Oregon Guidance for Assessing and Remediating Vapor Intrusion in Buildings

Department of Environmental Quality Overview of Oregon Guidance for Assessing and Remediating Vapor Intrusion in Buildings Brownfields and Land Revitalization 2011 Conference Spokane, Washington May 13, 2011 Rebecca Wells-Albers DEQ rthwest Region Brownfield Coordinator http://www.deq.state.or.us/lq/pubs/docs/cu/vaporintrusionguidance.pdf

OR DEQ Vapor Intrusion Guidance Team Bruce Gilles (Cleanup Program Manager) Robert Hood (Tanks Program) Henning Larsen (Cleanup Program) Ann Levine (Cleanup Program) Mike Romero (Cleanup Program) Seth Sadofsky (Cleanup Program) Paul Seidel (Cleanup Program) Rebecca Wells-Albers (Residential Heating Oil Tank Program)

Document Content Defines: Contaminants w/ VI potential Includes: Flow chart for Evaluation Framework Specifies: Generic Attenuation Factors for Soil Gas Guidelines on: Bounding investigations Sample locations, density, depth and frequency Methods of sample collection Methods of data analysis and interpretation General mitigation options and performance evaluation Case Studies

Impetus for Development Rapidly Evolving Field Oregon guidance unchanged since 2003 Experiences using Johnson and Ettinger Modeling Sensitivity to site-specific inputs Difficulty in measuring transport parameters Cases of under-prediction Availability of large EPA empirical database of subslab, soil gas and ambient air data

Major Changes in Evaluation Framework site-specific J&E Modeling Site-specific attenuation reflected in subslab/indoor data relationship Soil gas/subslab become essential site data Greater emphasis on indoor air data Verification of conditions with direct sampling Use of generic soil gas/subslab attenuation factors

Attenuation Factor Concept AF = vi C C sv ia where: AF vi = Attenuation factor between soil vapor and indoor air, unitless C sv = Concentration in soil vapor medium, ug/m 3 C ia = Concentration in indoor air, ug/m 3 α

Data Source (US EPA 2008) AF vi residential = 200 AF vi industrial = 1000 SubSlab Vapor vs. Indoor Air 1,808 148 Indoor Air (ug/m3) 12 1 0.08 0.007 0.007 1 148 Subslab Vapor (ug/m3) 22,026 3,269,017

CSM 1 for source area(s) and plume area(s) show potential for vapor intrusion for current and/or future uses Please review both sides of the flow chart! 1. Is groundwater contaminated above RBCs? 3. Collect sub-slab and/or soil gas samples and screen against RBCs 3 2. Is source area soil contaminated above RBCs 3? Rule out vapor intrusion pathway for groundwater for current and future uses 4. Are maximum concentrations for sub-slab and/or soil gas above RBCs 3? Rule out vapor intrusion pathway for sub-slab and/or soil gas for current & future uses 5. Are maximum concentrations for sub-slab and/or soil gas below Hot Spot levels? Rule out vapor intrusion pathway for soil for current & future uses 6. Collect indoor air samples 1. CSM = Conceptual Site Model 2. VOC = Volatile Organic Chemical 3. RBC = Risk-Based Concentrations 4. FS = Feasibility Study 5. EE/CA = Engineering Evaluation/Cost Analysis 7. Are indoor air results conclusive and below RBCs 3? 8. Rule out current exposure, retain future uses in CSM 1. Removal or remedial action is possible at any stage. 9. Complete FS 4 for Remedial Action or EE/CA 5 for Removal Action

Bounding VI Investigations Default is set at 100 ft from soil and/or GW sources Sources are defined as soil and groundwater contamination exceeding default RBC Distance (LOF) may be adjusted based on sitespecific data Increased for large, deep sources Decreased for small, shallow sources Petroleum vs. HVOCs Preferential pathways

Sample Locations Residential near center of home Within known source areas Adjacent to/within utility trenches Interior preferred over exterior Minimum of several feet from exterior walls

Soil Gas Sample Density Risk/Compliance Determination Residential Minimum of 2 Commercial Graduated based on square footage Other factors: proximity to source, subsurface heterogeneity, internal partitioning, use of statistical methods 5 foot depth for soil gas Outside footprint of structure Where there is no structure Crawlspace Sub-slab (~6 inch depth below slab) Lab Methods

Subsurface Sampling Frequency/# Events For initial screening Consideration of seasonal fluctuations (up to an order of magnitude), source strength, hydrologic conditions Target worst-case conditions Typically compares maximum measured values to soil gas RBCs Hot Spots defined as subsurface conc. >100x soil gas RBCs for carcinogens, >10x for n-carcinogens preference for clean up

Indoor Air Sampling When subsurface investigation indicates RBCs exceeded May not be appropriate at active facilities w/ operational sources (gas stations, dry cleaners) May be useful in making a decision to defer action at an operating facility At many sites becomes primary line of evidence Can be used to establish absence of current risk, unlikely that it addresses future risks Crawl space sampling: attenuation between crawl space and indoor air assumed.

Interpreting Indoor Air Data Factoring in ambient contributions, indoor sources Subtracting out ambient levels Evaluate contaminant ratios (e.g. PCE and daughter compounds) Response to seasonal changes, HVAC operation Typically, a minimum of two events to demonstrate compliance

Data Interpretation IA<Amb<RBC Amb<IA<RBC IA<RBC<Amb RBC<IA<Amb RBC<Amb<IA Amb<RBC<IA Acceptable risk, no indication of indoor/subsurface source Acceptable risk, potential subsurface or indoor air source Acceptable Risk, no significant indoor or subsurface source unusual distribution Unacceptable risk, primarily from ambient, with unknown contribution from subsurface/indoor sources Unacceptable risk, primarily from indoor /subsurface w/contribution from ambient source Unacceptable risk, primarily from indoor/subsurface source RBC Ambient Permutations of Indoor Air Sampling Results Relative VOC Concentrations Indoor Air

Mitigation and Remediation If VI risks is identified - an FS (or CAP) should be prepared to evaluate remedies. This may include: Site Wide Remedies Institutional Controls Engineering Controls Guidance does not prescribe technology or design Addressed primarily by reference to existing EPA guidance Requires stamp of professional engineer

Performance, Monitoring, and Compliance Slab-on-grade and basement construction, likely using soil gas RBCs and pressure measurements as demonstration of effective mitigation for SSD systems Periodic Indoor/outdoor air measurements for mitigation based on HVAC adjustments (i.e. increased air exchange, positive pressurization) Looking for input from regulated community, consulting community on other aspects

Thank You