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1 � <br /> 1 Groundwater elevation measurements from the monitoring wells indicate the magnitude of the <br /> Horizontal hydraulic gradient at the site to be very low (i e, less than approximately 0 0001 feet per <br /> feet),with an apparent direction toward the south and southwest <br /> ' Petroleum analytes or constituents generally are not detected in groundwater samples collected from <br /> monitoringwells located less than 100 feet down adient of the affected soil -5 and MW-6 <br /> I r a' (MW ) <br /> ' I Therefore, the detections of TPHd in monitoring well MW-2, which is screened across petroleum <br /> affected soil, likely represents either petroleum entrained on soil particulates in groundwater(turbidity) <br /> 1 l or globules of petroleum collected with the groundwater sample and are not representative of dissolved <br /> l phase petroleum The TPH concentrations in MW-3 and MW4 represent conditions at the <br /> rsoil/groundwater interface <br /> 1 l Shallow groundwater within and downgradient of the petroleum affected soil is not currently used and <br /> is not anticipated to be used in the near future A well survey was conducted by ATC in 2000 that <br /> ' L searched Department of Water Resources (DWR) files, performed a site and vicinity reconnaissance, <br /> 1 and contacted the City of Stockton and California Water Service for wells within 2000 feet of the site <br /> i vicinity (ATC 2000) According to ATC, the nearest well is located approximately 400 feet southeast <br /> 1 of the site and is a monitoring well The nearest well potentially used for drinking water is a domestic <br /> well located approximately 1,300 feet to the south of the site In addition, San Joaquin County <br /> Department of Public Health Services ordinances require a minimum of 50-foot sanitary seal at the top <br /> 1 k of any public water supply well These sanitary seal requirements would preclude shallow affected <br /> E water at the site from future use as a source of-municipal water The nearest surface water is the <br /> N Stockton deepwater channel, located approximately 650 feet north of the site <br /> The following is a summary of findings from the October 2004 CAP <br /> 1 r 1 The lateral extent of reported petroleum-related detections in groundwater is limited to the <br /> L vicinity of the petroleum-impacted area and the volume is small <br /> 2 No dissolved "plume" of petroleum affected groundwater associated with this petroleum- <br /> impacted area is present —h m m M <br /> 3 it is highly unlikely that flus localized area of petroleum affected shallow groundwater will <br /> 1 i r migrate beyond its current limited spatial extent given that the release occurred at least 16 years <br /> l ago <br /> 4 Shallow groundwater is not and likely will not be used directly as a source of drinking water <br /> 1 5 Environmental impacts (e g ,to groundwater supply wells or surface water bodies) outside the <br /> I immediate area of the former UST location are not likely to occur under current conditions <br /> 1 L <br /> 35 Human Health Risks <br /> The October 2004 CAP identified the environmental screening levels (Eels) applicable to the petroleum <br /> 1 constituents detected at the Stockton Elevator Table 5 compares the maximum concentrations of <br /> petroleum constituents detected in vadose zone soil to environmental screening levels (ESLs) The <br /> L comparison below is of soil site conditions to $SLS for deep soils (>3m bgs)where groundwater is not <br /> a current or potential source of drinking water as applied to the Residential Land use screening levels <br /> L 14 <br /> R 1C0NTGRAMStockton\CAP\CAP ADDENDUM <br /> 1 � <br />