ARCHIVED REPORTS_2003 FEASABILITY STUDY REPORT AND SITE ASSESSMENT WORK PLAN

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S E C O R 2003 Feasibility Study Report and Site Assessment Work Plan July 18, 2003 Page 8 ■ During May of 2003, a step-drawdown test and a constant-rate aquifer pumping test were performed to estimate hydraulic characteristics for the Upper A-Zone and the A-Zone aquifers beneath the site. Results of the step-drawdown test performed in the Upper A-Zone indicate the maximum sustainable extraction rate for the wells screened in this zone should not exceed 0.9 gpm. In addition, for effective dewatering, the spacing of wells that will be used in dewatering the Upper A-Zone should also not exceed 25 feet from center to center. Results also indicate that extraction from the Upper A-Zone influenced monitoring well MW- 24A, which is screened in the A-Zone. This may indicate that hydraulic communication exists between the Upper A-Zone and the A-Zone aquifers beneath the site. Results of the constant rate aquifer pumping test performed in the A-Zone determined this aquifer could sustain a pumping rate of 9.25 gpm. Also, drawdown was observed in monitoring wells located 60 feet away from the pumping well at a pumping rate of 9.25 gpm. An average value of approximately 294 ft2/day and 0.41 was estimated for T and SY, respectively. Based on the A-Zone saturated thickness of 20 feet, the average K estimated was 15 ft/day(0.0052 cm/sec). In addition, the zone of influence of the pumping well was calculated to be 264 feet. This was confirmed by the drawdown data observed in monitoring wells during the pumping test. (SECOR, 2003d). 3.0 NATURE AND EXTENT OF CONTAMINATION Hydrocarbon compounds have been detected in the subsurface as a result of the five previously reported spills at the site. The results of investigations and actions related to these releases have been used to develop the following summary of the extent of fuel hydrocarbons in the subsurface. 3.1 Soil Contamination The highest petroleum hydrocarbon concentrations (TPHd, TPHg, and MtBE) detected in soil were 14,000 3,700, and 7.6 milligrams per kilograms (mg/kg), respectively. These hydrocarbon compounds were detected in shallow soil located around the loading rack area and near Tank 137, the transmix tank. The location of these maximum concentrations appears to be consistent with the areas where previous spills have occurred. Previous investigations indicate that there are three main areas at the site where soil has been impacted by petroleum hydrocarbons: 1) the area northeast of the loading racks, 2) the area surrounding Tank 137, and 3) the area around the former Key Lock facility. The lateral extent of soil contamination appears to be limited to these general areas and does not extend offsite. Concentrations of petroleum hydrocarbons in these areas appear to be the highest around the capillary fringe (between 3 to 8 feet bgs). However, detections of petroleum hydrocarbons have been reported as deep as approximately 29 feet bgs. The vertical extent of hydrocarbons in soil is adequately defined. Additional soil sampling will be conducted, as described in Section 10, to further delineate the lateral extent of hydrocarbons onsite. Soil analytical data tables and figures presenting hydrocarbon distribution in soil are presented in Attachments D and E, respectively. • I:\Chevron\1001621\REPORTS\2003\2003FS\FS 2003 revD.doc