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PRIVILEGED & CONFIDENTIAL hydrocarbons (TRPHs) were found at concentrations ranging from 10 parts per million rf (ppm) to 31 ppm, which is well below the Maximum Contaminant Level (MCL) of 100 ppm as set forth by the Regional Water Quality Control Board (RWQCB). Based on the above-mentioned analytical results, it was concluded that the on-site soil contamination, although below regulatory action levels, was likely caused by the spilling of waste oil and motor oil at the former on-site gasoline service station. There was no indication of diesel or gasoline contamination. Groundwater was expected at a depth of approximately 60 feet bgs, and was not sampled during this Subsurface Investigation. February 1997, Follow-Up Phase II Subsurface Investigation ' Building Analytics completed a Follow-up Phase II Subsurface Investigation in February 1997, which included the installation and testing off three monitoring wells. The following is a summary of the findings from the investigation: + The groundwater flow direction in February 1997 was measured to be to the northeast, with a hydraulic gradient of 0.0025; • TPH-g at levels up to 1,300 ppm, and benzene at levels up to 0.39 ppm, were reported in the soil samples collected from Boring B2, at depths between 35 and 55 feet bgs; + TPH-g and BTEX were reported in groundwater samples collected from MW-1 or MW-3; • Benzene was not reported in the groundwater sample collected from MW-2; + TPH-g (1.6 ppm), ethylbenzene (120 ppm) and xylenes (370 ppm) were reported in the groundwater sample collected from MW-2; and + Methyl-tert-butyl ether (MTBE) was not reported in any of the soil or groundwater samples collected. Following the February 1997 Follow-up Phase II Subsurface Investigation, the SJCEHD ' requested that an additional soil and groundwater monitoring well be installed between previously drilled borings P-1 and P-2. Building Analytics submitted a Work Plan for an Additional Soil Boring, Monitoring Well Installation and Quarterly Groundwater ' Monitoring to the SJCEHD on July 25, 1997, which was approved on August 5, 1997. I OBJECTIVE AND SCOPE OF WORK ' The first objective was to perform an additional assessment of subsurface soil conditions beneath the subject site to further investigate the potential source of contamination. ' The second objective was the further investigation of on-site groundwater conditions to further assess the extent of the known groundwater contamination. ' To accomplish the objectives, Building Analytics performed the following tasks: a. Submitted a Work Plan and Well Permit to the SJCEHD; b. Marked the boring location and called Underground Service Alert (USA) to perform utility clearance; 2 197501-Stockton 1