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Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites

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Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites EPA 510-R-15-001 Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites U.S. Environmental Protection Agency Office of Underground Storage Tanks Washington, D.C. June 2015 Contents Recommendations .......................................................................................................................... 1 Background ................................................................................................................................. 1 Overview Of Petroleum Vapor Intrusion (PVI) ........................................................................... 2 Scope And Applicability .............................................................................................................. 3 Recommended Actions For Addressing PVI ............................................................................... 3 Supporting Technical Information ................................................................................................ 10 1. Petroleum Vapor Intrusion (PVI) ....................................................................................... 11 2. Typical PVI Scenarios ......................................................................................................... 33 3. Site Characterization And Conceptual Site Model (CSM) ................................................. 39 4. Lateral Inclusion Zone ....................................................................................................... 44 5. Vertical Separation Distance ............................................................................................. 48 6. Mobile And Residual Light Non-Aqueous Phase Liquid (LNAPL) ...................................... 57 7. Groundwater Flow And Dissolved Contaminant Plumes .................................................. 61 8. Soil Gas Profile ................................................................................................................... 66 9. Clean, Biologically Active Soil ............................................................................................ 75 10. Non-PHC Fuel Additives ..................................................................................................... 81 11. Seasonal And Weather Effects .......................................................................................... 96 12. Vapor Intrusion Attenuation Factor (α) .......................................................................... 100 13. Computer Modeling Of Petroleum Vapor Intrusion ....................................................... 106 Glossary ....................................................................................................................................... 117 ii Tables 1. Recommended Actions For Addressing PVI At Leaking Underground Storage Tank Sites ........ 7 2. Summary Of Characteristics Of Typical Scenarios Of Petroleum Vapor Sources And Potential Receptors .................................................................................................................. 36 3. Re commended Vertical Separation Distance Between Contamination And Building Floor Foundation, Or Crawlspace Surface ......................................................................................... 52 4. Equations For Target Indoor Air Screening Concentration s For Volatile Chemicals ................ 85 5. Example Target Residential Indoor Air Concentrations For EDB And 1,2-DCA ....................... 85 6. Equations For Groundwater And Soil Gas Screening Levels Based On Target Indoor Air Screening Levels ....................................................................................................................... 86 7. E xample Screening Concentrations For EDB And 1,2-DCA In Groundwater And Soil Gas ...... 88 8. Comparison Of Risk Levels And Achievable Analytical Detection Limits For The Lead Scavengers EDB And 1,2-DCA In Indoor Air ............................................................................ 89 iii Figures 1. Flowchart For Addressing PVI At Leaking Underground Storage Tank Sites .......................... 9 2. Conceptual Model Of Typical Petroleum Hydrocarbon Release ........................................... 13 3. Difference In Potential For PVI Based On Type Of Source: a) LNAPL b) Dissolved Phase. .... 33 4. Typical Scenarios Of Potential PVI Sources And Potential Receptors ................................... 35 5. Lateral Separation Distance Between Source Of PHC Contamination And Hypothetical Receptor ................................................................................................................................ 45 6. Vertical Separation Distances Between Source Of PHC Contaminants And Hypothetical Receptor: (a) Dissolved Source, (b) LNAPL Source ................................................................ 49 7. Conceptual Model Illustrating The Potential For Vapor Intrusion For a) Free-Phase LNAPL Source, b) Residual-Phase LNAPL Source, And c) Dissolved-Phase Source ............... 58 8. Typical Vertical Concentration Profile In The Unsaturated Zone For PHCs (Plus Methane), Carbon Dioxide, And Oxygen ............................................................................... 66 9. Relationship Between Source Vapor Concentration And Vapor Intrusion Attenuation Factor (α) As A Function Of Vertical Separation Depth Between Contaminant Source And Base Of Building (Receptor) ......................................................................................... 101 10. Rescaled Figure 9 That Expresses Source Vapor Concentration In Conventional Units ..... 103 iv Acronyms 1,2-DCA 1,2-Dichloroethane (also known as ethylene dichloride or EDC) ATSDR Agency for Toxic Substances and Disease Registry BTEX Benzene, Toluene, Ethylbenzene, Xylenes (there are three isomers of xylene) CFR Code of Federal Regulations CSM Conceptual Site Model EDB Ethylene Dibromide (also known as 1,2-dibromoethane) IUR Inhalation Unit Risk ILCR Incremental Lifetime Cancer Risk IRIS Integrated Risk Information System ITRC Interstate Technology & Regulatory Council JEM Johnson-Ettinger Model LNAPL Light Non-Aqueous Phase Liquid MTBE Methyl Tertiary-Butyl Ether NAPL Non-Aqueous Phase Liquid OIG Office of Inspector General OSWER Office of Solid Waste and Emergency Response OUST Office of Underground Storage Tanks PHC Petroleum Hydrocarbon PPRTV Provisional Peer Reviewed Toxicity Value PVI Petroleum Vapor Intrusion RBCv Risk-based Concentration, Soil Vapor RfC Reference Concentration (inhalation) RSL Regional Screening Level (for Chemical Contaminants at Superfund Sites) SIM Selective Ion Monitoring TAME Tertiary-Amyl Methyl Ether TBA Tertiary-Butyl Alcohol TEL Tetraethyl Lead TMB Trimethylbenzene TML Tetramethyl Lead TPH Total Petroleum Hydrocarbons UST Underground Storage Tank VI Vapor Intrusion VISL Vapor Intrusion Screening Level VOC Volatile Organic Compound v Disclaimer This document presents current technical recommendations of the U.S. Environmental Protection Agency (EPA) based on our current understanding of petroleum vapor intrusion (PVI) into indoor air from subsurface sources. This document provides technical information to EPA, state, tribal, and local agencies. It also informs the public and the regulated community on how EPA intends to implement its regulations. This guidance document does not impose any requirements or obligations on the EPA, the states, or local or tribal governments, or the regulated community. Rather, the sources of authority and requirements for addressing subsurface vapor intrusion are the relevant statutes and regulations. Decisions regarding a particular situation should be made based upon statutory and regulatory authority. Decision-makers retain the discretion to adopt or approve approaches on a case-by-case basis that differ from this document. Contact information for your state’s UST-implementing agency may be found at http://www.epa.gov/oust/states/statcon1.htm. EPA may revise this document in the future, as appropriate. vi Recommendations This document provides technical information to regulatory personnel from the U.S. Environmental Protection Agency (EPA) and state1, tribal, and local agencies for investigating and assessing petroleum vapor intrusion (PVI) at sites where petroleum hydrocarbons (PHCs) have been released from underground storage tanks (USTs). This document is comprised of two parts: Recommendations, which provides a description of EPA’s recommended approach for addressing PVI, and Supporting Technical Information, which provides detailed technical information supporting the recommendations. Background In 2002, EPA’s Office of Solid Waste and Emergency Response (OSWER) issued draft vapor intrusion guidance, OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Draft Vapor Intrusion Guidance) (EPA, 2002).2 This draft guidance explicitly states that it is not recommended for addressing petroleum vapor intrusion (PVI) at UST sites regulated under Subtitle I of the Solid Waste Disposal Act through the Hazardous and Solid Waste Amendments of 1984. In 2009, EPA’s Office of Underground Storage Tanks (OUST), at the request of partners and stakeholders, initiated a collaborative effort to develop a technical guide for petroleum vapor intrusion. Further highlighting the need for information on PVI, EPA’s Office of Inspector General later that year released an evaluation report, Lack o f Final Guidance on Vapor Intrusion Impedes Efforts to Address
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