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` �arhrhr GrMWWVAUW Mar ADWO Report <br /> 148M Wesi Frontage Road Manteca,Cafifomla <br /> BACKGROUND <br /> Work performed at the site by previous consultants included investigations by Earth <br /> Treatment Systems, Inc (ETS), of Merced, California, Delta Environmental Consultants, <br /> Inc (Delta), of Rancho Cordova, California, and Nations Groundwater Associates of <br /> Sacramento, California In August 1988, MW-1 and MW-2 were installed by ETS. In April <br /> and May 1989, Delta installed MW-3 and MW-4 In November 1989, Delta conducted soil <br /> sampling during the removal of three 10,000-gallon underground fuel storage tanks. Delta <br /> installed MW-5 through MW-8 in November and December 1989 Aegis began a program <br /> of monthly monitoring and quarterly sampling of the wells in January 1991 In <br /> November 1991, Aegis supervised drilling and completion of MW-9 (Figure 2) The <br /> previous consultants' groundwater data, along with Aegis' data, are included in Table 1 <br /> GROUNDWATER MONITORING <br /> On April 8, 1993, Aegis personnel collected measurements of depths to groundwater from <br /> the nine wells Since January 1993, groundwater levels rose in all wells (Figure 3) an <br /> average of approximately 1 49 feet; ranging from 1 38 to 1 72 feet (fable 1) Figure 4 <br /> is a potentiometric surface map of the shallow water-bearing zone on April 8, 1993 On <br /> the basis of the April 8 measurements, the groundwater flow direction is estimated to be <br /> generally to the southeast, at a gradient of approximately 0 0014 ft/ft <br /> . Groundwater measurements are summarized in Table 1. All groundwater elevation <br /> measurements were made according to the Aegis standard operating procedures (SOP) <br /> included in Attachment 1 <br /> WATER SAMPLING AND ANALYSIS <br /> On April 8, 1993, Aegis personnel collected groundwater samples from the nine wells. <br /> Well DW-1 was resampled on May 27, 1993, to confirm if an anomaly similar to diesel <br /> exists The samples were collected according to the Aegis SOP included in Attachment <br /> 1, and submitted under chain-of-custody to Pace Inc., of Novato, California, a state- <br /> certified analytical laboratory The samples were analyzed for concentrations of- <br /> • total petroleum hydrocarbons (TPH), as gasoline, by modified EPA Method <br /> 8015, <br /> • benzene, toluene, ethylbenzene, and total xylenes by modified EPA Method <br /> 8020, <br /> • TPH, as diesel, by EPA Methods 3510/8015 (MW-1 through MW-4 and <br /> DW-1), and <br /> 90.097F OMR -2 <br />