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1 FIRST QUARTER, 1997 GROUNDWATER MONITORING REPORT USA STATION##65-LODI FEBRUARY, 1997 , 2.1.2 Local HvdroQeolo2y Groundwater elevations in S-I and S-2 were approximately 1-foot below MSL when the wells were drilled in 1987 The groundwater elevations at the site ranged between 5 and 6-feet below MSL from January 20, 1989 to April 18, 1989 By September, 1991, the water level elevation had dropped to approximately 13-feet below MSL Groundwater elevations have since recovered to 1987 levels The direction of groundwater flow and magnitude of the hydraulic gradient across the site have remained relatively consistent,_flowing=southeriymat-a-gradient=between=0 002 and 0-004-feet/feet(ft/ft) A summary of water level records are presented in Table 1 2.2 Summary of Previous Investigations , A limited site investigation completed in March, 1987 detected petroleum hydrocarbon compounds in the soil and groundwater beneath the site The investigation included he drilling ' and sampling of four soil borings two, of which were completed as groundwater monitoring wells (S-I and S-2) r In August, 1987, Applied Geosystems completed the installation of three additional groundwater monitoring wells (MW-I, MW-2 and MW-3) USA requested that Applied Geosystems complete four additional monitoring wells (MW-4, MW-5, MW-6, and MW-7) in the downgradient direction to further define the lateral extent of the impacted groundwater" Applied Geosystems then prepared a Problem Assessment Report (PAR) after completing monitoring wells MW-6 and MW-7 The PAR concluded that petroleum hydrocarbon impacted water had migrated beyond the property boundaries, and that the groundwater in the upper ' aquifer, above 42-feet below ground surface (bgs) was not in hydraulic continuity with the deeper aquifers It was their opinion that further delineation of the impacted soil and water was not required , On February 8, 1993, Western Geo-Engineers (WEGE) completed monitoring well MW-8 to a depth of approximately 60-feet bgs The well is downgradient approximately 8-feet southeast of r the tank field This well has consistently contained total petroleum hydrocarbon(TPH), benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds On March I4, 1995 WEGE completed a one day vapor extraction treatability test The test was performed using monitoring wells MW-4, S-1, S-2, and MW-8 Test results are summarized in the WEGE report "Results of Pilot Test for Vapor Extraction.", dated April 17, 1995 USA retained Park to prepare a Remedial Action Plan (RAP) rationale design of the necessary environmental remediation and sampling activitiess at he sitewere presented in Park's ' November, 1995 RAP and in a February 28, 1996 letter to he County 2 r