Soil vapor extraction (SVE) is a very common and cost-effective method of removing chlorinated solvents such as tetrachloroethylene (PCE) and gasoline from the soils at a contaminated site. SVE is a form of vacuuming contaminants from the subsurface soils. The contamination contained in the vapor phase in vadose (un-saturated) soils are vacuumed to the surface through machinery, and subsequently destroyed through incineration or carbon. Subsurface soils at a site might be conducive to SVE.
Typically, a pilot test is performed prior to construction and operation of the full scale SVE system to ensure the adequate full design of the system. Information from the pilot test allows The Reynolds Group (TRG) to ensure adequate capture of the contamination, determine size of the remediation system, and install the correct number of wells. Sometimes the pilot test can be performed as part of the initial installation and operation of the SVE system, with operation continuing at the end of the pilot test, if the regulator allows, to save time.
When an SVE system is started, the concentrations of contaminants in the subsurface that are extracted are at their maximum. Once the system has operated for some time, there is a dramatic drop in concentrations and then, after a sufficient operating period, the concentrations “flat line” – a condition called “asymptotic”. When asymptotic conditions are attained, it is time to conduct a series of rebound tests to satisfy the regulator that the contaminant concentrations will not bounce back significantly. If concentrations do bounce back, the SVE system has to be re-started and run again until asymptotic conditions are again reached. Once the SVE system has run its course, regulators typically require more soil borings – called confirmation borings – to assess the soils “post remediation”. Finally, once a “No Further Action” letter is received from the regulator, the entire system must be decommissioned and demobilized and all wells must be destroyed.
Health Risk Assessment Services
A large challenge at many sites is the potential for Human Health Risk to tenants and the residences adjacent to the site. SVE can reduce accumulated vapors from beneath the building slabs that may have the potential to intrude into the indoor air spaces. For example, existing PCE shallow soil vapor concentrations at the depths considered to be deleterious to health (5 and 10 feet below ground surface) can be mitigated by the proposed SVE operation. TRG routinely performs Human Health Risk Assessments (HHRA’s) that evaluate the need for further vapor mitigation to acceptable levels.