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kA KLEINFELDER 6 CONCLUSIONS AND RECOMMENDATIONS u The following conclusions and recommendations summarize Kleinfelder's findings. For additional details refer to the body of this report and Discussion of Findings in Section 5.- 6.1 CONCLUSIONS ` 1. Based on surveyed elevations of the four monitoring wells at the site and two depth to groundwater surveys, Kleinfelder evaluated depth to groundwater, groundwater flow direction and gradient. Based on a survey conducted on October 29, 2003 and December 18, 2003 groundwater was found to be approximately 55 to 60 feet bgs. Groundwater flow direction was calculated to the southwest at a gradient ranging from 0.010 to 0.012 ft./ft. 2. Based on the groundwater elevation data, the subject site appears to be down-gradient of the northern offsite property (Former Shell Station) and partially downgradient to cross- gradient from the trucking operation located east of the site. The CalTrans maintenance yard located south of the site appears to be down-gradient from the subject site. 3. Based on the analytical results presented in this report, no requested petroleum constituents or volatile organic compounds were detected from three groundwater samples, two collected from perimeter monitoring wells MW-1 and MW-3 and one from monitoring well MW-2 (located in proximity to the former onsite UST area). A groundwater sample collected from perimeter monitoring well MW-4 was reported to contain TPH-G and three oxygenates TBA, MTBE and TAME. MTBE was detected at 790 µg/1 which exceeds State Primary and Secondary Maximum Contamination Limits for Drinking Water Standards of 13 and 5 µg/l, respectively. Since MW-4 appears to be immediately downgradient of the adjacent former Shell station (northern property boumdary), it appears that the current and or past operation of the adjacent gas station are impacting groundwater beneath the northern portion of the site, and has the potential to { impact soils on site. 4. Because no requested petroleum constituents or oxygenates were detected in groundwater samples collected from monitoring well MW-2 ( located in proximity to the former onsite UST area) or from MW-1 (situated downgradient of the former UST location), it does not appear that the former onsite UST operations have impacted groundwater beneath the former UST area. 5. TPH-D and/or TPH-MO were detected in two 4-point composite soil samples and three discrete soil samples in the washdown area. TPH-D concentrations ranged from 4.2 to 16 mg/kg. TPH-MO ranged from 4.0 to 52 mg/kg. Arsenic and Mercury were also detected in soil in this area which exceeded Residential PRG goals. However it is Kleinfelder's i i 36274/ST03RI919 Page 16 of 19 �c)2004 Kleinfelder,Inc. January 5,2004 I