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The groundwater treatment program received a big boost with the implementation of soil vapor extraction systems (SVE) in 1993. The systems remove the VOCs that are in the soil above the groundwater. This layer of soil, between the surface where the contaminants were originally located and the groundwater is called the vadose zone. Because the VOCs move relatively slowly through the vadose zone, much of those contaminants are still there. The SVE system essentially "vacuums" the vaporized contaminants out of the soil and pumps them to a treatment plant where the contaminants are filtered and the clean air is released. Removing VOCs from the vadose zone by SVE is generally quicker and less costly than later removing them from the groundwater. To date, approximately 1.3 million pounds of contaminants have been removed from McClellan through SVE.
Depending on the type of contaminants present and the anticipated future use of the site, the Air Force and state and federal regulatory agencies may decide the best treatment is to remove the contaminants and the associated soil and dispose of it in an approved disposal facility. Frequently, this remediation method is employed at old landfill sites that may contain a variety of waste materials ranging from fuel drums to laboratory glassware.
An engineered cap over a contaminated area protects human health and the environment from future exposure while leaving the contaminants in place. In some cases, caps are accompanied by an engineered liner under the contaminant to prevent migration of the contaminant either into the atmosphere or down to the groundwater. This alternative is only used if it is compatible with the nature of the contaminants and future use of the area. Institutional Controls Institutional controls eliminate or limit exposure to humans by restricting land use and activities that can occur on the site. These restrictions, including permitting, zoning, deed restrictions, fencing, inspections, and enforcement, remain with the land indefinitely. These measures not only protect human health and the environment, but they are also tools to protect the other cleanup systems on site as well.
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