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s 1 <br /> 'Brown and Caldwed <br /> Consultants 6 <br /> F 723 S Street <br /> Sacramento <br /> California 95814-7092 <br /> (916)444-0123 <br /> FAX(916)444-8437 <br /> October 9, 1990r f <br /> 0ICT 19 1990 <br /> EivViRON,�AENTAL HEALTH <br /> i R' • f� ,1f`r•i�ri <br /> Mr. Kyle Christie <br /> ARCO Products Company <br /> .2000 Alameda de las Pulgas <br /> I Post Office Box 5811 <br /> j San Mateo, California 94402. 017-4986.0511 <br /> 1 <br /> ij <br /> Subject: Quarterly Groundwater Sampling Results, ARCO Station 2093, <br /> Tracy, California <br /> Dear Mr. Christie: i <br /> This letter report:describes th April 1)angroundwater <br /> undwater sampling at ARCO Products Company <br /> (ARCO) Station '2093 at 34 Tracyard, Tracy, California. ARCO has authorized <br /> quarterly water-level measur ents sampling for' analysis of benzene, <br /> ethylbenzene, toluene, and xylen total petroleum hydrocarbons (TPH) in all of the <br /> wells on the site., In addition to these analyses, the California Regional Water Quality Control <br /> Board, Central Valley Region (Regional Board) has requested the groundwater samples be <br /> analyzed for purgeable halocarbons, specifically 1,2-dichloroethane. On April 18, 1990, Brown <br /> ' and Caldwell personnel collected groundwater samples from the seven on-site monitoring wells <br /> (ATR-1 through ATR-7). The purpose of the monitoring wells is to characterize hydrocarbon i <br /> occurrence in groundwater beneath the site. <br /> Figure 1 shows the location of the monitoring wells, benzene concentrations in groundwater <br /> i samples collected from these wells, and the direction of groundwater flow at the time of the April <br /> 1990 sampling. j <br /> Field Methods <br /> I <br /> Prior to sampling the wells, a diaphragm pump (operated by Armour Petroleum Service) was <br /> used to purge approximately three well volumes of water from each well. The pH and specific <br /> conductance of the discharged water were monitored periodically and found to be relatively stable <br /> during the evacuation of water. <br /> i <br /> 9 <br /> I, <br />