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Site Characterization and Soil rtentediation Plan: 7500 west Eleventh Street, Tracv, ('A. Page 14 hydrogeology of the area, the groundwater flow direction of which is to the north beneath the 7500 West Eleventh Street site. ❑ It is proposed to locate monitoring wells MW-2, AfW=S;- MW-6 and S-a short distance beyond the east and west perimeters of the plume of hydrocarbons to confirm its lateral extent and to serve a sentries in the event that the plume expands in those directions ❑ MW-7 is intended to check for the presence of analytes of �. concern in groundwater directly north and across West Eleventh Street from the former filling station. It will also provide a monitoring location on, or in advance of, the central axis of the plume. Analysis of samples from that well will also permit an evaluation of the rate of reduction of concentrations of analytes of concern with distance from the sources of fuel leakage. ❑ Monitoring wells MW-3 and MW-4 will be located at the ! down-gradient edge of the former sites of the underground tanks in the area where the concentration of analytes of concern in soil and groundwater are expected to' be the CFreatest Those two wells will be used to monitor concentrations of analytes of concern in groundwater and the change in those concentrations over time. :i The depths of the eight monitoring wells will be guided by the presence or absence of visual and olfactory indicators of the presence of hydrocarbons in F soil samples recovered from the well borings as they are drilled, together with a synthesis of the data obtained from the soil probe and hydro-punch phase of the site characterization program. Specifically, the depth of each well will be designed to penetrate at least 10 feet below the deepest point at which soil is affected by hydrocarbons For planning purposes, it has been assumed that each well will be a minimum of 20 feet in total depth. Permits for proposed wells will be obtained from the SJCPHS The monitoring well borings will be advanced using an 8-in., open-stem auger drilling rig '! operated by a drilling contractor holding a C57 license issued by the California Contractors State License Board. A California-licensed geotechnical engineer will log the borings- The well casings will be of 2-in- diameter PVC with 0.02- in., machine cut screen slots. These and other details of the well construction are shown on Figure 11. While the borings for the proposed monitoring wells are being drilled, the '• drilling equipment will be used to recover soil samples in clean brass tubes sic I� �