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U, c j O/A www.atcassociates.com r' farm operations and was described as being a source of water for a labor camp. This well is-up-.- , L g � ti and Y � Y Y plume. � - gradient of the.Site and is not like) to be affected b a hydrocarbon Historic data collected at the Site suggest that the localized contaminant plumes are defined Lwithin the vicinity of the release source (i.e. UST system). On-site upper aquifer(19-23 feet bgs) monitor wells and on-site lower aquifer monitor wells (25-32 feet bgs) suggest the dissolved-phase contaminants (TPHg and MTBE) are confined to the shallow water bearing unit (approximately 10 feet bgs) and further defined to non-detectable laboratory levels. 7.0 CONCLUSIONS L • Based on the analytical results, plume stability, historic contaminant plume distribution and field observations, the lateral and vertical extent of TPHg and MTBE-impacted soil and groundwater are defined. Vertical on-site delineation in soil and groundwater of TPHg and MTBE to non-detectable levels has been completed. Lateral off-site delineation of TPHg and MTBE in groundwater to non-detectable levels has been completed. • Remaining low concentrations of dissolved contaminants will continue to degrade until cleanup goals are achieved. • Dissolved contaminants at the Site are localized and exhibit either a stable or decreasing ` statistical trend. • Data collected to date indicate the Site does not appear to represent a significant risk to human health and the environment based on current RWQCB criteria. The potable Ldrinking water source is provided by the Stockton East Water District derived from The Calaveras River System (New Hogan Reservoir) and Stanislaus River System (New Melones Reservoir). _ L • Recent investigation to address data gaps identified by the SJCDEH reported de minimis concentrations of TPHg, benzene and MTBE in soil and groundwater indicating that the + contaminant plumes continue to shrink and reported concentrations continue to decrease. L 8.0 RECOMMENDATIONS L'' Based on available data collected from previous subsurface investigations and groundwater monitoring activities, it is ATC's professional opinion that natural attenuation is occurring at the L Site and that dissolved contaminant concentrations will continue to decline until cleanup goals are achieved. Therefore, the site should be granted no further action required status. L L Quik Stop Market No. 132 July 21, 2011 ATC Project Number 75.62503.3206 Page 5 of 5