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0 Qwrlerly Groundwater Mon4onng Reporl man <br /> 14800 West Frontage Road Manteca California <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 <br /> April and May 1989, Delta installed MW-3 and MW-4 In November 1989, Delta <br /> conducted soil sampling during the removal of three 10,000-gallon underground fuel <br /> storage tanks Delta installed MW-5 through MW-8 in November and December 1989 <br /> Aegis began a program of monthly monitoring and quarterly sampling of the wells in <br /> January 1991 In November 1991 , Aegis supervised drilling and completion of MW-9 <br /> (Figure 2) The previous consultants' groundwater data, along with Aegis' data, are <br /> included in Table 1 <br /> GROUNDWATER MONITORING <br /> On January 18 1994 Aegis personnel collected measurements of depths to groundwater <br /> from the nine wells Since November 23, 1993, groundwater levels dropped in all wells <br /> . (Figure 3) an average of approximately 1 24 feet, ranging from 0 7 to 1 41 feet (Table 1) <br /> Figure 4 is a potentiometric surface map of the shallow water-bearing zone on <br /> January 18, 1994 On the basis of the above measurements, the groundwater flow <br /> direction is estimated to be generally to the southeast and southwest, at a gradient of <br /> approximately 0 01ft/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 /> Aegis personnel collected groundwater samples from the nine wells The samples were <br /> collected according to the Aegis SOP included in Attachment 1 , and submitted under <br /> chain-of-custody to Pace Inc , of Novato, California, a state-certified analytical laboratory <br /> 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 /> 90 0971 OMR 2 <br />