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May - 13 . 2004 2 :06PM Neil 0• Anderson & Assoc. No-5095 P. 3 ,— ! THIRD QUARTER,2003 GROUNDWATER MONITORING REPORT ,1A114AR OIL DISTRIBUTION NOVEMBER 2003 Groundwater Analysis Groundwater samples were analyzed for TPH G and TPH D by EPA Method 8015M and for BTEX, 1,2-DCA, EDB, and the fuel oxygenates (MTBE, TBA, DIPE, ETBE, and TAME) using EPA Method 8260B. The analyses were conducted by SunStar Laboratories Inc., a California State-certified laboratory, in accordance with state guidelines and EPA protocol. SITE EVALUATION Groundwater Flow and Gradient Based on depth to groundwater measurements taken on September 11, 2003, the depths to groundwater ranged from 6532 feet bgs in monitoring well MW-1 io 65.93 feet bgs in MW- 7A. The relative groundwater elevations ranged from 36.95 feet below mean sea level (MSL) in MW-5 to 37.20 feet below MSL in MW-7A. All groundwater elevations were measured to the nearest 0.01-foot relative to the surveyed top of casing elevation. The elevations are based on the surveys conducted by JPCA on August 30, 2000 and GI-11I on May 29, 2003). The surveys were completed by setting the comer of the cement sidewalk on the southeastern comer of the store as the benchmark with an assumed elevation of 30 feet MSL. Monitoring wells MW-613 and MW-7B were drilled to 95 feet bgs and have only 5 feet of screen. For these reasons, MW-6B and MW-713 are not being used to calculate hydraulic gradient or flow direction. Bas e other eight wells, the direction of groundwater flow has been calculated to be trendin outheast ith a relatively flat hydraulic gradient of approximately 0.0006-feet/foot across theeet-site. Calculated groundwater elevations are summarized in Table 1, and shown on Figure 4. Groundwater Analytical Results Al] ten wells are included in this discussion of sampling results. TPH G was detected in the samples from all of the monitoring wells except MW-5, MW-613, MW-7A and MW-7B. Where detected, TPH G ranged from 240µg/1 in the sample from MW-6A to 53,000µgll in the sample from EW-1. Benzene was detected in the samples from all of the wells except MW-5, MW-6A, MW-611, MW-7A and MW-713 at concentrations ranging from 360µg/1 in MW-2 to 34,000µg/I in MW-1. r Toluene was detected in the samples from all of the wells except MW-5, MW-6A, MW-6B, MW-7A and MW-7B at concentrations ranging from 30µg/1 in MW-3 to 20,000µgl1 in EW-1. Ethylbenzene was detected in the samples from all of the wells except MW-5, MW-6A, MW-6B, MW-7A and MW-713 at concentrations ranging from 8.7µg/l in MW-4 to 3,400µg/I in EW-1. 5 r