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Soil recovered from the core barrel was classified on-site using the Unified Soil Classification System Soil samples were collected by hand driving a 1 25-inch diameter by 6-inch length brass tube into the center of the drill core (2-inches in diameter) Each soil sample was lined with Teflon T11 sheets, capped, and sealed Each sample was labeled, placed in a resealable plastic bag, and stored in an ice-chilled cooler Select soil samples were forwarded to a state certified analytical laboratory for chemical analysis Strict chain-of-custody procedures were followed from the time the samples were collected until the time the samples were relinquished to the laboratory Additional soil from each sampled interval was placed and sealed in plastic bags to allow the accumulation of volatile organic compound (VOC) vapors within the airspace in the bags A portable photo-ionization detector (PID) was used to measure VOC concentrations from each sample in parts per million by volume (ppmv) PID results are included on the boring logs presented in Appendix C Well Installation Stratus retained Woodward Drilling Company of Rio Vista, California (C57 #710079) to drill and install wells MW-16 through MW-20 using a truck mounted drill rig equipped with hollow stem augers Geologic and analytical data obtained from borings B-44 through B-48 were used to guide the screening intervals and locations of the wells installed during this phase of investigation Since each well was installed in close proximity to previously logged borings B-44 through B-48, soil samples were not collected from the well borings Each well was constructed using 4-inch diameter PVC well casing and 0 01-inch diameter factory slotted well screen Well MW-16 was screened from approximately 82 to 102 feet bgs, well MW-17 was screened from approximately 78 to 98 feet bgs, well MW-18 was screened from approximately 85 to 105 feet bgs, well MW-19 was screened from approximately 90 to 105 feet bgs, and well MW-20 was screened from approximately 100 to 115 feet bgs A filter pack of LonestaJm 42112 sand was placed in the annular space around the well, from the bottom of the casing to approximately 3 feet above the top of the well screen Approximately 4 feet of bentonite was placed on top of the filter pack and hydrated with clean water to provide a transition seal for the well The remaining annular space around the well casing was backfilled with neat cement up to surface grade A 12-inch diameter traffic rated vault box was placed over the wells, and a watertight locking cap was placed on the top of the well casing Well details, and Department of Water Resources (DWR) well completion forms, are provided in Appendix C During the installation of monitoring well MW-20, Woodward Drilling Company inadvertently released a string of 7 hollow stem augers (35 feet auger length) into the neat cement surrounding the well MW-20 casing Attempts were not made to recover the augers from the borehole due to the physical constraints of the work area (within the Patterson Pass Road shoulder), the time of day that the augers were dropped (shortly before nightfall), and the possibility of damaging well MW-20 during auger recovery efforts SJCEHD concurrence was obtained prior to leaving the hollow stem augers in the subsurface The depth at which the hollow stem augers became cemented around the well casing is not known On February 23, 2006, Stratus personnel measured the total depth of well MW-20 at approximately 114 2 feet below the top of the well casing Given that the well was constructed to approximately 115 feet bgs and was unobstructed, K\Bp Arco for UR5141001Repor1s16100 assessment rpt&sem update doc Page 5 5MA TU5