Soil Gas Surveys & Vapor Intrusion Modeling
Soil vapor investigations provide a rapid and cost effective way to investigate sites potentially impacted by volatile organic compounds (VOCs), including chlorinated and fuel hydrocarbons, or by methane and hydrogen sulfide. The data can be used to identify contaminant sources, determine their extent, and model for vapor intrusion.
Intrusion of subsurface vapors into buildings can cause an unacceptable risk to the occupants. VOCs in the subsurface, whether in soil or groundwater, can migrate upward through the soil and enter buildings. Regulators routinely require human health risks be evaluated, including this pathway, before site closure.
EnvApps follows all soil vapor survey protocols appropriate to the project location, including the following by the U.S. Environmental Protection Agency, California Department of Toxic Substance Control and the Los Angeles Regional Water Quality Control Board:
- Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (Interim Final); December 14, 2004; DTSC
- Advisory – Active Soil Gas Investigations; January 28, 2003; DTSC & LARWQCB
- User’s Guide for Evaluating Subsurface Vapor Intrusion into Buildings; February 22, 2004; U.S. EPA
Risk is evaluated using fate and transport models to predict indoor air concentrations from vapor intrusion. EnvApps routinely runs the Johnson-Ettinger model for vapor intrusion screening evaluations. Indoor air sampling is conducted, if unacceptable cancer risk to building occupants is determined.
EnvApps has worked under direct contract to the DTSC, performing soil gas surveys and indoor air intrusion modeling as part of Preliminary Environmental Assessments (PEAs) and Targeted Site Investigations (TSIs).
Example Projects:
DTSC Indoor Air Modeling - EnvApps installed 18 permanent, multi-stage, soil vapor probes at an orphaned drycleaner site under direct contract to the DTSC. The project was complicated due to the presence of an unexpected shallow perched water zone. EnvApps conducted indoor air modeling (soil vapor intrusion) evaluations for compounds encountered in the soil gas and groundwater.
Quick Turnaround Soil Gas Survey - A former drycleaners was identified by a Phase I report somewhere within a large parcel of multiple properties, which were in escrow. One of the buyers contacted EnvApps to locate the former drycleaners and perform a soil vapor survey. Within two days, EnvApps reviewed historical records, located the former drycleaners, mobilized to the site, and completed a soil vapor survey. In another two business days, a draft summary report stating no significant impact was detected was submitted to the client. Within an additional week, the $14 million purchase was completed.
Methane Evaluation in Landfill - Installed 150-foot deep, multi-stage probes for methane monitoring within a landfill. The purpose was to evaluate methane conditions prior to development as a big-box retail center.
Soil Gas Survey for RCRA Part B Facility Closure - EnvApps performed an extensive soil gas survey and obtained RCRA Part B closure for a former solvent recycling facility. |
