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r S EC ® R <br /> r • <br /> Cleanup Plan <br /> October 27, 2003 <br /> r Page 9 <br /> 3.2 Groundwater Contamination <br /> rThe highest reported concentrations of TPHd, TPHg and MtBE in groundwater at the site were <br /> 1,900,000, 740,000, and 45,000 pg/I, respectively. These concentrations were detected in the <br /> rshallow groundwater(Upper A-zone and A-zone) around the loading rack area and near Tank 137. <br /> SPH has historically been detected in wells MW-1 UA, MW-3UA, MW-7A, MW-8A, MW-14A, MW- <br /> 15A, MW-16, and MW-36UA through MW-42UA. These wells are located around the loading rack <br /> r area and near tank 137. During the second quarter of 2003, SPH was not detected in any <br /> monitoring wells (SECOR, 2003a). <br /> r Groundwater at the site has been separated into three water bearing zones (Upper-A zone, A-zone, <br /> and B-zone). In the shallow aquifers (Upper A-zone and A-zone), concentrations of TPHd, TPHg <br /> and MtBE do not appear to be defined down-gradient of the site. In the B-zone, concentrations of <br /> r TPHd, TPHg, and MtBE appear to be defined downgradient of the site. During the second quarter of <br /> 2003, highest concentrations of TPHd, TPHg, and MtBE in the B-zone were 140 pg/I, <50 pg/I, and 2 <br /> pg/l, respectively. <br /> rThe vertical extent of hydrocarbons in groundwater is defined by B-zone wells MW-12B, MW-13B, <br /> MW-22B, MW-23B, MW-50B, and MW-64B. These wells are screened from approximately 55 feet <br /> bgs to 65 feet bgs. <br /> rSecond quarter 2003 groundwater elevation and analytical figures are resent <br /> Y 9 presented in Attachments D. <br /> ' 4.0 SELECTED REMEDIATION ALTERNATIVE SUMMARY <br /> Based on the results detailed in SECOR's 2003 Feasibility Study and Site Assessment Work Plan, <br /> r dated July 18, 2003 (SECOR, 2003d), a groundwater oxygenation system has been selected to <br /> remediate hydrocarbons dissolved in groundwater. Biannual product removal from monitoring wells <br /> with separate phase hydrocarbons (SPH) and limited excavation in the former Keylock area are also <br /> ' proposed to mitigate hydrocarbon mass from source areas. These remedial technologies will be <br /> relatively easy to implement, enhance the biodegradation of hydrocarbons to levels near or <br /> consistent with Basin Plan's Water Quality Objectives (WQOs), will not impact the short and long- <br /> term operations of the terminal, and have the lowest net present value over a ten-year period. <br /> 4.1 Remedial Objectives <br /> ' The remedial objective for the site are to: protect off-site groundwater, achieves compliance with the <br /> WQOs (pursuant to CAO) and minimizes impacts to short-and long-term terminal operations. <br /> Specific remedial goals that have been identified to achieve these remedial goals are listed below. <br /> r4.2 Remedial Goals <br /> r ■ The proposed biannual removal of product from all onsite monitoring wells containing SPH <br /> should reduce aqueous phase hydrocarbons onsite; <br /> ■ The proposed limited excavation should remove hydrocarbon mass from the former Keylock <br /> ' area (Figure 7) and reduce aqueous phase hydrocarbons onsite; and, <br /> I:\Chevron\1001621\REPORTS\2003\2003-Cleanup Plan\Cleanup Plan.doc <br />