Critical Exposure Pathways
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Transcript of Critical Exposure Pathways
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Critical Exposure Pathways
Workshop #13
October 17, 2007
Elizabeth Callahan, MassDEP
John Fitzgerald, MassDEP
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Workshop Overview
7:00 – 7:40– CEP Concepts &
Process (EC)– Q&A
7:40 – 8:30– Vapor Intrusion
Pathway (JF)– Q&A
8:30 – 8:40 BREAK
8:40 –9:20– Regulatory Guidelines
& Rules of Thumb (EC)– Q&A
9:20- 10:00– Technical Guidelines &
Rules of Thumb (JF)– Q&A
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CEP Concepts & Process
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CEP Definition – 40.0006
(a) vapor-phase emissions of measurable concentrations of OHMs into the living or working space of a pre‑school, daycare, school or occupied residential dwelling; OR
Critical Exposure Pathways mean those routes by which OHM(s) released at a disposal site are transported, or are likely to be transported, to human receptors via:
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CEP Definition – 40.0006 (cont.)
(b) ingestion, dermal absorption or inhalation of measurable concentrations of OHMs from drinking water supply wells located at and servicing a pre‑school, daycare, school or occupied residential dwelling.
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Risk and Required MitigationR
isk
No Significant No Significant RiskRisk
Imminent HazardImminent Hazard • must promptly eliminate
• must eventually achieve for a Permanent Solution
No RiskNo Risk
CEP CEP
• must eliminate, mitigate or
prevent pathway, to the extent feasible
No Substantial No Substantial HazardHazard
• must achieve for a Temporary Solution
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Why Do We Care about CEPs?
• CEPs address Exposure Pathways in schools, day cares, and homes, where frequency of exposure is likely high
• Uncertainties in chemical toxicity information and risk characterization
• Sensitive populations (e.g., infants, children, fetal development, compromised immune systems)
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Statutory Basis - CEP
Section 3A(g)
Chapter 21E Permanent Solution Requirements• Achievement of “No Significant Risk” (HI,
ELCR)• Where feasible, a permanent solutions shall
include measures to reduce to the extent possible the level of OHM to the level that would exist in the absence of the disposal site (i.e., “background”)
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Section 3A(h)
Feasibility Criteria• No technology exists
• Costs outweigh the benefits• Expertise not available• No available disposal location
Statutory Basis - Feasibility
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Regulatory Requirements –IRAs and CEPs
• 40.0414(3) – IRAs are presumed to require the elimination and/or mitigation of CEPs
• 40.414(4) IRAs are presumed to require the prevention and/or mitigation of CEPs
These are REBUTTABLE PRESUMPTIONS, based on feasibility
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Condition of Substantial Release Migration (SRM) - 40.0006
a condition at a disposal site that includes any of the following:…
(d) releases to groundwater that have been or are within one year likely to be detected in a public or private water supply well;
…(f) releases to groundwater or to the vadose zone that
have or are within one year likely to result in the discharge of vapors into school buildings or occupied residential dwellings.
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SRM Condition - Notification
• 72 hour notification condition**
• Requires an IRA
* * where such condition is associated with a release for which notification otherwise is or has at any time in the past been required (40.0313(5))
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Life Cycle of a CEP
NotifyCondition Conduct
IRA**
** Action presumed, unless measures are not feasible and no IH exists or is likely to exist
Feasibility Evaluation
IRA Action
No IRA Action
IRAC
Phase IIIFeasibility Evaluation
No Action
ActionPhase IV/V/ROS
feasible
IRAC
Condition**** addressed?
** ** without continued operation of an Active Remedial System
yes
notfeasiblenot
feasible
feasible
IRA cont’d
no
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CEP
• Expedites consideration of cost-effective measures to eliminate, reduce or prevent exposures in schools, day cares and homes from vapors or drinking water
• Front loads the background feasibility evaluation into the IRA where a Critical Exposure Pathway exists
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MCP Feasibility Evaluations – 40.0860
• Selection of Remedial Alternatives• Permanent Versus Temporary Solutions• Reducing OHM below UCLs• Critical Exposure Pathways• Technologies that Reuse, Recycle, or Treat OHM• Achieving or Approaching Background
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Feasibility Considerations
• OHM concentration• OHM toxicity• OHM persistence• Uncertainty in site
characterization, complexity of site conditions
• Cost of mitigation alternatives
• Effectiveness of mitigation alternatives
• Timing
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Critical Exposure Pathways
Cost
Benefit @ conc 100
Feasibility Considerations
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Critical Exposure Pathways
Benefit @
conc 1Cost
Feasibility Considerations
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Conceptual Site Model
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Vapor Intrusion Phenomenon
P
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Building Depressurization
Furnace combustion
Stack Effects
Wind
Exhaust Fans
P to 50 Pa
Up to 20-25’
Strongest 3-6‘
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Winter
frost layer
windows closed…
Less fresh air infiltration
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Dry Soils?
(Water) Vapor Intrusion
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Slab
Basement
Moisture Considerations
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Soil Moisture (v/v) Distribution
0
5
10
15
20
25
30
35
0-5 6-10 11-15 16-20 21-25 >25
Soil Moisture Value (% by volume)
Nu
mb
er
of
Sa
mp
les
0.06
MassDEP Site Data- Subslab soil samples
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Fresh Water Lens
Infiltration
VOC plum
e
fresh water lens
well
groundwater flow
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Lines of Evidence Approach
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GW concentration
Sub Slab Soil Gas Conc
Indoor Air Data
PID Screening Cracks/Annular
Spaces/Floor Drains
Typical Indoor Air Conc.
Chemical Forensics
Basement vs. upper floors
Modeling
Lines of Evidence
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Petro
300’ – 500’
Chlorinated VOCsFreshwater Lens
Depth
Conc vs GW-2 Std
Groundwater
Type Contaminant
Distances
Ethanol Effects?
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Sub-Slab Soil Gas Data – Typical Observations
Chlorinated VOCs
10 – 100X Dilution
Petro:
100 – 1000X Dilution
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Indoor Air Data
Typical Indoor Air Conc.
Chemical Forensics
Basement vs. upper floors
> Published Values?
Use of Chemicals in Building?
Should be higher in lower level(s) unless HVAC Issues
MtBE – Usually not from GW
Petro – Check Chromatograms
Chlorinated VOCs – Degradation Products? Cis 1,2-DCE?
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Mitigation
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Seal Cracks/Spaces & Earthen Floor
Seal/Vent Sumps; Seal/modify floor drains
HVAC/Heating System Modifications
Sub-Slab Depressurization System
Overpressurization Systems
Hierarchy
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SSDS
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Feasibility of Vapor Intrusion Pathway Elimination
Benefit $ Benefit
< $5K
Less Uncertainty
Typical Costs
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Drinking Water Wells
Two Flavors…..
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Private Water Supply Wells
Defined in 40.0006 of MCP:
< 15 Service Connections; or
< 25 People for 60 Days
FOR HUMAN CONSUMPTION (i.e., not irrigation well)
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Public Water Supply Wells
>15 Connections or Servicing >25 Individuals for at least 60 days/year
Community: Municipal/District Systems
Non Community: Restaurants, Camps, Golf Courses, Apartments, Schools
Defined 40.0006 via 310 CMR 22.02:
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Critical Exposure Pathway
Private Wells
POTABLE water
Non-Community Public Supplies
(on-site well)
Residential Residential School
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Not All CEPs are Reportable….
CEPs are a sub-universe of Conditions of Substantial Release Migration (SRM)
SRMs require reporting ONLY when associated with a Release that is otherwise Reportable
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MtBE @ 9 g/L
Unknown Source
Gas
> RC
Not ReportableReportable SRM/CEP
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Unknown Source
MtBE @ 79 g/LReportable SRM/CEP
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Mitigation
Drinking Water Treatment Systems
Point of Entry
Point of Use
High VOCs (Showering/Dermal)
Lower Level VOCs
Low to Moderate MtBE
Lower Metals
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Mitigation
Drinking Water Treatment Systems
Air Stripping VOCs
VOCs Petroleum
Metals Perchlorate
Activated Carbon
Reverse Osmosis
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Mitigation
Drinking Water Treatment Systems
Problem Contaminants (Cost/Benefit Issue):
MtBE
Ethanol
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Feasibility of Drinking Water Pathway Elimination
Benefit $ Benefit
< $5K
Less Uncertainty
Typical Costs
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Regulatory Guidelines
& Rules of Thumb
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When to be Concerned about a Possible Vapor Intrusion Pathway
• Site conditions, events • Complaints of odors• Saturated soils, NAPL beneath or
immediately adjacent to the structure• Groundwater concentrations > GW-2
standards within 30 feet of building foundation, groundwater depth 15 feet or less
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Groundwater Concentrations < GW-2
Generally, further investigation of indoor air pathway and CEP issues is not warranted
Exceptions– Odors, OHM likely attributable to groundwater
contamination observed in structure – Earthen floor, field stone foundation, and/or
groundwater sumps with COC chlorinated contaminants
– NAPL/saturated soils within 30 feet of structure
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When to be Concerned About a Possible Drinking Water Well Impact
• Groundwater OHM plume proximate (500 feet) to a water supply well that serves a school, day care, or residence
• Potential migration in bedrock to well
• MtBE or chlorinated contaminants
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“Measurable Concentrations” in Drinking Water
• 8000 series are appropriate for determining the presence of OHM in the course of investigating the extent of the disposal site
• 500 series (lower detection limits) should be used for drinking water well and tap samples
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“Measurable Concentrations” in Indoor Air
• OHM conc. attributable to the disposal site at or above the Reporting Limit for commonly used air testing methods (TO-15/APH) with commonly reported method detection limits
• OHM conc. distinguishable from indoor air levels absent vapor intrusion (e.g.,chemicals from household products and building materials)
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Typical Indoor Air Concentrations
levels of OHMs that can be found in any building, absent a vapor intrusion pathway
=
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Typical Indoor Air Concentrations
MassDEP’sUpper
Percentile Values (UPVs)
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Regulatory GuidanceUpper Percentile Values (UPV) and CEPs
Generally, if conc. is below listed UPV
– Can assume indoor air pathway does not exist
– Can terminate CEP evaluation
Exception OHM where UPV is at a level of significant risk (HI > 0.2 ELCR > 1 x 10-6)
– Evaluate additional Lines of Evidence
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If conc. is above UPVs– Evaluate additional Lines of Evidence
Upper Percentile Values (UPV) and CEPs
Regulatory Guidance
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GW concentration
Sub Slab Soil Gas Conc
Indoor Air Data
TO-15/APH PID Screening Cracks/Annular
Spaces/Floor Drains
Typical Indoor Air Conc.
Chemical Forensics
Basement vs. upper floors
Modeling
Lines of Evidence
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CEP Feasibility Guidance
• Low Level Drinking Water Well Contamination
• Owner-Occupied Residential Properties
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Low Level Drinking Water Well ContaminationMtBE concentrations 5 ug/l or less
CEP Feasibility Guidance
“Categorically Infeasible” to eliminate, mitigate or prevent CEP due to chemical-specific issues,
including treatability
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CEP Feasibility Guidance
Owner-Occupied Residences where concentrations do not pose a Significant Risk
Owner May Decline Measures to address CEP (i.e., owner determines benefits do not
justify costs)
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CEP Feasibility Documentation
• Description of the Critical Exposure Pathway (CSM)
• List of measures evaluated to prevent, eliminate or mitigate the CEP
• Estimated costs of measures and explanation of how costs were determined
• Description of basis for determining measure(s) feasible or infeasible
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Technical Guidelines and Rules of Thumb
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Soil Gas Investigations - Placement
rainwater &
snowmelt….…displaces
& re-solubilizes diffusing
soil vapors
Outdoor probe
negative bias
Interior sub-slab
probe
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Sub-Slab Probes
Minimum of 2 in normal sized home
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Aluminum Screw Lid
PVC Threaded Cap For ½” Pipe
(Approx 1 inch OD)
Tapered Stopper w/ C enter Hole
Expanding Grout (Outer Hole)
Rigid 3/16” O.D. Tubing “Hanging” in Drill Hole
Concrete
Sub - Slab Soils Inner Hole
Push-on cap
Example Soil Gas Probe Construction
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When to Sample
January December
Conc
Conc
Conc
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How to SampleTO-15 or APH Summa Canister 4 hour TWA Consider Outdoor Sample
At least two probes Grab PID/GC/Summa Purge 5 probe volumes Sample rate 100–200 mL/min
Water Table Interface Well! Antecedent Precip? 4+/- Rounds (Chlor VOCs)
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Soil Gas PID < VPH Policy?
Screen utility annular spaces/foundation cracks with PID meter
Analyze soil gas via GC or GC/MS.
Chlorinated SolventsPetroleum Only
Install soil gas probes beneath potentially impacted structure [and near any PID “hits”]
Assessing Lines of Evidence
Significant Indoor Air Impacts Unlikely Evaluate Data
Yes No
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Petroleum < soil gas trigger levels per VPH/EPH Policy?
Chlorinated Solvents in soil gas < Conc in Building Air?
Assessing Lines of Evidence
Significant Indoor Air Impacts Unlikely
Sample Indoor Air via TO-15 or APH
< Typical Indoor Air and NSR?
Assume impact or obtain more Lines of Evidence
Yes No
Yes
No
Sub-Slab Soil Gas Data
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Assessing Lines of Evidence
More Lines of Evidence…
Chemistry of Air Samples:Breakdown productsIn-building sourcesOutdoor air qualityFresh vs weathered petroBasement vs upper floors
ModelingJohnson & EttingerSite-specific inputs
Totality of Evidence For
Totality of Evidence Against
Conceptual Site Model
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Sub Slab Depressurization Systems
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SSDS
- 0.005” W.C.
OK
Bottom Line
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Typical Design FeaturesSSDS
Terminate with 180 Elbow 2’ above Roof
3” PVC Sch 40 Piping. Slope Horizontal Runs 1/8”/Ft to Extraction Point
Fan outside home or in
attic
Hard-wire On/Off Switch
Manometer or Gauge with Marked Ranges
12” Diameter Suction Pit
> 2 Probes
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SSDS – Concerns & Considerations
Discuss placement/construction/operation with bldg occupants
Seal cracks/voids/earthen floors (VOC-free sealants!)
Consider pre-design diagnostic tests
Consider back- drafting concerns
Seal or ensure integrity of floor drains
Seal and vent sumps (provide access to sump pumps)
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SSDS
O&MConfirm operation of system and negative pressure at extraction point.
Submit Remedial Monitoring Report.
Periodic Air Testing (every 1-2 years)
Startup
Document negative pressure in at least two sub-slab probes
Document reduction in indoor air contaminants within 2-4 weeks
Instruct building occupants to periodically check extraction pressure