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Groundwater Assessment Report ARCO Facility No 2186 Stockton,Califomia Page 4 initial 5 feet of each boring were advanced with a hand auger and/or post hole digger to reduce the possibility of damaging underground utilities Soil borings were then advanced using a drill ng equipped with 8-inch diameter hollow stem augers Soils were classified onsite using the Unified Soil Classification System Boring logs detailing soil stratigraphy are presented in Appendix C Drilling locations are shown on Figure 2 Soil samples were collected at 5-foot intervals during the advancement of the borings using a California-type, split-spoon sampler equipped with three precleaned brass tubes The ends of the bottom-most, intact tube from each sample interval were lined with TeflonTM sheets, capped, and sealed Each sample was labeled, placed in a resealable plastic bag and stored in an ice-chilled cooler 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 collected from each sampling interval was placed and sealed in plastic bags to allow the accumulation of volatile organic carbon (VOC) vapors within the airspace in the bags A portable photoionization 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 Monitoring wells MW-5 through MW-7 were installed to a depth of approximately 80 feet bgs In each well the screen consisted of 20 feet of 0 02-inch factory slotted PVC, installed from approximately 60 to 80 feet bgs A filter pack of Lonestar #3 sand was placed in the annular space around the well screen from the bottom of the screen to approximately 2 feet above the top of the screen Wells MW-5 through MW-7 were surged for approximately 10 minutes to seat the filter pack around the well screen prior to installing a sanitary seal Two feet of bentonite was placed on top of the filter pack to provide a sanitary seal for the wells The boreholes were backfilled with neat cement up to surface grade A traffic rated vault box was placed over each well and a watertight locking cap was placed on the top of each well Well construction details are included with the boring logs in Appendix C Well Development and Surveying Monitoring wells MW-5 through MW-7 were developed on August 24, 2001, using a surge block and groundwater pumping Delta returned to the site on September 13, 2001, to collect groundwater samples from the newly installed wells Field data sheets from well • development and groundwater sampling are presented in Appendix D The newly installed groundwater monitoring wells will be incorporated into the site quarterly monitoring program A copy of the surveyor's report is included in Appendix E P\ARCO\2186\REPORTS\2186report doc