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�y First Quarter 2003 Groundwater Monitoring Report Eckert Cold Storage,Manteca,California April 23,2003 Page 2 • FIELD OBSERVATIONS No separate phase petroleum was noted in the wells, but a moderate petroleum odor was noted in groundwater recovered from MW-8.Field observation sheets are included in Attachment B. GROUNDWATER ELEVATIONS The average groundwater elevation was approximately 0.57 feet higher on March 28, 2003, than the previous sampling event conducted on December 9, 2002. The groundwater elevation contours (Figure 3, Attachment A) estimated from the depth to water measurements indicate the groundwater gradient was generally towards the northwest on March 28, 2003. Historical groundwater data collected by WHF, Inc. (previous consultant) indicates a highly variable gradient at the site. Review by Condor of historical groundwater gradient information provided by WHF indicates there are potential inconsistencies in the data and possibly components of the interpretation of those data, especially related to MW-5 measurements. However, Condor agrees that the general historical groundwater gradient is predominantly towards the northwest at the site. The highly variable gradient at the site may be related to domestic/supply well pumping both on site and off site. At times in the past, the water table slope has been very flat (very gentle groundwater gradient). When this occurs, any slight variability in groundwater measurements and the tolerance for error for the water level measurement devices can result in apparent groundwater elevation contours that are not particularly coherent. Therefore, when the water table at the site is relatively flat, it may be more representative to depict the groundwater gradient with a three-point construction using groundwater elevation data from three site monitor wells that circumscribe the site, allowing triangulation of the contaminant plume, including the contaminant source area. Consistent with this, Figure 4, Attachment A, shows the groundwater gradient • direction and magnitude using monitor wells MW-4, MW-6, and MW-7. On March 28, 2003 the groundwater gradient was 0.0013 ft./ft. towards the north, as shown. Groundwater elevation data for March 28,2003 are presented in Table 1, below_ Table t —Groundwater Elevation Data(March 28,2003) Monitoring Screened Interval(bgs) TOC Elevation Depth To Water Groundwater Well Elevation. MW-1 13 -28 38.09 17.86 20.23 MW-2 15-30 37.90 17.65 20.25 MW-3 15-30 38.31 18.08 20.23 MW-4 12-27 37.84 17.78 20.06 MW-5 14-34 41.22 20.98 20.24 MW-6 13-33 37.65 17.38 20.27 MW-7 1 13—33 38.22 17.95 20.27 MW-8 1 17-37___ 37.76 17.63 20.13 'TOC Elevation: Elevations are measured from the top of the well casing and are referenced to NGS Benchmark HS4486,elevation 35.03 feet using NAVD 88 datum. All measurements are in feet. LABORATORY ANALYTICAL RESULTS The groundwater samples collected from monitor wells MW-4, MW-8, and domestic well DW-1 were analyzed for BTEX, TPH-G, and selected gasoline oxygenates/additives including MTBE by "Argon Laboratories of Ceres, California. MW-2 was not sampled as damage to the well casing during installation of the well prevents placement of bailers and pumps down the well. In a letter dated March 7, 2003, Condor proposed that the groundwater monitoring program be reduced to include quarterly sampling of MW-4, MW-8, and the domestic well; annual sampling of MW-5 and MW-7; and no further � 3 CONDOR