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. .. Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, C.4. Page 10 the 72-acre area of concern to the site characterization program that is shown on Figure 2. p was The ma at the time the initial site characterization produced in stages, starting - program was conducted and completed in its present form as part of the extended site ` characterization program. It should be carefully noted, however, that the accuracy of that map should not be considered to comply with normal professional engineering standards. Because it is impossible for one person to conduct a survey of even approximate accuracy, the SJC survey party included a civil engineer supported by one, and for a portion of the time, two field technicians. in addition to the limitations of the surveying methods employed, windy conditions on the site, which were typical of those that often prevail in the Tracy area, considerably reduced the efficiency and accuracy with which the tape survey could be performed, as did the need to run tapes across West Eleventh Street, a busy four-lane highway that could not be closed, thus posing safety concerns for the surveying crew. We also note that the cost of production of Figure 2 has greatly exceeded the cost of SJC's original estimate for a survey prepared by a California- licensed surveyor employing modern surveying technology. To protect our client from these excessive and unrecompensed expenses, SJC completed a large portion of the base line and offset surveying on a pro Bono basis. "} SJC's engineer used an engineer's level to determine the surface elevations at exploratory borings and groundwater-quality monitoring well locations and to compute the casing elevations of the wells. To ensure the accuracy of those elevations and to provide the ability to relate them to regional topographic and hydrogeologic features, the elevations were calculated by running a leveling traverse from San Joaquin County Benchmark No. AA394, located on the west side of Chrisman Road some 1,000 ft. south of its intersection with West Eleventh Street. That Benchmark's elevation is 52.584 ft. MSL. 5.2 Detection of Underground Utilities To provide safe working conditions, before any site characterization work that involved r= digging,gg' g, drilling or probing into the subsurface, the whole of the on-site and off-site area where such work was to be performed was surveyed by the United Services Agency (U.S.A.). That agency marked the locations of gas and water supply pipes, electric lines and other utility infrastructure present beneath the surface. 5.3 Locations of Additional Exploratory Barings and Monitoring Wells r' The principal objectives of this phase of the extended site characterization were to delineate the down-gradient outer limits of the plume of hydrocarbons emanating from the former sites of the underground storage tanks and pump islands on the 7500 West =' Eleventh Street property; to establish the depth to which groundwater has been affected by fuel hydrocarbons in the area close to the former sites of the fueling station's pump f islands, which area was the most severely affected by releases of fuel hydrocarbons to the underground; and to explore further the suspected source of a secondary plume of affected groundwater at the southern boundary of the subject property. i J sic