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<br /> November 18, 1991
<br /> Mr. Chuck Carmel
<br /> ARCO Products Company
<br /> Post Office Box 58I1
<br /> San Mateo, California 94402 017-5690-0-1/1
<br /> Subject: 1991 Third Quarterly Report for ARCO Station 2133,
<br /> 2908 Benjamin Holt Drive,Stockton, California
<br /> Dear Mr. Cannel:
<br /> This report presents the third quarterly water levels and analytical 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 July 15 and 16, 1991
<br /> under Task Order 2133-91-5A. There are fifteen on-site wells: E-2 through H-12,PR-1,PR-2,
<br /> - BHD-1, and BHD-2 (Figam 1). Although all of the wells were scheduled to be sampled during
<br /> this sampling event,six (E-3, E-4, E-5, E-h,E-7, and E-9) of the fifteen wells were dry or did
<br /> not recharge enough for sampling after purging:'Therefore, a total of nine wells were sampled,
<br /> The most likely cause of some of the wells near the extraction well gahtg dry is the operation
<br /> of the groundwater extraction system.
<br /> Field and Analytical Methods
<br /> Brown and Caldwell personnel measured depth-to-water levels,supervised purging of each well,
<br /> and Collected groundwater samples at the site. Refer to Exhibit A for detailed field methods
<br /> description. A copy of the field notes containing the pH,electrical conductivity,and temperature
<br /> readings is included as Exhibit B.
<br /> Ali groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPH•G)
<br /> and benzene, ethylbenzene, toluene, and xylenes (BETX) by Modified U.S. Environmental
<br /> Protection Agency Method 8015/5030.
<br /> Results
<br /> The groundwater extraction system at this site has been in operation since Jure 1991. Since the
<br /> start-up,the system has been pumping at a rate of approximately 10.1 gal]ot;s•per minute QTm).
<br /> The groundwater extraction system has influenced the groundwater flow pattern locally,as shown
<br /> in Figure 1. Table 1 (Exhibit C)presents the water-level data for this site in tabular form, and
<br /> Table 2 (Exhibit D) presents historical flow direction and gradient data for this site. Figure I
<br /> also shows the water-level elevations for each well and the contours of equal water-level
<br /> elevation calculated from the July 15, 1991 data.
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