Overview of US EPA’s Vapor Intrusion Guidance

VAP CP Summer CoffeeJuly 14th, 2015

Carrie RasikOhio EPA CO- Risk AssessorCarrie.Rasik@epa.ohio.gov

US EPA’s Vapor Intrusion Guidance

• OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air

• Finalized June 2015• Replaces 2002 OSWER “Draft VI Guidance”

http://www.epa.gov/oswer/vaporintrusion/

http://www.epa.gov/oswer/vaporintrusion/

Document Highlights• Multiple Lines of Evidence• Spatial and Temporal Variability• Sampling Considerations• VI Chemicals of Potential Concerns• VISL Calculator• Revised Attenuation Factors

Multiple Lines of Evidence

• Site history, pathway completeness, media data, hydrologic and geologic information, VISL comparison, etc.

• Reduces false-negative/positive conclusions• Greater confidence

Spatial and Temporal Variability

• Hourly, Daily, Seasonally, Buildings– “Field observations and measurements demonstrate that

indoor air concentrations can exhibit significant temporal variation within a day and between days and seasons in an individual residential building (EPA 2012a; Holton et al. 2013ab)”

– “Field experience indicates there may be substantial spatial variability in sub-slab soil gas concentrations even over an average-sized footprint of a residential building (EPA 2015)

• Can span at least an order of magnitude and often more• Keep in mind when trying to determine “representative”

or “reasonable worst case” exposure scenario

Spatial and Temporal Variability: Some Examples (not an inclusive list)

• Depth to groundwater• Heterogeneities in the subsurface materials • Weather conditions• Building operations• Building construction and age• Interior compartmentalization• Adventitious openings• Developed vs undeveloped (advection)

Sampling Considerations at a Glance• Several rounds at multiple locations

– “an individual sample (or single round of sampling) would be insufficient to characterize seasonal variability, or variability at any other time scale (EPA 2015)

• Bulk soil not recommended quantitatively• Soil gas survey

– Multiple depth intervals between source and building(s), including immediately above vadose zone source

– If collecting shallow- collect close to building, at depths below the respective building foundation, and no less than five feet below ground surface, depending on site-specific conditions

• “Near-Source” soil gas– Very useful at undeveloped properties

More Sampling Considerations at a Glance

• Sub-slab sampling– Typically 3 sub-slab samples at buildings < 1,500 sq ft – Include central locations– Measure pressure difference

• Indoor Air– Building survey– Time-integrated samples– Paired with sub-slab and ambient– Useful to support mitigation/remediation systems

VI Contaminants of Potential Concern

• Known or reasonably expected COPCs from a release

• Change in “volatile”: toxicity + Henry’s Law constant OR Vapor Pressure– Henry’s Law Constant > 10^-5 atm m^3 mol-1); OR– Vapor pressure > 1 mm Hg

• Current chemical list on VISL

Vapor Intrusion Screening Level (VISL) Calculator

• Excel spreadsheet • List of volatile and toxic chemicals• Medium-specific, risk-based target concentrations

– indoor air– sub-slab/“near-source” soil gas– groundwater

• Derive risk/hazard from media concentrations• Estimates indoor air concentrations • C/I and residential scenarios• Groundwater temperature adjustment• Frequent toxicity data updateshttp://www.epa.gov/oswer/vaporintrusion/guidance.html

Attenuation Factors

Other Items of Note

• EPA does not recommend using OSHA PELs/TLVs

• Lateral inclusion zone of 100 feet• Reasonable maximum exposure• ICs/mitigation measures in conjunction with

source remediation• Cis-1,2-DCE as indicator

Implications on Ohio EPA DERR VI Guidance

• J&E Model?• VISL additions from “volatile” change?• Specific sampling frequency?• Petroleum-Only Releases Separate Guidance?• OthersVAP staff will be discussing in the near future US EPA’s Guidance document and it’s implications on Ohio EPA’s document

Thank You!