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r.. �- REMEDIAL ACTION PLAN ,.. USA STATION#65 - LODI NOVEMBER, 1995 4.2 Local Hydrogeology �- Applied Geosystems reported that the groundwater elevations at the site ranged between 5 and 6-feet below MSL from January 20, 1989 to April 18, 1989. When WEGE resumed water level monitoring in September of 1991 the water level elevation had dropped an additional 8-feet to approximately 13-feet below MSL. Since 1991 when WEGE resumed monitoring, the water level has fluctuated both up and down. Water levels recorded in June, 1995 ranged from approximately 10 to 13-feet below MSL. The most recent water level readings indicate that overall water levels across the site have dropped approximately 0.5-feet since March, 1995. The direction of groundwater flow and magnitude of the hydraulic gradient across the site have remained relatively consistent. The direction of flow is generally to the southeast between `r MW-1 and MW-5, and to the southwest between MW- 5 and MW-7. The magnitude of the gradient is between 0.002 and 0.003- feet/feet(ft/ft). A summary of WEGE water level records is L. contained in their "Quarterly Monitoring Report- April to June, 1995". 5.0 VAPOR EXTRACTION TESTING AND RESULTS REVIEW 5.1 Vapor Extraction Testing and Sampling Methodology To approximate the performance of using vapor extraction to remediate hydrocarbon affected soils from the unsaturated and groundwater zones, vapor extraction tests were performed on r•. wells MW-4, S-1, S-2,and MW-8 in March, 1995. Vapor extraction testing was done by WEGE and is reported in their"Results of Pilot Test for Vapor Extraction" dated April 17,1995. During each test, a vacuum was applied to each of the test wells: MW- 4 was vented for approximately 1 hour and 10 minutes, S-1 was vented for approximately 50 minutes., S-2 was vented for approximately 1 hour, and MW- 8 was vented for approximately 5 hours. Air flow rates were observed at the well and the induced vacuum was measured and recorded. During the test, vacuum gauges (manometers) were used to measure vacuum in the monitoring wells adjacent to and in the vicinity of the well being tested. Following each test, a vapor sample was collected for submittal to the laboratory for TPH and BTEX analysis. 5.2 Analytical Results from Vapor Sampling .. Results of laboratory analyses of vapor samples collected during the test indicated that TPH G and BTEX concentrations were detected in all wells sampled. Highest concentrations of TPH and i, BTEX in vapor samples analyzed in the laboratory were detected in well S-2 at 63 mg/l (ppm), which corresponds to approximately 15,000 parts per million by volume (ppm v/v) TPH. The highest vapor concentration recorded by the field equipment was 243 ppm in MW-8. A summary ... of the analytical results of the vapor samples may be observed in the WEGE report. 4