avoiding short term risks, and allowing breakdown of contamination in buried wastes over time. Alternatives 4, and 5 provide the next most protection because they eliminatc exposures, avoid short tenn risks, but do not allow breakdown of contamination in buried wastes due to installation of a RCRA cap.

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TABLE 4: COMPARATIVE ANALYSIS SUMMARY OF REMEDIAL ALTERNATIVES-NEW O-FIELD

Criteria Alternative I No Action

Alternative 2 Permeable Cover with Groundwater Bio-Enhancement

Alternative 3 Low-Permeability Cover with Groundwater Bio-enhancement

Alternative 4 RCRA Cap with Constructed Wetland

Alternative 5 RCRA Cap and Subsurface Barrier with Monitored Natural Attenuation

Alternative 6 Full-Scale Excavation. On-site treatment with Off-Site Disposal and Monitored Natural Attenuation

Alternative 7 Full-Scale Excavation,Dn­site Treatment with On-Site Disposal and Natural Attenuation

Alternative 8 Permeable Cover, Bio-Beneficial Sediment Cover, and Groundwater Bio-Enhancement with Weiland Buffer

Overall Protection of Human Health and the Environmcnt

V' ~ ~ ~ ~ ~(I) ~(Il ~

Compliancc With ARARs

NA ~'" ~(" ~ ~ ~ ~ ~("

Long-Tcnll Effectiveness and Pemmllencc V' ~ ~ ~ ~ ~ ~ ~ Reduction of Toxicity. Mobility, and Volumc V' • • V' V' ~ ~ • Short-Term Effectiveness V' ~ ~ ~ ~ • • ~ ImpIcmcntabi Iity

~ ~ ~ ~ • • • ~ Total Cost (30-Year Present W011h)

$0 S4.58 1.000.00 $4.349.00000 $6.892.000.00 $3.671,000.00 $37.543.000.00 $36.248.000.00 $3.648.000.00

Stale Acceptance -­ -­ -­ -­ -­ -­ -­ --Community ACccpt<tllce -­ -­ -­ -­ -­ -­ -­ --Notcs: 6. - [11 companson with Olher :Iltcrnativcs. comp[ics well with criteria.

• - In comparison with othcr alternatives. panial1y complies with criteria. V' ~ In comparison with other ahentatives. does not comply as well with criteria. NA - NO! Applicable . •• • Not yct detennined

COSt estimates arc based upon 2008 dollars. Total costs are rounded to the nearest $1000. Tota[ Net Cost rounded to nearest S1.000. (I) Alternatives 6 and 7 arc comparatively more proteclive lhall the other alternatives with alternative 6 being thc 1I10st protective of all the ahemativcs. However. thesc altemativcs involve short-term risks assoeiatcd

with excavation of cllClllical·filled munitions. (2) The permeable cover utilized in these altemativcs is subject to approval of a variance: see Table 7.

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Compliance with Applicable or Relevant and Appropriate Requirements

There are no chemical-specific ARARs for the COC in soiVsediment. However, the USEPA guidance for COC in soil is considered a To Be Considered (TBe) requirement (USEPA, 1994a and 1998). Alternatives 2 through 8 would comply with the TBC for soil.

Alternatives 4, 5, 6 and 7 would comply with action- and location-specific ARARs because they would mitigate potential impacts from each action to protected resources at APG. It should be noted that in order for the permeable and less pemleable covers (Alternatives 2, 3, and 8) to comply with the State landfill requirements, their designs must qualify for a variance from a standard impermeable landfill cap design. COMAR 26.04.07.26 allows for a variance from the specific requirements of the regulation, as long as the alternative method employed would provide at least the same degree of protection as compliance with the regulation would provide. COMAR 26.04.07.21 D also states that the Department shall consider alternative proposals for landfill closure based upon an engineering analysis of the site. Each aItemative satisfics the requirements of COMAR 26.04.07.18H (Final Cover Material), 26.04.07.2 I (Sanitary Landfill Closure), and 26.04.07.22 (Sanitary Landfill Post-Closure Monitoring and Maintenance). Altematives 2, 3, and 8 comply with all othcr idcntified ARARs including Federal and State regulations regarding surface water protection and Federal and State regulations regarding wetland protcction. For a list of ARARs associated with the Selected Remedy, see Table 7.

As a condition of cap construction ill accordance with the variance, treatment of shallow contaminated groundwater in lieu of reduced infiltration that would be afforded by an impermeable cap is required to prevent migration of untreated groundwater beyond thc site. The construction of covers and wetlands would be accomplished in a maImer that complies with the requirements of Maryland regulations requiring control of fi.lgitive particulate emissions (dust) and control of erosion and stornlwater/sediment nmoff. Wastes generated by the remediation would be managed in compliance with solid and hazardous waste managemcnt regulations. Activities would also be conducted in a manner consistent with applicable wetland and coastal zone protcction regulations.

2.10.1.2 PrillulIJ' Balllllcillg Criteria

Long-Term Effectiveness

Alternatives 2-8 would provide long-ternl effectiveness and some degree of permanencc. The risk to future receptors is reduced/mitigated for all these alternatives by covering waste and implementing digging restrictions (Altematives 2, 3, 4, 5, 7, and 8), limiting/preventing infiltration (Altematives 3, 4, 5, 7) eliminating waste at the site (Altematives 6 ), or trcating wastc/contamination (Altemativcs 2, 3, 4, 6, 7, and 8). For the permeable cover options (Alternatives 2 and 8), the leaching of infiltrated water through the zone of unsaturated soil and waste beneath the cover enhances CWM degradation, and, as a result, leaching through the cover will mobilize other dissolved COCs. Alternative 2 will provide some VOC treatment by bio-cnhancement whilc

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Alternative 8 will provide extensive VOC treatment by bio-enhancement, wetlands, and the sediment cover. The low-permeability cover and RCRA cap options (Alternatives 3, 4, and 5) have a lower potential for CWM degradation above the water table and the RCRA cap options (Alternatives 4 and 5) will require vents that may pose potential CWM release threat. Full-scale excavation (Alternatives 6 and 7) offers the lowest incident of residual risk except for some habitat destruction.

Alternativcs 2-8 would provide various adequate long-term controls. Altematives 2, 3, 4, 5, and 8 will require long-term LUCs to protect the integrity of the cover/cap and to prevent contact with contaminants in the buried waste and groundwater. Altematives 6 and 7 will also require long-term LUCs due to residual contamination in soil. All Alternatives (2-8) would will require long-term groundwater monitoring. The subsurface ban'ier in Alternative 5 may require partial hydraulic control/groundwater treatment to maintain containment.

The degree of permanence for the cover alternatives (Alternatives 2, 3, 4, 5, and 8) is dependent on the effectiveness of long-term maintenance and LUCs. The thorough access restrictions already in place at APG, along with additional land-use and groundwater restrictions, security measures, and maintenance of warning signs could effectively control human contact with harnlful levels of contaminants in the long term, preventing activities which would disturb the disposal trenches and preventing groundwater use. The bio-enhancement component in Altematives 2, 3, and 8 will require periodic recharge but the wetland construction component in AItematives 4 and 8 has a self-sustaining replenishment of organic carbon. Altemative 8 also includes a sediment cover which includes a self-sustaining replenishment of organic carbon. The excavation alternatives (Alternatives 6 and 7) would provide long-term effectiveness and permanence. Any existing groundwater contamination left after excavation is likely to naturally attenuate due to biodegradation (the breakdown of chemicals by biological activity) and immobilization (the binding of chemicals in forms that will not move or cause toxicity). In summary, Alternatives 6 and 7 provide the greatest degree of permanence. Capping and cover alternatives all provide a similar degree of permanence. Those cap or cover alternatives which require the least maintenance due to incorporation of naturally sustaining wetlands (Alternatives 4 and 8) or robust barriers (Alternative 5) provide slightly more pennanence than those that do not (Alternatives 2 and 3).

Reduction of Toxicity, Mobility, and Volume Through Treatment

Alternative 5 does not reduce toxicity, mobility, or volume tlu'ough treatment. Alternativcs 6 and 7 use treatment to stabilize and solidify contaminated excavated soils, and thus decrease toxicity and mobility of buried wastes. For Altematives 6 and 7, the source is removed, the treatment is irreversiblc, and no residual remains after treatment.

Alternative 2, 3, 4 and 8 leave the source in place and the VOCs in groundwater are treated in-situ through various processes. Alternatives 2, 3, and 8 use the in-situ destruction (bioremediation) process. Alternatives 4 and 8 use the phytoremediation in a constructed wetland or wetland buffer to treat groundwater. Alternative 8, in addition to

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combining the bioremediation process and the phytoremediation process, uses organic carbon sequestration of VOCs and inorganics in the wetland buffer and sediment cover.

Altematives 2 and 8 also allow treatment of chemicals in buried waste by allowing infiltration of water and subsequent treatment through the bioremediation process and the phytoremediation process. With the exception of Alternative 5, toxicity and volume are reduced for the other altematives through each alternative's treatment process described above.

Short-Term Effectiveness

Implementation of Alternatives 2-8 would require proper engineering controls and health and safety procedures to protect remedial workers, the community, and the environment. There is negligible risk to remedial workers for Alternatives 2, 3, and 8, moderate risk for Altematives 4 and 5, and high risk for Alternatives 6 and 7. Excavation alternatives (Alternatives 6 and 7) would involve more risks to remedial workers due to the likely presence of UXO and CWM in the disposal trenches. Risk to the community is negligible except for Alternatives 6 and 7, where the risk is moderate. Workers would be protected through thc use of appropriate personal protective equipmcnt and air monitoring equipment.

Thc capping altell1atives (Alternatives 2, 3, 4, 5, and 8) would achieve RAOs within a pcriod of months after implementation (e.g., 12 to 19 months); however, the excavation alternatives (Altell1atives 6 and 7) would take years (e.g., 65 to 77 months, not including down-time due to weather, eagle-nesting season or safety precautions required by unexpected challenges posed by UXO/CWM).

Implementability

Altell1ativcs 2, 3, 4, and 8 would be relatively easy to implemcnt because materials, equipment, and skilled labor are readily available. Altemative 5 would require some specialty contractor work to construct the barrier, and Altematives 6 and 7 would require additional safety engineering controls and involve high hazard work. For all the alternatives 2-8, the technology is implementable. For Alternatives I through 5, implementation is straightforward. Altemative 8 would involve some technical challenges to place the sedimcnt cover. Altematives 6 and 7 arc technically challenging to implement due to the potential complexity of the buried waste and the substantial safety hazards associated with its excavation and treatment. For all actions, treatment proccsses are easily monitorcd, and additional actions are not incompatible.

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Cost

The total costs of remedial alternatives addressing the New a-Field Area are;

Alternative I No Action $0

Alternative 2 Permeable Cover with Groundwater Bio-Enhancement $4,587,000

Alternative 3 Low-Permeability Cover with Groundwater Bio-Enhancement $4,349,000

Alternative 4 RCRA Cap with Constructed Wetland $6,892,000

AI ternati ve 5 RCRA Cap and Subsurface Barrier with Monitored Natural $3,671,000 Attenuation

Alternative 6 Full-Scale Excavation, On-Site Treatment, Off-Site Disposal $37,543,0006

and Monitored Natural Attenuation

Alternative 7 Full-Scale Excavation, On-Site Treatment, On-Site Landfill, $36,248,000' and Monitored Natural Attenuation

Alternative 8 Pel111eable Cover Bio-Beneficial Sediment Cover, and $3,648,000 Groundwater Bio-Enhancement with Wetland Buffer

6 Cost does not include additional treatment and disposal costs for CWM and UXO or disposal of the stockpiled soil from the pushout area removal actions. 7 Cost does 110t include additional treatment and disposal costs for CWM and UXQ.

Cost of the cover/cap alternatives (Alternatives 2, 3, 4, 5, and 8) have the lowest degree of uncertainty for capital cost, but also have the highest degree of uncertainty for long­term costs. This unceltainty is due to the need for long-term O&M monitoring, and the possibility that the monitoring could trigger requirements for further investigation and remediation. The uncertainty in cost estimates for the excavation alternatives (Alternatives 6 and 7) is duc to uncertainty in wastc volume estimates and also the fraction of waste that is hazardous by RCRA characteristic. Jf the fraction of waste that is hazardous by RCRA characteristic is greater than the assumed estimate, the cost of Alternatives 6 and 7 would be much higher than estimated. If long periods of downtime (due to weather, eagle-nesting season or safety precautions required by unexpected challenges posed by UXO/CWM) are encountered, the overall project durations and costs will be significantly impacted. Also, costs for these alternatives do not include treatment and disposal of UXO and CWM; costs for treatment and/or disposal would be substantial. They also do not include disposal of stockpiled soil from the New a-Field Pushout Area Removal Actions.

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2.10.1.3 ModifYing Criteria

State and Community Acceptance

State representatives and the public were provided an opportunity to review and comment on the alternatives presented in the Proposed Plan for remedial action at New O-Field. Comments provided during the public review period are addressed in the responsiveness summary. Based on a thorough review of the remedial altel11atives and public comments, MDE concurs with the Selected Remedy.

2.11 PRINCIPAL nlREATWASTES

The principal threat to human health and the environment at New O-Field is direct exposure to shallow buried CWM and other waste materials. This exposurelrelease could occur as a result of inadvertent human activity, animal burrowing or natural erosion processes. Leaching into groundwater is also a primary release mechanism, with seasonal fluctuations in the groundwater table (estimated at 6.5 f1) high enough to enter into the trenches (trench depths estimated at 6-10 f1). Groundwater currently discharges directly into the man-made pond. Principal threat wastes will be addressed by the selected remedy. Erosion that could result in exposure of and release from buried waste will be controlled through installation of the permeable soil cover. Transport of chemicals via groundwater will be reduced through in situ treatment downgradient of the source area.

There arc no identified risks for industrial workcr exposure to the environmental media at the OOA.

2.12 SELECTED REMEDIES

2.12.1 lEW O-FIELD GROUNDWATER AND SOURCE AREA

The Selccted Remedy for the New O-Field groundwater and source area is Alternative 8, Permeable Cover Bio-Beneficial Sediment Cover, and Groundwater Bio-Enhancement Barrier with Wetland Buffer (Figure 6). Alternative 8 is expected to meet all the specific RAOs determined, based on a review of available data and all ARARs. The remediation costs for Alternative 8, as estimated in the Proposed Plan (EA 2008a), for New O-Field are presented in Table 6. The total estimated cost, rounded to the nearest $1,000, for this site is $3,648,000. A summ3lY of the cost breakdown is as follows:

• Estimated Present Worth Capital Cost: $1,874,000 • Estimated Present Worth O&M Cost: $1,774,000 • Estimated Total Present Worth Cost: $3,648,000 • Estimated Construction Timeframe: 12 Months • Estimated Time to Achieve RAOs: Circa 2010

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The Selected Rcmedy for New O-Field groundwater and source area is intended to prevent human and ecological exposures to COCs at levels presenting unacceptable risk and to prevent migration of COCs from thc site. The Selected Remedy is designed to reduce or eliminate the potential risks to human or ecological receptors via containment of impacted soil and site LUCs.

The Selected Remedy will include the following actions:

• Installation of a 1.6 acre 2 ft thick permeable soil/sand cover over the trenches and the WP-contaminated soil generated during the Pushout Area Removal Actions (to include penneable geotextile fabric, a minimum of 18 in. of clean soil, 6 in. of topsoil, and vegetation);

• Placement of a vegetated bio-beneficial sediment cover over the bottom of the open water of the pond composed of sand or soil amended with a carbon source such as topsoil, chitin (shrimp or crab shell), or compost placed in lifts to minimize mixing with underlying sediment (may also include a surface layer of gravel or stone to am10r against erosion, or an underlying layer of permeable geotextile to prevent mixing);

• Installation of an in-situ bio-enhancement balTier system to address VOC contamination in groundwater by using existing wells in the area for injection of nutrients and microbes directly downgradient from the trenches and potentially along the entire depth of the aquifer to the underlying clay layer while a groundwater-filled depression in this area will be filled with limestone/lime to aid in controlling pH and provide a centralized point for extraction;

• Construction of a vegetated wetland buffer composed of sand or soil amended with organic carbon including installation of a 25-ft barrier 400 ft along the shoreline of the open water of the pond, encompassing approximately y" acre;

• Placement of coir fiber logs between the wetland and the open water to help armor and stabilize the wetland;

• Implementation of LUCs for New O-Field that, to reduce the potential for future risks, maintain the future land use as militarylindustrial and prevent future residential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Implementation of additional LUCs for New O-Field that would prevent digging, groundwater use or other activities in the area of the covers, buffer or groundwater treatment area that are incompatible with remedy effectiveness as long as chemical concentrations remain elevated above levels that allow for UU/UE;

• Implementation of LUCs for the OOA that, to reduce the potential for ftlture risks, maintain the future land use as military/industrial and prevent future residential land use (i.e. housing, elementary and secondary schools, child care facilities, and playgrounds) including utilization of groundwater as drinking water as long as chemical concentrations remain elevated above levels that allow for UUIU E;

• Long-term groundwater monitoring (4 monitoring wells would be installed for performance monitoring with 2 sampling events in the first year) and surface

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warer monitoring; • Long-term O&M of the permeable cover, wetland buffer, bio-beneficial sediment

cover, and groundwater treatment systems; and, • Five year reviews for 30 years.

The purpose of the permeable soil cover with armored toe is to provide adequate soil containment in this area, thereby protecting human and ecological receptors from exposure to buried materials and chemicals and preventing migration and volatilization of chemicals into the atmosphere and surface water. This permeable cover will achieve thc remedial goal of preventing erosion that may expose buried wastes; it will also allow infiltration that will reduce risks by breaking down CWM. This will also reduce site­wide wildlife exposures to COC in soil by covering over and preventing exposure to the highest concentrations of COCs in soil. The cover will also address risks to plants by covering over bare areas and replacing them with a vegetated surface.

The soil cover will consist of a penneable geotextile or barricr material (to prevent animals from burrowing), a minimum of 18 in. of clean soil, 6 in. of topsoil, and vegetation. Stockpiled soil from the pushout area removal actions will be placed under the permeable cover. The toe of the cover would also be armored with Class I rip-rap, due to the proximity to the IOO-year floodplain. The total area occupied by the two open trenches and the covered disposal trenches is approximately 1.6 acres. During construction activities, appropriate erosion control measures will be implemented. Construction will proceed in the following order: surface clearance of UXO; removal of existing surface vegetation; placement of stockpile soil; placement of permeable geotextile and clean soil; and, placement of topsoil and vcgetation. Long-term monitoring and maintenance of these areas will include periodic mowing and repairs due to settling and erosion. Inspections will be conducted to ensure continued integrity of the permeable cover.

An in-situ bio-enhancement system consisting of a central treatment cell and peripheral batTier will be implemented to achieve the rcmedial goal of addressing VOCs and other contamination in the groundwater by providing containment/treatment required by the state of Maryland variance; prcventing funher degradation of surface water associated with groundwater discharge to the pond; and protecting ecological receptors from chemicals in groundwater secps. As needed, baseline studies will bc used to evaluate the natural biodegradation of contaminants in groundwater at New O-Field to determine thc most appropriate nutrients and delivery system for enhancement of the process. Once the studies are complete, the full-scale implementation of an in-situ bio-enhancement system will involve the installation and operation of an active system that uses injection and cxtraction wells to deliver nutrients and microbes to the central treatment zone located at the ccnter of the VOC plumc immediately downgmdient of the trenches. These microbes will utilize the nutrients to break down contamination and create chemical conditions that will trap metals in forms that are not toxic or mobile. If necded, direct injection well points may also be used to extend groundwater treatment area over a wider region perpendicular to groundwater flow, prior to discharge into the pond. Proposed groundwater amendments include emulsified oil which will scrve as an electron donor/nutrient. Amendment with oil, combincd with the other remedial components at

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New O-Field, is expeeted to provide treatmelll and eontainment for VOCs, metals, and many CWM degradation produets. If the other ehemieals sueh as explosives beeome an issue, or if metals do not respond to the proposed treatment, zero-valent iron eould be used to aid in sequestering metals. The eontingent remedial solutions would be developed and implemented as needed in eonsultation with EPA and MOE. Long-term groundwater monitoring will be required to evaluate the effeetiveness of the system.

A wetland buffer will be eonstrueted and bio-benefieial sediment eover will be plaeed over the bottom of the open water area of the pond to aid in produeing eonditions that treat groundwater and proteet the loeal environment. These are not eonsidered part of the overall bioremediation system addressing groundwater leaehing from beneath the penneable eover. However, they will aid in breaking down or trapping chemieals in groundwater that has already moved beyond the zone of bioremediation before they are transported beyond the pond or released to surface water. They will also aeeomplish the RGs of preventing or drastieally redueing exposures of waterfowl to WP in sediment and exposures of aquatic organisms to chemicals in sediment and surfaee water. The eonstmcted wetland will include installation of a 25-ft barrier 400 ft along the shoreline of the open water of the pond, eneompassing approximately Y. acre. The wetland buffer will eonsist of sand or soil amended with an organic carbon source. A revetment of organic material will be placed between the wetland and the open water to help armor and stabilize the wetland. The wetland buffer will be vegetated with plants that eontribute additional organie earbon to the system, thus providing a naturally regenerating system that eontinuously treats and sequesters contamination. Several variables that will be determined in the Remedial Design phase are the type of organie earbon to include in the wetland substrate (options include topsoil, eompost, peat, and ehitin), and the plalll speeies.

For the bio-benefieial sediment eover, a I ft thick layer of cover material will be placed over the bottom of the open water area of the pond. The cover will consist of sand or soil amended with a source of carbon such as topsoil, chitin (shrimp or crab shell), or compost. In areas where the mean water depth is less than one foot, the eover may be less than a foot thick to avoid complete filling of the pond and wetlands. [n thesc areas, the cover will be plaeed over a permeable geotextile to limit mixing with the sediments beneath. It will stop at the mean water level and be vegetated with appropriate wetland speeies. In certain areas, it might also include a surfaee layer of gravel or stone to armor against erosion, or an underlying layer of permeable geotextile to prevent mixing, although the geomorphology of the pond represents a low-energy environment where significant sediment erosion or deposition is not expected. The cover may be placed in lifts to minimize mixing with underlying sediment. The cover will be placed over existing vegetation, whieh will provide an underling layer of organic carbon. The cover surface will be vegetated with submerged aquatic vegetation through seeding. The addition of the carbon to the sediment cover material will help create conditions that are highly redueing and very anaerobie. These conditions encourage the activity of microbes that break down chlorinated compounds such as those detected in New O-Field groundwater. The same conditions that encourage these microbes also serve to trap metals in fomls that are non-mobile, non-bioavailable, and non-toxic.

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Construction of the wetland buffer and bio-beneficial sediment cover will be conducted in immediate sequence. Construction will proceed with surface clearance of UXO, placement of coir fiber logs, placement of mixed sand and carbon in the wetland and as the sediment cover over the bottom of the pond, and then vegetation of the systems. Long-term monitoring will include monitoring ofthc vegetative cover and periodic repair and maintenance to control erosion.

The achievement of remedial action objectives will be measured through performance monitoring. This will include monitoring of the integrity of the soil cover, sediment covcr, and wctland buffer and monitoring of surface water and groundwater concentrations of COCs. Monitoring data and inspection results will be presented and evaluated in periodic monitoring reports.

For the soil cover and sediment cover/wetland buffer, the remedial response will be considered complete upon completion of construction and initial inspections to ensure cover integrity. After the remedial response is completed, LTM will include periodic inspections to ensure cover integrity. Any erosion of cover material, settlement of fill, or other breeches in the covers will be corrected as part of the routine maintenance procedures.

The effectiveness of the remedy in relation to the two RGs for groundwater will be determined using the following perfomlanee monitoring achievement criteria:

o Achievement of a reduction in groundwater concentrations of COCs to levels predicted not to cause risk to aquatic organisms in surface water. Both surface water and perfomlance monitoring wells installed downgradient of the treatment zone will be sampled periodically. Risk to aquatic organisms will be evaluated in periodic monitoring reports through a comparison of average groundwater concentrations in performance monitoring wells to benchmarks protective of aquatic life exposed to pond surface water. Comparisons will be conducted in accordance with the EPA guidance "Methods for Evaluating the Attainment of Cleanup Standards (EPA 1992). The site-specific criteria for groundwater necessary to achieve this risk reduction in surface watcr will be determined based on monitoring in cooperation with the Army, EPA and MOE, and will be identified not later than the first five year review.

o For those chemicals that exceed site-speci fie criteria protective of aquatic organisms (or temporary criteria until these criteria are developed), achievement of conditions that degrade or decrcase mobility and toxicity of chemicals in groundwater. In sittl bioenhancement utilizes natural processes; therefore, an initial period of several years may be requiTed to reduce concentrations of chemicals exceeding criteria. Therefore, one of the RGs is to establish conditions that degrade or decrease mobility and toxicity of chemicals in groundwater. Achievement of this RG will be indicated by a consistent and marked reduction in concentrations of dissolved-phase CVOCs, cationic metals and CWM in groundwater at the performance monitoring wells over several successive annual monitoring periods. The rate or trend of

53

dissolved-phase contaminant decrease considered indicative will be determined in consultation with Army, EPA, and MOE not later than the first five year review.

The site-specific criteria used to evaluate groundwater in the perfonnance monitoring wells will be based in pan on accepted values from guidance, the scientific literature, and site specific data sets, i.e. National Ambient Water Quality Criteria, Suter & Tsao 1996, and regional background concentrations. These values will be adjusted to provide site­specific criteria using the results of monitoring, which are expected to document factors that affect the linkage between groundwater and surface water. These factors will include groundwater and surface water hydrology and chemistry. Such factors cannot presently be quantified because in-situ treatment and the installation of other remedial measures at New O-Field will cause changes to hydrology, groundwater, and surface water chemistty that will influence transport and toxicity. These changes (i.e. pH, hardness, flow, water quality, physical conditions, and natural attenuation) must be incorporated into the development and achievement of sitc-specific criteria to ensure that they realistically reflect conditions at the site. Achievement of these site-specific criteria will signal achievemcnt of response completc/RGs and initiation of long term maintenance. Thcy will also provide a standard against which future monitoring results can be compared as p3l1 of long term maintenance.

Dcvelopment of final site-specific criteria may require several years of monitoring to provide data that link groundwater concentrations to protection of reccptors exposed to surfacc watcr based on post-remedial site-specific conditions. Until these criteria can be developed, temporary criteria derived from guidance and the scientific literature will be used to protect aquatic receptors in the surface water. These are summarized in Table 5 for groundwater COCs. The values in Table 5 were selected based on the best available benchmarks protective of aquatic life, with EPA WQC given greatest preference. If EPA WQC were not available, either Rcgion 111 BTAG screening values or benchmarks derived from literature-based sources were selected based on availability and tcchnical defensibility.

While the values in Table 5 arc protectivc for exposures to individual CYOCs, they do not account for combined effccts of CYOCs. As is the case for individual chemicals of concem, a site-specific criterion will be developed for total CYOCs using the results of monitoring. Until site-specific criteria can bc developed for individual and total CYOCs, a temporaty criterion of 100 ug/L has been selected as a concentration to which total CYOCs in groundwater will be comparcd during monitoring. This conservative criterion is based on the post groundwater treatment surface water discharge limits for total CYOCs established in the Old O-Field ROD. This criterion is not site-spccific for New O-Field. Toxicological data for New O-Field indicatc that total CYOC concentrations of up to 1078 ug/L mixed CYOC producc no statistically significant effects on aquatic organisms as indicated by toxicity tests perfot1ned using surface water from the New 0­Field seeps. It is expected that 539 ug/L CYOC, which is half of this no effccts concentration, would also provide a prccautionary criterion. Either this valuc or another value based on site-specific data from New O-Ficld monitoring will be adopted as the final critcrion for total CYOCs.

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Once remediation has achievcd demonstrable, consistent reduction rates for dissolved phase contaminants in groundwater, and resulting achievement of acceptable risks for surface water exposures, a ramp-down/exit strategy will be developed and implemented in conjunction with the first five year review. The strategy will be based on the risk- and technology-based site-specific criteria that incorporate overall protectiveness for the combined suite of dissolved-phase groundwater and surface water contaminants. These criteria will form the framework for continued monitoring and remediation optimization evaluations and provide eventual ramp down and site closure criteria. Criteria will thus provide comparison values for evaluating whether additional injections are required as part of long term maintenance of the remedial system.

Following the remedial actions at the site, contamination will remain that may exceed residemial criteria throughout O-Field OU4. Therefore, based on expected future military industrial land use, LUCs will bc implemented to prohibit housing, elementary and secondary schools, child carc facilities, and playgrounds at New O-Field (Figure 7). Additional LUCs will be implemented to prevcnt digging, or other activitics in thc area of the covers, buffer or groundwater treatment area that are incompatible with remcdy effectiveness (Figure 7). O-Field is located in a restricted portion of the Installation. Access to the restricted area is limited to properly cleared personnel or individuals in an escorted capacity. A wide variety of physical security countermeasures to include barrier systems, sensors and random patrols by law enforcement personnel are in placc to prevent unauthorized access. LUCs will be implemented using fencing, signage, and notation in the post GJS.

LUCs will be maintained until the conccntration of hazardous substances in the soil are below concentrations that allow for unlimited use and unrestrictcd exposure. The Remedial Design will be submitted in accordance with the remedial design schedule provisions of the FFA and will include an LUC component describing the dctails of LUC implementation and maintenancc, including periodic inspections. The Anny shall be responsible for implememation, maintenance, periodic reporting, and enforcement of LUCs in accordance with the Remedial Design. Although the Army may transfer these responsibilities to another palty by contract, property transfer agreemcnt, or through other means, the Army shall remain ultimately responsible for remedy integrity and shall: (I) perform CERCLA 121(c) 5-year reviews; (2) notify the appropriate regulators and/or local government representatives of any known LUC deficiencies or violations; (3) provide access to the property to conduct any necessary responsc; (4) retain the ability to change, modify or terminate LUCs and any related deed or lease provisions; and (5) ensurc that the LUC objective is met to maintain remedy protectiveness.

As a condition of property transfer or lease, the Army may require thc transferee or lessee in cooperation with other stakeholders to assume responsibility for various implementation actions. Third-party LUC responsibility will be incorporated into pCllinent contractual, propcrlY, and remedial documentation, such as a purchase agrcement, deed, lease, and Remedial Design addendum. To the extent permitted by law, a transfer deed shall require thc LUCs imposed as part of a CERCLA rcmcdy to run with the land and bind all propcrty owners and users. The Army acknowlcdges the responsibility for all original liability under CERCLA.

55

Table 5 Temporary Criteria Used to Evaluate Remedy Effectiveness Prior to Establisbment

f S' S 'fi C ' 0 Ite- 'DeCI IC ntena

Criteria*

Analyte Guidance/ToxicologBackground ical Criteria

Concentration A ISource)

CWM De!!radatioll Products (m!!/L)

DIISOPROPYL METHYLPI-10SPHONATE NA 500 rBI

ISOPROPYLMETI-1YLPI-10SPJ-10NIC ACID NA 500 rEI

METHYLPHOSPI-10NIC ACID NA 87 rCI

Dissolved Metals (J.IJ!/L)

1.9 150 rD1 COPPER

ARSENIC

38.4 9 rDl

ZINC 34.1 120 rDl

Volatile Oraallic Compoullds (J.IJ!/L)

610 rEI

I, I,2-TRICHLOROETHAI\TE

I, I,2,2-TETRACHLOROETHANE NA

1200 rEI

I, I-DlCI-1LOROETI-1ANE

NA

47 rEI

1,I-DICI-1LOROETHENE

NA

NA 25 rEI

1,2-DlCHLOROETHANE 100 rEI

I,2-DICHLOROETHENE (TOTAL)

NA

590 rEI

I,2-DICHLOROETHENE, CIS-

NA

NA 590 rEI

1,2-DICHLOROETHENE, TRANS­ 970 rEI

TETRACI-1LOROETHENE

NA

I II rEI

TRlCHLOROETHENE

NA

NA 21 rE1 VINYL CHLORIDE 930 fE]NA

*The greater of the two listed values wlil be used as the benchmark, A - Background values are t.he arithmetic mean of concentrations detected in groundwater under APG's Reference Sampling and Analysis Program. B - Literature-based No Adverse Effects Concentration for methylphosphonic acid from Baul1lmer, J., R. Hoke, W. McCulloch, S. Hartzell. Acute and Chronic Toxicity of Two Phosphonic Acids to Freshwater and Marine Organisms. Poster. Society for Environmental Toxicology and Chemistry North American Conference, 2004. C - Literature-based No Adverse Effects Concentration for ethylmethylphosphonic acid from Baummer, J., R. Hoke, W. McCulloch, S. Hartzell. Acute and Chronic Toxicity of Two Phosphonic Acids to Freshwater and Marine Organisms. Poster. Society for Environmental Toxicology and Chemistry North American Conference, 2004. D - Criterion Continuous Concentration from EPA 2006, Recommended National Water Quality Criteria. Some values are dependent on alkalinity and will require additional adjustment for hardness prior to use; a default value of 100 mg/L CACOJ was used for this table. E - Freshwater screening value from EPA 2006 Region 3 BTAG Screening Values.

56

If the Army intends to transfer ownership of any site, the Army may, if Federal andlor State law allows, upon transfer of fee title grant thc State an environmental covenant or easemcnt that will allow the State to enforce LUC terms and conditions against the transferee(s), as well as subsequent property owner(s) or user(s) or their contraclOrs, tenams, lessees, or other parties. This covenant will be incorporated by reference in the transfer deed and will run with the land in accordance with State realty law. This Statc enforcement right will supplement, not replace, the Army's right and responsibility to enforce LUCs.

Pursuant to CERCLA Section 121 (c), reviews are conducted no less than every 5 years when remedial actions are taken which result in any hazardous substances, pollutants, or contaminants remaining at the site above levels that allow for unlimited use and unrestricted exposure 10 ensure that the remedy remains protective of human health and the environment. Although this Alternative will contain COC-impacted soil, the site will have residual contaminants at levels requiring the Army to conduct 5-year reviews in accordance with CERCLA.

2.12.2 OTHER O-FIELD AREAS

Thc selected remedy for the OOA is implementation of LUCs, which will be put in place to prohibit residential land use including housing, elememary and secondaly schools, child care facilities, and playgrounds at this site, and restrict use of groundwater as drinking water. Due to the concerns that UXO and CWM may be present at the sitc, coupled with the proximatiy of the OOA to Ncw O-Field and Old O-Field where residential land use is prohibited, residential land use would not be appropriate at the OOA. As a result, residential adults and children were not included in the risk assessmcnt as receptors of concern. Figure 7 presents the arca boundaries where the LUCs for the OOA will be applied and maintained. The Remedial Design will be submined in accordance with the remedial design schedule provisions of the FFA and will include an LUC component describing the details of LUC implementation and maintenance, including periodic inspections. The Army shall be responsible for implementation, maintenancc, periodic reporting, and enforcement of LUCs in accordance with the Rcmedial Design. Although the Army may transfer these responsibilities 10 anothcr party by contract, property transfer agrecment, or through other means, the Army shall remain ultimately responsible for remedy integrity and shall perform the following: (I) CERCLA 121 (c) 5-year reviews; (2) noti fication of the appropriate regulators and/or local government representativcs of any known LUC deficiencies or violations; (3) provide access to the property to conduct any necessary response; (4) retain thc ability to change, modify, or tenninate LUCs and any related deed or leasc provisions; and (5) ensure that the LUC objective is met to maintain remedy protectiveness.

As a condition of the property transfer or lease, the Army may require the transferee or lessee in cooperation with other stakeholders to assume responsibility for various implemcntation actions. Third party LUC responsibility will be incorporated into pertinent contractual, property, and remedial documentation, such as a purchase agrcement, deed, lease, and Rcmedial Design addendum. To dle extent permitted by law, a transfcr deed shall require LUCs imposed as part of a CERCLA rcmedy 10 rim with thc land and bind all property owners and users.

57

Table 6 Cost Summary for Alternative 8--Permeable Cover Bio-Beneficial Sediment Cover,

and Groundwater Bio-Enhancement with Wetland Buffer UNITICOMPONENT UNIT OUANTITY PRICE COST

Permeable Cover Bio-Beneficial Sediment Cover CAI'ITAL

Site PrcDaratioli and RCDortin~ S158,000

Administmtive Costs8 S5,000

Remedial Desion/Work Plan

Lumn Sum 0.5 SIO,OOO

Report S75,000 S75,000

Erosion and Sediment Control Plan

1.0

Report S15,000 S15,000

Remedial Action Completion Report

1.0

Report 1.0 S60,000 S60,000

Office Trailer & Portable Toiletb,C 5500 S3,000

Site PrcDaratioll (I\1odified Lc"cl 0 PPE) S225738

Mobilizalion/Demobilizalion

Month 6.0

Event 2.0 510,000 S20.000

Dceon Pad (50' x 50' aSPhalt with 8x8" curbst 54,586Lunm Sum 1.0 S4,586

Erosion COlllfOI- Silt Fence and Bermsb LUllll) Sum S3,687 S3,682

Clearing & Grubbill Ob

1.0

Acre S6,637 S12,61O

Up.l.{radc Exislill~ Entrance Road ll

1.9

Linear FOOl 800 S55.00 S44,000 Access Road Construction (80% in upland/20% in marsh)b Linc~)f Foot 1,300 S62.20 580,860

UXO Clearance ofSunnort Areas (2-man team)' Day 40 SI,500 S60,000

Soil Cover Construction (Modified Level D PPE) S390,266

Rental of Construelion Equipment Month 6.0 S12,000 S72,OOO

Unclassified Fill, 6" Lifts, 16" Deepb 512.09 5111,168

Imported Topsoil, 6" Decpb

Cubic Yard 9,195

1,668 S41.91 569,906

Anchor Trcnehb Cubic Yard

Linear FOOl 1,200 53.31 S3,972

#2 Ri Jrap Armor $49,213.00 S49.213

Gcolextilc Drainage Fabricb L5 I

Square FOOl 94,113 $0.83 S78,114

Hvdroseedilll.! (includes 1101 soot areas)b Acre S3,102 S5,894

BiD-beneficial Sediment Cover $128,919

Rental ofConslruction Equipment (Cranelbackhoc)

1.9

S12,000 S24,000

Sand, 6" Lifts, 12" Deeph

Monlh 2.0

S59,774

Weiland Substrate Matcrial (composl!peatmixlurc)b

Cubic Yard 3,904 S15.31

Cubic Yard 390 S75.00 S29,282

SQllare Fool 10,890 59,039

J-1ydrosccdingb

Geolexlile Drain<l"c Fabricb SO.83

S3,102 56,824

Sllblolnl (clH!inecrinl!, rounded)

Acre 2.2

5902,924

Proiect Manallcmcnt (8% of enllincering) S72,OOO

Base SUOIJOrl (3% of enllinecring) S27,OOO

TOlal CalJilal SI,002,000

58

Table 6 (continued) Cost Summary for Alternative 8--Permeable Cover, Bio-Beneficial Sediment

Cover, and Groundwater Bio-Enhancement with Wetland Bufth UNIT

COMPONENT UNIT OUANTITY PRICE COST

PERMEABLE COVER BIO-BENEFICIAL SEDIMENT COVER Icontinuedl

ANNUALO&M

Administrative Actions· S5,300

S-Year Review (on an annual basis)b S7,600Rcoort 0.5 S3,800

Public Education Lump Sum 0.5 S2,000 SI,OOO

Institutional Controls/Oversight Lump Sum 0.5 S1.000 S500

Lone-Term Maintenance S15,478

Maintenance of Fencc/Waming Signs Lump Sum 0.5 S500 S250

Mowing (4 acres)b Event SI,52310 S15.228

Subtotal (annual O&M. rounded) S20,800

Present Worth ofO&M (30 years) S408,000

Total Present Worth (30 \'ears (iil3% discount rate) 51,410,000

GROUNDWATER BIOENHANCEMENT BARRIER WITH WETLAND BUFFER

CAPITAL

Site Prenar4ltion and RCDortilll! SI78000 Lump

SIO,OOOAdministrative Costsa Sum 0.5 55,000

Remcdial DesignIWork Plan Report 525,000 525,000 Lump

Treatability Studies

1.0

5100,000 5100,000

Erosion and Sediment Control Plan

Sum 1.0

1.0 515.000 515,000

Otlicc Trailer & POl1able Toilctb

Reoort

Month 6.0 5500 53,000

Long-Icon Monitoring Plan RCj)ori 1.0 530,000 530,000

Groundwater Bioenhancement Barrier S293,292

UXO Clearance (1 leam)' 15 51,500 522,500 Square

Installation of Edible Oil Pemleable SalTier (0.3 acre)

Dav

Foot 13,068 519.00 5248,292

Iniection Point Installation - lOft centers Dav 15 51.500 522,500

Microbial cultures for bioaugmemation Liter 10.0 5250 52,500

Wetland Bufler Installation SI19978

UXO Clearance (2-m<ln team) 51,500 545,000 Rcntal of Constnlction Equipmcnt (excav<ltorlbackhoe)

Dav 30

512,000 Sand (6" lifts. average of I fOOl deep over 25 fOOl

Month 1.0 512.000 Cubic

buffer)b S12,475 Cubic

Carbon Source Material (compost/peat mixture)

Yard 815 515.31

575.00 56,111 Linear

Coir fiber 100 5

Yard 81

400fOOl 522.50 59,000 5quare

\Vclland Vegel<llion Planting~ Foot 10,890 53.25 535,393

59

Table 6 (continued) Cost Summary for Alternative S-Permeable Cover, Bio-Beneflcial Sediment

Cover, and Groundwater Bio-Enhaneement with Wetland Buffer UNIT

COMPONENT OUANTITYUNIT PRICE COST

GROUNDWATER BroENHANCEMENT BARRJER WITH WETLAND BUFFER (continued\

Performance Monitorin2 & O\'crsi2ht S194,022

UXO Clearance (one 2-miln EOD teamt Day SI,500 S7,500

Well Installation (Additional Monitori'm Wells\"

5.0

S3,000Well 4.0 S12,000

PerfOnllanCC Monitoring (2 evenIs in veal' I)b,C Event 2.0 S60,036 SI20,072

Construction Oversightb S18,150 S54,450

Subtotal (cl1Q.inceri1H!, rounded)

Month 3.0

S785,292 Project Mnnagcmcnl (8% of engineering) S63,000

Base Sunnort (3% of cngincerinl') S24,000 Total CaDital S872,000

ANNUALO&M

Administrative Actions S5,300

5-Ycar Review (all an annual basis)b ReD0!1 0.50 S7,600 S3,800 Lump

Public Education 0.50 S2,000 SI,OOO Lump

Institutional Controls/Oversight

Sum

Sum 0.50 SI,OOO S500

Lon1!-Term Maintenance S44,632 Lump

Maintenance of FenceIWarnin[! Signs S500 S250 Lump Sum 0.50

Maintenance of Injection Points Sum 1.00 S3,000 S3,000

Reinjection (Edible Oil) ,

S124,146 S41,382

Groundwater/Surface Water Monitorine: S19,812

SamDle Labor, PreD., & RetlMing (400 hrs/even!)'

Year 0.33

S60.50 57,986

Sampling Equipment

Hour 132

S2,500 S825

Aaucous SamlJle Analvscsc,d

Evcnt 0.33

Evenl S33,336 SII,OOI

Subtotal (annual O&M, rounded)

0.33

S69,700

Present Worth ofO&M (30 vears) SI,366,000

Total Present \Vorth (30 years (a) 3% discount rate) S2,238,000

60

Table 6 (continued) Cost Summary for Alternative 8--Permeable Cover, Bio-Beneficial Sediment

Cover and Groundwater Bio-Enhancement with Wetland Buffer,

COMPONENT [ UNIT IOUANTITY I UNIT PRICE COST

COMBINED COSTS

Capital Costs, Pemlcable Cover, Bic-Beneficial Sediment Cover S I,002,000

Annual O&M (Present Worth), Pcnl1cable Cover, Bic-Beneficial Sediment Cover $408,000

Capital Costs, Groundwater Bioenhanccmcnt BalTier with Wetland Buffer $872,000

Annual O&M (Present Worth), Groundwater Bioenhanccmcnt Barrier with Weiland Buffer $1,366,000

Total Present Worth (30 ycars@ 3% discount rate) S3,648,000

I. Costs arc based on existing site knowledge and are for evaluating remedial altcmatives only. 2. Assumes that all administrative actions will be accomplished as part of a site-wide institutional controls program; therefore, administrative costs for each area of concern are equal to 50% of the IOlal expense.

Notes:

Costs include GIS entry of land-use restrictions into the Master Plan and other administrative setup costs.

h Unit costs from RACER 2007.

Costs based on a vendor quote.

Long-term monitoring for groundwater & surface water conducted annually for the first five years and once evel)' five years for the next 25 years (averages to 0.33 per year for costing purposes). Assumes collection of 20 samples plus QC. Analyses include TCL VOCs, CWM degradation products (organosulfur, DIMPIDMMP, IMPA/MPA, and thiodiglycol), TAL metals, and natural attenuation parameters (pH, total dissolved solids, chloride, nitrate/nitrite, sulfate/sulfide, felTous iron, redox potential, dissolved gases, and lotal organic carbon).

Cost based on engineer's estimate using cost data from previous projects.

61

If the Army intends to transfer ownership of any site, the Anny may, consistent with federal and state law, upon transfer of fee title grant the State an environmental covenant or easement that will allow the State to enforce LUC temlS and conditions against the transferee(s), as well as subsequent property owner(s) or user(s) or their contractors, tenants, lessees, or other parties. This covenant will be incorporated by reference in the transfer deed and will run with the land in accordance with State realty law. This state enforcement right will supplement, not replace, the Army's right and responsibility to enforce LUCs.

2.13 STATUTORY DETERMINATIONS

USEPA and MDE support the Selected Remedies as necessary to adequately and cost­effectively protect human health and the environment. The Selected Remedies will meet the following statutory requirements of CERCLA 121(b): to be protective of human health and the environment; to comply with ARARs; to be cost-effective; and to use pemlanem solutions and alternative treatment technologies to the maximum extent practicable. The Selected Remedy will reduce toxicity, mobility, and volume of source material through in situ bioremediation via injection of edible oi I. The Selected Remedies utilize a pcrmanent solution to the maximum extent practicable.

The following sections discuss how the Selected Remedies meet these statutory requ irements.

2.13.1 PROTECTION OF HUMAN HEALTH AND TIlE ENVIRONMENT

The Selected Remedies for New O-Field and the OOA will be protective of human health and the environment through implementation of the remedial design, confirmation monitoring, and implementation of LUCs. The implementation of LUCs will be protective of human health by preventing future housing, elementary and secondaJy schools, child care facilities, and playgrounds.

The Selected Remedy (Altcrnative 8) for New O-Field will meet RGs and address the COC-impacted soil, sediment, surface water and groundwater. The Selected Remedy for New O-Field is protective of human hcalth through limitations on direct contact with the COCs in soil provided by LUCs and the permeable soil cover. It is protective of terrestrial wildlife through limitations on direct contact withlingestion of the COCs in soil provided by the soil permeable cover. The Selected Remedy is protective of aquatic organisms and wildlife through limitations on direct contact with/ingestion of COCs in the sediment provided by the wetland buffer and biobeneficial sediment cover. It is protective of aquatic organisms and wildlife through limitations on direct contact with/ingestion of COCs in the groundwater discharging to surface water. This is achieved through treatment of groundwater prior to discharge by the wetland buffer, biobeneficial sediment cover, and in situ bioremedialion zone. The remedy components also reduce contaminant migration. The permeable soil cover controls migration through runoff and erosion. The wetland buffer and sediment cover control migration of COCs in sediment. Groundwater treatment via the wetland buffer, bio-beneficial sediment cover,

62

and in situ bioremediation zone reduces contaminant concentrations 111 groundwater before it discharges to surface water.

The implementation of the remedy may destroy some established habitats. Re-vegetation will eventually address the replacement of habitat. To protect workers, onsite activities will be conducted in accordance with Occupational Safety and Health Administration (OSHA) requirements for workers at remedial sites (29 Code of Federal Regulations [CFR] 1910).

Data from monitoring will verify whether the Selected Remedy at New O-Field was effective in attaining the RGs.

2.13.2 COMPLIANCE WITll ApPLICABLE OR RELEVANT A D ApPROPRIATE

REQUIRE~'IE TS

The Selccted Remedy for New O-Field will comply with location-specific ARARs regulating wetlands, floodplains, and proximity to surface water, and ecological receptors. The Selected Remedy will also be conducted in compliance with action­specific ARARs related to erosion and sediment control, dust emissions, hazardous and non-hazardous waste disposal, ordnance and explosive waste removal, landfill closure, and monitoring. Table 7 presents the ARARs for the Selected Remedy for New O-Field.

2.13.2.1 ARARs Regarding Wildlife amI Habitat

The preferred remedy will be conducted in accordance with the Bald Eagle and Golden Eagle Protection Act (16 U.S.C. 668(a) and 50 CFR Part 10) and COMAR 27.01.09.03, Threatened and Endangered Species Protection, which are identified as applicable. Bald eagles have previously nested in the vicinity of ew O-Field. Other threatened and endangered species have not been recorded at the site. The prcferred remedy will bc conducted in coordination with post natural resources personnel to ensure compliance with relevant restrictions, including work restrictions within 500 meters of eagle nests during breeding season.

COMAR 26.04.01.04 regarding tidal wetlands, COMAR 27.01.05 regarding clearing of forcsts, and COMAR 27.01.09.0 I and -.04 rcgarding habitat protcction in Chesapeake Bay Critical Areas are identified as applicable ARARs. The selccted remedy will comply with substantive requirements of these COMAR through preservation/restoration of wctlands and avoidance of forest impacts. Two distinct advantages of the preferred remedy ovcr other alternatives are minimization of disturbance to wetlands, forests, and Critical Area habitat, and incorporation ofre-vegetation of the site with native vegetation.

63

2.13.2.2 ARARs Regarding Wells, Particulate Maller, and Erasion COlllrols and Water Quality

eOMAR 26.04.04.07, eOMAR 26.04.04.10, and eOMAR 26.04.04.11 are identified as applicable ARARs regarding well installation, responsibilities and closure. eOMAR 26.11.06.03 is identified as an applicable ARAR regarding particulate matter emissions during construction.

eOMAR 2617.01.07 and eOMAR 26.17.01.11 regarding sediment and erosion controls are identified as applicable. Substantive requirements regarding sediment and erosion control will be documented in the remedial design and will incorporate applicable sediment and erosion control measures.

eOMAR 26.08.02.03 is identified as rclevant and appropriate and 40 eFR 122.4I(a)(I) and eOMAR 26.08.03.01 are identified as applicable ARARs, respectively. These regulations address discharge of water and relevant water quality criteria. They will be applicable if it is necessary to discharge purge water from wells as part of sampling or in situ bioremediation.

2.13.2.4 ARARs Regarding Landfill Closure

The Selected Remedy (Alternative 8) for New O-Field provides the risk and hazard reduction necessary to address contamination at the site. However, the permeable cover design differs from the specifications for a typical landfill cap provided in State of Maryland regulations. The Army, as the Lead Agency, in consultation and in agreement with the USEPA, requested from MDE consideration that a variance from the ARAR regarding the closure of sanit3ly landfills (eOMAR 26.04.07.2]) would be appropriate in this casco [n general, the permeable cover design does not meet the specifications in the eOMAR for landfill closure. Howcver, eOMAR 26.04.07.26 (Variances) states that the state "shall grant a variance when the design or method of operation proposed in the variance application has been shown by the applicant to the satisfaction of the Approving Authority to conserve and protect the public health, the nanlral resources, and environment of the State, and to control air, water, and land pollution to at least the same extent as would be obtained by compliance with the regulation." When combined with thc groundwater treatment components of the remedy, the permeable cover is part of a total final remedy that attains a level of protectiveness and containment consistent with a eOMAR-compliant impermeable cap. The permeable cover and groundwater treatment systems will be properly constructed, maintained and monitored to ensure that the level of environmental protectiveness is equivalent to a eOMAR-compliant impermeable cap. An additional justification for the permeable cover is that, based on the site conditions, use of an impermeable cap in the final rcmedy could result in a comparatively grcater risk to human health and the environment.

64

The variance was requested based on the following considerations:

I. The bottom portion of the buried material in trenches is expected to be present beneath the water table. Therefore, installation of an impermeable cap on the site would not eliminate contamination of groundwater leaving the site. Chemicals may enter groundwater from buried waste below the water table as well as liquids leaking from buried containers above the water table. Also, as material beneath the water table deteriorates and settles, dry material above will sink and eventually enter the water table. Therefore, the proposed permeable cover and associated systems which serve to treat groundwater provide a remedial solution which is equally ifnot more protective than installation of an impermeable cover.

2. New a-Field is unique in that the buried contents of the trenches are likely to contain CWM, including nerve agent, in containers and munitions. The most effective means of breaking down and suppressing CWM is hydrolysis under wet or moist conditions. The type of dry conditions that would be expected under an impenneable cap would preserve munitions and encourage persistence of CWM should it be released. This increases the long tem1 risk of release of CWM and exposures for nearby workers and the environment.

Installation of a permeable soil cover over the trenches would allow gradual infiltration of precipitation. Infiltration is a key factor in the continued breakdown of both the CWM and the munitions that may contain them. I.nfiltration allows the gradual corrosion and breach of intact munitions, which physically decreases their explosive potential and allows breakdown of the CWM inside. The introduction of water below the cover hydrolyzes the agent to form degradation products, the majority of which are relatively non-toxic. It also serves to keep the soil moist, preventing combustion of buried white phosphorus and suppressing evaporative release of agent. Therefore, the continued contact with infiltrating water allowed by a permeable cover significantly reduces the persistence of toxic CWM in the subsurface as well as the risk of catastrophic release. This rationale is consistent with that used previously to support the placement of a permeable cover at nearby Old a-Field, where infiltration is accepted as a key component of treatment. I.n addition to treating CWM above the water table, the proposed remedial alternative provides the benefit of leaching of buried material above the water table and then treating leachate by the groundwater bioremediation component of the remedy. A groundwater bioenhancement bioremediation zone is planned as an essential treatment feature that will work to treat and contain leached chemicals. Injection of other treatment materials in conjunction with bioremediation may also be conducted on an as needed basis in consultation with EPA and MOE. A constructed wetland buffer and bio-beneficial sediment cover aid in breaking down contamination in groundwater that has already moved beyond the zone of bioremediation. The end result of this rcmedial approach is a reduction of contaminant mass and toxicity over time.

65

3. Installation of an impermeable cap on the site would potentially require passive landfill gas vents to the open atmosphere. If chemical agent was released in the subsurface due to a breach of a container, the chemical agent could pose a hazard to site workers if released through landfill cap vents or through lateral migration beyond the extent of the impemleable cap membrane. A pe1111eable cover does not provide a direct open conduit to the subsurface (i.e. vent). A permeable cover minimizes the potential for release of a chemical agent to the surface by allowing for infiltration that will hydrolyze and break down any CWM that has dispersed into the subsurface.

In response to the request for a variance, MDE provided a letter, included as an attachment to the PRAP and this ROD, stating that the request would be viewed favorably if the following conditions were adequately addressed in the Record of Decision for this site:

I. The permeable cover with an in situ groundwater treatment system will be implemented to ensure treatment of all impacted groundwater before it exits the treatment zone or area of attainment. The area of attainment shall be defined as the disposal trenches and the biological treatment zone (emulsified oil).

2. Long-teml operation and maintenance activities will be implemented to protect the integrity of the permeable cover and in situ groundwater treatment system with monitoring adequate to meet the needs of the MDE Federal Facilities Division (FFD).

3. Long-teml monitoring of groundwater and surface water will be implemented to monitor the effectiveness of the permeable cover and in situ groundwater treatment system at New O-Field and to evaluate the potential migration of contaminants toward Watson Creek. Again, this monitoring program must meet the neecls of the MOE FFD in evaluating the adequacy of the remecly and the continued use of the variance provision contained in COMA R.

The total thickness of the soil layers in the perllleable cover are specified as 2 feet in keeping with the cover thickness specifications in COMAR 26.04.07.1 OF and COMAR 26.04.07.18H, which are identified as relevant and appropriate ARARs. COMAR 26.04.07.22, which specifies post-closure inspection and maintenance requirements, is identified as relevant and appropriate. As required by the variance, long term monitoring of the permeable cover will include routine inspections.

66

Table 7: New O-Field AetionfLoeation-Specifie Federal and State Applicable or Relevant and Appropriate Requirements which are the Substantive Requirements

F dO hFIloun lilt e 0 OWlll~ R Ie~u ahons Environmental Action or Status Consideration as an ARAR

Laws and Affected Regulations Resource

Federal Action & Location Soecilic ARARs Bald and Golden Protection of Applicable The Act prohibits "laking" of eagles. including their Eagle Protection Act eagles, their paris, pm1s, nests or eggs. The Act defines "lake" as 16 U.S.c. 668(a) and and their nests. "pursue, shoot, shoot ai, poison, wound, kill, capnlre, 50 CFR Part 10 trap. collect, molest or disturb. In anticipation of the

removal of the bald eagle from the threatened species list, the Fish and Wildlife Service has used "interpretation" to expand the definition of"dislurb" 10 include actions thai significantly interfere with Ilannal breeding, feeding, or sheltering behavior. The recently published National Bald Eagle Management Guidelines (USFWS, 2007) recommend nest buffers of330 to 660 n, and the APG Bald Eagle Management Plan (2007) continues to lise the 500 meter butTer. These guidelines and management plan arc to·be-collsidcred (TBe) criteria for complying with the ARAR.

Compliance with Establishing Applicable Applicable unless state standards are lllore stringent. efflucnt limitation effluent Prohibits discharge 10 surface watcr unless effluent standards limitations COnf0n11S with stnndards for toxic pollutullls. 40 CFR 122.41 (a)( I) standards Requirements apply 10 any wastewater from

decontamination during sampling and COnSlnlClioll or to any water extracted from wells requiring discharge to surface water.

Maryland Action Specific ARARs [Well] Construction Construction Applicable Establishes requirements for well construction, well St'alldards standards for wells design, construction m<lterials and conslTUction COMAR 26.04.04.07 procedures. Well Owner's Maintenance and Applicable Requires well owners to maintain wells so that Responsibilities protection of groundwater is protectcd and wells can be identified. COMAR 26.04.04.10 t!roundwater wells [Well] Abandonment Well aballdonl11cnl Applicable Establishcs standards for abandollmclll of wells. Standards standards COMAR 26.04.04.11 SanilalY Landfills Sanitary landfill Relevant & These COMAR scctions establish requirements for COMAR operations Appropriate operations of sanitary, rubble and nOIl~hazardous

26.04.07.10F, industrial landfills. Establishes requiremcnts for 26.04.07.18H d<lily cover and fin'll cover. The remedy for the site

does not constilUte "operntion" of a landfill. However, the closure requiremcnts established by COMAR 26.04.07.21 Sanitary Landfill - Closure presume that there is cover soil (daily cover and final cover) in place <lS specified by these opernting procedures that will minimize hazard to thc integrity of a low-penncability cap layer and also rcducc impacts ofdifferelllial settling. The final cover thickness requiremcnts ofthc operating procedures are, therefore, relevant and appropriate requircments.

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Table 7: New O-Field Action/Location-Specific Federal and State Applicable or Relevant and Appropriate Requirements which are the Substantive Requirements

F d' I FII R Ioun 111 t Ie o OW1l1!! e!!u atlOns Environmental Action or Status Consideration as an ARAR

Laws and Affected Re!!ulations Resource

Sanitary Landfill San italy landfill Relevant and Establishes requirements for closure of Closure COMAR closure Appropriate sanitary, rubble and industrial waste Iundfills, 26.04.07.21 including specifications for the closure cap.

MDE has thus far granted a variance from standard cap requirements 10 allow the pcnneable cover with treatment systems specified in the preferred remedy. This variance according to COMAR 26.04.07.26 is granted on the basis that the preferred remedy is equivalently protective in comparison 10

the impcnneable cover specified in COMAR 26.04.07.21.

Sanitary Landfills - Sanitmy landfill Relevant and Establishes requirements for post-closure Post-Closure post-closure Appropriate inspections and maintcnance for Inndfills. Monitoring llnd inspection and Long tCllll monitoring will include routine Maintcnance maintenance inspections. COMAR 26.04.07.22 Varianccs COMAR Sanitary landfill Relevant and Establishes the framework for obtaining 26.04.07.26 vanances Appropriate variances to the requiremcnts of the solid

waste management rcgulations, including closure cap requirements. MOE has thus far granted a variance from standard cap requirements to allow the permcable cover with trcatmcnt systems specified in the nreferred remedy.

PaI1icuiate Matter Air quality Applicoblc Estnblishes requirements for control of COMA R 26.11.06.03 general emission particulate matter emissions from materials

standards, handling and constmction, including road prohibitions, traffic. Also requires prompt removal of soil and restrictions from paved surfaces.

Sediment Control Design Standards and Specifications COMAR 26.17.01.11

Provides sediment control design standards and sDecifications.

Applicoble Incorporates by refcrence the guidance document that provides standards and specifications for erosion and sedimcnt control in Maryland.

Application for Outlines Applicable Defincs thc information that must be Approval of Erosion info11l1ation for submitted to MOE concerning sediment and and Sedimcnt the developmcnt erosion control for construction activities. Control Plans of erosion and The plan included in the remedial design COMAR26.17.0107 scdimcnt control provides the sediment and erosion control

plans information necessary for MOE 10 vcrify substantivc compliance with desiun criteria.

Maryland - Location Silecific ARARs Tidal Wctlands Wetlands Applicable Applies to the construction and management COMi\R 26.24.01­ of property in wetlands. .04

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Table 7: lew O-Field ActionfLocation-Specific Federal and State Applicable or Relevant and Appropriate Requirements which are the Substantive Requirements

F d' FIIoun 10 the 0 owin2 Re2ulations

Environmental Action or Status Consideration as an ARAR Laws and Affected

Re!!ulations Resource Forest and Tree Provides Applicable Requires that tree clearing be minimized, and Clearing COMAR requirements for that when tree clearing is necessalY. trees be 27.01.05 trec c1carillt! olanlcd in a ChcsaDcake Bav Critical Area. Habitat Protection Provides for the Applicable Establishes Critical Area Buffer 100 fl in width Areas COMAR protection of along tidal shorelines in which COnSlnlClioll is 27.01.09.01 and -.04 habilalS along not pcnnincd without a variance.

shorelines Threatened and Endangered Applicable Outlines the process for the protection of Endangered Species species. thrcalcncd and endangered species when Protection COMAR development is proposed in a critical area. 27.01.09.03 EffluCJ1l Limitations EmUcnl Applicable Applicable if more stringent than federal COMAR 26.08.03.01 dischilrge standards. Prohibits discharge to water of the

permits and State unless authorized by a discharge permit or limilations the discharge is a controlled discharge that does

not contravene the surface water quality standards established by the State to protect legitimate beneficial water lIses. Requirements apply 10 any w3stcwnter from decontamination during sampling and construction or to any water extracted from wells requiring discharge to surface water..

Water Quality Discharge of Relevant and Water quality standards may be considered COMA R 26.08.02.03 water to surface Appropriate relevant standards for surface water as relevant

water bodies 10 any water extracted from wells requiring dischame lO surface water.

2.13.3 COST EFFECTIVENESS

In thc Icad agcncy's judgment, thc Sclcctcd Rcmcdy for Ncw O-Ficld and thc OOA rcprcscnt a rcasonablc valuc for thc moncy to bc spcnt. In making this dctcnnination, thc following dcfinition was uscd: "A rcmcdy shall bc cost-cffcctivc if its costs arc proportional to its ovcrall cffcctivcncss." [NCr Scction 300.430(f)(I)(ii)(D)]. This was dctcrmincd by cvaluating thc "ovcrall cffcctivcncss" of thosc altcrnativcs that satisficd thc thrcshold critcria (i.c., wcrc both protcctivc of human hcalth and thc cnvironmcnt and ARAR-compliant). Ovcrall cffcctivcncss was cvaluatcd by asscssing thrcc of thc fivc balancing critcria (long-tcnn cffcctivcncss and pCl111anCnCc; rcduction in toxiciry, mobiliry, and volumc through trcatmcnt; and short-tcrm cffcctivcncss). Ovcrall cffcctivcncss of cach altcrnativc was comparcd and cvaluatcd to dctcrminc cost­cffcctiveness.

Thc cstimatcd prcscnt worth cost of thc Sclcctcd Remcdy, Altcl11ativc 8, for thc Ncw 0­Field itc is $3,648,000 and it is thc most cost-cffcctivc aftcr considcring thc other cvaluation criteria.

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The costs associated with the implementation and maintenance of the use restrictions for the OOA Site and the New O-Field Site are combined.

2.13.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE TREATMENT

TECHNOLOGIES (OR RESOURCE RECOVERY TECHNOLOGIES) TO THE MAXIMUM

EXTENT PRACTICABLE

The Army and USEPA, in coordination with MDE, have detemlined that the Selected Remedy for New O-Field and the OOA represents the maximum extent to which permanent solutions and alternative treatment technologies can be utilized in a practicable manner. The Selected Remedy provides the best balance of trade-offs 111

terms of the five balancing criteria and considering State and community acceptance.

The Selected Remedy addresses the materials constituting a risk to human health and the environment at New O-Field through stabilization (via the permeable cover), immobilization (through treatment of metals in groundwater), and breakdown (through treatment of CYOCs and CWM in groundwater), achieving significant reduction in the migration of COCs in soil, sediment, groundwater, and surface water which satisfies the criteria for long-term effectiveness. The Selected Remedy does not present shOIt-term risks in excess of the other alternatives. There are no special implemcntability issues that set the Selected Remedy apart from any of the other alternatives evaluated. The time required for mobilization, construction, and finalization of the Selected Remedy is estimated to be approximately J2 months, with additional time required for in situ bioremediation, maintenance and monitoring.

2.13.S PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT

The Selected Remedy utilizes treatment of groundwater as a principal element and, therefore, satisfies thc statutory preference for treatment as a principal element.

2.13.6 FIVE-YEAR REVIEW REQUIREMENTS

Contaminants may remain onsite above levels that allow for unlimited use and unrestricted exposure. Therefore, CERCLA 5-year reviews will be performed for New O-Field and the OOA.

2.14 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERRED ALTERNATIVE

IN THE PROPOSED PLAN

There are no significant changes to the Preferred Alternative for New O-Field in the Proposed Plan for Remedial Action: O-Field Study Area, O-Field Operable Unit 4: New O-Field Groundwater and Source Area and OOA (EA 2009).

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3. RESPONSIVENESS SUMMARY

The final component of the Record of Decision is the Responsiveness Summary. The purpose of the Responsiveness Summary is to provide a summary of the public's comments, concems, and questions about the New O-Field groundwater and source area remediation, the selection of LUCs as the remedy for the OOA, and the Army's responses to these concerns.

APG held a public meeting on Februaly 26, 2009 to formally present the preferred remedy presented in the proposed plan and the other remedial altematives considered, and to answer questions and receive comments. The tTanscript of this meeting is part of the administrative record for the site. During the public comment period, APG also received written comments. All comments and concems summarized below have been considered by the AmlY and EPA in selecting the remedies for New O-Field and the OOA.

This responsiveness summary is divided into the following sections:

3.1 Overview. 3.2 Background on community involvement. 3.3 Summary of comments received during the public comment period and

APG's responses. 3.4 Sample newspaper notice announcing the public comment period and the

public meeting.

3.1 OVERVIEW

At the time of the public comment period, the Army had endorsed a preferred alternative for New O-Field and the OOA. At the OOA, APG proposed maintaining current land use controls to prevent any residential use of the area. At New O-Field, APG proposed installing a penneable cover over the trenches and white phosphorus­contaminated soil; implementing an in-siru bio-enhancement barrier with a wetland buffer; and, placing a bio-beneficial sediment cover over the bottom of the open water area of the pond. The public seems to concur with the preferred alternative although a few community members prefer excavation of New O-Field.

3.2 BACKGROUND AND COMMUNITY INVOLVEMENT

APG has maintained an active public involvement and infoJ1l1ation program for the Installation Restoration Program since the early 1990s. Community members have actively parricipated in information sessions, tours, and public meetings, as well as serving as members of APG's Restoration Advisory Board. APG's community relations activities specifically related to the New O-Field and the OOA Proposed Plan included the following:

• APG has discussed the O-Field Study Area on an alUlUal basis with the Restoration AdvisOlY Board since the Board's creation. Infonnation on the remedial plans for New O-Field and the OOA was presented most recently at Board meetings on May 29, 2008 and January 29, 2009.

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• APG released the Proposed Plan for public conunent on February 20, 2009. Copies were available to the public through APG's administrative record locations at the Edgewood and Aberdeen branches of Harford County LibralY and Miller Library at Washington College in Kent County.

• A 30-day public comment period on the Proposed Plan extended from February 20 to March 23, 2009.

• APG placed newspaper advertisements announcing tlle public comment period and meeting in The Aegis, The Avenue, The Cecil Whig, The East County Times alld The Kent County News (Appendix A). The initial notice of availability of the Proposed Plan was published in the newspaper The Aegis on 20 February 2009. Follow-up notices were also published in The Avenue on 25 February 2009, the Kent County News on 26 February 2009, the East County Times on 26 February 2009, and The Cecil County Whig on 20 February 2009.

• APG prepared and published a fact sheet on the Proposed Plan. On February 24, APG mailed copies of this fact sheet to more than 2,300 citizens and elected officials on its Installation Restoration Program mailing list. The fact sheet included a form, which citizens could use to send APG their comments.

• On February 26, APG held a public meeting at Vitali's Restaurant in Edgewood, Maryland. Representatives of the Army, EPA and MDE were present. APG representatives presented infoll11ation on the site and on the proposed cleanup actions. Community members had an opportunity to ask questions and submit comments.

3.3 SUMMARY OF COMMENTS RECEIVED DURING THE PUBLIC COMMENT PERIOD AND

AGENCY RESPONSES

Comments raised during the public comment period on the Proposed Plan are summarized below. The comments are categorized by source.

3.3.1 COMMENTS FROM THE PUBLIC MEETING

Comment No. I: Ms. Ruth Ann Young (Restoration Advisory Board community member) asked if the vegetation would need to be harvested periodically.

Response No. I: The treatment of groundwater will be done in the zone of bioremediation. It is not expected that there will be a need to harvest the plants or material that dies back nanrrally each year in the winter. The vegetation is not intended to be a phytorcmediation remedy where the plants uptake the compounds. Thc primary purpose of the vegetation is to help stabilize the cover and provide organic matterlcarbon to the soi I.

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Comment No.2: Ms. Young asked what the altitude or highest point is at the site and whether storm surges are a consideration.

Response No.2: The highest point at the site is about 12 to 14 feet above mean sea level. The proposed remedy does include some armoring against wave action, and there is some buffering by the Gunpowder River and Watson Creek and by a narrow constriction near the marsh. Water has come up to New O-Field during major storms, but there are narrow portions of the waterbody that constrict flow.

Comment No.3: Mr. Clark Row (Restoration Advisory Board community member) asked if modeling had been performed for 10,20, or 40 years to determine the impact of carbon build-up through natural dieback of wetland plants and the flow of materials into the pond.

Response No.3: Such modeling has not been performed. Patt of the goal for the wetland buffer is to maintain enough sand and sediment cover so that even with the organic carbon added as part of the design, the buffer does not impede the flow of groundwater. Ponds like the one at New O-Field will fill up with organic matter over time as the vegetation dies back. In this case, a pond existed before this one that had a lot of organic matter and some sand, and the addition of more organic matter will need to be considered. In the case of groundwater treatment, more organic matter is desirable because it creates the low-oxygen conditions to help break down the chemicals. The purpose of the sediment cover is to mitigate contact with waterfowl. The goal is not to maintain the pond. If the pond fills up, it is not going to hurt the remedy.

Comment No.4: Ms. Young asked under this type of perfonnance-based contract if payment correlates to a certain amount of work being performed or is there a payment schedule set up in advance. She also asked if someone confirms that the work has been satisfactorily perfonned.

Response No.4: The Army manages the contract and requires the contractor to meet certain milestones before they are paid. Mi lestones completion is contingent upon meeting relevant quality control standards. The contract includes up to ten years of long­term monitoring to ensure the remedy is effective.

Comment No.5: Mr. John Fairbank (Maryland Department of the Environment) asked the speaker to clarify that institutional controls would be part of the remedy.

Response No.5: Land use control language is included in the Record of Decision.

Comment No.6: Mr. Fairbank commented that land slopes down toward the southeastern edge of the cover, and that the edge of the cover will be built up from the ground surface. He asked if water moving down the slope towards the cover will pond up behind the southeastern edge of the cover.

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Response No.6: Run-off control and grading to prevent ponding will be part of the remedial design.

Comment No.7: Mr. Fairbank asked where the pumps would be located that will be doing the re-circulation of the material injected.

Response No.7: The system is portable and will periodically be brought in and used for pumping and pulling selectively.

Comment No.8: Mr. Fairbank asked if any problem was anticipated with thc oil injected as part of the bioremediation flowing through the limestone.

Response No.8: As part of the remedy, an existing depression near the center of the groundwater plume will be filled with limestone to aid in controlling pH. A low percentage of edible oil is being used for the bioremediation injections, and it is expected that, based on porosity and previous experience, the flow through the limestone and surrounding soil will be good. The ArnlY will monitor to see if there is an impact over time.

Comment No.9: Ms. Elisabeth Green (Maryland Department of the Environment) asked how deep the pond is and whether it is tidally influenced.

Response No.9: Topographical surveys of the site have been recently conducted to ensure accurate elevations are used in the remedial design, including a depth survey of the pond. The surveys show the depth varies greatly. Large sections of the pond are two to four feet in depth, and there are some areas that are one to two feet deep. These variances in depth will be considered in the remedial design. The pond is tidally influenced. A tide gauge is being installed to take measurements and correlate with the tide in the Gunpowder River to determine the long-ternl mean water level.

3.3.2 COMMENTS FROM THE QUESTIONNAIRE INCLUDED WITH THE FACT SHEET

As part of its fact sheet on the Proposed Plan, APG included a questiOlmaire that residents could return with their comments. APG received 12 fornls. The alternatives preferred by individuals remrning comment f0I1115 were:

o Alternative No. I - Take No Action o Alte111ative No.2 - Pel111eable Cover with Groundwater Bio-Enhancement o Alte111ative No.3 - Low-Permeability Cover with Groundwater Bio­

Enhancement I Alternative No.4 - RCRA Cap with Constructed Wetland o Alternative No.5 - RCRA Cap and Subsurface Barrier with Monitored

Natural Attenuation 2 Alternative No.6 - Full-Scale Excavation, On-Site Treatment, Off-Site

Disposal and Monitored Natural Attenuation 2 Alternative No.7 - Full-Scale Excavation, On-Site Treatment, On-Site

Landfill, and Monitored Natural Attenuation

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6 Alternative No.8 - Permcable Cover, Bio-Beneficial Sediment Cover, and Groundwater Bio-Enhancement Barrier with Wetland Buffer

One individual did not select a prcferred alternative. Written comments included on some of the forms regarding the proposed actions are summarized bclow. Some forms noted a preference for an alternative but did not contain any comments.

Comment '0. 10: (Commenter selected Alternative 7) "Remove majority of hazard from seeping into water."

Response No. 10: Alternative 7 would remove waste from contact with the groundwater, but excavation poses substantial safcty hazards to site workers and the surrounding community. Therefore, the Army and regulators prefer Alternative 8. By approaching the problem from another perspective and treating the groundwater after the chemicals have moved into it, people's hcalth is protected and the safety hazards are greatly reduced. Groundwater at the site is not currently being used as a drinking water source and is not expected to be in the future; however, Alternative 8 will treat the groundwater and reduce contaminant levels to levels that will not impact aquatic life.

Comment No. 11: (Commenter selected Alternative 8) "Seems like a well thought out common sense approach. Go for it! I remember a-field well."

Response No. 11: APG appreciatcs and acknowledges the comment.

Comment No. 12: (Commenter sclected Alternative 8) "Alternative 8 appears the best alternative, the implementation of which provides the best solution to the problem. Additionally, it is the long-term solution. "

Response No. 12: APG appreciates and acknowledges the comment.

Comment No. 13: (Commenter selected Alternative 6) "I am concerned of the health issues these chemicals have to the community of Oliver Beach."

Response No. 13: Protection of human health is one of the driving forccs behind the investigation and cleanup of contaminated sites, and the priority for APG and the regulators. The human health risk assessment examines whether the site currently poses a risk to workers or the surrounding commlmity; it found that there arc currently no risks. The Selected Remedy will prevent erosion and migration that could increase risks. As discussed above, groundwatcr is cUITently not being used as a drinking water source and excavation poses significant safety hazards. Alternative 8 will keep the wastc on Army property instcad of moving it to an off-site landfill and allow thc Army to rcmediate the waste.

Comment No. 14: (Commentcr sclccted Alternative 8) "#8 is the prefcrred solution. Kccp up the good work with kecping the future of wetlands in mind."

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Response No. 14: APG appreciates and acknowledges the comment.

Comment No. 15: (Commenter selected Alternative 7 as their first choice and Altemative 6 as their second choice) "Containment to stop the groundwater from flowing into the community while our children play in the river and streams surrounding Edgewood. If the Federal government can't handle it and protect civil community, the State should step in. Thank you for allowing us to give our opinion."

Response No. 15: APG and the regulators agrec that protection of human health and the environment is the most important criterion in investigating and remediating contaminated sites, and any alternative must meet this criterion. Excavation under Alternatives 6 or 7 involves significant safety hazards to workers and the sUHounding community from possible CWM release or explosion. Alternative 6 also involves significant safety hazards o·om the increased truck traffic required to remove the excavated materials o·om the site. Altemative 8 will treat the groundwater before it leaves the area, contain the waste on Army property, and can be implemented without high hazard risks.

Comment No. 16: (Commenter did not select an alternative)" J like most of#6 but not the higher risks for the remediation workers. Some action needs to be taken. I'm not comf0I1abie with any of the alternatives in each one's entire proposal."

Rcsponse No. 16: APG appreciates the review of the proposal and acknowledges New O-Field is a complcx site. APG and the regulators selected Alternative 8 because it offers greater protection from safety hazards to site workers and the sUHounding community, while remediating the waste on Army property.

Comment No. 17: (Commenter selected Alternative 6) "Clean up the arca - Clean up the source and start a real cleanup of the Chesapeake bay - It's no wonder there are so many instances of cancer in our area. Get the contaminants out of the area and to a safe disposal site."

Response No. 17: Protection of ecology and the Chesapeake Bay is one of the driving forces behind the investigation and cleanup of contaminated sites, and a priority for APG and the regulators. The ecological risk assessment examines whether the site poses a risk to ecology and waterbodies near the Chesapeake Bay. As discussed above, the selected remedy is designed to protect wildlife and ecological communities. APG and the regulators selected Alternative 8 because it not only protects plants and wildlife but also includes habitat improvements such as wetland constnlction and planting of submerged aquatic vegetation.

Commcnt No. 18: (Commenter selected Alternative 8) Alternative 6 would be preferable, but the difference in cost is too great for it to be considered."

Response No. 18: APG appreciates the review of the proposal. APG and the regulators selected Alternative 8 because it offers greater protection from safety hazards to site workers and the sUHounding community; it is also cost effective.

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4. REFERENCES

Baummer, J., R. Hoke, W. McCulloch, S. Hartzell. Acute and Chronic Toxicity of Two Phosphonic Acids 10 Freshwater and Marine Organisms. Poster. Society for Environmental Toxicology and Chemistry North American Conference, 2004.

EA Engineering, Sciencc, and Technology, Inc. (EA). 2007. Data Evaluation and Risk Characterization Jor New O-Field. Aberdeen Proving Ground, Maryland. Edgewood Area, APG, M D: US Army Directorate of Safety, Health, and Environment (DSHE).

EA Engineering, Science, and Technology, Inc. (EA). 2009. Proposed Plan for Remedial Action for Army Environmental Database-Res/oration (AEDB-R) Site EAOF04: O-Field Study Area Operable Unit 4: New O-Field Groundwater and Source Area and Other O-Field Areas (OOA). Aberdeen Proving Ground, Maryland. Edgewood Area, APG, MD: US Army Directorate of Safety, Health, and Environment (DSHE).

General Physics (GP). 2008. Feasibility Study for O-Field Operable Unit (OU) 4:New O-Field and Other O-Field Areas. Preparcd for APG, DSHE. Revised from draft document by EA Engineering, Science, and Technology. June 2008.

General Physics (GP). 2007. Addendum to the Remedial Investigation Report for the 0­Field Study Area: Other O-Field Areas Investigation. Prepared for APG, DSHE.

IT Corporation (IT). 2002. Remedial Investigation (Rl) Report for the O-Field Study Area. Contract No. DA3 I-94-D-0064. Edgewood Area, APG, MD: US Army Directorate ofSafcty, Health, and Environment (DSHE).

Shaw Environmental, Inc. (Shaw), 2004. New O-Field Groundwater Evaluation: Assessment of Natural Attenuation. Edgcwood Area, APG, MD: Directorate of Safety, Health and Environment. Draft Final. October 2004.

U.S. Environmental Protection Agency (EPA). 1996. Application oj the CERCLA Municipal Landfill Presumptive Remedy to MilitCIIJl Lalldfills. EPA Office of Solid Waste and Emergency Response. Directive No. 9355.0-67FS. EPN540/F-96/020.

U.S. Environmental Protection Agency (EPA). 2006. Recommended National Watcr Quality Criteria. EPA Office of Water.

U.S. Environmental Protection Agency (EPA). 2006. EPA Region III Freshwater Screening Bcnchmarks. Accessed at: htlp:llwww.epa.gov/reg3hscd/risk/eco /btag/sbv/fw/scrcenbench.hlm.

U.S. Geological Survcy, U.S. Department of the Interior (USGS). 1991. Groulld-Water, Sill/ace-Water, alld Bot/om-Sedimellt COII/aminatioll in /he O-Field Area, Aberdeeu Provillg Ground, MCllyland, and the Possible Effects oj Selected Remedial Actions on Ground-Water. Open-File Report 89-399.

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78

FIGURES

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CeDI County

Baltumre County

Baltimore

O-Fleld Stu

Harford County

O·FIELD STUDY AREA AEERDEEN PROVING GROUND, MARYLAND

Anne Arundel County

Ll!gend

• Aberdeen Proving Ground N

1000 0 2000 Feet A.

Chesapeake Bay

Kent County

FIGURE I

APG md VicInity

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BUSH RIVER

)

\

!!te+-~I1+ 1

I~"<"_~ h k

~~~ ~ I:~

AREA

,'( ~,

O-FIELD STUDY ."'

~ "

~'f: 'r

CHESAPEAKE BAY

GUNPOVVDER RIVER

N

MAXWE LL r::::::;::;.POINT ~

2000 0 2000 Feel

O-FIELD STUDy AREA ABERDEEN PROVING GROUND, MARYLAND

FIGURE 2

Location of Q-Field

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/

\

FIGURE 3

O·Fielci Study Area Operable Units

OTHER O.fIELD AREAS (OU4)

Legend

O.field Boundaries o Open Wat~/Pond

Roads o Forest Wetland

400 o 400 Feel

GUNPOWDER RIVER

WATSON CREEK (OU3)

J----=-OT'O

O_F~LD(OU /& o 2)

~

NEW a-FIELD

a-FIELD STUDY AREA ABERDEEN PROVING GROUND. MARYLAND

N

A

~ NEW O·FIELD

GROUNDWATER AND SOURCE

AREA (OU4)

/ ~

o

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POND

MARSH

1--­

/'OPEN GROUHlt

TRENCHES WATER () /' HOW 1/ /'

COVERED /' lRENCHES

EXCAVATED ARE OVERGROWN WITH REEDS

COVERED lRENCHES

Legend

Boundaries of Removal Action Excavations Trenches

_ Staged Soil Pile o Open WaterlPond

Roads D Forest

Wetland

100 o 100 200 300 Feet i

a-FIELD STUDY AREA ABERDEEN PROVING GROUND, MARYLAND

FIGURE 4

New Q-Field Disposal Features

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Watson Creek (aU 3)

.., - .. Ol

0" Old ., \ a-Field ","

~ OlOUs 1 ..",II & 2 '"

'----..• o .. '"

Ol

o'" Other .. •a-Field Areas

•"'. .. 0

• 0

" 0 '"0 .. 'll>

==-- • '" • 0"New a-Field • •(aU 4) •

•

o

Legend

fa Soil Samples Trenches

Grouncmatel Samples Wetland .. • Sediment Samples Open Water • Sur face Water and

ForestSediment Samples N

Roads A / I

400 o 400 Feel

FIGURE 5 a-FIELD STUDY AREA

ABERDEEN PROVING GROUND. MARYlAND O-Field Sample locations

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..

STAGED SOIL MOVED

• UNDER THE • PERMEABLE

COVER

L

Legend

Trenches Wetland

Roads D Open Water

Well Clusters D Forest

100 o 100 Feel

GROUNDWAlER B10REMEDIA1l0N

Bio"lhllllICt1'It1l1 Usillg Pulll_Pull.,jedion

ol.ll1lendmems and LhneS1olle.fll"

lIe11'f'SSlOII

FIGURE 6 D-FIELD STUDY AREA

ABERDEEN PROVING GROUND. MARYLAND New O-Field Remedial Design

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Legend

Trenches Wetland

Roads o Open Water

D Forest

Lues malnlalnlng current Induslnal use o and preventmg resldenllalland use

Lues restncllng aCh'lltles Incompatible with the remedy, such as disturbance 01 covers or mcompahble use 01 groundwater

400 o 400 Feel

\

J I

( ~/

FIGURE 7

0-FIELD STUDY AREA Neo.... a-Field and OOAABERDEEN PROVING GROUND, MARYLAND

Proposed land Use Conbols

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APPE 'D1X A

SAMPLE NEWSPAPER NOTICE ANNOUNCING THE PUBLIC COMMENT PERIOD AND PUBLIC MEETING

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u.s. ARMY INVITES PUBLIC COMMENTON ITS PROPOSED PLAN FOR REMEDIAL ACTION AT NEW O·FIELD

AND OTHER O·FIELD AREAS

Thil L~S :(mry 01 .<fb.rdilil" Pro\ iPfg Ground (:1.1'0) unites IhilpuMit: 10 COffUfNtfll on it!;

Propo!.JdPlan/or P..,.lilalal.it:UOIl Ot ().F!.id SlUa) .!.na Op.Toblil Un!l4: .\..... O-Fi.ld GrolJlrt04 al.rQNiS!JU~il.ir~a and Ozhu O-Fie/d .~n:z_

FACT SHEET WEBSITE APG hasprtpartda fact !bret.ton the )'oucU1le~more abow. obt.ainingthe Proposed Plan that includes il commmt ProposedPbn andpro\ide commmlS fOImth.ncanbemumedloAPG Ifyou th:ougb the APG Web Sne at all. not on APG 5 mailing list. you can ~'\\w.apg..anny.mil Click on Safety. request a copy ofthe faet meet by coaDing HeUh.and En'"iromnent; En\'Vonmmul A..l>(j's 24-bourcwlfonmentallnfonnanon Coru.c-unon and Restoution Dni!ion; lInt at (~IO)171-SB42or (SOO)APG-999S EmiromnmtalRfiloratlon Cleanup

Program.\YRITTE" CO)nIE"TS The 30-d.aypublic comm!nt pmod on the proposed action tlte.nds from Fnday :!O PLllUC)IEElL'G February 1009through~londay23 Much 1009 Wrinm commmu,pownukedby APG irwia:s lhtpublic te attendamtering M~23,shouldbe sml to' on :\IT_ Ken Stuhiw, Program :\lsnager Direeto~1II! ofPublic Work! Dale ThursdaY,February 16,2009 ...."I"l'?': 1l\INE·APG·IO Tlme.6:30p.m.-infomul Building E5 771 Ahgnoha Road peller information semon Ab~deenProving Ground, l1.1D 21010, 715p.rn.-presenlanon Mr. Frank Va\Ta Place. Balhoomal Vitali's Rutauranl as. EndrorDnentalProtection Agency 1709 Edgewood ROild 1650 Arch Street (3HSIl) Edgewood,MD 11040 Philadelphia,PA 19103 ~ls.. Elisabt'lh Crun The meelmg location is l\ntt'lchair Milryland Dt'panmt'nt oflht' EndrOrDnwt acct'5.Sible, and anintt'rpreter for the ftda;Jfacilitits Dj"won hearingimpaut'd is anililble ~;th 71-houts I sao WashmgtonBeult'\':lrd. Swte 645 ad\'anct' notice (call 800-....1'0-9998). Baltimort,t\.fD 21230

PROPOSED AC110~

APG is proposing 10 lue aCllon at Nt'\\' ()'Field and the Other O--Field Areas. !\ew 0­Field is a iorma dispoul silt' thaI is no longel actin COnIamimnion at the siteincludu chemicalw~rfarenulerial-rtlatt'dw~lItburitd in trtDcht's; soh'uzu andmtlalsin ground~·att'Jdischa.rging10 a pond; andm.elah andv..hitt phosphoNSinpondsednnt'nl. That' IS the pott'l'ltial risk thaltJORon or other proces.s.ts could anow contamInanUIO bt' rtluud Inthe Other ()'Field .-\reas disposal w~s suspected, butinnstigation found no elidmce ofsigrufic ant cont.a.muution otha thut spou dic UDt'.'q)lodtd ordnlllce.

ALTER"A11\"1:S EYALLUED FOR:>LW O·F1ILD A"D OlliER O· FlELD ..\REAS

~I aht'lJliltins~"tre tvamltdforO--Fidd Optnble Unat -l Theseindudt 1.:'\0 Action :.Per:m.ublr CO\'f:r "ith Crouncnnlrr Bio-£nhannmt'Dt 3.Lol\·¥rmubilil)· COl'rr "ith Groundll"11lrr Bio-£ntunct'-mn.1 -l_Rrsourn Conun'ltion Ind Rt:co\'rl')' (RCR~) Cap mth ComtJ'1lclt'd Wrdlnd ~.RCR~ Cap and Sabsmau Burirr"ith :\lonitorrd :'\llUnl Anrnuation 6.full-SnIr uU\'IooD"itb Orr-Silt Dilposal and :\Ionitond ~lroral.-\neDnadoD

7.full-Scale [.J:Cuaoonmth On-Silt Di.sponI aod :\Ionilortd ~alUnl."ltt'DUldoD

8.Pertllublr CO\'f:r "ith Armond Tor, Bio+Bt'DdicialMdimt'DI CO\'f:r, IDd Croundwaltr Bio-£nhancelDellol "ilb \\'edlnd BlllreT

Butd on an analySIS ofthe ahemam'u, APG prefen AhtmilUn S fOI the sitt remedy, 1bis includes a ptmltabIe co\'tJ o\"er "'-.ult buned in trenches with annor against tlOIIOD; a ""tthnd buffer llld CO\'a O\·U the pond udlme:nu and se~s; tnhanctmtIU ofproceuu th.a.t break do"'nchtmicalsio groundwater; land use cOnIJols; and long ItmI optnlions, maintenance, and monitoring. Thr prrfmrd ahemati\'emay bt modified or new ahtmarinunay be de\'tloptd based on public input The final ahtmatin weclt'd ",iII be docummttd Ul a Record efDecmoD thaI summarizes the decision-.m.a.k:ing process_ .o\.PG wiII sumnurizt' andrtspondlo conunenlSlecei\'rd during the commmtperiodas part of the Rtcord ofDecision. Copiu oftht Ftaubilit}' Study llldtbt Proposed Plan art' a\'ailable forrt\,ew al tbe APG mfocnationltpOmories, The rtpositories alt located at tht Edgewood and Abeldrw branches of Hanord (ounly Library and Miller ubrary at WashingtonCollegr in Kent County.

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APPE 'D1X B

MARYLA '0 DEPARTMENT OF THE ENVIRONMENT RESPO 'SE TO VARIANCE REQUEST FOR EW O-FIELD REMEDY

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MARI'LAND DEPARTMENT OrHIE ENVIRONMENT 1800 Washington Boulc\'urd. Baltimore MD 21230 410-537-3000 • 1-800-633-6101 MDE.

Martin O'Malley Shari T. Wilson Governor Secretary

Anthony G. Brown Roben M. Summers. Ph.D. Lieutenant GO\'cmor Deputy Secretary

July 15.2008

Commander US AmlY Garrison, Aberdeen Proving Ground AlTN: IMNE·APG-SHE·R! Ms. Cindy rowels Building E5771 Mag.nolia Road Aberdeen Proving Ground, MD 21010-5401

Re; Finnl Remedy for New a-Field. Request for Vorionec, leiter dated June 4.2008

Dcar Ms. Powcls:

The. Federal Facilities Division (FFO) oflhe Mnryland Dep3Jtmenl orlhe Environment'S (MDE) Ha1..nrdous Waste Program has completed its review of the referenced communication. This lettcr describes the Anny's proposed final relnedy for New O·Field, which is il fomler disposal area in the restricted area of Aberdeen Proving Ground. ·Ille proposed final remedy for New O·Ficld is a pcnncable cover with an in silU groundwatcr treatment-systcm, consisting of:J groundwater biocnh:mcemcnt barrier, a COrlslructcd wetland buffer and a bio-beneficial sediment cover. The Army is conducting this action in compliance with the Comprehensive Environmental Response, Compensation, nnd Liability Act (CERCLA).

The proposed remedy requires a v:uiance to the State's landfill closure regulations for landfills, Which are Applicable or RclcvnJll and Appropriatc R(.'quircment Wider CERCLA. The FFD in consullation '\~th MDE's Solid Wastc Prognuu bas re,·iewoo the proposed action and the requested variwlce. If implemented and monitored adequately the proposed remedy should be as protecti\'c as the State's landfill closure regulations as stated in Code of Maryland Regulations (COMAR) 26.04.07.10 and 26.04.07.21. Consequently, in accordance with the variance provision contained in CO~IAR 26.04.07.26, the Army's request for a variance \\ill be considered favorably if th<- follo\\ing conditions are adequately addressed in the Record of Decision for this site:

i. The penneablt cowr with :m in situ groundw.ltcr treatment system will be implemented to ensure treatment of all iOlJXlCled groundwater before il exits the treatment zone or aTea of :1I1ainmem. The area of anainmcm shall be defined as the disposaltrcnches and the biological tTCaUDcnt zone (emulsified oil).

www md~ Sllu~.md.u.. TTY U.cn 1..$Ol).73S·U5S Via \lU)tJrlIl. Rd*) Sen I(~

Ms. Cindy Powels Page Two

Ii. Long·tcnn operations and maintenance activities will be implcmenlcd to prolccllhc integrity of the pcmleablc cover and in silU groundwater treatment system with monitoring adequall' 10

meel the needs of the FFD.

iii. Long-lcnn monilOrin~ of groundwater and surface water will be implemented 10 monitor the effectiveness ofthc pcnncable cover and in situ groundwater trc,atmCnl syslem at New O-Field and to cvaluatc the potential migration of eontaminall1s toward Watson Creek. Again this monitoring program must meet the needs of the FFD in evaluating the adequacy of the remedy and the continued use of lhe variance provision contained in COMAR.

If you have any questions, please contact me at (410) 537-4238.

Sinct~rcly,

Heather Njo Remedial Project Manager, Federal Facilities Division

HN:lm

cc: Mr. Frank Va\T8 Mr. J-Iorado Tablada Mr. Harold L. Dye, Jr.

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