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EPA’s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (2002)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

Questions?

Delonda AlexanderRemediation Unit Supervisor

Dry-Cleaning Solvent Cleanup Act Program 919-707-8365

delonda.alexander@ncdenr.gov