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Ms. Julie Raining <br /> February 4, 1992 <br /> Page 2 <br /> adjacent to the stormwater basin, were dry or contained insufficient water for sampling when <br /> visited on January 8 and 9, 1992. In addition, the recovery Well, RW2, and the air stripper <br /> system were not operating on either day. The system is down for repair of the blower and <br /> discharge booster pump motors. <br /> Samples were collected from monitoring Well BC7, located immediately adjacent to the <br /> stormwater basin; Wells BC10 and BC11, located across the irrigation ditch to the north of <br /> the basin; plus monitoring Wells BC12, BC13, BC14, BC15, and BC16, located in the <br /> subdivision north of and downgradient from the basin. The locations of the monitoring wells <br /> in relation to the stormwater basin and Recovery Well RW2 are shown on the site map <br /> presented in Attachment B. The eight samples collected in January 1992 were submitted to <br /> BC Analytical's state-certified laboratory in Emeryville, California, for determination of <br /> chloroform concentration using Environmental Protection Agency Test Method 601. <br /> The January 1992 chloroform concentrations declined at five of the monitoring locations <br /> from the values reported previously and increased slightly at three monitoring locations. <br /> Chloroform concentrations declined at monitoring Wells BC10, BC12, BC13, BC15, and <br /> BC16, since the previous sampling visit, which ranged from two to six months depending <br /> on the well location as shown on the data summary table in Attachment A. Chloroform <br /> concentrations increased slightly at monitoring Wells BC7, BC11, and BC14. The increased <br /> concentrations reported for Wells BC7 and BC 11, may be due to the air stripper having been <br /> down for repair during the month preceding the January 1992 sampling visit. All of the <br /> reported concentrations were well below the drinking water standard for chloroform except <br /> for the sample from well BC11, which had a reported concentration equal to the limit of 100 <br /> micrograms per liter. <br /> Water table elevation contours and the direction of flow for the shallow groundwater, based <br /> upon water level measurements made on January 8 and 9, 1992, are illustrated on the <br /> groundwater elevation contour map included in Attachment B. In addition to the monitoring <br /> wells sampled in January 1992, water level measurements was also made at monitoring <br /> Wells BC9 and BC17. Well BC9 is located downgradient across the irrigation ditch north <br /> of the stormwater basin and Well BC17 is located in the subdivision north of the basin. <br /> The general direction of groundwater flow remains northwesterly, at an average gradient of <br /> about 0.0015 feet per foot (ft/ft). The January 1992 gradient is slightly steeper than the <br /> 0.0014 ft/ft gradient observed at the site in December 1991, but is consistent with the range <br /> of groundwater gradients observed at the site over the last year. Water levels measured in <br /> monitoring wells associated with this project declined about 0.29 to 0.35 feet between <br /> December 1991 and January 1992. Despite the absence of drawdown associated with <br /> groundwater extraction during the past month, water levels in monitoring wells remain at <br /> Brown and Caldwell <br />