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7.4 SUBSURFACE INVESTIGATION <br /> To further characterize the extent of gasoline constituents in the southeast corner of the <br /> site, two onsite wells and two offsite well are proposed. Wells MW-17 and MW-18 are <br /> proposed onsite at the locations shown on Figure 3. Wells MW-19 and MW-20 are <br /> proposed offsite, across Pacific Avenue, near well MW-8 (Figure 3). All four of these <br /> wells will be screened in the C-zone,which is approximately 55 to 65 fbg. <br /> A CRA geologist will supervise the drilling and describe encountered soils using the <br /> Unified Soil Classification System and Munsell Soil Color Charts. After clearing the <br /> boring to 5 fbg with an air- or water-knife, soil samples will be collected at 5-foot <br /> intervals to the bottom of each well boring (approximately 65 fbg). Soil samples will be <br /> screened in the field for organic vapors using a photo-ionization detector (PID). CRA <br /> will prepare a boring log for each well boring, and PID measurements will be recorded <br /> on the boring logs. <br /> CRA will perform this work under the supervision of a professional geologist or <br /> engineer. <br /> 7.5 MONITORING WELL INSTALLATION <br /> Wells MW-17 through MW-20 will be screened from approximately 55 to 65 fbg. The <br /> wells will be constructed using 2-inch-diameter Schedule 40 PVC casing, a filter pack <br /> that will be placed from the bottom of the well screen up to 2 feet above the top of the <br /> well screen, followed by a 1-foot-thick bentonite transitional seal, and cement grout to <br /> grade. Actual well construction details will be based on soil types and field conditions <br /> encountered during drilling. The wells will be secured with a locking cap under a <br /> traffic-rated well box. <br /> 7.6 WELL DEVELOPMENT AND SAMPLING <br /> Upon waiting at least 72 hours after well installations,Blaine Tech Services,Inc. (Blaine) <br /> will develop the new groundwater monitoring wells. At least 72 hours after well <br /> development Blaine will sample the new groundwater monitoring wells and have the <br /> samples analyzed for the gasoline constituents mentioned below. <br /> 240854(29) CONESTOGA-ROVERS&ASSOCIATES <br />