Vapor Intrusion Guidance UpdatesVAP CP Training

October 27, 2015Audrey Rush

Ohio EPA DERRaudrey.rush@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, June 2015 – Final Guidance

• VI and Petroleum Vapor Intrusion (PVI) companion document supersede and replace the Draft VI Guidance

US EPA’s Vapor Intrusion Guidance

• Intended for use at any site and any building or structure on a site being evaluated under– CERCLA– RCRA corrective action– EPA’s brownfield grantees

Vapor Intrusion is… The migration of volatilechemicals from the subsurface into overlying

buildings.

Dissolved contamination

LT Diffusion

Vadose zone

Building zone of influence

Wind effectsEnclosed space

CracksQsoil

Air streamlines

Convection

Top of capillary zone

Water Table

Stack effects

Mixing in indoor air and inhalation

Advection/Convection

Diffusion

Phase partitioningCgw to Csoil gas

Petroleum Vapor IntrusionUS EPA – OUST– June 2015

• US EPA – approach to VI from CHCs is inappropriate and “overly conservative” for addressing VI from PHCs under aerobic conditions.

• LNAPL floats

• PHCs biodegrade rapidly under aerobic conditions.– If complete, water and carbon dioxide. – If incomplete - intermediate degradation products usually

less toxic than the parent PHCs.

Inclusion (or Exclusion) Zones for PVI

shorter lateral and vertical distances for further sampling

Key Recommendations

• CSM, DQOs and Work plan

• Limit analysis to compounds of concern in subsurface and indoor air

• Assess VI using multiple lines of evidence

• Generally supports direct collection of indoor air

• If risk conclusion is that indoor air meets risk goals when known subsurface source exists, multiple rounds of data are preferred (reduce Type II error)

Key Recommendations• Select sampling and analytical methods capable of

detecting COCs less than risk-based levels– Consider variability in lab analysis – include duplicates

• Collect ground water samples from wells screened across the top of the water table

• Consider seasonal and building/receptor-specific sampling strategy to capture RME concentrations

VI Key Recommendations

• Consider background

• Identify conditions that warrant prompt action– Explosive or short-term hazards

• Modeling is most appropriately used in conjunction with other lines of evidence– Confirm reliability of results

• Mitigation

Compounds of VI concernGuidance # COCs Volatility Toxicity

HLC>1E-05 VP>1 MW<200 toxic? route to route

USEPA 2002 and Ohio EPA

201090+ x "exceed risk" yes

VAP generic stds 82 x, AND x RfC, IUR no

2015 US EPA, VISL

depends on scenario x, OR x

pure source vapor>risk

goalsno

For VAP

• COC List Recommendation:– Release History (Phase I)– Use VISL for front line COC list– Pathway analysis, including preferential pathways

(current and reasonably anticipated)– Justify eliminating further assessment in Voluntary

Action Documents

CSM, DQOs, and Work plan

• CSM – update as information becomes available http://epa.ohio.gov/portals/30/rules/CSM%20Guidance%204-27-15%20Final.pdf– Consider “worst first” approach– Preferential pathways– Utilize exclusion distances (100 feet laterally (two houses) or vertically

from ‘boundary’ of subsurface vapor concentrations of potential concern)• Boundary is defined in US EPA guidance as VISL level • No preferential pathways, significant soil cover absent• Diffusion driven (not advective)

Sampling Considerations• Ground water

– Screen across the top of gw zone– Capture temporal differences– Appropriate statistical representation

• Exterior Soil Gas– Near source less variable, provides info on ‘potential’– Collect as close to receptor as possible, preferably subslab– Beware of the advective envelope– Leak testing– Typically grab samples– May be variable with weather conditions (record wind speed, direction,

precip, temp)

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

• Indoor Air– Building survey – COCs, preferential pathways, HVAC– Time-integrated samples – 24 hour/6 L summa– Sorbent methods for longer term– Multiple rounds recommended– Paired with sub-slab and ambient– Useful to support mitigation/remediation systems

Applicable Standards• GNS for indoor air – Tox and exposure

• Medium-specific “standards”? Not really – VAP standard is the exposure point concentration – indoor air!

• Medium-specific concentrations determined to meet the indoor air applicable standard

How to Determine?

• US EPA Guidance– VISL, based on AF database

• 2010 Ohio EPA VI Guidance – – Generic attenuation factors– J&E modeling, default inputs and/or site-specific

18

US EPA Attenuation Factors

VI Guidance - Modeling

• When suitably constructed, documented, and verified, mathematical models can provide an acceptable line of evidence supporting risk management decisions pertaining to vapor intrusion. In certain situations (e.g., future construction on vacant properties), it is particularly useful to employ mathematical modeling to predict reasonable max indoor air concentrations because indoor air testing is not possible.

Modeling

• Most appropriately used in conjunction with other lines of evidence.

• Calibrate, run uncertainty analysis, run with “reasonable worst case”

• Generally reserved for situations where observed, direct measurements cannot be obtained.

• Assumes factors exist that effectively attenuate

Risk Assessment and Management Framework

• Occupational Exposures (OSHA PELs)– enforceable occupational standards developed in 1971 using info available at

that time– Intended to protect workers against catastrophic (e.g., organ damage) and

subtle (e.g., sensory irritation) effects– Not intended to protect sensitive workers, tox data different– Does not apply to uncontrolled release of haz subs or petroleum

• Short-term or acute exposures – ATSDR (acute and minimal risk levels), PPRTVs – IRIS will work to develop expanded science policy direction to address short-term

exposures

• Potential Explosion Hazard – chemical-specific LELs –10% LEL in subslab, crawl space, indoors warrants prompt action

Response Actions• Remediate source

• Engineered exposure controls

• Monitor to assess and verify performance and effectiveness of remedial systems and engineered exposure controls

• Institutional controls

Mitigation

• Immediate Response for Existing Buildings– Sealants – Over-pressurize with HVAC– install or maintain vapor traps for sewers and

drains– Increase building ventilation

• Active Depressurization

Mitigation System Monitoring

• Generally two phases:– Initial post-construction (more intensive)– Subsequent to operation (periodic)

• Indoor air – direct measurement recommended

• Pressure field measurement across subslab used to demonstrate the system has attained hydraulic control and communication over building footprint or source area.

Thank You