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BeBrown and Caldwell <br /> Consultants <br /> 723 S Street <br /> %Awl Sacramento <br /> caiNornia 95814-7092 <br /> (916)444-0123 Iftr <br /> ri <br /> FAX(916)444-8437 'E C E IL; <br /> February 26, 1990 ENVIRONMENTAL HEALTH <br /> PERMIT/SERVICES <br /> Mr. Kyle Christie <br /> ARCO Products Company <br /> 2000 Alameda de las Pulgas <br /> Post Office Box 5811 <br /> San Mateo, California 94402 017-3174-05/1 <br /> Subject: Quarterly Groundwater Sampling Results, ARCO Station 2093, <br /> Tracy, California <br /> Dear Mr. Christie: <br /> This letter report describes the September 1989 groundwater sampling at ARCO Products <br /> Company (ARCO) Station 2093 at 3425 Tracy Boulevard, Tracy, California. ARCO has <br /> authorized quarterly water level measurements and groundwater sampling for analysis of benzene, <br /> ethylbenzene, toluene, and xylene (BETX) and total petroleum hydrocarbons (TPH) in all of the <br /> wells on the site. In addition to these analysis, 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 September 18, 1989, <br /> Brown and Caldwell personnel collected groundwater samples from the seven on-site monitoring <br /> wells (ATR-1 through ATR-7). The purpose of the monitoring wells is to characterize <br /> hydrocarbon occurrence in groundwater beneath the site. <br /> Figure 1 shows the location of the monitoring wells, benzene concentrations in groundwater <br /> samples collected from these wells, and the direction of groundwater flow at the time of the <br /> September 1989 sampling. <br /> Field Methods <br /> Prior to sampling the wells,a diaphragm pump (supplied by Armour Petroleum Service) was used <br /> 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. Table 1 presents the pH and specific conductance measurements <br /> taken in the field. <br /> Groundwater from each well was sampled using a teflon or a disposable polyethylene bailer <br /> equipped with a bottom-emptying valve. The sample was drained directly from the bottom valve <br /> into four 40-milliliter glass bottles with Teflon-lined septa. The samples were stored on ice in <br />