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2.2 Well Construction and Development Ground water was first encountered during drilling of AW-9 at approximately 12.5 fbg, and stabilized at 10.10 fbg, as measured on April 24, 1992. AW-9 was installed to a depth of 28.5 fbg using 6-inch-diameter, flush-threaded, Schedule 40, PVC blank casing, and 0.010-inch, slotted PVC casing. Based on initial water depth encountered and results of previous investigations, the slotted casing was installed from 8.5 fbg to the total depth of the boring and completed with blank casing from 0.5 to 8.5 fbg to provide adequate annular space for grout materials. Monitoring well installation procedures and construction details are included in the boring logs (Appendix E). During installation, AW-9 was surged prior to sealing the well to: (1) reduce possible smeared sediment on the sidewall of the boring; (2) compact annular filter-pack sand to enhance filter-pack utility; (3)restore the natural hydraulic conductivity of the formation; and (4) remove foreign sediment to ensure turbid-free ground water samples. The monitoring well was developed on April 7, 1992, by removing 10 casing volumes of ground water. General field procedures for monitoring well development and field survey forms are presented in Appendix F. 2.3 Well Survevins, Fluid-Level Monitoring, and Ground Water Sampling The top of casing elevations for Monitoring Wells AW-1 through AW-4 were originally surveyed on October 22, 1990, by Associated Professions. After installation of ground water Monitoring Wells AW-5 through AW-8, all wells were surveyed on May 7, 1991, by Land Improvement Services. AW-9 was tied into the May 7, 1991 survey on April 9, 1992; subsequently an elevation error in the May 7, 1991 survey was noted and all wells were resurveyed on May 7, 1992. Surveying activities were performed by California-registered surveyors. Elevations used in the surveys were in reference to a local benchmark with an elevation of 31.50 feet msl (NGVD-1929); a railroad spike set in an island on the approximate centerline of East Grantline Road, 19.5 feet west of the centerline of the railroad spur tracks. Prior to ground water sampling on April 7 and 24, 1992, the depth to fluid in each well was measured to one-hundredth of a foot from a surveyed, permanent mark on the top of casing of each well casing. Survey data and fluid-level measurements are presented in Table 1. Ground water elevations and elevation contours estimated from the April 24 monitoring data are shown in Figure 3. General field procedures for monitoring and sampling are included with the field survey forms in Appendix F. As part of this supplemental site investigation, ground water samples were collected from all monitoring wells on April 7, 1992. Confirmation sampling was conducted on April 24, 1992. Due to the cold storage breakage of a Miter amber sample container collected from AW-9, two additional liters were collected on April 27, 1992, to ensure sufficient sample volume. 3