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- Stockton community water supplies were also surveyed as part of defining the physicalsical char- actenstics T- of the site Recent conversations with City representatives disclosed that Stockton receives its drinking water supply from the surface water of New Hogan Reservoir and groundwater at various locations throughout the City and San Joaquin County Based on a list of active water supply wells provided by California Water Services, there are three addi- tional groundwater-supply wells located between a 1/2- to 1-mile radius of the site These wells are located at Ellis Street East, Commerce and Wyandotte, and East Poplar between San Joaquin and Hunter 2.2 Impact Composition, Distribution, and Residual Levels 2.2.1 Impact Composition Soil and groundwater chemistry data for samples collected from the site suggest impact consists of compounds found in gasoline Laboratory analysis have identified total petroleum hydrocarbons calculated as gasoline (TPH g), benzene, toluene, ethylbenzene, and xylenes (BTEX compounds) This information is consistent with the fact that the site was used as a service station Physical and chemical characteristics for the target compounds, BTEX, are presented in Table 1 It is probable that several years of soil vapor extraction (SVE) has skewed the residual hydrocarbon composition so that it now resembles a mixture of relatively high molecular weight compounds 2.2.2 Primary Source Data regarding the primary source of the petroleum hydrocarbon residuals in soil and groundwater are extensive, but there is no specific release information It is assumed that past practices with respect to petroleum hydrocarbon fuel storage and distribution are responsible to some degree Available data (groundwater monitoring and site soil chemistry) indicate that the primary sources of petroleum hydrocarbons were the former gasoline USTs (northeastern portion), and the southern end of the product island located northeast of the former gasoline USTs (Figure 3) These site improvements were removed in 1988, consequently, all primary sources have been removed from the site 2.2.3 Secondary Source Distribution and Residual Levels The secondary sources of petroleum hydrocarbon residuals were identified as (1) soils impacted with petroleum hydrocarbons, and (2) groundwater containing dissolved petroleum hydrocarbons The current concentration and physical extent of these residuals has been significantly reduced by the application of approximately 2 years of SVE which has been performed at the site The operation of the former SVE system was terminated when the • 3201337B/1918REV 3 August 31, 1995