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CLEARWATER G R O U P I N C Enc iranmentaf Srrc ire< ' 4.0 RESULTS 4.1 Water Level Monitoring Data ' On February 27, 1996, the depths to groundwater in the five monitoring wells ranged from 20 00 to 2125 feet below grade Groundwater elevations, calculated for ' the purpose of estimating flow direction and gradient, were 2 5 to 3 feet higher than the groundwater elevations on November 30, 1995 As Figure 3 indicates, groundwater flow is toward the northwest The groundwater gradient is 17% across ' most of the site, but is only 0 5% between MW-2 and MW-6 This change in gradient appears as a flattening of the water table west of the former USTs, which is consistent with the water table configuration during previous monitoring events 4.2 Groundwater Analytical Results ' TPHg and/or benzene were detected in samples collected from all monitorin ice t MW-4 d MW-6 No analytes were detected in MW-4 or MW-6 The highest detected concentrations of TPHg and benzene were 33,000 parts per billion (ppb) and 67 ppb, respectively, in MW-2 Concentrations of TPHg and benzene were 300 ppb and 16 ppb, respectively, in monitoring well MW-5 A summary of groundwater elevations and analytical results is presented on Table 1 Hydrocarbon concentrations are presented graphically on Figure 4 A copy of the laboratory report and chain-of-custody form is attached as Appendix B ' 5.0 RECOMMENDATIONS In September 1995, Clearwater installed two vapor extraction wells and two air ' sparging wells that were used for a pilot test at the site The results of the tests were presented in the Report on Site Assessment Activities, Pilot Test, and Quarterly Groundwater Monitoring, dated December 15, 1995 At that time, Clearwater ' recommended submittal of a corrective action plan (CAP) that would present the remedial approach for the site, including the proposed number and types of wells to be used in the remedial system Mr Michael Infurna of the PHS/EHD indicated that the CAP should also include a Feasibility Study (FS) of alternative remedial methods A December 8, 1995 letter from Walt Petit of the State Water Resources Control Board (SWRCB) to the Regional Water Boards and Local Oversight Program 4 Directors recommends accelerated evaluation and closure of "low risk" sites Mr i ' D-101 1Q96 3 Apnl 18, 1996