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L Pombo Ranch Facility August 17,2004 Subsurface Investigation Report& Second Quarter Groundwater Monitoring ' Upon termination, the boring into the saturated zone was completed as a monitoring well and backfilled with concrete grout, after a Bentonite seal has ' been placed. The boring for the monitoring well was of a diameter at least 4 inches greater than the 2-inch diameter of the well casing to be used. The cuttings from the drilling operation were containerized on-site during drilling for proper disposition. The proper method of disposal will be dependent upon results of laboratory analysis. This disposal will be the responsibility of the client ' unless other arrangements are made. 1 2.2 Well Construction All materials used in well construction were thoroughly cleaned prior to introduction into the boring. A cement and Bentonite grout was placed at the bottom of the boring as necessary. After the seal had been allowed to set long enough to support the weight of the casing, a 2- inch diameter well casing (PVC) with end cap and factory perforations for placement in the saturated was placed in the boring. The casing and end caps were threaded; no PVC cement was used. ' The filter pack was placed to extend two feet above the perforated casing zone. A Bentonite seal 2- to 3-feet thick was placed in the annular space above the filter pack followed by a cement grout to the surface. Seal and filter pack elevations were determined by the underlying geology and actual elevation at each well location. All well heads were surveyed to within 0.01 feet using an assumed datum of 53 feet as shown on the USGS Tracy Quadrangle topographic map ' (photo-revised 1981). 2.3 Well Development and Sampling The wells were developed until the well water appeared clear of sediment and ' allowed to stabilize for twenty-four(24) hours prior to sampling. All soil and groundwater samples were properly labeled with date collected, ' project number, sample coordinator, and sample identification. Field records document the above information and other significant data, such as names of on- site personnel, sampling methods, date and time of sampling, the number of well ' volumes removed before sampling, preservatives added, and any filtration performed on samples. ' The samples were refrigerated immediately for delivery to the laboratory and under no circumstances were opened by anyone other than laboratory personnel. Chain of Custody records were maintained at all times. 7