COMPLIANCE INFO_FILE 7 - Laserfiche WebLink

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Remediation of Vadose Zone Soil at the Tracy Yard During a soil vapor extraction remedial action, the rate of VOC mass removal is generally highest early in the remedial action. Typically, under continued soil vapor extraction, the mass removal rate decreases significantly over time, and approaches zero as extraction continues. If this condition occurs for the remedial action at the Tracy Yard, the benefits of the remediation will be reviewed to determine whether continued operation of the remedial action is warranted. This review will include the following: • Determine whether there is a demonstrated continued reduction in soil vapor concentrations as a result of continued vapor extraction; • Determine whether there is a demonstrated continued reduction in the extent of the soil vapor plume as a result of continued vapor extraction; and, • Evaluate the technical practicality and incremental benefit of achieving further reduction in VOC concentrations in vadose soil, based on asymptotic patterns of constituent concentrations in ground water and soil vapor. These evaluations will be made based on the ground water and soil vapor monitoring program described in Section 6. A-Zone Ground Water Plume Control As part of this remedial action, a ground water monitoring program will be implemented. This ground water monitoring program is described in Section 6 - Operation and Monitoring of the Remedial Action, and will consist of periodic measurement of ground water elevations and collection of ground water quality samples at select site monitoring wells. The purpose of this monitoring program is: • Verification of reduction of VOC concentrations in A-zone ground water as a result of ground water extraction at dual phase extraction wells and at plume margin wells; and, • Documentation of lateral containment of the VOC plume in the A-zone as a result of ground water extraction at dual phase extraction wells and plume margin wells. 4-12