Virginia VRP Vapor Intrusion Fact Sheet
An Introduction
Introduction
• Result of internal ORP working group:
– Jerry Grimes – VRP Project Manager – Pat McMurray – ORP Risk Assessor – Ahmet Bulbulkaya – ORP Risk Assessor
Background
• In early 2007:
– VRP had been dealing with the VI issue since the late 90’s. – Had in place Tier III groundwater screening values for industrial/residential exposure based on J&E model. – Had sub-slab soil gas screening levels in place based on an alpha of 0.1. – ITRC Document had just come out.
Concerns
• Every site we had to start from scratch. We knew we needed some characterization guidance. • Trending towards sub-slab soil gas but nothing screening out. • Rumors that the EPA was going to come out with a less conservative sub-slab alpha (0.02). • Increasingly uncomfortable with our J&E-based groundwater screening values. Some assumptions were hard to defend.
Outcomes
• Vapor Intrusion Fact Sheet • Revised Tier III VI based screening levels
– Sub-slab soil gas – Groundwater – Deep soil gas
• Mitigation Systems put on hold
Goals of Fact Sheet
• Simple and strait forward (no complicated flow charts). • Conservative but should screen some sites out. • Couldn’t be used as a tool to screen out sites that were “really bad”. • Use the ITRC document as much as possible. • Defensible sound assumptions.
What the Fact Sheet Covers
• Section 1 - Introduction • Section 2 - Basic Site Characterization Requirements • Section 3 - Screening for Vapor Intrusion COCs • Site 4 – Site-specific Vapor Intrusion Evaluation
Basic Site Characterization Requirements
• Soil – Not a strict requirement for VI • Groundwater – At least 3 locations near release. Samples near site boundary may be necessary. • Soil gas – 2-3 samples near every suspected release area.
– Interior – subslab near dry cleaning machine, drains, or storage area. – Exterior – Deep soil gas. Above capillary fringe at least 5 feet below surface.
Characterization (cont.)
• Indoor air – Currently not part of screening. Can be part of site specific VI evaluation. • Off-site – Groundwater concs at property boundary. Sometimes deep soil gas. • Sampling and analytical – Refer to ITRC document. Also mention some EPA SOPs for TO-15.
Screening for VI COCs
• Screening Values
– J&E vs Empirical
• Start w/ acceptable indoor air and work backwards using an attenuation factor. • Or can start with an indoor air background concentration.
– J&E: the attenuation factor is developed through a model. – Empirical: alpha developed through analysis of VI database.
Screening for VI COCs
• We decided to go with the empirical approach.
– Groundwater: alpha = 0.001 – Deep Soil Gas: alpha = 0.01 – Subslab Soil Gas: alpha = 0.03
Screening for VI COCs (On-site)
• On-site release
– Sub-slab in all potentially impacted buildings.
• If below screening value you’re done. • If you are above, conduct a site-specific vapor intrusion investigation.
– No buildings; use groundwater and deep soil gas screening levels. – Can also work for off-site.
Site-specific VI Evaluation
• • • • Multiple lines of evidence Indoor Air Samples Possible Site Specific alpha Johnson and Ettinger Modeling
Next up
• Mitigation Systems
– Need specs – Need to hammer out O&M requirements – Opt out concept