Vapor Intrusion Guidance Updates VAP CP Training October 27, 2015 Audrey Rush Ohio EPA DERR

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 volatile chemicals from the subsurface into overlying buildings. Dissolved contamination LTLT Diffusion Vadose zone Building zone of influence Wind effects Enclosed space Cracks Q soil Air streamlines Convection Top of capillary zone Water Table Stack effects Mixing in indoor air and inhalation Advection/ Convection Diffusion Phase partitioning C gw to C soil gas

Petroleum Vapor Intrusion US 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 concern Guidance# COCsVolatilityToxicity HLC>1E-05VP>1MW<200toxic?route to route USEPA 2002 and Ohio EPA x "exceed risk"yes VAP generic stds 82x, AND xRfC, IURno 2015 US EPA, VISL depends on scenario x, ORx pure source vapor>risk goals no

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 – 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

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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