ARCHIVED REPORTS XR0001331 - Laserfiche WebLink

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June 9, 1993 "AF, . ARCO Service Station 2168, Stockton, California Working To Restore Nature • ASSESSMENT OF SOIL AND GROUND WATER The drilling operations, soil sampling, well construction and development, and water sampling are summarized below Our field methods are described in an attachment to this report Copies of the Chain of Custody Records and laboratory reports for soil and water samples are attached Work was conducted according to field methods outlined in our Work Plan No 31009-4W, dated April 7, 1992, and our addendum to Work Plan No 31009- 4W, dated August 11, 1992 Drilling, Soil Sampling. and Well Construction On January 11, 12, and 13, 1993, a geologist from RESNA observed Jcon Exploration (Jcon) of Yuba City, California, drill four 8-inch-diameter and two 10-inch-diameter soil borings (B-13 through B-19) and install two ground-water monitoring wells (MW-4 and MW-5) and 1 four vapor-extraction wells (VW-4 through VW-7) in the borings Soil samples were collected during drilling at approximately 5-foot intervals for possible laboratory analyses and to evaluate the geology beneath the site Samples were identified using visual and manual methods and classified according to the Unified Soil Classification System (Plate 4) During drilling, ground water was encountered at approximately 41 to 43 feet below surface grade (bsg) Descriptions of the materials encountered are presented in the Logs of Borings (Plates 5 through 19) Soil beneath the site consists primarily of silt to clayey silt to a depth of approximately 33 feet bsg, with lenses of clay, silty sand, and sand. Soil from approximately 33 feet bsg to ground water consists of sand and silty sand I Jcon installed ground-water monitoring wells MW-4 and MW-5 in borings B-14 and B-16, respectively, and vapor-extraction wells VW-4 through VW-7 in borings B-13, B-17, B-18, and B-19, respectively Well construction details are illustrated on the Logs of Borings Four soil samples were collected from the drill cuttings and composited into one sample in the laboratory for analyses Analytical results of the composite soil sample were used to evaluate disposal options of the drill cuttings Results of analyses are g y presented in the attached Laboratory Reports On February 5, 1993, at ARCO's request, Dillard Trucking of Byron, California, disposed of the drill cuttings at BFI Landfill, Livermore, California (verification letter attached) Monitoring Well Develo meat and Sampling On January 20, 1993, a technician from RESNA developed the ground-water monitoring wells, field methods for development are described in an attachment to this report On January 26, 1993, we measured the water levels, conducted subjective analyses of ground water, and collected groundwater samples from wells MW-4 and MW-5 for laboratory 0209ccar 3I009-7 2