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� pp <br /> �G3C <br /> CLEAR"�WATER <br /> G R O U P I N C <br /> int rrnnme, nl Sern,ert <br /> QUARTERLY GROUNDWATER MONITORING REPORT .yS'� <br /> THIRD QUARTER 1997 <br /> Former Conrady Service Station <br /> 1002 North Yosemite Avenue <br /> Stockton, California <br /> November 18, 1997 <br /> BACKGROUND <br /> No aboveground structures are present at the subject location,it is a vacant lot enclosed by a chain-link fence <br /> Records indicate that the subject site was used as a gasoline service station from 1961 to 1978, and that the <br /> underground fuel storage tanks were removed in 1980 <br /> The following subsurface investigations have been conducted at the site <br /> • A limited soil gas survey in 1990 by Evax Technologies,Inc ,the soil gas survey Indicated the possible <br /> presence of petroleum hydrocarbons in the soil <br /> • GeoAudit drilled and sampled six soil borings(up to 36 5 feet deep), laboratory analysis of soil samples <br /> collected by GeoAudit indicated the presence of relatively low levels of ethylbenzene in the soil around the <br /> western edge of the property <br /> • In October 1993, GeoAudit installed and sampled three groundwater monitoring wells(MW-1 through MW-3)at <br /> the request of the San Joaquin County Public Health Services Environmental Health Division(PHS/EHD), the <br /> results of the initial site assessment are presented in GeoAudit's November 1993 Monitoring Well Installation <br /> and Quarterly Report <br /> • At the request of the PHS/EHD,Clearwater installed monitoring wells MW-4 and MW-5 in August 1994 and <br /> installed MW-6 in September 1995 in order to assess the downgradient limits of the hydrocarbon plume <br /> • In September 1995,Clearwater also supervised the drilling of two vapor extraction wells(VW-1 and VW-2), <br /> two air spargmg wells(SW-1 and SW-2)and one 81-foot deep investigative soil boring(CPT-7),a pilot test <br /> was conducted, and the results were presented in Clearwater's Report on Site Assessment Activities, Pilot Test, <br /> and Quarterly Groundwater Monitoring, dated December 15, 1995 <br /> In letters dated August 21, 1996 and March 25, 1997,the PHS/EHD stated that both the soil and groundwater <br /> contamination plumes have been laterally delineated <br /> GROUNDWATER MONITORING FIELD ACTIVITIES <br /> Date of field activities September 19, 1997 <br /> Wells monitored/sampled MW-1 through MW-6 <br /> Analytes tested TPHgasolme, BTEX,and MTBE <br /> Analytical methods EPA Methods 8015/8020(modified) <br /> Laboratory American Environmental Network of Pleasant Hill,CA <br /> Remarks All wells were gauged and purged of at least three well volumes prior to sampling Also, dissolved <br /> oxygen (DO)in the groundwater was measured downwell near the top of screen in each well Prior to purging, the <br /> DO measurements were collected using a field instrument <br />