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URS • Ms Lon Duncan Page 3 San Joaquin County Environmental Health Department February 4, 2003 Drilling and Monitoring Well Installation On November 4,2002,Cruz Brothers Utility Locators of Scotts Valley, California, completed four potholes using an air knife digger on the northern side of Channel Street, near the intersection of Channel and El Dorado Streets Utility pipes were encountered in the first three potholes at approximately 3 feet below ground surface(bgs) The fourth pothole was completed between two abandoned utility lines to a depth of 5 feet bgs A soil boring was later attempted at this location and encountered an abandoned sewer line at a depth of 6 feet bgs Because of the high density of utility lines beneath the street and the sidewalk, and an active construction site located on the opposite side of El Dorado Street, no other potential well locations were identified in this area Therefore, a well could not be installed at this location See Figure 2 for the locations of utilities in the attempted drilling location Three potholes were then completed at the second proposed well location on the sidewalk west of El Dorado Street An unmarked utility pipe was discovered in the first pothole,an irrigation pipe was encountered in the second pothole, and the third pothole was cleared to 5 feet bgs On November 5, 2002, Gregg Drilling and Testing of Martinez, California, drilled and installed a dual- completion groundwater monitoring well (MW-1 IM/D) on the sidewalk west of El Dorado Street(Figure 2) The boring was drilled using a limited access, track-mounted, hollow stein auger(HSA)drill rig with I-inch-outside-diameter(OD) augers to accommodate the installation of a nested pair of 2-mch diameter groundwater monitoring wells The total depth of the boring was 56 5 feet bgs First groundwater was encountered at 20 feet bgs Dual-completion monitoring well MW-11M/D was constructed using 2-inch-internal diameter(ID), schedule 40,flush-threaded polyvinyl chloride(PVC)well casing Five feet of 0 020-inch machine-slotted well screen was set in the deeper water bearing zone from 48 to 53 feet bgs A Monterey No 3 silica sand filter pack was installed from the bottom of the boring to 2 feet above the well screen A 10-foot bentonite seal was placed above the sand pack to separate the two filter packs A second 20-foot well screen was installed from approximately 13 to 33 feet bgs The upper sand pack was placed from 11 5 to 35 feet bgs A 3-foot bentonite seal was placed above the upper sand pack, and neat cement was used to seal the remaining annular space to the surface The surface was completed with a 12-inch flush-mounted well box, and locking, water- tight well cap were placed on the wells Well construction details are shown on the boring log in Attachment B Field and Laboratory procedures are presented in Attachment C Soil cuttings and wastewater generated during the drilling activities were placed in labeled 55-gallon Department of Transportation (DOT)-approved steel drums and stored at ARCO station#2130 at 7906 North El Dorado Street in Stockton,pending disposal A composite soil sample was collected from the soil cuttings and submitted to the Sequoia Analytical Laboratory in Sacramento, California, for analysis of TPHg, benzene, toluene,ethylbenzene, and xylenes(BTEX), and total lead under an accelerated 48-hour turnaround time The soil was hauled by Dillard Environmental Services to Altamont Landfill and Disposal Facility in K V5 BP ARCO\044931Regulatory Correspondence14493 WIR doc