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41' Brown and Caldwell`' <br /> Consuitants <br /> F4 E Al" <br /> rrr 3 S 5:reet EIVEDK <br /> Sacramento <br /> �.• ,:ter,,a sa,a <br /> 7092 MAY 18 1990 <br /> '�3 1a-1-:ia23 <br /> V Q'� 44-1-84,i7 ENVIRONMENTAL HEALTH <br /> PERMIT/SERVICES <br /> May 14, 1990 <br /> Mr. Kyle Christie <br /> ARCO Products Company <br /> 2000 Alameda de las Pulgas <br /> Post Office Box 5811 <br /> San Mateo, California 94402 017-4986-05/1 <br /> Subject: Quarterly Groundwater Sampling Results, ARCO Station 2093, <br /> Tracy, California % <br /> Lla � <br /> Dear Mr. Christie: <br /> This letter report describes 0and <br /> 89 grou water sampling at ARCO Products <br /> Company (ARCO) Station 2cy Bou vard, Tracy, California. ARCO has <br /> authorized quarterly water leved ndwater sampling for analysis of benzene, <br /> ethylbenzene, toluene, and xylto petroleum hydrocarbons (TPH) in all of the <br /> wells on the site. In addition , 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 December 27 and 28, <br /> 1989, Brown and Caldwell personnel collected groundwater samples from the seven on-site <br /> monitoring wells (ATR-1 through ATR-7). The purpose of the monitoring wells is to <br /> characterize 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 /> December 1989 sampling. <br /> Field Methods <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 /> Groundwater from each well was sampled using a teflon or a disposable polyethylene bailer <br /> equipped with a bottom-emptying valve. For each well, the samples were drained directly from <br /> the bottom valve into four 40-milliliter glass bottles with Teflon-lined septa and inspected to <br /> ensure that no air bubbles remained within the bottles. The samples were stored on ice in a <br />