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S E C O R Conceptual Site Model Chevron Service Station#9-6171 March 25, 2005 Page 32 8.0 GROUNDWATER FLOW AND TRANSPORT MODELING In order to extract and remediate volatile organic compounds In site soils and groundwater associated with past dry-cleaning activities at the Lincoln Village Shopping Center (LVSC) and the area immediately surrounding the LVSC, LFR installed a soil vapor (SVET) and a groundwater (GWET) extraction and treatment system The location, installation, and operational-history of these systems is summarized above and described in several Levine- Fricke documents (LFR, 1998a, LFR, 1999, and LFR, 2003) As part of the Phase I Interim Remedial Action Plan (TRAP), LFR conducted constant- discharge pumping and recovery tests In the A-Zone Aquifer in 1997 These tests were conducted to assess hydrogeologic properties beneath the site vicinity and to evaluate the optimum sustainable pumping rates for the proposed groundwater extraction and treatment system The results of these tests were used to evaluate aquifer properties and aid in the design and implementation of the initial GWET system The was original GWET system expanded in 2003 to reduce PCE concentrations in the B- 9 Y Zone aquifer beneath the LVSC and in the A-Zone aquifer downgradient of the site Before expanding the GWET system, LFR conducted step-drawdown and constant-discharge pumping tests In the A- and B-Zone aquifers for the site vicinity on July 24 and 25, 2001 (LFR, 2003) Hydrogeologic properties determined from the aquifer testing were used to prepare a conceptual groundwater flow model using MODFLOW to simulate groundwater flow conditions at the site MODFLOW Is a three-dimensional, finite difference groundwater I flow model developed by the United States Geological Survey The MODFLOW model was prepared to simulate groundwater flow conditions in the A- and B-Zone aquifers, estimate appropriate groundwater extraction rates at the site and evaluate the capture zone for volatile organic compounds in groundwater in the A and B zones beneath the site vicinity The results of the model and capture zone evaluation conducted by LFR Indicate that the area beneath Chevron service station 9-6171 is entirely within the capture zone established during operation of the GWET system Therefore, any potential petroleum hydrocarbon Impacts associated with past activities at the Chevron service station should eventually be captured and treated by the GWET system However, given the complexity of the GWET system, It is difficult to make accurate predications regarding the size and geometry of the capture zone without a better understanding of the pumping schedule and sampling history of the Individual wells in the system N IFdes\Projects\Chevron\Retaill#9-6171\Site Conceptual Model\FINAL_CSM doc