ARCHIVED REPORTS XR0002702 - Laserfiche WebLink

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Three monitoring wells and one boring were originally planned to be placed on this site. The constraints for this site, caused by the electrical transmission line running diagonally across the parcel, limited this investigation to the revised placement of three wells. WELL INSTALLATION A review of the topographic setting of the site region suggested that the regional groundwater gradient is toward the west. The location of the wells took into consideration the potential for any down-gradient migration of hydrocarbon contamination, logistical concerns, underground and overhead utilities, and the need to calculate the site specific groundwater gradient. The detailed location of the new wells is shown on Figure 2 . The monitoring wells were installed by West Hazmat Drilling Co. using an eight inch-diameter hollow stem auger. A drilling permit ' was obtained from the San Joaquin County Public Health Agency prior to the drilling. A copy of the permit is included in Appendix A. The wells extended to a depth of approximately 55 feet based on encountering groundwater at a depth of approximately 44 to 46 feet. Soil samples were collected at intervals of 5 feet were observed and logged by the Certified Engineering Geologist. The geologic units encountered in boring 1 are backfill for approximately the upper 20 feet, then underlain by fine-grained deposits consisting primarily of silty clay to clayey sand typical of flood plain deposits. Borings 2 and 3 encountered native deposits at depths of 2 to 3 feet below the ground surface. Water was first encountered at approximately 44 to 46 feet below grade. The boring and well construction log, for each well, is presented in Appendix A. Each well is constructed of 2 inch diameter PVC pipe. The bottom of each well is approximately 55 feet. A threaded end cap was placed on the bottom of the pipe. The 0. 02 inch slotted casing extends from the bottom of the well to a depth of 35 feet with solid pipe above. The sandpack is Lonestar # 3 sand and extends from the base of the well to a depth of approximately 32 feet. A transition seal of approximately 3 feet of bentonite was placed above the sand and the remainder of the annular space was sealed with grout. The top of the well is set in a traffic-rated surface vault. The casing is capped with a vapor-proof locking cap. SOIL ANALYSIS Soil samples collected at each 5 foot level, commencing at approximately 25 feet for MW-1, 20 feet for MW-2 and 11 feet for MW-3, were labeled as MW-1 sample depth, MW-2 sample depth and MW-3 sample depth. The samples were analyzed for TPH (Stoddard) and BTEX. The results are summarized below in Table 1. The certified laboratory report with detection limits is presented in Appendix B. 4