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Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 13 tanks had been removed from the site had indicated the presence of elevated concentrations of petroleum hydrocarbons. 3.5 Grouting of Push-probe Borings In conformance with the requirements of the SJCPHS, shortly after soil sampling and measurement of depth to groundwater in each push-probe boring was completed, it was grouted to the surface using a Portland cementgr out. 3.6 Installation of Groundwater-quality Monitoring Wells On April 26 and April 27, 2000, seven (7) groundwater-quality monitoring wells were installed on the 7500 West Eleventh Street site, at the locations shown on Figure 8. The monitoring well borings were advanced using a drilling rig equipped with an 8-in., open-stem auger. Each well has a total depth of 22 ft. The well casings were 2-in. diameter PVC with 0.02-in., machine cut screen slots. These and other details of the well } construction are shown on the well logs, copies of which are compiled in Appendix A. The uniform 22-ft. depth of each of the seven groundwater-quality monitoring wells was selected based on the presence or absence of visual and olfactory indicators of hydrocarbons in soil samples recovered from the push-probe borings, together with a synthesis of all of the geotechnical and groundwater-quality data obtained from the 1' phases of the site characterization program performed up to that time. That depth was generally sufficient to penetrate through the zone of soil affected by petroleum hydrocarbons without penetrating through the stratum of clays and silty clays that appears to form an arealy-extensive aquitard beneath the site at depths varying between 16 and 25 ft. BGS. 3.6.1 Selection of Location for Groundwater-quality Monitoring Wells Data from observations made at the time the tanks and piping were removed from the subject property and during the drilling of the push-probe borings, together with early analytical data regarding the concentrations of fuel hydrocarbons in groundwater ? !, provided a basis for selecting optimal groundwater-quality monitoring well locations. The selected well locations and the rationale for them are described below. Monitoring well MW-1 was located on the eastern side of the subject property close to i Chrisman Road, some 260 ft. south of the center line of West Eleventh Street to serve as an up-gradient groundwater-quality monitoring well. It is in an area where, based on the preliminary subsurface characterization data available at the time, the subsurface was expected to be free of, or only slightly affected by petroleum hydrocarbons. MW-2, MW-3, and MW-4 were aligned along the West Eleventh Street frontage of the subject property to provide information regarding the distribution of gasoline and diesel in groundwater due to leakages that had occurred in the area where the fueling station's sic