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"..' <br /> _S <br /> t <br /> BraBrown and Caldwell <br /> Consa�tants <br /> FAX 9'f5i-44-8437 <br /> r <br /> February 24. 1992 FEB 2 7 1997 <br /> E' VIRONIVILNTAL,-rtALJ-•j <br /> PE'RMfTISERVIC,ES <br /> Mr. Chuck Carmel <br /> ARCO Products Company <br /> Post Office Box 5811 <br /> San Mateo, California 94402 0I7-5690-0411 <br /> Subject: 1911 Fourth Quarterly Report for ARCO Station 2133, <br /> 2908 Benjamin Holt Drive, Stockton, California <br /> Dear Mr. Carmel: <br /> This report presents the fourth quarterly water levels and analytic.] results of groundwater <br /> sampling performed at ARCO Products Company (ARCO) Station 2133 located at 2908 <br /> Benjamin Holt Drive in Stockton, California. The work was performed on October Sand 9, <br /> 1991, under Task Order 2133-91-5A. There are fifteen on-site wells: E-2 through E-12, <br /> PR-1, PR-2,BHD-1, and BHD-2 (Figure 1). Although all of the wells were scheduled to be <br /> sampled during this sampling event, eight(E-3,E-4,E-5, E-5, E-7, E-9,PR-2, and BHD-2) <br /> of the fifteen wells were dry or did not recharge enough for sampling after purging. <br /> Therefore,a total of six wells were sampled. The most likely cause of some of the wells rear <br /> the extraction well going dry is the operation of the groundwater extraction system. <br /> Field and Analytical Methods <br /> Brown and Caldwell personnel measured depth-to-water levels, supervised purging of each <br /> well, and collected groundwater samples at the site. Refer to Exhibit A for detailed fie:c; <br /> r f methods description. A copy of the field notes containing the pH,electrical conductivky,and <br /> temperature readings is included as Exhibit B. <br /> All groundwater samples were analyzed for total petroleum hydrocarbons as gasoline(7TH-G) <br /> and benzene, ethylbenzene, toluene, and xylenes (BETX) by Modified U.S. Environmental <br /> Protection Agency Method 801515030/8020. In addition,groundwater from sample wells E-8 <br /> and BHD-1 were analyzed for nitrates by EPA Method 3000. <br /> Results <br /> The groundwater extraction system at this site has been in operation since June 19)]. Since <br /> the start-up,the system has been pumping at a rate of approximately 10.1 ga!lons per minute <br /> (gpm). The groundwater extraction system has influenced the groundwater flow pattem <br /> locally, as shown on Figure I. In September 1991, the pumping rate was reduced to <br /> approximately 5.5 gpm because too large of an area was being influenced when the pumping <br /> rate was 10.1'-- Table I (Exhibit C)presents the water-level data for this site in tabular <br /> form, and Table 2(Exhibit D)presents historical flow direction and gradient data for this site. <br /> 5(9(W LP0RTS4)Cr91 QTR3tPr <br />