Department of Energy

ROCKY FLATS FIELD OFFICE P.O. BOX 028

GOLDEN. COLORADO 80402-0028

e <A / % 'A

UNK 2 0 1GS7 97-DOE-05168

Mr. Tim Rehder, Manager Rocky Flats Project U. S. Envhonmental Protection Agency, Region VHI 999 18tii Street Suite 500 Denver, Colorado 80202-2466

Mr. Joseph SchieffeUn, Permitting and Compliance Unit Leader Federal FacUities Program Hazardous Materials and Waste Management Division Colorado Department of PubUc Health and Envhonment 4300 Cheny Creek Drive Soutii Denver, Colorado 80222-1530

Dear Mr. Rehder and Mr. Schieffelm:

Enclosed is a copy of the final Conective Action Decision/Record of Decision for Operable Unit 1, 881 Hillside, includhig the signatures of all parties, for your records. Thank you for your cooperation during the fmahzation of this important decision document.

If you have any questions, please contact Sandi MacLeod at 966-3367.

Sincerely,

62520 - R8 SDMS

2 4 5 I T T

9DAiU\^^-Gail HiU, Acting Group Lead

Regulatoty Liaison Group

Enclosure

cc w/Enc: G. Kleeman, EPA C. Spreng, CDPHE Administrative Record

cc w/o Enc: J. Legare, AMEC, RFFO S. MacLeod, ERWM, RFFO N. Castaneda, ERWM, RFFO J. Rampe, PLD, RFFO T. Howell, OCC, RFFO A. Sieben, KH

-<L

EFA/ROD/R08-97/195 1997

EPA Superfund Record of Decision:

ROCKY FLATS PLANT (USDOE) EPA ID: CO7890010526 OUOl GOLDEN, CO 03/12/1997

CORRECTIVE ACTION DECISION/RECORD OF DECISION DECLARATION

SITE NAME AND LOCATION Rocky Flats Environmental Technology Site, Operable Unit 1: 881 HiUside Area, Jefferson County, Colorado

STATEMENT OF BASIS AND PURPOSE This decision document presents the selected remedial action/corrective action for the Rocky Flats Envhonmental Technology Site (Rocky Flats) Operable Unit (OU) 1: 881 Hillside Area, located near Golden, Colorado. The selected remedial action was chosen in accordance with the Comprehensive Environmental Response Compensation and LiabiUty Act (CERCLA) of 1980, as amended by the Superfund Amendments and Reauthorization Act (SARA) of 1986, die Colorado Hazardous Waste Act (CHWA) and to tiie extent practicable, the National OU and Hazardous Substances PoUution Contingency Plan (NCP). The Resource Conservation and Recovety Act (RCRA) is administered through tiie CHWA by tiie Colorado Department of PubUc Healtii and Envhonment (CDPHE). OU 1 was investigated and a remedial action was selected in compUance with the Federal FaciUty Agreement and Consent Order - Interagency Agreement'(IAG) signed by the U.S. Department of Energy (DOE), the State of Colorado, and the U.S. Envhonmental Protection Agency (EPA) on Januaty 22,1991. The selected remedial action is also consistent witii the Federal FaciUty Agreement and Consent Order - Rocky Flats Cleanup Agreement (RFCA) signed by DOE, tiie State of Colorado and EPA on July 19,1996. RFCA is now the goveming cleanup agreement for Rocky Flats, and the selected remedy for OU 1 vnH be implemented in accordance with RFCA. The remedial action selection is based on the administrative record fUe for OU 1, and the State of Colorado concurs on the selected remedy.

ASSESSMENT OF THE SITE Actual or threatened releases of hazardous substances from this site, if not addressed by hnplementmg the response action selected in this Corrective Action Decision/Record of Decision (CAD/ROD), may present a future threat to pubhc health, welfare, or the envhonment

DESCRIPTION OF THE SELECTED REMEDY OU 1: 881 HUlside Area is one of sixteen geographicaUy defined OUs at Rocky Flats tiiat are identified in the IAG. RFCA consoUdates these sixteen operable units into a fewer number, but OU 1 remains as a separate operable unit due to the fact tiiat it is farther along in the administrative process and is nearing completion. OU 1 is composed of eleven Individual Hazardous Substance Sites (IHSSs). The selected remedy presented in this CAD/ROD includes three primaty components:

1. This action addresses the principal threat posed by OU 1 by excavating subsurface soil contamination at IHSS 119.1, a former drum and scrap metal storage area, thereby removing the cunent source of groundwater contamination. The major components of tiie selected remedial action at EHSS 119.1 (SoU Excavation and Groundwater Pumping) include: • Excavation of approximately one thousand to two thousand cubic yards of

contaminated subsurface soUs at IHSS 119.1; • Extraction and then ultiiaviolet/hydrogen peroxide and ion-exchange treatment of

contaminated groundwater from the excavation; and

• Eitiier thermal-treatment and replacement of excavated soU into the original excavation, disposal of excavated soU in an on-site waste disposal ceU, or off-site disposal of excavated soil

2. Institutional controls wiU be maintained throughout the OU larea m a manner consistent with RFCA, the Rocky Flats Vision, and the Action Levels and Standards Framework (ALF) (Attachment 5 to RFCA). These documents recognize that the reasonably foreseeable future land use for the OU 1 area is restricted open space. The institutional controls wiU ensure that the restricted open space land use is maintained for the OU 1 area and that domestic use of groundwater witfain the OU 1 area is prevented. If the reasonably foreseeable fumre land use for the OU 1 area changes when final sitewide land use decisions are made, this remedy wiU be reexamined to ensure protection of human health and the environment The specific mechanisms (for example, deed restrictions) to ensure the implementation and continuity of the necessaty institutional controls have not been included in this CAD/ROD. Currentiy, these mechanisms are envisioned to be placed in the Fmal Sitewide CAD/ROD or in this CAD/ROD during one of the five-year reviews of this document However, should the Final CAD/ROD not occur or not include these instimtional contixil mechanisms, this OU 1 CAD/ROD wiU be revised to include them, tf it does not aheady include them as a result of a five-year review. The instimtional controls can also be removed at one of the above times, if it is deemed appropriate to do so by the parties.

3. Because of the groundwater and land use controls, the low amounts of contamination hi OU 1 outside of IHSS 119.1, and the low levels of risk associated with the contamination, no remedial action wiU be taken at the remaining ten IHSSs in OU 1.

Any surface soU contaniination at OU 1 wiU be addressed jointiy with surface soU contammation at the 903 Pad, Mound and East Trenches area (formerly OU 2).

STATUTORY DETERMINATIONS The selected remedy for OU 1 satisfies the statutoty requirements of CERCLA Section 121. The selected remedy is protective of human health and the environment compUes with Federal and State requirements that are legaUy ^pUcable or relevant and appropriate to the remedial action, and is cost-effective. This remedy utiUzes permanent solutions and altemative treadnent technologies to the maximum extent practicable and satisfies the stamtoty preference for remedies that employ treatment that reduces toxicity, mobiUty, or volume as a principal element Because this remedy wiU result in hazardous substances remaining in groundwater, a review wiU be conducted within five years after commencement of the remedial action to ensure that the remedy continues to provide adequate protection of human health and the environment

fJft'^D^'^? Jessie RoDCTSon, Manager Date U.S. Department of Energy, Rocky Flats Field Office

Max H. Dodson, Assistant Regional Administrator Dale Office of Ecosystem Protection and Remediation U.S. Environmental Protection Agency, Region VIII

Howard Roitman, Director Date Hazardous Materials and Waste Management Division Colorado Department of Public Health and Environment

Jessig/Roberson, Manager U.S. Department of Energy, Rocky Flats Field Office

Date

Max H. Dodson, Assistant Regional Administrator Office of Ecosystem Protection and Remediation U.S. Environmental Protection Agency, Region VHI

Howard Roitman, Director Hazardous Materials and Waste Management Division Colorado Department of PubUc Healtii and Environment

Date

Date

DECISION SUMMARY

STTE NAME. LOCATION AND DESCRIPTION

The Rocky Flats Environmental Technology Site is located approximately sixteen mUes northwest of downtown Denver, in northem Jefferson County, Colorado. A copy of a site location map is attached (Figure 1). Most Rocky Flats stractures are located within the industriaUzed area of Rocky Flats, which occupies approximately four hundred acres and is surrounded by a buffer zone of approximately 6,150 acres. OU 1 is located adjacent to and on the south side of the Rocky Flats hidustrid area, on the hillside south and east of Building 881 and north of Woman Creek (Figure 2).

Geological Setting Rocky Hats is located along tiie eastem edge of the soutiiem Rocky Mountain region, immediately east of the Colorado Front Range. The site is located on a broad, eastward-sloping pediment that is capped by aUuvial deposits of Quatematy age (i.e.. Rocky Flats AUuvium). The tops of aUuvial-covered pediments are nearly flat but slope eastward at fifty to two hundred feet per nule. At Rocky Flats, the aUuvial-covered pediment surface is dissected by a series of east-northeast trending stream-cut vaUeys. The bases of tiie vaUeys containing Rock Creek, North and South Walnut Creeks, and Woman Creek Ue fifty to two hundred feet below the elevation of the older pediment surface. These vaUeys incise mto the bedrock underlying aUuvial deposits, but most bedrock is concealed beneath coUuvial material accumulated along the gentie vaUey slopes. The highest point m the immediate vicinity of OU 1 is BuUding 881, which is approximately six thousand feet above mean sea level. The lowest point is at Woman Creek, about 5,830 feet above mean sea level.

Surface Water Rock Creek, North and Soudi Walnut Creeks, and Woman Creek arc intermittent streams that flow generaUy from west to east at Rocky Hats. Surface water within Woman Creek, which flows along the base of the BuUding 881 hillside south of OU 1, and which is not diverted to Mower Reservoh flows into Woman Creek Reservoh, which is part of the Standley Lake Protection Project The water hi Woman Creek Reservoh is detained and then pumped to Walnut Creek drainage downstream of Great Westem Reservoh. The South Interceptor Ditch (SID) crosses OU 1 between the security area and Woman Creek.

Land Use Land use within ten mUes of Rocky Hats includes residential, commercial, industrial, parks and open space, agricultural and vacant and institutional classifications. Most residential use within five mUes of Rocky Hats is located northeast east and southeast of Rocky Hats. Commercial development is concentrated near residential developments north and southwest of Standley Lake and around Jefferson County Airport, located approximately three mUes northeast of Rocky Hats. Industrial land use within five mUes of the site is primarily quanying and mining operations. Natural resources associated with the quarrying and mining activities include sand, gravel and coal. Irrigated and non-irrigated croplands, producing primarily wheat and barley, arc located north and northeast of Rocky Hats and in scattered parcels adjacent to the east boundaty of the site. Several horse operations and smaU hay fields are located south of Rocky Hats. Much of the vacant land adjacent to Rocky Hats is rangeland.

OU 1 OU 1 is composed of eleven IHSSs, which are specific locations where solid wastes, hazardous substances, poUutants, contaminants, hazardous wastes, or hazardous

constituents may have_been disposed or released to the environment withm the Rocky Hats site at any time. Figure 2 shows the locations of these IHSSs and a description of each IHSS is provided in Table 1.

SITE HISTORY AND ENFORCEMENT ACTIVITIES

Rocky Flats is a govemment-owned, contractor operated faciUty that is part of the nationwide nuclear weapons complex. The site was operated for the U.S. Atomic Energy Commission (AEC) fixim its inception during 1951 until the AEC was dissolved in 1975. ResponsibiUty for Rocky Hats was then assigned to the Energy Research and Development Admmistration (ERDA), which was succeeded by DOE in 1977. Until 1992 operations at Rocky Flats consisted of fabrication of nuclear weapons components from plutonium, uranium, stainless steel and betylUum. BuUding 881, which is adjacent to OU 1, was used for enriched uranium operations and stainless steel manufacturing. The laboratories in BuUding 881 also performed analyses of the materials generated in production. Parts made at the plant were shipped elsewhere for assembly. Support activities at Rocky Flats included chemical recovety and purification of recyclable transuranic radionucUdes and research and development in metaUurgy, machining, nondestractive testmg, coatings, rcmote engineering, chemistty and physics. These activities resulted in the generation of radioactive, hazardous and mixed wastes. On-site storage and disposal of these wastes has contributed to hazardous and radioactive contamination in soils, siuface water and groundwater. OriginaUy the site was named the Rocky Hats Plant but in 1994 it was rcnamed the Rocky Hats Environmental Technology Site to better reflect its new mission of envhonmental restoration and the advancement of new and mnovative technologies for waste management characterization and remediation.

On January 22,1991, a Federal FaciUty Agreement and Consent Order (i.e., the IAG) was signed by DOE, EPA and flie State of Colorado. Wiflun tiie IAG eleven IHSSs were assigned to OU 1: 102, 103,104,105.1, 105.2, 106, 107, 119.1.119.2, 130 and 145 (see Table 1 for a description of these IHSSs and Figure 2 for the location of each IHSS within OU 1). The IAG provided guidance and direction for investigating the OU 1 IHSSs. As per flie IAG, draft and fmal Work Plans and a draft and final RCRA FacUity Investigation/Remedial Investigation (RFI/RI) report were prepared and submitted to the regulatory agencies. The RFI/RI report for OU 1 was prepared for submittal of documentation and data necessaty to determine if the risk frora the OU 1 IHSSs warrants the need for remedial action.

During 1992, as an interim action, a French Drain was constracted across a portion of OU 1 to protect Woman Creek from contaminated groundwater present in OU 1. The French Drain, along with an extraction weU, coUects contaminated groundwater moving towards Woman Creek. The coUected groundwater is transported to an ultraviolet/hydrogen peroxide and ion-exchange water treatment system located m BuUding 891. In addition, during 1994, plutonium contaminated suiface soU "hot spots" that were located in IHSSs 119.1 and 119.2 were removed from OU 1. This hot spot removal was conducted under an Accelerated Response Action per the IAG.

The Proposed Plan and Draft Modification of flie Rocky Hats RCRA Pemiit for OU 1 (Proposed Plan) was prepared and released for pubUc comment in May 1996 pursuant to die IAG and consistent wifli tiie draft RFCA. On July 19,1996, DOE, EPA and tiie State of Colorado signed the final RFCA, which has replaced the IAG to become the governing cleanup agreement for Rocky Hats. Pursuant to the "Operable Unit Consohdation Plan" in RFCA, OU 1 wiU continue through tiie CAD/ROD process wifli EPA as the lead regulatoty agency.

HIGHLIGHTS OF COMMUNITY PARTICIPATION

The first Fmal Phase HI RFI/RI report for OU 1 was submitted to EPA and CDPHE m November 1993 and the Revised Final Phase HI RFI/RI report was submitted in June 1994. The Proposed Plan for OU 1 was released to the pubUc in May 1996, and was made available in bofli the administrative record and in infonnation repositories maintained at Front Range Community CoUege, the EPA Superfund Records Center, CDPHE, tiie Standley hak& Libraty and the Citizens Advisoty Board. The notice of availabiUty for tiiis document was published in the Rocky Mountain News on May 13,1996. A pubUc comment period on the Proposed Plan was held from May 13 to July 12,1996. A pubUc hearing was held on June 19,1996. At this hearing, representatives from DOE gave a presentation fliat summarized the contamination and risks at OU 1, as weU as the preferred remedial altemative for OU 1. DOE also responded to questions about OU 1. In addition, pubhc comments on the Proposed Plan and Etaaft Permit Modification were received and recorded during the pubUc hearing. This record, as weU as responses to the written comments received during the public comment period, is included in the Responsiveness Summaty, which is part of this CAD/ROD. This decision document presents the selected remedial action for OU 1: 881 Hillside Area at Rocky Hats, chosen in accordance wifli CERCLA, as amended by SARA and to the extent practicable, the NCP. The decision for OU 1 is based on the administrative record.

SCOPE AND ROLE OF OIJ 1

Because of the complexity of the Rocky Hats site, the site was divided into sixteen geographicaUy defined OUs in the IAG. CAD/RODs have already been finaUzed and signed for three of these OUs (OU 11, OU 15 and OU 16). In aU three cases a No Action decision was detemiined to be appropriate. Although many of the remaining thirteen OUs have been consoUdated in RFCA, OU 1 remains as an individual operable unit The selected remedial action presented in this CAD/ROD includes addressmg subsurface soU contamination at IHSS 119.1, a former dram and scrap metal storage area. This action addresses the principal threat posed by OU 1 by excavating contamination sources in subsurface soils, thereby removing the current source of groundwater contamination, and by extractmg and treating contaminated groundwater contained at IHSS 119.1. Based on the results of flie final RH/RI, DOE has detemiined fliat the remaining IHSSs wifliin OU 1 are already in a protective state with regard to human health and the environment Thus, no further action relative to these remaining IHSSs wiU be taken. Any surface soU contamination at OU 1 wiU be addressed jointiy with surface soU contaniination at the 903 Pad, Mound and East Trenches area (formerly OU 2, which has been consoUdated mto the Buffer Zone OU in RFCA). Any additional groundwater associated with OU 1 wUl be managed consistent with the Integrated Water Management Plan. Surface water and suspended sediments transported from OU 1 have historicaUy flowed into Woman Creek or the South Interceptor Ditch (SID). Since Woman Creek and the SID are bemg evaluated as part of OU 5: Woman Creek Priority Drainage, surface water and associated sediments originating from OU 1 wiU be addressed as part of OU 5.

SUMMARY OF SITE CHARACTERISTICS

Geology Geologic units present at tiie 881 Hillside Area include tiie Rocky Flats AUuvium at the top of the hillside, coUuvium and artificial fill along central portions of the hUlside, and Woman

Creek VaUey AUuvium at the base. These thin (three to eighteen feet) (juatematy age surficial units are underlain by thick (six hundred to eight hundred feet) Cretaceous claystones, sUtstones and sandstones of the Laramie Fonnation. The uppermost portion of the Laramie Formation is dismrbed as a result of slumping on die hillside and also contains numerous fractures primarily due to weathering. This portion of the Laramie Formation is often refened to as the weathered claystone and may be up to twenty-five feet thick in some areas.

Surface Features/Surface Water Hydrology Several erosional and depositional processes have combined to produce gentiy rolling to moderately steep slopes on the 881 Hillside. The tenam has been recontoured in several areas at various times during the constraction of BuUding 881, the placement of fiU and waste materials in several IHSSs, road grading, and the constraction ofthe SID and French Drain.

Surface water primarUy occurs at OU 1 foUowing precipitation and snow melt events after the soils have become saturated due to infUtration. Suiface runoff generally flows south, where it is intercepted by the SID, and subsequentiy flows to the C-2 Pond where it is batched and sampled before being pumped to the Walnut Creek drainage.

HvdrogRnlngy Groundwater occurs under unconfined conditions within the unconsoUdated Rocky Hats AUuvium, coUuvium, fiU, and weathered claystone section ofthe Laramie Formation. This interval is designated as tiie Upper Hydrosfratigraphic Unit (UHSU). Below this, groundwater is limited to the more porous beds within the Laramie Formation and is usuaUy confined. This deeper section of strata is designated as the Lower Hydrostratigraphic Unit (LHSU).

UHSU groundwater is not present across the entire 881 HUlside (OU 1). Groundwater in the unconsoUdated material typicaUy is confined to northwest-southeast Uending erosion incisions in the bedrock surface, refened to as paleochannels, which are masked by the overlying materials. The extent of groundwater within these paleochannels varies with seasonal changes in precipitation rates. UHSU groundwater also occurs sporadicaUy within the upper portion of the Laramie formation within fractures and along slump block gUde planes. As previously discussed, a French Drain was instaUed between the 881 Hillside and Woman Creek to mtercept this shaUow unconfined groundwater, and it extends to a maximum depth of twenty-eight feet below top of bedrock. The French Dram acts as an effective hydrauUc barrier to horizontal migration of UHSU groundwater into Woman Creek.

Vertical migration between the UHSU and the LHSU is limited by the extremely low hydrauUc conductivity of the claystones within the Laramie Fonnation. The hydrauUc conductivity of these claystones (1 x 10"* cm/sec) is approximately three orders of magnitude less than that of flie overlying unconsoUdated sediments (1x10'^ cm/sec), and as a result the vertical component of migration is extremely smaU compared to the horizontal component In addition, the porous saturated sandstones ofthe LHSU are lateraUy discontinuous, with intervening claystone aquitards effectively limiting horizontal migration within the LHSU.

Recharge to the UHSU is minimal, and occurs primarily through infiltration of precipitation. InfUtration rates range from approximately two inches per hour for initial infUtration to as Uttie as one half hich per hour for imal (saturated) infiltration. Discbarge occurs largely through evapotranspiration and suiface discharge at seeps and into the SID. Total volumes of UHSU groundwater at OU 1 varies annuaUy and seasonaUy, but the Final

Phase in RH/RI report (June 1994) estimated the volume to be approximately 5.0 to 5.8 acre-feet

Flora /Fauna Grassland habitats are dominant at OU 1, representing about 82% of the total area. Nme percent is either developed or disturbed; marsh habitat occupies 4%; woodland habitat constitutes 4%; and shrab habitats account for the remaining 1%. A restored wetiands was created to mitigate damages resulting from installing the French Drain. WUdlife species are typical of those in similar habitats throughout the fooflulls area. As a result of limited ephemeral surface water, aquatic species with short life cycles and small habitats, such as l^nthic macroinvertebrates, have developed as opposed to fish populations.

Site Contamination A detaUed methodology was developed during the Hiase HI RFI/RI for detennining the nature and extent of contamination at OU 1. Using this methodology, analytes within the foUowing chemical classes werc analyzed: volatUe organic compounds (VOCs), semivol^e organic compounds (SVOCs), pesticides, polychlorinated biphenyls (PCBs), metals, and radionucUdes. The foUowing media were assessed for the presence of contamination: surface soU, subsurface soU, groundwater, surface water/seeps, and sediments. Based on this analysis, VOCs, SVOCs, metals, and radionucUdes were identified as contaminants at OU 1 (see Table 2). Note that the data in Table 2 does not reflect the 1994 surface soU hotspot removal

From tills and otiier data coUected, flie Phase III RFI/RI concluded fliat m OU 1 only IHSS 119.1 contains a significant source of contamination in the subsurface soU. The primary contaminants identified at IHSS 119.1 are as foUows: carbon tetrachloride; 1,1-dichloroethene; tetrachloroethene; 1,1,1-trichloroethane; trichloroethene; and selenium. No radioactive contamination was identified hi the subsurface soU at IHSS 119.1. Also, based on the data coUected during the Phase m RFI/RI, the other IHSSs in OU 1 were not found to be contamination source areas and do not conbibute significantiy to groundwater contamination. Therefore, the oflier IHSSs do not warrant any further remedial action, and, as previously stated in the "Scope and Role of OU 1" section of this CAD/ROD, the selected remedial action for OU 1 addresses subsurface soU contamination and groundwater contammation at IHSS 119.1.

Groundwater in OU 1 is contaminated by VOCs and metals (see Table 2). Releases of VOCs within IHSS 119.1 are presumed to have occurred in the form of dense non-aqueous phase Uquids (DNAPLs). This conclusion is based on the fact that drums at this IHSS contained unknown quantities and types of solvents, coupled with the presence of chlorinated solvent concentrations in groundwater at levels approaching 7% of the solubiUty limits of the substances. The presence of mobUe or residual DNAPL at this location is inferred only, smce DNAPL has not been directiy observed, and maximum measured concentrations of VOCs in subsurface soU is less than 2.0 mg/l. Table 3 Usts monitoring wells in the vicinity of IHSS 119.1 and theh contaminant concentration range for the Contaminants of Concem (COCs) for the years 1987 through 1995. The locations of these wells are shown on Figure 3. Chily two of the weUs (974 and 4387) have concentrations exceeding 1% of the compound solubiUty.

The lateral extent of groundwater contamination is generally Unuted to an area north of tiie SID. The occurrence of contammants in LHSU groundwater is Umited to relatively low levels of VOCs (less than 100 ^g/1) and locaUzed occurrences of metals, particularly selenium (concentrations ranging from below background to fifteen times the background levelof80|ig/l).

A soU gas survey was conducted during early 1996 to more accurately define the extent and approximate volume of contaminated subsuiface soU that wiU be excavated at IHSS 119.1. Based on this soU gas survey, two potential subsurface soU contamination source areas were identified (see Figure 3), resulting in an approximate total volume of subsurface soil to be excavated between one thousand and two thousand cubic yards.

Fate and Transport In general, contaminant migration at tiie site was evaluated m terms of the identilfied patiiways at OU 1. Migration of VOCs and metals in groundwater at IHSS 119.1 is restricted to northwest-southeast oriented channel features incised on the bedrock surface. The observed extent of groundwater contaniination originating from IHSS 119.1 was compared with the predicted extent to confirm the accuracy of the hydrogeologic conceptual model. Contaminant transport rates were estimated by calculating groundwater seepage velocity and contaminant-specific retardation factors (see Table 3). The observed migration distance of VOC and metal contamination originating from IHSS 119.1 (approximately three hundred feet) falls within the predicted range. After implementation of the substiiface soU removal action presented in this CAD/ROD, the present source of this groundwato-contaniination wiU be eliminated.

RadionucUdes and SVOCs m surface soils are susceptible to redistribution by wind or surface water erosion events. Surface soils at OU 1 werc contaminated with wmdblown low-level radionucUdes transported from the 903 Pad area, and any remaining surface soU contamination wiU be addressed jointiy with surface soU contamination at the 903 Pad area. Surface water is intercepted by the SID and wiU be addressed as part of OU 5.

SUMMARY OF SITE RISKS

As part of flie Phase m RFI/RI conducted for OU 1, a Baseline Risk Assessment (BRA) was prcparcd to identify any current or potential future risks to human health and the envfronment The BRA evaluated health risks from surface soil, subsurface soU, groimdwater, surface water, and sediments within the OU 1 boundaries.

The surface soU hot spot removal action conducted at OU 1 for plutonium, americium and uranium contaniination reduced the risk from this contaminant group and medium by 1(X) times. The risk from surface soils was reduced to 1 in lOO.CXX) (lOr) after the OU 1 hot spot removal was completed. This contaminant group contributed the highest risk to a human receptor in the OU 1 BRA. With respect to subsurface soils and groundwater, the primary contaminants identified in the Phase m RFI/RI were: carbon.tetrachloride; 1,1-dichloroethene; tetrachloroethene; 1,1,1-trichloroethane; trichloroethene; and selenium.

The BRA identified potential health risks from these contaminants associated with current and possible future exposure scenarios at OU 1. The scenarios originaUy examined in the OU 1 BRA are as foUows: current on-site commercial/industrial; cunent off-site residential; futurc on-site commercial/mdustrial; future on-site ecological reserve; and future on-site residential. However, not all of these scenarios are considered vaUd or currentiy possible.

The Rocky Hats Future Site Use Working Group, consisting of participants from DOE, EPA, CDPHE, and major stakeholders, recommended in tiie June 1995 "Futore Site Use Recommendations" report that the future on-site residential land use scenario not be considered. The commercial/mdustrial exposure scenario was recommended for use within the industrial area of the plant and the open space exposure scenario was recommended for

flie buffer zone. These recommendations arc consistent with the conceptual land uses in the ALF and with the R o c ^ Flats Vision. The OU 1 area Ues on the border between these two anticipated land uses. DOE has not yet made a final determination regarding the future land uses for OU 1. This determination wiU be consistent with RFCA and the Rocky Hats Vision and wiU take into consideration flie fact that the hillside at OU 1 has shown the potential for landsUdes and slumphig. This would make the constraction of stractures at OU 1 compUcated and problematic. In addition, as stated in the ALF, domestic use of groundwater wiU be prevented through institutional controls.

There are no health risks associated with the future open space park exposure scenario from OU 1 subsurface soU or groundwater since there are no exposure routes available from either medium. The carcinogenic risk calculated in the OU 1 BRA for the future on-site commercialAndustrial worker in the industrial arca from subsurface soUs and groundwater is 2.4 X 10"*. This risk is sUghtiy above EPA's acceptable risk range of 10^ to 10"*.

The Phase HI RFI/RI identified no significant environmental risk; therefore, environmental risks warrant no further examination.

In conclusion, actual or threatened releases of hazardous substances from this site, if not addressed by implementing the response action selected in this CAD/ROD, may present an imminent and substantial endangerment to pubhc health, welfare, or the environment

DESCRIPTION OF ALTERNATIVES

Six candidate remedial altematives were compUed from the treatment technologies that passed a detaUed screening process conducted during the Corrective Measures Study/FeasibiUty Smdy (CMS/FS), including the No Action altemative. A description of each remedial altemative is given below. The six remedial altematives are: No Action (Alternative 0), Institutional Controls with the French Drain (Altemative 1), Groundwater Pumping and SoU Vapor Extraction (Altemative 2), Groundwater Pumping and SoU Vapor Extraction with Thermal Enhancement (Altemative 3), Hot Afr Injection with Mechanic^ Mixing (Altemative 4), and SoU Excavation with Groundwater Pumping (Altemative 5). For Altematives 2,3,4 and 5, the volume of soil to be remediated was estimated, from the results of a recent soil gas survey performed at OU 1, to be between one thousand and two thousand cubic yards of soU (approximately a fifty feet by fifty feet by twelve feet deep excavation). During implementation of the remedy, confirmatoty soil sampling wiU be performed to detennine where the excavation can be terminated, based on cleanup levels identified in the ALF.

Alternative 0: No Action The No Action altemative is reqiured by CERCLA as a baseline altemative with which to compare other altematives. The No Action altemative uses results of the Baseline Risk Assessment to define exposure levels to human and envfronmental receptors at the site under existing conditions, and specificaUy excludes remedial activities.

Use of the existing French Drain groundwater coUection system would be discontinued under this altemative. Groundwater would, therefore, flow toward Woman Creek. The only activity associated with the No Action altemative is groundwater monitoring to detect changes in contaminant concentrations or migration patterns. Monitoring would begin immediately and would continue untU a determination could be made that monitoring is no longer required. Existing wells no longer deemed necessaty would be abandoned as appropriate.

10

No remedial time frame is estabUshed for this altemative since the altemative reUes solely on natural contaminant degradation and attenuation processes to meet Remedial Action Objectives (RAOs). A thhty year monitoring time frame is assumed, in accordance with EPA guidance. It is esthnated fliat it wiU cost approximately $1.9 million to implement this remedial alternative and continue monitoring groundwater for thirty years.

Alternatjye 1; Institutional Controls with the French Drain Altemative 1 seeks to achieve RAOs by restricting access to weUs impacted by OU 1 contaminants through mstitutional controls, whUe contmuing to treat groundwater coUected by tiie existmg French Drain at the BuUding 891 water treatment system. Institutional controls would also be employed to prevent domestic groundwater use at OU 1. Further degradation of groundwater would be minimized by continued containment and treatment of the groundwater. Subsurface contaniination sources would eventuaUy be depleted by dissolution to groundwater, although the length of time for this to occur would be quite extensive.

The existing French Drain and BuUding 891 treatment system would continue to operate untU no longer deemed necessaty based on contaminant concentrations in the groundwater. Groundwater monitoring would conthiue for as long as required to verify that contammant concentrations in groundwater have been permanentiy reduced below appropriate liinits. WeUs no longer deemed necessaiy for monitoring would be abandoned as appropriate.

No remediation time frame is defined for Altemative 1 since the French Drain system is currentiy operational and would conthiue to operate untU acceptable contaminant concentrations are achieved. Based on current operations of the existing French Drain system, it is reasonable to assume that due to the slow groundwater coUection rate, operation of the French Drain system would be required for an extensive period of time before RAOs are achieved. Experience with similar remedial actions at similar sites suggests that extremely long time frames are reqiured for complete contaminant depletion. For the purpose of preparing a cost esthnate, a thhty year time frame for remedial activities is assumed, based on EPA guidance. Based on this time frame, the esthnated cost for completion of Altemative 1 is $17.5 miUion.

Alternative 2: Groundwater Pumping and Soil Vapor Extraction Altemative 2 seeks to achieve RAOs by dewatering the identified IHSS 119.1 source area using conventional pumping techniques, and by implementing a localized soU vapor extraction (SVE) system. Risk from contaminated groundwater would be eliminated by extraction and treatment whUe further degradation of groundwater would be mmimized by removal of contammant sources through SVE.

SVE would enhance volatilization and subsequent contaminant recovety fixim saturated soUs, unsaturated soils and groundwater at OU 1. SVE targets contaminants fliat have partitioned to the aqueous phase, have adsorbed onto subsurface soils, exist in a free phase or occupy soU pore spaces m a vapor phase. Discrete pools of groundwater located m IHSS 119.1 would be extracted via the existing French Drain and one to three additional recovety wells. CoUected groundwater would be treated by the existing BuUding 891 water treatment system or other appropriate faciUty. These same areas, once desaturated, would be subjected to SVE to enhance the removal of any residual contaminants.

SVE can be significantiy influenced by site geology and contaminant characteristics. Geological factors that can hifluence flie success of SVE include depth to groundwater, subsuiface soil/rock type and surface permeabiUty. At OU 1, flie subsurface soUs contain large amounts of clay which would inhibit the effectiveness of tfais tecfanology. Contaminants tfaat are effectively recovered by SVE exfaibit a vapor pressure of 1.0 mm of

11

mercuty or more at 2CLdegrees Celsius and wfaicfa faave a dimensionless Henty's Law constant greater tfaan 0.01. Tfae contammants identified at OU 1 would be amenable to recovety by SVE.

It is also assumed that the vapor extraction wells in IHSS 119.1 would be approximately two to six inches in diameter. The wells would be operated cycUcaUy to enhance recovery and would be used in combination with a granular activated carbon (GAC) unit to treat extracted vapors. Tfae existing Frencfa Drain and BuUding 891 treatment system would continue to operate during tfae remedial activities, but after remediation of tiie source is complete tfae Frcncfa Drain would be decommissioned and groundwater coUection and treatment would cease. Groundwater monitoiing would be performed consistent witfa tfae Integrated Water Management Plan after completion of tfae remedial action.

The remediation time frame, wfaicfa is considered to be the time until protection is acfaieved by tfae remedial action, is esthnated to be approximately five years for Altemative 2. Based on tfais time frame and otfaer tecfanical hiformation defining flus altemative, tfae estimated cost for completion of Altemative 2 is $8.1 milUon.

Altemative 3: Groundwater Pumping and SVE with Thermal Enhancement Altemative 3 seeks to acfaieve RAOs by combining SVE as described in Alternative 2 witfa tfaeimal recovety enfaancement tecfaniques. Groundwater extraction and treatment would be employed to address groundwater contamination, wlule SVE witfa thermal enfaancement would be used to remove contamination sources. Tfais altemative considers two innovative treatment tecfanologies tfaat can effect an increase in subsurface soU temperamres and thus enhance SVE: radio frequency heating and electrical resistance (ofamic) heating. Tfaese technologies are discussed in detaU in the OU 1 CMS/FS report In gdneral, these thermal enhancement techniques enhance tfae success of tfae SVE by increasing the temperature in the subsurface soU whicfa aUows more complete and faster volatiUzation, and thus recovety, of organic constituents in tiie soU. The increase hi temperature of the subsurface soU also assists in dewatering the area by vaporizing pore space moismre.

As m Alternative 2, die existing French Drain and BuUdhig 891 treatment system would continue to operate untU rcme^tion of tfae contamination source is complete, at wfaicfa time tiie Frcncfa Drain would be decommissioned and groundwater coUection and tteatment would cease. Groundwater monitoring would be performed consistent witfa tfae Integrated Water Management Plan after completion of flie rcmedial action.

The rcmediation time frame for Altemative 3 is esthnated to be three years. Based on tfais time frame and other technical infonnation defining fliis altemative, the estimated cost for completion of Altemative 3 is $7.5 mUUon.

Alternative 4: Hot Air Injection with Mechanical Mixing Altemative 4 seeks to acfaieve RAOs tfarougfa an in-situ tecfanology tfaat combines faot afr stripping witii vigorous mixing of subsurface media. Contaminated groundwater at IHSS' 119.1 would be remediated tfarougfa extraction and treatment in tfae BuUding 891 faciUty, and tfae IHSS 119.1 subsurface soU contamination source would be addressed witfa faot afr injection and mechanical mixing.

This tecfanology operates under the same basic principles of SVE and thermal enfaancement discussed previously, but combines these principles witfa vigorous mecfaanical mixing to increase tfae effectiveness oftfae subsurface soU tteatment Tfae primaty tiieatment system in this altemative would consist of a caterpillar mounted drUl rig witii specialized drilling equipment. The driU equipment is capable of deUvering treatment reagents, such as hot air

12

or steam, via piping in_a hoUow driU bit sfaaft that faas mixing/cutting blades four to twelve feet in diameter.

Groundwater extraction weUs would be placed m previously tteated soU columns. Dewatering of a smaU area prior to treating the initial soU column would be accomplished via an extt:action weU driUed witfa conventional drilling equipment Extracted groimdwater would be treated in the existing BuUding 891 treatment system. The treattnent columns, or driU shafts, would overlap by tiiirty percent to ensure adequate tt:eatment througfaout tfae entire site. Four to six columns can be treated per day, depending on site conditions.

The existing Frencfa Drain and BuUding 891 treatment system would continue to operate during tfae rranedial activities, but after remediation of tfae source is complete tfae Frencfa Drain would be decommissioned and groundwater coUection and treatment would cease. Groundwater monitoring would be peiformed consistent witfa tfae Integrated Water Management Plan aft^ completion of the remedial action.

The remediation time frame for Altemative 4 is estimated to be two years. Based on this time frame and otfaer tecfanical hiformation definmg tfais altemative, tfae esthnated cost for completion of Altemative 4 is $4.3 miUion.

Alternative 5: Soil Excavation with Groundwater Pumping Alternative 5 is intended to achieve RAOs tfarougfa excavation of contaminated subsurface soils and contaminated groimdwater beneatfa IHSS 119.1. Based on tfae report of a recent soU gas survey that was performed at IHSS 119.1 ("Sampling and Analysis Report -Identification and Delineation of Contaminant Source Area for Excavation IDesign Purposes", April 1996), tfae estimated volume of soU that wiU be excavated from IHSS 119.1 is one thousand to two thousand cubic yards (approximately fifty feet by fifty feet by twelve feet deep).

Contaminated groundwater would be extracted from tfae excavation and treated in tfae BuUding 891 water treatment system. The excavated subsuiface soils would either be treated on-site with a tiiennal desorption unit and retumed to the excavation, disposed in an on-site disposal ceU, or disposed off-site.

Tfae existing Frencfa Dram and BuUding 891 treattnent system would continue to operate during the remedial activities, but after remediation of flie source is complete the French Drain would be decommissioned and groundwater coUection and tteatment would cease. Groundwater monitoring would be peiformed consistent with the Integrated Water Management Plan after completion of the remedial action.

The remediation time frame for Altemative 5 is estimated to be four to six montfas. Based on this time frame and other technical infonnation defining this altemative, the estimated costs for completion of Altemative 5, depending on faow flie excavated soU is managed, is as foUows: if the soU is treated on-site and retumed to the excavation the cost is approximately $3.5 miUion; if the soU is disposed off-site tfae cost is approximately $3.9 milUon; and if tfae soil is disposed in an on-site disposal ceU without tt:eatment the cost is approximately $3.3 miUion.

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SUMMARY OF THE COMPARATTVE ANALYSIS OF ALTERNATIVES

Threshold Criteria

Overall Protection of Human Healtii and the Envfronment: Altemative 5 provides the best overaU protection of human faealtfa and the environment by providing the largest reduction in exposure potential within tfae shortest amount of time through removal of the contammation source. Altematives 2,3 and 4 provide tfae next best level of overaU protection of human faealtfa and tfae envhonment based on tfae fact that fliey are designed to reduce exposure potential through in place remediation of flie contamination source at IHSS 119.1. However, these altematives involve technologies tfaat are not proven to be effective in tfae clay soils tiiat are present at IHSS 119.1. Tfaerefore, they would not be as thorougfa in removing the contamination source as Altemative 5, and tfaey also involve longer remediation timeframes. Alternative 1 protects fauman faealtii and tfae ̂ ivhonment by coUecting and treating contaminated groundwater, as weU as by implementing certain instimtional conttols to reduce exposure to tfae contaminants, but it does not address the contamination in the subsurface soU and, therefore, is not as protective as tfae previously discussed altematives. FinaUy, Altemative 0 offers tfae least amount of protection to fauman faealtfa and tfae envfronment because it does not involve any source removal, containment or other conttols.

CompUance with AppUcable or Relevant and Appropriate Requirements TARARs): The ARARs that have been identified and analyzed for eacfa altemative for the contaminants of concem at IHSS 119.1 are as foUows:

• Classifications and Numeric Standards (5 CCR 1002-8,3.8, So. Platte River Basm)

• Colorado Basic Standards to Dty Creek):

carbon tetrachloride

1,1-dichloroediene

tetracliloroetiiene

1,1,1 -tricfaloroetfaane

tricfaloroetfaene

selenium

r Surface Water (5 CCR 1002-8, 3.1, J

0.25 Ug/L

0.057 ^ig/L

0.8jig/L

200^g/L 2.7 ug/L 20 ̂ g/L (acute); 5 fig/L (cfaronic)

• Colorado Hazardous Waste Regulations (6 CCR 1007-3 Parts 264 and 268) • Colorado Afr PoUution Conttol Regulations (5 CCR 1001-5, Regulation 7) • Colorado Nongame, Endangered or Threatened Species Conservation Act (CRS 33-2-

101).

Tfae State contends tiiat 5 CCR 1002-8,3.12 (Site Specific Water QuaUty Classifications and Standards for Ground Water) and 5 CCR 1002-8,3.11 (Basic Standards for Ground Water) are ARARs. DOE disagrees witfa tfais contention. Botfa parties reserve tfaefr respective rigfats to raise tiiis issue and supporting arguments in any relevant forum. The parties do not anticipate that this disagreement wUl ripen into a fonnal dispute because 5 CCR 1002-8, 3.12 adopts tiie standards set fortii m 5 CCR 1002-8, 3.1 and 3.8, and tiiese standards are consistent with tfae enforceable standards set fortfa in tfae ALF. In addition, 5 CCR 1002-8,3.11 contains standards wfaicfa are generaUy consistent witfa or less stringent tiian tfie standards set fortii m 5 CCR 1002-8,3.1 and 3.8.

14

Altematives 2,3,4 and3 are expected to meet aU of tfae above identified ARARs, wfaUe Alternatives 0 and 1 are expected to meet aU ARARs except that they may not meet tiie Colorado Basic Standards for Surface Water. Therefore, Altematives 0 and 1 rank low under this criterion.

Primary Balancing Criteria

Long-Term Effectiveness and Permanence: Altemative 5 provides tfae faigfaest level of long-term effectiveness and permanence since it removes botfa groundwater contamination and subsurface soU contamination sources in IHSS 119.1, and tfaercby prcvents any furtfaer contamination of groundwater. Altematives 2,3 and 4 also rcmove groundwater contaniination, but arc not as effective at rcmoving subsurface soU contamination sources because tfae tecfanologies used in these altematives have not been proven effective in the clay soils at IHSS 119.1. Altemative 1 provides even less long-term effectiveness and permanence since it only rcmoves groundwater contamination, but not subsurface soU contamination sources. Altemative 0 provides tfae lowest level of long-term effectiveness and permanence since it does not treat or remove any contamination at IHSS 119.1.

Reduction of Toxicity. MobUity. or Volume Tfarougfa Treatment: Altemative 5 provides the highest reduction of mobiUty because it removes tfae primaty source of contamination and treats contaminated groundwater, tfaereby preventing any furtfaer migration of contaminants. In addition, if tfae excavated soU is ttreated, as discussed in tfae "Description of Alternatives" section, Altemative 5 also provides tfae highest reduction of toxicity and volume tfarougfa treatment Altematives 2,3 and 4 provide tfae next faigfaest level of toxicity, mobility and volume reduction since tfaey involve groundwater tteatment as weU as in place treatment of the subsurface soU contammation source. Altemative 1 provides less reduction of toxicity, mobiUty and volume througfa treatment because it treats only contaminated groundwater and does not address the subsurface soU contamination. Altemative 0 ranks lowest in this categoty because it treats neitfaer groundwater nor subsurface soU contamination, and tfaus provides no reduction in toxicity, mobiUty or volume tfarougfa treatment

Short-Term Effectiveness: This criterion evaluates community, environmental and site worker protection during tfae implementation of tfae remedy. It also evaluates tfae effectiveness and reUabiUty of protective measures during implementation and tfae time untU RAOs are acfaieved.

Altematives 0 and 1 rank faigfaest under tfae community, envfronmental and site worker protection duiing implementation portion of tfais criterion because tfaey involve no disturbance of tfae existing site and littie or no worker involvement Altematives 2,3,4 and 5 involve some site disturbance, but tfae disturbance is not expected to create a significant impact on tfae community, tfae environment or site workers. Altemative 3 faas the potential to present increased hazards to site workers due to the heating of flie subsurface soU.

For the effectiveness and reUabiUty of protective measures during implementation and for tfae time until RAOs arc acfaieved, Altemative 5 ranks tfae faigfaest Excavation faas been proven to be tfae most effective and reUable of tfae tecfanologies presented faere wfaen appUed to clay soils. In addition, DOE anticipates tfaat U wiU take only four to six monflis for RAOs to be acfaieved once implementation of Alternative 5 faas begun. Tlie amount of time until RAOs are achieved for Altematives 2,3 and 4, once hnplementation of flie altemative has begun, is five years, tfaree years and two years, respectively. Altematives 0 and 1 are tfae least effective and reUable since tfaey do not address tfae subsurface soU contamination

15

source. Also, the amount of time until RAOs are achieved for these two altematives is unknown, but likely to be quite extensive, since they rely on natural degradation of the contaminants.

ImplementabiUty: Tfais criterion evaluates the technical and administrative feasibiUty of implementing the altematives including the availabiUty of materials and services needed during implementation, as weU as tfae abiUty to monitor tfae effectiveness of tfae remedy.

Altemative 1 is tfae most easUy hnplementable because it represents tfae current condition at OU 1. The only additional woik that it would involve would be to implement institutional conttols at OU 1 and perform groundwater monitoring. Altemative 0 is tfae next most easUy implementable altemative because it involves only decommissioning tfae French Drain and performing groundwater monitoring. Altemative 5 is tfae next most implementable altemative. Excavation faas b e ^ proven to be effective and implementable in clay soils, and tfae equipment necessaty to perfonn tfae excavation is readUy avaUable. Also, tfae effectiveness of Altemative 5 can be easUy monitored.

Altematives 2,3 and 4 use intrusive treatment methods that may pose technical problems, and are, therefore, less implementable tfaan tfae otfaer altematives. For example, soU vapor exttaction (Altematives 2 and 3) cannot be reliably conducted in clay soils. Alternative 3 is even more difficult to implement flian Altemative 2 because it is stiU an experimental tecfanology. Altemative 4 is the most difficult option to implement because of the sloping, unstable lUUside that tfae driU rig would faave to work on, and because of tfae limited supply of the specialized equipment that is needed.

Cost: This criterion evaluates the capital cost for each altemative, long-term operation and maintenance (O&M) expenditures required to sustain i t and post-closure costs occurring afler the completion of remediation. Future expenditures are adjusted to present worth amounts by discounting aU costs to a common base year using present worth cost analysis.

Altemative 0 is tfae least costiy since it involves only decommissioning tfae Frencfa Drain and perfomiing groundwater monitoring for thirty years. Tfae total estimated cost of Altemative 0 is $1.9 milUon. Altemative 5 is tfae next least costiy altemative, witfa the foUowing estimated costs of completion: $3.3 milUon if the excavated soU is placed directiy into an on-site waste disposal ceU, $3.5 mUUon if the excavated soU is treated on-site with a thermal desorption unit and placed back into tfae original excavation, and $3.9 miUion if tfae excavated soU is disposed off-site. The cost estimates are based on an excavation volume of KXX) to 20()0 cubic yards of soU (50 feet by 50 feet by 12 feet deep excavation), wfaicfa was estimated as tfae appropriate soU excavation volume m the recent soU gas survey at IHSS 119.1. These cost estimates include aU costs of soil excavation, handling and management of tfae soU, operation of tfae Frencfa Drain and groundwater treatment plant for one year (or untU tfae soil faas been excavated), and groundwater monitoring for tfairty years.

Altemative 4 is more costiy tfaan Altematives 0 and 5, wifli an estimated total cost of $4.3 milUon. Tfais estimate is based on tfae same volume of soU as Altemative 5 (1000 to 2000 cubic yards), and includes aU costs of performing tfae faot ah injection and mecfaanical mixing, operation of tfae Frencfa E>rain and groundwater treattnent plant for two years, and groundwater monitoring for tfairty years.

Altemative 3 is more costiy tfaan the previously discussed altematives, witfa an estimated total cost of $7.5 milUon, whicfa is also based on a soU volume of lOCiO to 2000 cubic yards for treatment This cost estimate mcludes all costs of perfonning tfae soU vapor extraction witfa tfaermal enfaancement operation of the French Drain and groundwater treattnent plant

16

for three years, and groundwater monitoring for thirty years. Altemative 2 is even more costiy, witfa an estimated total cost of $8.1 milUon. Again, tfais cost estimate is based on a soU volume of 1000 to 20(X) cubic yards for treatment It includes aU costs of performmg the soU vapor exttaction, operation of the Frencfa Drain and groundwater treattnent plant for five years, and groundwater monitoring for thirty years.

Altemative 1 is tfae most expensive altemative, witfa an estimated total cost of $17.5 miUion, wfaicfa is based on tiie long-term operation of the French Drain and tfae water treatment plant for fliirty years and groundwater monitoring for thirty years.

Modifying Criteria

State Acceptance: This criterion addresses tfae State's comments and concems regarding tfae appropriateness of tfae selected remedy. Tfae State of Colorado was represented on flie E>ispute Resolution Committee tfaat selected tfae preferred remedial altemative for OU 1 and agrees witfa tfae selection. Tfae State faas no outstanding, significant comments or concems with the selected remedy.

Community Acceptance: This criterion evaluates tfae selected remedy in terms of issues and concems raised by tfae pubUc tfarougfa the pubUc involvement process. At the pubUc hearing for the OU 1 Proposed Plan on June 19,1996, DOE received one comment from the pubUc tfaat was supportive ofthe preferred remedial altemative. During tfae pubhc comment period for the OU 1 Proposed Plan, DOE received one set of written comments from the pubUc, wfaicfa, in general, expressed concem for fundhig and timmg of tfae selected remedy, and requested clarification on several issues in the Proposed Plan. These comments are addressed in tfae attached Responsiveness Summaty.

Anticipated Damages to Natural Resources: Altematives 2,3,4 and 5 wiU not result in any irreversible damages to natural resources and wiU improve the quaUty of soU and groundwater by excavation and tteatment Altemative 1 wiU not result in any irreversible damages to natural resources and wiU improve tfae quaUty of groimdwater by tteatment Altemative 0 wiU not result in any irreversible damages to namral resources, but wUl continue to degrade the quaUty of groimdwater since tfae altemative does not involve any remedial activity. Measures to control and reduce tfae risk of damages to namral resources wiU be considered prior to beginning tfae remedial activity.

THE SELECTED REMEDY

The selected remedy for OU 1 includes tfaree prhnary components:

1. Excavating subsurface soU contamination at IHSS 119.1, a former drum and scrap metal storage area, tfaereby removing tfae current source of groundwater contamination. Tfae major components of tfae selected remedial action at IHSS 119.1, described in detail below, include: • Excavation of approximately one tfaousand to two tfaousand cubic yards of

contaminated subsurface soUs at IHSS 119.1; • Extraction and then ultraviolet/hydrogen peroxide and ion-exchange treatment of

contaminated groundwater from tfae excavation; and • Eitfaer thermal tteatment and replacement of excavated soU into the original

excavation, disposal of excavated soU in an on-site waste disposal ceU, or off-site disposal of excavated soil.

17

This portion of theselected remedy for OU 1 was cfaosen by tfae Dispute Resolution Committee (DRC) on August 25,1995, as part oftfae dispute resolution process tfaat is defined m the IAG, which was the goveming cleanup agreement at tfae time of tfae decision. At tfaat time, tfae DRC was composed of DOE's Assistant Manager for Environmental Restoration, EPA's Federal FaciUties Brancfa Cfaief, and CDPHE's Program Manager for tfae Hazardous Waste Control Program. In cfaoosmg tfae remedial action for IHSS 119.1, tfae DRC was interested in conttolUng groundwater contamination through source removal. The DRC deteimmed that Altemative 5, SoU Excavation with Groundwater Pumpmg, is tfae most appropriate remedial action for IHSS 119.1. This remedial action includes excavation of approximately one fliousand to two thousand cubic yards of contaminated subsurface soils at IHSS 119.1; exfraction and tfaen ultraviolet/faydrogen peroxide and ion-exchange treattnent of contaminated groundwater at IHSS 119.1; eitfaer tfaermal tteatment and replacement of excavated soU into tfae original excavation, disposal of excavated soU in an on-site waste disposal ceU, or off-site disposal oftfae excavated soU; and groundwater monitoring consistent witfa tfae Integrated Water Management Plan.

Tfae comparative analysis of alternatives sfaows tfaat Altemative 5 rates best for overaU protection of human health and the envfronment; compUance with ARARs; long-term effectiveness and permanence; and reduction of toxicity, mobiUty, or volume tfarougfa treatment Altemative 5 rates liigfaer tfaan tfae otfaer altematives for short-term effectiveness, and rates good for implementabiUty and anticipated damages to natural resources. Altemative 5 is expected to take tiie least amount of time to acfaieve protection at IHSS 119.1 (four to six montfas), and is tfae least expensive altemative except for Altemative 0, whicfa is to perfonn no remedial action. In addition, Altemative 5 satisfies tfae CERCLA stamtoty prcfercnce for remedies tfaat employ treatment as a principal element and acfaieves tiie Remedial Action Objectives set for OU 1.

Tfae principal components oftfae IHSS 119.1 remedial action selected to meet these RAOs and remediation goals are described below:

Excavation of soU: Excavation of contammated subsurface soUs wiU begin at IHSS 119.1 in the two contamination source areas identified during tfae recent soU gas survey. The location of tfaese two areas can be found on Figure 3. From tfae soil gas survey results, it is estimated tfaat tfae amount of soU tfaat wiU be excavated is approximately one tfaousand to two tfaousand cubic yards. During tfae excavation, sampling wiU be perfonned to confirm tfae point at wfaicfa aU contaminated subsurface soU has been removed, in accordance with flie ALF. In addition, during implementation of the selected remedy, E)OE wiU perform confirmatory soU sampling downgradient of IHSS 119.1 to verify tfaat a contamination source does not exist there. A detailed sampling and analysis plan for both of tfaese confirmatoty sampling activities vnH he prepared as part of tfae Remedial Design for OU 1. A detaUed soil excavation plan wiU also be prepared as part of tfae Remedial Design.

Groundwater extraction and freatment: Groundwater wiU be extracted from tfae excavation and wiU be fransferred to tfae existing BuUding 891 ultraviolet/faydrogen peroxide and ion-excfaange water treattnent system for final tt:eatment and discharge. After aU contammated subsurface soil faas been excavated and all contaminated groundwater faas been extracted from the excavation, the French Drain system wiU be decommissioned and its use wiU be discontinued. The final details of tfae grouiidwater extraction and the decommissioning of tfae Frencfa Drain wiU be presented in the Remedial Design for OU 1.

18

HandUng and management of excavated soU: DOE is considermg three options for managing the excavated soU: on-site treatment and placement back mto the original excavation, disposal in an on-site waste disposal ceU, or off-site disposal. DOE's preferred method of managing tfae excavated soU is to tteat tfae soU on-site in a thermal desorption unit to levels tfaat wiU be identified and approved m tfae Remedial Design. Tfae treated soU would tiien be placed back into tfae original excavation. Again, tfae final details of faow tfae excavated soU wiU be bandied and managed wiU be prepared as part of tfae Remedial Design and wiU be in accordance witfa RFCA.

Groundwater monitoring: DOE anticipates fliat groundwater monitoring wiU be performed at IHSS 119.1, consistent wifli tfae Integrated Water Management Plan, after tfae remedial action is complete. Tfae details of tfais groundwater monitoring wiU be presented in tfae Remedial Design.

It is possible tfaat cfaanges to the remedial activities described above may be made as a result of the remedial design and constraction processes. Any such cfaanges, in general, would reflect modifications resulting from die engineering design process.

2. Instimtional conttols wiU be maintamed througfaout tfae OU 1 area m a manner consistent with RFCA, the Rocky Hats Vision, and the ALF. TTiese documents recognize that the reasonably foreseeable futurc land use for tfae OU 1 area is restricted open space. Tfae institutional conttols wiU ensure that flie restricted open space land use is maintained for the OU 1 area and tfaat domestic use of groundwater within tfae OU 1 area is prevented. If the reasonably foreseeable future land use for the OU 1 area cfaanges when final sitewide land use decisions are made, this remedy wiU be reexamined to ensure protection ofhuman faealtfa and the environment The specific mechanisms (for example, deed restrictions) to ensure tfae implementation and continuity of tfae necessary institutional controls faave not been included in this CAD/ROD. Currentiy, tfaese mecfaanisms are envisioned to be placed in tfae Final Sitewide CAD/ROD or in this CAD/ROD during one of the five-year reviews of this document However, sfaould tfae Final CAD/ROD not occur or not include tfaese institutional control mecfaanisms, tfais OU 1 CAD/ROD wiU be revised to mclude them, if it does not already include tfaem as a result of a five-year review. Tfae institutional conttols can also be removed at one of tfae above times, if it is deemed appropriate to do so by tfae parties.

3. Because of tfae groundwater and land use confrols, tfae low amounts of contamination in OU 1 outside of IHSS 119.1, and tfae low levels of risk associated witfa tfae contamination, no remedial action wiU be taken at the remaining ten IHSSs in OU 1.

Implementing tfae selected remedy wiU not result in any hreversible damages to namral resources. Wetiands wiU not be injured; flood elevations wiU not be affected; soU and groundwater wiU be temporarily disturbed during excavation activities, but wiU not be permanentiy hnpacted; and no permanent displacement or loss of wUdUfe wiU result from tfae hnplementation of tfae selected remedy.

The selected remedy wiU achieve tfae Remedial Action Objectives set for OU 1, wfaicfa were identified in tfae CMS/FS report as foUows:

Prevent flie infaalation of, ingestion of, and/or dermal contact wifli VOCs and inorganic contaminants in OU 1 groundwater tfaat would result m a total excess cancer risk greater than KT* to 10"* for carcinogens, and/or a Hazard Index greater flian or equal to one for non-carcinogens.

19

•

• Prevent migration of contammants from subsurface soils to groundwater that would result in groundwater contamination in excess of potential groundwater ARARs for OU 1 contamination.

• Prevent migration of contaminants in OU 1 groundwater from adversely impacting surface water quaUty in Woman Creek.

These RAOs were selected to address the primaty risk exposure pathways identified for OU 1, which are groundwater and subsurface soil pathways. The preliminaty remediation goals (PRGs) for these RAOs dealing with groundwater and subsurface soils were identified in tfae CMS/FS report by examining botfa risk-based and ARAR-based values. The exposure route of groundwater ingestion resulted in the highest potential risk to a future on-site resident so tfae Colorado Basic Standards for Groundwater, found in 5 CCR 1002-8, 3.11.5 and 3.11.6 were selected as appropriate PRGs for OU 1.

Subsequent to tfae selection of PRGs m die CMS/FS report faowever, RFCA was finaUzed and is currentiy the goveming cleanup agreement for Rocky Flats. The remediation goals in RFCA are based on the protection of surface water and are specified in tfae ALF. Therefore, the remediation goals for the contaminants at OU 1 are based on the ALF. RFCA also identifies points of compliance for aU remedial activities conducted at Rocky Hats, which wiU be used for tfae remediation of OU 1.

DOCUMENTATION OF SIGNIFICANT CHANGES

The OU 1 Proposed Plan for Rocky Hats was released for pubUc comment on May 13, 1996. The Proposed Plan identified Altemative 5, SoU Excavation witfa Groundwater Pumping, as tfae preferred remedial altemative. DOE reviewed all written and verbal comments submitted during tfae public comment period. Upon review of these comments, it was determined that no significant cfaanges to flie remedy, as it was originaUy identified in tfae Proposed Plan, were necessaty.

20

RESPONSIVENESS SUMMARY

OVERVIEW

Tfae Proposed Plan for OU 1 was avaUable for pubUc review and comment from May 13, 1996, through July 12,1996. In addition, a pubhc hearing was held on June 19,1996, at which oral and written comments were soUcited. Tfais Responsiveness Summaty provides a summaty of tfae comments on tfae OU 1 Proposed Plan tfaat were received during the pubUc comment period, as weU as DOE's responses to tfae pubUc's concems. AU comments received during the pubUc comment period were considered in the final selection of tfae remedial altemative for OU 1.

SUMMARY OF COMMENTS RECEIVED DURING PUBLIC COMMENT PERIOD AND DOE RESPONSES

DOE soUcited written and oral comments from the pubUc on the OU 1 Proposed Plan during the pubhc comment period and at tfae pubUc bearing. A summary of tfae comments tfaat were received and DOE's responses are provided below:

Comment: A member of tiie community at tfae pubUc bearing stated tfaat tfae selection of tfae preferred remedial altemative was logical and looked like it would move Rocky Hats forward toward cleanup and closure.

Response: No response necessaty.

Comment: A written comment was received tfaat expressed concem over the apparent lack of funding for the implementation of the selected remedy, considering that tiie remediation of IHSS 119.1 is ranked number 12 on tfae Environmental Restoration (ER) Ranking in RFCA. The commenter was concemed that tfae remedial action must be conducted with fifteen monflis of completing the Remedial Investigation/FeasibiUty Study (RI/FS), accordmg to CERCLA.

Response: Fhst whUe DOE is faced witfa significant budget cuts tfaat wiU affect tfae activities tfaat can be completed at Rocky Flats in FY97, final decisions on site priorities and funding for FY97 faave not yet been made. Tfae ER Ranking is mtended to be a guide to funding and remediating tfae top priority IHSSs on-site, based on various factors including available funding, timing and project stams. The IHSSs do not faave to be remediated in the exact order that tfaey appear on tfae ranking Ust Tfaerefore, DOE is not certain that tfais remedial action wiU not be funded m FY97. Second, the section of CERCLA quoted in tiie written comment (CERCLA Section 120(e)(2)) refers to the entire site, not specificaUy to any particular operable unit In addition, cleanup at Rocky Hats has been govemed by an enforceable agreement (first tfae IAG and now RFCA) since 1991. EPA faas said that DOE is in compUance with CERCLA time frames as long as it is in compUance with this enforceable agreement Tfaerefore, tiie remedial action presented in tfais CAD/ROD does not faave to be implemented witfain fifteen montfas of tfae final CAD/ROD.

Comment: A written comment was received that expressed concem over the management of the excavated soUs in Altemative 5. Because three options were listed for the management of the soUs, the commenter was concemed tfaat a complete evaluation of flie

21

altematives could not faave been accomplisfaed. Also, die commenter questioned tfae option of on-site disposal of tfie excavated soU and stated tfaat more detaU sfaould be given on tfae management of tfae excavated soU.

Response: Altfaough three options are presented in the Proposed Plan for managing the excavated soU, tfae ftmdamentsds of Altemative 5, as compared to flie otfaer altematives under flie nine criteria reqiured by CERCLA, are the same under each option, and the comparison results are also the same. For example, regardless of the metfaod of faandling the excavated soU, provided it is in compUance with aU appUcable laws and regulations, Altemative 5 is stUl overaU the most protective of fauman health and the environment based on the removal of the contamination source in the subsurface soU. The evaluation of altematives was not dependent on tfae method of managing the excavated soU to show tfaat Altemative 5 is tfae most appropriate altemative. In addition, separate cost estimates were provided in the Proposed Plan for eacfa different option of soU management under Altemative 5. In aU three cases Altemative 5 is the least expensive altemative, other than the No Action altemative.

The intent of tfae on-site disposal option for tfae excavated soU is to dispose of tfae soU in a permitted on-site waste disposal ceU, ifsuch a unit exists on-site at the time that this remedial action is perfonned. Botfa the disposal unit and tfae soU would meet aU appUcable requirements before on-site disposal would occur. If sucfa a disposal unit does not exist on-site, one of tfae otfaer two options wiU be employed. As stated in tfae CAD/ROD, it is currendy DOE's preference to treat the excavated soU on-site in a thermal desoiption unit and place it back into the excavation, provided that the treated soU meets soU put-back requirements estabUshed by RFCA. The details for managing tfae excavated soU, includhig necessaty freatment reqiured permits, and appUcable laws and regulations, wiU be included in tfae Remedial Design, along witfa aU of tfae details of implementing flie selected remedy.

Comment: A written comment was received tfaat questioned wfaetfaer a faealtii assessment by tfae Agency for Toxic Substances and Disease Registty (ATSDR) faas been or wiU be performed at Rocky Hats.

Response; A faealtfa assessment by ATSDR is scfaeduled for Rocky Hats by tfae year 2002. This is based on available resources at ATSDR and tfae prioritized needs of tfae wfaole DOE complex for faealtfa assessments to be performed. DOE is using tfae results of the Baseline Risk Assessment for OU 1, which includes a PubUc Health Evaluation and an Environmental Evaluation, to move forward witfa tfais remedial action.

Comment: Written comments were received tfaat expressed concem over vague language in tfae Proposed Plan regarding the conclusions in tfae RFI/RI on tfae extent of contamination and tfae need for remedial action at OU 1.

Response: Tfae RH/RI report, wfaicfa is avaUable for review m the Admmistrative Record and pubUc reading rooms, does definitively detennine tfae need for furtfaer remedial action at eacfa IHSS in OU 1 and presents in detail tfae information used to make those determinations. The RFI/RI concluded tfaat only IHSS 119.1 contributes significantiy to groundwater contammation and contains subsurface soU contamination at levels tfaat warrant a remedial actipn. Based on tfae data contained in tfae report, tfae RH/RI also concluded tfaat tfae remainder of the IHSSs at OU 1 are already in a protective state (i.e., do not contribute significantiy to groundwater contamination and do not contain contamination at levels that warrant a remedial action). Due to tfae Ihnited scope of the Proposed Plan, a summaty of tfaese conclusions and data was presented and references were made to tfae

22

RFI/RI in tfae ProposedJ^lan, ratfaer tfaan repeat in detaU tfae information already presented in tfae RFI/RI report. For tfae cfaaracterization of IHSS 104, the Proposed Plan only referred to a review of documentation. However, conclusions on tfae cfaaracterization of IHSS 104 were also based on mvestigation data, as presented in tfae RFI/RI report

Comment: A written comment was received tfaat expressed concem over tfae requfrement m tfae IAG to hicorporate actions tfaat are completed pursuant to CERCLA autiiority mto tfae Rocky Hats RCRA permit

Response: RFCA now requires that CDPHE incorporate only final conective action decisions into the Rocky Hats RCRA pennit in order to satisfy the requirement to include a conective action element in tfae permit In addition, RFCA states tfaat activities requfred under any concurrence CAD/R()D (wfaere botfa EPA and CDPHE concur witfa the CAD/ROD) wiU not require permits.

Comment: Written comments were received that questioned whetfaer RCRA listed faazardous wastes were disposed at OUl , based on the contaminants of concem tfaat were | identified in tfae Proposed Plan. Tfae commenter questioned whether tfae excavated soU | sfaould be bandied as a RCRA listed faazardous waste. '

Response: Based on tfae RH/RI, DOE does not faave any infonnation to indicate that ! spent solvents, which would have been RCRA listed hazardous wastes, were disposed at OU 1. Ratfaer, the VOCs listed in the Proposed Plan were identified as contaminants of concem based on sampling and analysis of tfae groundwater and soU that was conducted at OU 1 duiing die RFI/RL DOE cannot conclusively say tfaat tfaese VOC contammants are ! tfae result of tfae disposal of spent solvents (i.e., RCRA listed faazardous waste), tfaerefore, j tfae RCRA faazardous waste Usting does not apply to tfae contaminants, and the soU does not j contain a listed hazardous waste.

Tfae Remedial Design wiU describe in detaU faow tfae excavated soU wiU be managed. At tfais point, it is anticipated tfaat tfae excavated soU, wfaicfa itself is not a waste, would be considered envfronmental media containing faazardous constiments that exfaibit a faazardous waste characteristic for VOCs. The excavated soU would be treated in a thermal desorption unit FoUowing this treatment the soil would be sampled and analyzed to verify the successfiil removal of VOCs from tfae excavated soU. At that point tfae excavated soU would no longer contain hazardous constituents that exhibit a hazardous waste characteristic. Tfaerefore, land disposal restrictions (LDR) and minimum tecfanological requirements (MTR) would not apply to tfae excavated soUs.

Comment: A written question was received conceming tfae levels of radioactivity tfaat must be met before placement of soils contaminated with radionuclides is aUowed.

Response: Infonnation from the RFI/RI for OU 1 indicates tfaat radionucUde contamination is not expected m the subsurface soUs at OU 1. However, as required by RFCA, a working group consisting of representatives from DOE, EPA and flie State of Colorado are woiiang on developing site specific radionucUde clean-up and put-back levels for soU. The proposal by this woridng group will be available for public comment from September 1,1996, tfarougfa October 4,1996. A final decision on tfais issue is expected to be made by October 18,1996.

23

COLORADO

Slreel

f iqure

Generol Location of Rocky Flols Environmenlal

Technology Sile

24

N>

s iNOlviOuil. ntZMDOUS SueSIANCC SiTC (IHSS) MO IHSS OGSICNATION. OASHCO WHCRC QiSfuDBEO OURINC CONSTOUCTION or TRENCH DRAIN

ACtUAl. SCRAR U H A I . AND ORUU SIORACC ARCAS IN IHSS l i t BASED ON AERIAL PMOIOCRAPHS

AC1UAL DRUU STORACC AREA IN IHSS I I I . I BASED ON AERIAL PHOIOCRAPHS

CREEK/ORAlNACt

FENCE

fll Figure 2

Individual Hazardous

Substance Sile LocaLions

881 HiUside Area (OUl) In the Vidnity of IHSS 119.1

Volatile Chlorinated Hydrocarbon Head Space Concentractions

Figure 3

EXPLANATION

A Pre-1986 Wdls (Abandoned)

« Borehole Locations

o Groundwater WELLS (Alluvium)

• Groundwater WELLS (Bedrock)

e Piezometers

N Individual Hazardous Substance Sites

Fences

Dirt Roads

/ \ J Contours Intervals 10 ppm

ND = Not Detected NS = Not Sampled Head Space readings in ppm [detection fimit 0.1 ppm

Concentrations represent greatest readings from 0-22 feet below grades

^ ^ Estimated excavation Area using 20ppm head space concentrations as tiie cut off.

Estimated excavation area using 50ppm head space concentrations as tfie cut off.

fimRSJHY*og€ak>g% - tSSS. Oan/tale SsmpA^ ktcMform profk^d by

-li-

Scale - 1 : 2S0 1 inch represents appfoximately 21 feet

St«te Plane Coordinate Proiection Colorado Central Zone

Datum: N A 0 2 7

U.S. Depar tment of Energy

Rocky Flats Envi ronmental Techno logy Site

Plepaicd ^ ^

O j l « [ J O " " " V Mountain r W l r n d t Remediation Services, LLC.

GufnfAlc laiMBAllM tr«lea« Gna* lUAf n m Imlnmmmilil T«lMMisor « •

ra. ,m tu MdM. CO •M1^0«4

MAP ID: Fia6-1 April 2 6 . 1996

Table I Individual Hazardous Substance Site Descriptions

IHSS Number IHSS Name Description

102 Oil Sludge Pit Site

ApproxiniAtely 40 x 70 ft', area located approximately 180 feet south of Building 881 where 30 to SO drums of non-radioactive oily sludge were emptied in the U(c 1950s. The sludge was from the cleaning of two No. 6 fuel oil tanks, designated as IHSSs IOS. I and 105.2, and was backfilled when disposal operations ceased

103 Chemical Burial Site

Approximately 50 feet in diameter (2,000 fL'), the pit is circular is shape, and is located approximately ISO feet southeast of Building 881 on 1963 aerial photographs. Area was reportedly used to bury unknown chemicals.

104 Liquid Dumping Site

Reportedly a fonner (pre-1969) liquid waste disposal pond in arca cast of Building 88] - no exact location or dimensions of pit - location is uncertain due to poor quality of 1965 aerial photograph. Approximate dimensions are 50 x 50 ff.

105.1, 105.2

Out-of-Service Fuel Oil Tank Sites

Located immediately south of Building 881, these were storage tanks for No. 6 fiiel oil. Suspected leaks in 1972. Tanks closed in place through filling with asbestos-containing material and cement. IHSS 107, the Hillside Oil Leak Site, may have been caused by leakage from these tanks.

106 Outfall Site Overflow line from the sanitary sewer sun^ in Building 887. The outfall was used for discharge of untreated sanitary wastes in the 1950s and 1960s. Due lo concem about discharges from the outfall entering Woman Creek, several small retention ponds and an interceptor dilch were built in 1955 and 1979, respectively, to divert the outfall water to Pond C-2.

107 Hillside Oil Leak Site

Site of 1972 fiiel oil q>ill fiom Building 881 foundation drain outfall. A concrete skimming pond was built below the foundation drain outfall to contain the oil flowing from the foundation drain, ahd an interc^itor ditch was constmcted to prevent oil-contaminated water from reaching Woman Creek.

119.1, 119.2

Multiple Solvent Spill Sites

Fonner drum storage areas east of Building 881 along the southern perimeter road. IHSS 119.1 is the larger westem drum and scrap metal storage area, and appears to have contained mostly dmms in tfae southern part of tfae IHSS and mostly scrap metal in the northem part, although material was moved around frequently as documented by aerial photographs. IHSS 119.2 is the smaller eastem dmm and scrap metal storage area and appears to have contained mostly scrip metal. The dmms contained unknown quantities and types of solvents and wastes. The scrap metal may have been coated with residual oils and/or hydraulic coolants.

130 Radioactive Sile - 800 Arca/Tl

Area east of Building 881. Used between 1969 and 1972 to dispose of soil and asphalt conuminated with low levels of plutonium and uranium. IHSS 130 is referred to as the Contaminated Soil Disposal Area East of Building 881 in the HRR to better match the history of waste disposal; the site is included in the discussion of the 9(X) area at RFETS in that report. IHSS 130 contains approximately 320 Ions or 250 cubic yards which came from three sources: 1) plulonium-contaminated soil and a^halt, placed in September of 1969, 2) road asphalt and soil rad conuminated by leaking dmm in transit and 3) 60 cu. yds. of plutonium-conUminaled soil removed from around the Building 774 process waste tanks in 1972.

145 Sanitary Six-inch cast-iron sanitary sewer line that originates at the Building 887 lift sution and that Waste Line leaked on Ihe hillside south of Building 881. The line had conveyed sanitary wastes and low-Leak I level radioactive laundry effluent to the sanitary treatment plant from about 1969 lo 1973.

27

Table 2: Summary of Contaminants at OUl

Surface Soil

Subsurface Soil Groundwater

Surface Water/ Seeps Sediments

Inorganic Analytes

Selenium

Vanadium

Plutonium

Americium

Uranium

X*

X

X*

X*

X*

X*

Volatile Oi-ganic Compounds

l.I,l-Trichloroethane

Trichloroethene

Tetrachloroethene

Carbon Tetrachloride

i,2-Dichloroethane

Chloroform

1,1-Dichloroethene

1,2-Dichloroethene

cis-1.2-Dichloroethene

1,1,2-Trichloroethane

1,1-Dichloroethane

Toluene

Total Xylenes

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X**

X**

X

X

X

X

X

X

X

X

X

X**

X**

X

X

Semivolatile Oi-ganic Compounds |

Polynuclear Aromatic Hydrocarbons

Aroclor-1254

Aroclor-1248

X

X

X

X X

X 1

* Presence in these media is based on hot spot data. ** Presuined to be present as a coniaminani of these media because of the widespread nature of the contamination originating from

an off-site source.

28

Table 3: Summary of VOC Concentrations in Groundwater, IHSS 119.1,1987-1995 Well No.

0974

1074

0487

4387

37891

37991

32591

Compound

CCL4 1,1-DCE TCA PCE TCE

ecu 1.1-DCE TCA PCE TCE CCL, 1,1-DCE TCA PCE TCE

ecu 1.1-DCE TCA PCE TCE

ecu 1.1-DCE TCA PCE TCE

ecu 1,1-DCE TCA PCE TCE

ecu 1,1-DCE TCA PCE TCE

Range of Concentrations (ug/L)

5U-2 ,800 500U - 48,000 1.220-30.250 430-13.200 1.500-72,000

2.500E-5.000 42J - 120 SOU - 390 IOOU-49

790 - 3.600

46 - 2.600 2 U - 1 2 3.2 - 20 14 - 590

220 - 9.500

40U-2.100 1.400-11.000 1.700-20.000

61-7 .590 100 - 15.540

0.2U 0.2U O.IU

0.1U-7.1B O.IU-1.3 O.IU-0.2

0.2U O.IU

O.IU-16 O.IU-3.3

0.1 0.68 - 6 0 . 4 - 2

1-3 5 U - 1100

Note: Well 0587 had 12 ug/L TCE on (8/92). well 33491 had 1 not sampled. U=noc detected at or above method detection limit J=estimated value

ug/L TCE (11/94). and wclls 33691, and 38291 were , B=appeared in method blank, E=cslimatcd value, and

Compound

ecu 1.1-DCE TCA PCE TCE

Summary of VOC Physical Characteristics Solubility

(mg/L)

800 400 1360

150 IIOO

Specific Density (20") (g/cc)

1.59 1.22 1.34

1.62

1.46

Log Ko„. Octanol Water

Coefficient

2.83 2.13

2.47

2.60

2.53

Henry's Law Constant

(atm-mVmol)

0.0302 0.021

0.018

0.0153

0.0091 Compiled from Cohen. R.M., Mercer. J.W., and Mathews, J., 1993. DNAPL Site Evaluation: CK. Smolcy. Publisher

29