PVI Survey—Summary of State Responses

In the spring of 2012, shortly after the initiation of the ITRC PVI project, the team conducted a state survey to gain a national perspective as to how state environmental agencies address PVI sites. A coordinated response was requested from each state, which could be attributed to the state rather than an individual. The survey was to be completed by the PVI or VI experts within each state in coordination with other people, programs, and agencies involved with PVI. Survey responses were provided by 49 states (all states except South Dakota) and the District of Columbia.

A goal of the PVI Team is to give states (and others) a "PVI Tool Box" so that they can make confident, timely, and quality decisions related to PVI sites. The results of this survey have provided key supporting information for the development of this guidance document. Through this survey, the team gained an understanding of the current state of PVI issues across the country and identified potential regulatory barriers related to PVI solutions.

The following key findings from the survey are arranged to correspond with the chapters presented in this guidance document.

State Survey Results - Chapter 1. Introduction and Chapter 2. Characteristics of Petroleum Vapor Intrusion

• 49% of the states indicated they have guidance on the evaluation of PVI; 10% of the states indicated they had draft PVI guidance.
• 86% of the states include BTEX compounds as contaminants of concern related to vapor samples for PVI sites, although many will consider other compounds (such as MTBE and naphthalene) or TPH.
• 94% of the states consider distance between source and building as part of a site investigation. Exclusion distances ranged from 5 feet to 100 feet for dissolved PHC contaminants, and 15 feet to 100 feet for LNAPL.
• 78% of the states allow use of a generic residential slab attenuation factor. Factors vary from 0.00015 to 0.1. 38% of the states have a separate attenuation factor for commercial buildings. Factors vary from 0.00006 to 0.1.
• 48% of the states use "clean soil" to define which sites may be excluded from PVI assessment. Clean soil criteria may include VOC or TPH analysis of subsurface soil adjacent to or beneath the building, or measurements of fixed gases (O₂, CO₂, CH₄, and others).

State Survey Results - Chapter 3. Site Screening Using Vertical Screening Distance

• 70% of the states consider future land use when evaluating a site for VI.
• 58% of the states have confirmed a dissolved-phase PHC source causing VI (in the absence of residual phase LNAPL). Most (66%) of these occurred at off-site residences.
• 94% of the states consider preferential pathways during a VI evaluation. These pathways include storm/sanitary sewers and other utilities (90%), soil/bedrock fractures (70%), soil heterogeneity (68%), elevator shafts (64%), and other features such as basement sumps or cracks in the foundation.
• Aside from the presence of LNAPL or groundwater entering a storm/sanitary sewer or basement sump, 36% of the states reported observing an issue with preferential vapor migration associated with features such as cracks in foundations, utility bedding, and elevator shafts.

State Survey Results - Chapter 4. Site Investigation

• 42% of the states consider biodegradation as part of a PVI site investigation. Several states indicated that biodegradation will likely be included in future versions of state guidance.
• 80% of the states require either a formal or informal CSM as part of a VI investigation.
• 82% of the states employ a multiple-lines-of-evidence approach for VI investigations, with the majority of states weighing some lines of evidence (chemical data) more than others.

State Survey Results - Chapter 5. Modeling

• 74% of the states make decisions regarding the PVI pathway based on modeling information, although more than half of these also require additional PVI-specific investigations.
• 76% of the states do not have specific requirements or policies with respect to biodegradation in VI modeling (i.e., acceptable models or input parameters).

State Survey Results - Chapter 6. Vapor Control and Site Management

• 50% of the states have guidance on VI mitigation. Of these, less than half of the guidance specifically addresses PVI mitigation.
• 42% of the states do not require permitting for PHC mitigation. Other states may require air, building, electrical or fire permitting depending on the technology used. Local permitting requirements may also apply.
• Most (62%) of the states do not require a certified/licensed installer or licensed professional engineer for CVI or PVI mitigation systems.
• 56% of the states require chemical analysis of indoor air samples to monitor mitigation system performance. Other types of measurements (such as differential pressure readings, and chemical analysis of venting stack air) may also be required. 14% of the states do not require performance monitoring.
• 52% of the states require institutional controls for VI mitigation systems, most commonly when a site is to be closed with a mitigation system in place.

State Survey Results - Chapter 7. Community Engagement

• 50% of the states have guidance on community outreach related to contaminated sites. Of these, less than half specifically address VI.
• 80% of the states' outreach plans do not differentiate between CVI and PVI cases.
• 88% of the states require communication (for instance, sampling results or public meetings) with affected off-site parties.
• 56% of the states have tools for communication with non-English speaking communities.

State Survey Results - Appendix E. Common Types of Petroleum Sites

• 100% of the states responded that gasoline/diesel USTs ranked important to very important when assessing the PVI pathway. 86% of the states have confirmed a PVI occurrence related to a UST discharge.
• 57% of the states responded that refineries ranked important to very important when assessing the PVI pathway.
• 73% of the states responded that pipelines ranked important to very important when assessing the PVI pathway.
• 69% of the states responded that manufactured gas plants ranked important to very important when assessing the PVI pathway.
• 65% of the states responded that heating oil tanks ranked important to very important when assessing the PVI pathway.
• 88% of the states responded that bulk storage facilities ranked important to very important when assessing the PVI pathway.
• 20% of the states responded that exploration and production ranked important to very important when assessing the PVI pathway.

State Survey Results - Appendix G. Investigation Methods and Analysis Toolbox

• 62% of the states prefer TO-15 for analysis of PVI compounds.
• 70% of the states required either state or National Environmental Laboratory Accreditation Conference certification for laboratory analysis. Other states indicated that certification requirements are being considered.
• The majority of states require a 24-hour sample duration for residential settings and an 8- hour duration for nonresidential settings.
• 56% of the states do not specify duration for soil gas samples. Of states with specific requirements, most require a flow rate of less than 200 mL/minute.

Additional Findings for Confirmed PVI Occurrences

• 86% of the states confirmed a PVI occurrence related to a UST discharge.
• 58% of the states confirmed a dissolved-phase PHC source causing vapor intrusion (absence of residual-phase LNAPL).

For the 17 states that confirmed both types of PVI occurrences as noted above, a member of the ITRC PVI Team made phone calls to gain additional information. The following list summarizes the information obtained from those calls.

Alabama

Most PVI incidents from dissolved PHC groundwater plumes are due to direct migration into basements or sumps. A PVI incident occurred, however, from shallow soil contamination that off-gassed PHC vapors into an air conditioner intake for a building. Another PVI incident involved shallow groundwater contaminated with dissolved PHCs at about 2 feet bgs. The PHC vapors entered a cold joint between the building slab and the sidewalk.

Arkansas

A PVI incident occurred in a retail shopping center. Groundwater was at a depth of about 3 feet bgs and contained TPH-GRO concentrations of 50 to 100 mg/L. Vadose zone soils consisted of silty clay. A dual-phase vapor extraction system with horizontal piping was installed to mitigate PVI.

Arizona

Arizona has areas with shallow groundwater (10 to 15 feet bgs) and dry sandy soils or fractured rock vadose zones (low biodegradation potential). These conditions can enhance the potential for PVI from dissolved PHC sources in groundwater.

Colorado

The Colorado staff contacted knew of no PVI incidents with clean soil separating the dissolved PHC groundwater plume from the receptor.

Delaware

PVI incidents involving dissolved PHC groundwater plumes result from contaminated groundwater entering basements directly.

District of Columbia

District of Columbia staff reported a PVI incident from a dissolved PHC groundwater plume involving a dry p-trap in a basement drain.

Idaho

PVI occurred in residences with basements (7 to 8 feet bgs) and shallow groundwater (10 feet bgs) with benzene concentrations in groundwater of 10 to 15 mg/L. The vadose zone soils were sands and gravels.

Iowa

PVI occurred in a residence with a French drain and sump. Shallow groundwater with a benzene concentration of about 600 μg/L went into the French drain and sump.

Kentucky

A PVI incident occurred from a dissolved PHC groundwater plume entering a basement.

Maine

Maine staff reported PVI incidents from dissolved PHC groundwater plumes entering basement sumps. One PVI incident occurred from gasoline LNAPL at 12 feet below the bottom of a basement. The vadose zone soils were sandy.

Minnesota

Most PVI occurrences result from direct contact or preferential pathways connecting the groundwater (contaminated with dissolved PHCs) with a receptor. Most, if not all, occurrences were discovered by someone smelling a PHC odor. One recent PVI occurrence involved a LUST release with LNAPL and a dissolved groundwater plume migrating off site under slab-on-grade apartments. Groundwater was at about 15 feet bgs and the vadose zone soils were medium sands. Extensive pavement and the apartment complex may have prevented sufficient O₂ from entering the vadose zone soils. Petroleum odors were noticed in the apartments, so subslab depressurization systems and soil vapor extraction systems were installed to mitigate PVI.

New Hampshire

New Hampshire staff reported PVI incidents from dissolved PHC groundwater plumes that entered basements directly. PVI has also resulted from broken vent lines at operating gas stations.

New York

Most PVI occurrences result from direct contact of contaminated groundwater with a basement (some through preferential pathways such as subsurface utility lines). Most are discovered by someone smelling a PHC odor. In one case on Long Island. contaminated groundwater was 2 to 3 feet below the bottom of the homes (slab-on-grade). The vadose zone soils were sandy.

Ohio

A PVI incident occurred from a dissolved PHC groundwater plume entering a basement sump of a house.

Oklahoma

Oklahoma reported a PVI incident from a dissolved PHC groundwater plume at about 4 to 5 feet below the floor of the basement in a residential house. PVI occurred when it rained hard and infiltrating stormwater may have forced PHC vapors into the basement.

Rhode Island

A PVI incident occurred in a building with a basement (earthen floor) at a depth of about 10 feet bgs. Shallow groundwater was at about 11 to 15 feet bgs and was contaminated with dissolved compounds from a gasoline LUST.

Vermont

PVI incidents involving dissolved PHC groundwater plumes result from contaminated groundwater entering basements or basement sumps directly.