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Overview of Draft DWM Vapor Intrusion Guidance Document
Delonda AlexanderDry-Cleaning Solvent Cleanup Act Program
Superfund Section
May Look Familiar
Adapted from New Jersey Dept. of Environmental Protection’s Vapor Intrusion Guidance (2005)
EPA’s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (2002)
ITRC’s Vapor Intrusion Pathway: A PracticalGuideline (2007)
Introduction Addresses evaluation and mitigation of VI issues at sites under
cleanup programs in the DWM – assumes basic knowledge of VI concepts
UST developing separate petroleum guidance – contact person Karen Harmon (karen.harmon@ncdenr.gov or 919-707-8269)
Comingled VOC/petroleum contamination should use DWM guidance
Includes discussion of landfills and methane gas (courtesy of NJ DEP VI Guidance 2013)
Introduction
Always check with the specific DWM program with oversight before and during a VI investigation
Screening levels updated twice a year if necessary based on EPA screening level tables
VI guidance and screening levels are separate documents to facilitate updates
Screening Levels Indoor Air Screening Levels (IASL)
Start with EPA regional screening level (RSL) for residential or non-residential air at target cancer risk of 1.0E-06 then multiplied by 10 or 100 to derive DWM IASL at target cancer risk of 1.0E-05 and 1.0E-04
For non-carcinogens, EPA RSL at target hazard quotient (HQ) of 1.0 is divided by 5 to get a concentration corresponding to HQ of 0.2
Lower of cancer or non-cancer target concentration is adopted as the IASL
Screening Levels Groundwater Air Screening Levels (GWSL)
Uses method described in EPA Draft VI Guidance (2002)
GWSL (ug/L) = IASL (ug/m3) * 0.001 m3/L * 1/H * 1/α
Where: H = dimensionless Henry’s Law Constant at 25C [(mg/L –vapor)/(mg/L – H2o)]α = attenuation factor (ratio of indoor air conc. to source vapor conc.)
• Uses the IASL at a target cancer risk of 1.0E-05 or HQ of 0.2 and attenuation factor (α) of 0.001 (1000) for residential and non-residential exposure
Screening Levels Soil Gas Screening Levels (SGSL)
Uses method described in EPA Draft VI Guidance (2002)
SGSL (ug/m3) = IASL (ug/m3)/α
Where: α = attenuation factor (ratio of indoor air conc. to source vapor conc.)
• Uses the IASL at a target cancer risk of 1.0E-05 or HQ of 0.2 and attenuation factor (α) of 0.03 (33) for residential exposure and 0.01 (100) for non-residential exposure
Screening Levels Soil Gas Screening Levels (SGSL) for Non-
Residential Exposure
α=0.03 (33) (residential screening levels) must be used for structures that exhibit building characteristics similar to residential building characteristics, for example, presence of a basement or crawl space
If using α=0.01 (100), land-use restrictions protecting future use required
Attenuation Factor Study
To determine soil gas to indoor air attenuation factor for non-residential exposure
Based on data collected at Dry-Cleaning Solvent Cleanup Act (DSCA) Program sites and from EPA’s attenuation factor database
Data set consists of paired sub-slab or exterior soil gas and indoor air sampling results
Data screened using similar methodology from EPA’s 2012 Vapor Intrusion Database
Attenuation Factor Study
Baseline screen applied - include only chlorinated VOCs, include only data showing detections in both paired samples, only use exterior soil gas samples collected deeper than 5 feet below ground surface, etc. – data set is 355 estimated attenuation factors
Additional screen applied to baseline data set - source strength screen – data for soil gas concentrations less than 50 times the background levels were removed –data set reduced to 239 estimated attenuation factors
Attenuation Factor Study A reliability analysis was performed to further
evaluate the proposed attenuation factor – using DSCA target risk levels for PCE
Based on the reliability analysis, an attenuation factor of 100 (0.01) for non-residential exposure would be protective 99 percent of the time if applied to the set of data evaluated
Investigation
VI pathway should initially be considered a potential threat for all current or future buildings located within 100 feet of a source area or plume exceeding DWM screening levels
100-foot distance criterion does not consider aerobic degradation of petroleum hydrocarbons – check with specific DWM Program if petroleum hydrocarbons only
If co-mingled plume or NAPL present, 100-foot distance applies
Investigation Recommends that initial soil or groundwater samples be
analyzed for full suite of volatiles
Recommends only chemicals of concern identified in subsurface samples be carried through for soil gas, crawl space or indoor air sampling analysis
Does not recommend collecting indoor air samples that analyze for a chemical in use at a structure as part of operations without discussing with DWM
Investigation Groundwater
Typically first medium to be investigated
Collect groundwater samples as close as possible to structures under investigation
Soil Gas Sampling
Prefer the collection of sub-slab soil gas or soil gas collected as close to the structure as possible
Not all structures must be investigated – start at worst case and move outward
Investigation Sub-slab Soil Gas Sampling
Recommends that indoor air samples be collected concurrently with sub-slab soil gas samples – collect indoor air samples prior to sub-slab samples
May collect indoor air radon gas samples with sub-slab samples to estimate building specific attenuation factors
Investigation Exterior Soil Gas Sampling
Collect exterior soil gas samples as close as possible to structures being investigated – from a minimum of two sides of the structure
Recommends collection of soil gas at a depth within one foot above the capillary fringe and a minimum of 5 feet below ground surface (check with DWM Program if groundwater is less than 5 feet bgs)
For undeveloped land or future use, recommends a grid sampling approach across the site
Investigation Soil Gas Sampling Procedures
Permanent or temporary sampling points
Stainless steel canisters using EPA Method TO-15 most common – other sample containers and methods may be used with DWM approval
Passive sorbent samplers may be used for field screening
Flux chambers may be used with DWM approval
Investigation Pre-Sampling Evaluation
Building walkthrough at least one week before sampling –Indoor Air Building Survey and Sampling Form (App. B)
Recommend use of handheld field screening instruments to detect background indoor air sources and to survey suspected vapor entry locations
Provide Instructions for Occupants – Indoor Air Sampling Events (App. E) during the building walkthrough – list of actions that should be avoided before and during sampling event
Investigator should be prepared to educate occupants – EPA fact sheet, What You Should Know About Vapor Intrusion (App. C) recommended
Investigation Background
DWM does not typically subtract background air concentrations from the analytical results but will consider background concentrations when establishing remedial goals
To eliminate potential background sources, recommends that indoor air analyses be limited to chemicals of concern found in the subsurface
Investigation Crawl Space and/or Indoor Air Sampling
If groundwater and/or soil gas concentrations exceed DWM screening levels, typically the next step is collection of crawl space and/or indoor air samples
DWM does not consider any attenuation between crawl space air and indoor air – crawl space sampling less intrusive
Outdoor ambient air sample should be collected when crawl space or indoor air samples are collected unless DWM Program specifies otherwise
Investigation Crawl Space and/or Indoor Air Sampling Procedures
Passive samplers allow for the collection of indoor air samples over a longer time, up to 30 days, providing an average concentration over a longer exposure period
Sample duration determined by receptors and detection limits necessary to reach IASLs
One round of indoor air samples will likely not be sufficient to verify the presence/absence of VI – may be necessary to collect several rounds of indoor air samples
Does not go into great detail regarding Quality Assurance/Quality Control procedures
Data Evaluation and Screening Use a multiple lines-of-evidence approach and professional
judgment
Presence of contamination in subsurface Potential for vapors to migrate from source to buildings Groundwater data compared to GWSLs Soil gas data compared to SGSLs Crawl space and/or indoor air data compared to IASLs Preferential pathways Building conditions susceptible to vapor entry Background indoor air sources Indoor air results when HVAC running/not running
Data Evaluation and Screening Groundwater
Compare highest groundwater concentration present within 100 feet of any structure to the GWSLs
If GWSLs not exceeded, no further action – plume should be stable or shrinking to show that potential for VI will not increase in the future
If GWSLs are exceeded, further investigation necessary –typically collection of soil gas samples
Where soil contamination represents a potential source of VI, the use of groundwater data alone is not appropriate
Data Evaluation and Screening Soil Gas
Sub-slab and exterior soil gas should be compared to SGSLs
If SGSLs are not exceeded, typically no further investigation is necessary
If exterior soil gas results exceed SGSLs, typically sub-slab samples should be collected if possible before indoor air
If SGSLs are exceeded, crawl space and/or indoor air samples should be collected
Crawl Space – results should be compared to IASLs
Data Evaluation and Screening Indoor Air
DWM does not accept averaging of indoor air results
Indoor air results should be compared to IASLs – check with DWM Program with oversight for applicable level – target risk ranges from 1.0E-04 to 1.0E-06
For all DWM Programs, a confirmed exceedance of the IASL at a cumulative risk of 1.0E-04 or Hazard Index (HI) of 1 will require mitigation and/or remediation of the source
Data Evaluation and Screening Indoor Air
If indoor air results are below the IASL for target risk of 1.0E-06 and HI of 1, no further sampling typically required
If IASLs are exceeded in any co-located building space, then sub-slab and indoor air samples should be collected from the immediately adjacent building spaces – ratio of sub-slab soil gas to indoor air can assist in determining if VI is occurring
Remediation and Mitigation DWM’s primary goal is to remediate the source of the vapor
contamination such that the risk of VI is eliminated
When remediation is not feasible, preventative or mitigation measures may be necessary
Institutional or engineering controls may be considered that eliminate the potential for VI to occur under current or future conditions
Monitoring may be appropriate in some situations – for example when sub-slab soil gas exceeds SGSLs but indoor air is below IASLs
Remediation and Mitigation Recommend ITRC’s Vapor Intrusion Pathway: A Practical
Guideline (2007) for more detailed information regarding mitigation
At a minimum, typically recommend sealing openings and cracks, repairing compromised slabs and covering exposed sumps
Most common mitigation methods are installation of a sub-slab depressurization system (radon system) or installation of a vapor barrier (typically during construction)
Fact sheet regarding sub-slab depressurization systems included in Appendix D
Remediation and Mitigation Non-residential properties may require institutional controls
when future use may differ from the current use
Undeveloped parcels that contain source concentrations above screening levels typically require institutional controls prior to closure to ensure that VI will not occur for future exposures
If site-specific building parameters (e.g., ventilation rate changes, positive pressure controls, etc.) are used to address VI concerns, an institutional control may be necessary to ensure that the controls are maintained
Community Outreach
Recommend reading EPA’s The Seven Cardinal Rules of Risk Communication when preparing for community outreach
Two way communication with residents, business owners and local officials is critical to a successful investigation
The DWM Public Information Officer (PIO) should be consulted when preparing to hold a public information session or interacting with the media
Face-to-face meetings with residents or property owners generally offer a better opportunity to explain the investigation and what the sample results may mean
Recommended