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1 1 <br /> BROWN AND CALDWELL <br /> CONSULTING ENGINEERS \ �° <br /> ,1 ✓ 1 `"' <br /> August 28, 1989 "Y 1989 <br /> SEP � <br /> Ms. Laurie Cotulla, R.S. s y124��11� <br /> Environmental Health Division <br /> San Joaquin Local Health District <br /> 1601 East Hazelton Avenue <br /> Stockton, California 95201 017-3174-0511 <br /> Subject: Quarterly Groundwater Sampling Results, ARCO <br /> Station 2093, Tracy, California <br /> Dear Ms. Cotulla: <br /> This letter report describes the June 1989 groundwater sampling at ARCO Products Company <br /> (ARCO) Station 2093 at 3425 Tracy Boulevard, Tracy, California. ARCO has authorized <br /> quarterly water level measurements and groundwater sampling for analysis of benzene, <br /> ethylbenzene, toluene, and xylene (BETX) and total petroleum hydrocarbons (TPH). On June <br /> 21, and 29, 1989, Brown and Caldwell personnel collected groundwater samples from the <br /> seven on-site monitoring wells (ATR-1 through ATR-7). The purpose of the monitoring wells <br /> is to 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 /> June 1989 sampling. <br /> Field Methods <br /> Prior to sampling the wells, a centrifugal pump was used to purge approximately three well <br /> volumes of water from each well. The pH and specific conductance of the discharged water <br /> were monitored periodically and found to be relatively stable during the evacuation of water. <br /> Groundwater from each well was sampled using a teflon bailer equipped with a bottom- <br /> emptying valve. The sample was drained directly from the bottom valve into four 40- <br /> milliliter glass bottles with Teflon-lined septa. The samples were stored on ice in a closed <br /> ice chest from the time of collection through delivery to the laboratory. All purging and <br /> sampling equipment was washed with laboratory-grade detergent and tap water then rinsed with <br /> deionized water before each use. All groundwater generated during the purging and sampling <br /> process was temporarily stored on site in labeled drums pending laboratory results. ARCO <br /> will be responsible for the disposal of the groundwater stored on site. <br /> 723 S STREET SACRAMENTO,CALIFORNIA 958147092•(916)444-0123 <br />