ARCHIVED REPORTS XR0011743 - Laserfiche WebLink

Home Browse Search

Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, CA, Page 7 �} 4.0 INITIAL SITE CHARACTERIZATION PROGRAM 1 As was noted in Section 2.0, an initial phase of site characterization was conducted at the .` 7500 West Eleventh Street property in May 2000. The scope of that program included preparation of a site plan, a preliminary search for groundwater supply and agricultural wells in the area around the site, drilling 14 exploratory borings from which samples of `r soil and groundwater were recovered and analyzed for components of fuel hydrocarbons and installation of seven groundwater quality monitoring wells from which soil and r:3 groundwater samples were also recovered and analyzed. The borings drilled during the initial site characterization program were numbered PP-1 9 through PP-14 and the groundwater quality monitoring wells installed at that time were numbered MW-1 through MW-7. Their locations are shown on Figure 2. The logs of each well and boring are compiled in Appendix A. The results of analyses of samples of soil recovered from the wells and borings are presented in Table 3; the results of analyses of samples of groundwater recovered from the borings at the time they were drilled and the results of analyses of groundwater samples recovered from the wells during the several rounds of groundwater sampling that have been conducted since the time of their installation are presented in Table 4. =- The results of the initial site characterization were compiled in an engineering report that :,A was submitted to the SJCEHD (The San Joaquin Company 2001g). Synthesis and interpretation of the data revealed that surficial soils over a wide area of the 7500 West Eleventh Street site and the surrounding public rights of way and properties were affected by low concentrations of aged petroleum hydrocarbons that can be attributed to widely distributed drips and spills that have built up over the 80-year history of the site and adjacent areas and to bituminous macadam contained within shallow fill material. The affected areas are shown on Figure 12, but it should be noted that the concentrations of petroleum hydrocarbons in the shallow soils in those areas are of less than de minimus concern. The initial site characterization identified a primary plume of affected groundwater F=' migrating down gradient from the 7500 West Eleventh Street site. The primary source of =� this plume is the area where the pump islands of the now defunct fueling station were formerly located (see Figure 2 for location). The lateral extent of the plume was well defined to the south and west of its source but, in the easterly direction, its areal extent was only loosely defined'and, although it clearly extended northward from the property at 7500 West Eleventh Street to at least the north side of West Eleventh Street, the total extent of its migration in that direction was unknown because SJC had not been permitted E:J to implement subsurface exploration in those areas. A secondary plume of affected groundwater, originating in a small area just to the east of the Service Bay located at the rear of the Casa Mendoza restaurant was also identified. The areas where groundwater is affected by the plumes of fuel hydrocarbons are shown on Figure 13. The plume limits shown on Figure 13 were developed from a synthesis of all of the hydrogeological and geochemical data that had been accumulated by the time sic =i