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REG 603 UPDATE-6 2/21/92 has been stabilized and fully evaluated as to the influence it will have on the ground water plume. 4 . "The extent of groundwater contamination has not been physically defined. Additional monitoring wells will be required to define the contamination plume. Submit a work plan for the additional investigation. " At this time vapor extraction is removing contamination from both the soil and ground water beneath the site. The vapor extraction destruction equipment, "HIRTZ" Thermal Oxidizing unit, is undergoing a stabilization process, weekly adjustments of vapor recovery wells, natural gas and air dilution. Once this stabilization process is completed (estimated the end of February, 1992) , vacuum anflunce will be determined along with the estimated capture zone the vapor extraction as having on ground water. Until this evaluation is completed, the need for down gradient wells for lateral extent determination is premature. 2. 0 GROUND WATER • 2 . 1 REGIONAL AND LOCAL GROUND WATER FLOW Ground water flow direction in this region is to the west and towards south Stockton from the foothills of the Sierra Nevada Mountain Ranges, and towards the east from the Sacramento--San Joaquin Delta. At present, encroachment of saline waters from the Delta is impairing the quality of the ground water in the Stockton area. WEGE surveyed each well (top of casing) with a transit using the southwest corner of the current tank pad (see Figure 3 ) as the datum. Survey readings were recalculated to correct elevations to the USGS topographic map (USGS East Stockton Quad. , Figure 2 ) . Based upon ground water elevation measurements obtained thoughout the evaluation of this site, the overall local flow direction is to the east-northeast at a relatively flat slope. Measurements ..1..� ....3 T.. rl7 7nnI /L,4 .� AT \ .-.1,r V7 M -FI - 7 o Va_ine d on Lirune G ! , 1.771, t 1 1.yure -zz%j , 411vw u iiww .aii........i..+. .... the northeast and east, with a depression at monitor well MW1 and a ridge extending from MW10 towards MW2. This gradient map represents a period of discharge beneath the site, MW1 has a higher hydraulic conductivity (velocities) compared to MW10 and MW2, thus the area at MWI would dewater faster forming a valley or depression. On September 18, 1991, depth to ground water was measured from top of casing in all of the wells prior to the required quarterly ground water sampling. The flow direction was established to the PAGE 3