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• Groundwater Extraction and Treatment from Dual Phase Extraction The depth to groundwater is currently below the depth of the base of the on-site combination groundwater momton nglvapor extraction wells During the period of this seasonal fluctuation when groundwater rises into the well screen, we initially recommend that monthly 10-day DPE events be performed to help provide hydraulic control of the dissolved-phase hydrocarbons and MTBE DPE will be performed using the central . combination groundwater monitoeng/vapor extraction wells MW-1 and MW-9 as the extraction wells The proposed plume control system will utilize a DPE system carbon-adsorption groundwater treatment technology The DPE system consists of a Dekker 20 horsepower liquid ring pump capable of 29 ins-mercury and vapor treatment is performed by a Solleco thermal oxidizer equipped with a 500,000 Btu Eclipse Ratiomatic burner The extracted - groundwater is collected in a 500 gallon knockout tank equipped with a transfer pump The water is spray aerated into the thermal oxidizer where the hydrocarbons are stepped and oxidized The remaining water is filtered through two 1,000-pound activated carbon absorbers in series The treated eluent is stored in a 20,000-gallon Baker tank pending the results of laboratory analysis If appropriate the treated water is discharged to the sanitary sewer under permit with the municipal wastewater treatment facility Otherwise the water is hauled to an appropriate off-site facility for disposal Operation of the periodic 10-day DPE events and groundwater treatment system will conunence after obtaining the following approvals and permits • Approval of this CAP by the CRWQCB-CVR, and • Treated groundwater discharge agreement/permit from the PHS-EHD • Pre-approval from USTCF Groundwater Monitoring and Sampling for DPE Quarterly groundwater monitoring and sampling of all existing groundwater monitoring wells is recommended during the remediation process Groundwater samples will be collected and analyzed for TPH as gasoline and BTEX/MTBE/TBA/TAME/DIPE/ETBE using EPA Methods 8015 {M) and 8260, respectively As generally required by the SIVUAPCD-SR VES permits, weekly air samples will be collected at the inlet and outlet of the VES Monitoring will be conducted with a calibrated field instrument and the results will be compiled on monitoring logs that will be ma ntamed in a field logbook The information obtained from system monitoring will be used to fine-tune the system in order to achieve the desired operating conditions Treated groundwater will be sampled and analyzed according to the agreement/permit obtained • from the City of Tracy Page 14