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Site Characterization and Soil Remediation Plan: 7500 West Eleventh Street, Tracy, CA. Page 9 compounds, MTBE and total lead. Following a request from the SJCPHS, six additional samples were recovered from that same stockpile at the locations shown on Figure 9. These samples were analyzed for TPH(d), TPH(g), the BTEX compounds, fuel oxygenates and total lead. The results of those analyses are summarized in Table 4. All eight samples contained diesel at concentrations varying between 73 mg/Kg and 1,900 mg/Kg Gasoline was detected only in the first two samples recovered from Stockpile No_ 2. Sample SP2-1 contained 320 mg/Kg of gasoline-, SP2-2 contained 560 mg/Kg of that analyte. The concentrations of the BTEX compounds in the eight samples were either undetectable or very low. MTBE was detected in only two of the samples, at concentrations of 0.56 J mg/Kg and 4.5 mg/Kg.1.1 F-J PROPOSED SITE CHARACTERIZATION PROGRAM It is proposed to base the strategy for site characterization at the subject 3 property on the observational method developed by geotechnical engineers for similar investigations (Peck 1969), which has more recently been advocated by the U.S-EPA (U S.EPA 1997). Initially, information regarding the ' geochemistry and hydrostratigraphy of the site will be progressively developed using cost-effective soil probe and hydro-punch technology. Those techniques will be used to evaluate the degree to which soil and groundwater are affected at various locations at and in the vicinity of the former filling station As data is obtained from each exploratory location, it will be continuously evaluated and used by the California-licensed professional engineer in responsible charge of the work (the engineer), together with a synthesis of previously obtained information, to guide the selection of locations for additional exploration points. Finally, the database developed in this manner will be used to select optimal locations for groundwater-quality monitoring wells that will serve to evaluate accurately the lateral and vertical limits of the subsurface zone affected by hydrocarbons and to permit observation of changes of concentrations of analytes of concern in groundwater with time. Specific program elements are discussed below. Topographical Survey The first element of the site characterization program will be completion of a topographical survey of the subject property and adjacent areas. An accurate site plan prepared from that survey will serve as a base for graphical interpretation and presentation of the results of the site characterization program ' sic