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1 <br /> A S S O C I A T E S I M C <br /> construction logs were found for wells 22 and 23 <br /> Based on June 25, 1999 on-site water measurements, the underlying groundwater gradient <br /> direction is to the southeast The San Joaquin County Flood Control and Water Conservation <br /> District's Spring 1997 Groundwater Report indicates the inferred regional groundwater gradient <br />' is to the northeast Based on the distance from the site, it is possible that the on-site groundwater <br /> well (Well No 9) and the adjacent downgradient wells (Well Nos 3, 11, 22, and 23) may <br /> potentially be threatened should groundwater concentrations exceed California Primary <br /> 1 Maximum Contaminant Levels (MCLS) for drinking water However, no petroleum hydrocarbon <br /> constituents tested currently exceed established MCLs <br />' An on-site search for surface waters indicated there were no streams, ponds, or canals within <br /> 2,000 feet of the site <br />' It should be noted that pump test data for the on-site and adjacent wells was not available for <br /> review during the well survey <br /> 1 7.0 (DISCUSSION <br /> Based on the analytical results and field observations, soil and groundwater beneath the location <br /> of the former USTs are currently impacted by petroleum hydrocarbon constituents The <br /> impacted soil appears to be generally limited to the upper 50 feet of the soil column Laterally, <br /> 1 impacted soil appears limited to an area within approximately ten feet from the former UST <br /> excavation (as exhibited by MW1 data) <br />' Initial groundwater analytical data suggest petroleum hydrocarbons do not exceed current <br /> California Primary MCLs for drinking water <br />' No benzene or MTBE was detected in any of the soil or groundwater samples collected and <br /> analyzed during the June 1999 investigation <br />' ATC reviewed Department of Water Resources (DWR) groundwater well construction logs, San <br /> Joaquin County well installation permits, and conducted a site walk in the vicinity of the site to <br /> identify any groundwater wells located within a 2,000-foot radius of the site Based on the <br />' distance from the site, it is possible that the on-site domestic well and four adjacent <br /> downgradient wells may potentially be threatened should groundwater concentrations exceed <br /> California Primary Maximum Contaminant Levels (MCLs) for drinking water However, no <br />' petroleum hydrocarbon constituents tested thus far exceed established MCLs <br /> In the judgment of ATC, additional groundwater monitoring appears appropriate to confirm the <br /> stability of current dissolved hydrocarbon concentrations in groundwater <br />' w\I 48851reports\Supp1 Invest doc 7 <br />