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b G nl 3 Color Spot, Inc. v -� August 16, 1991 (488168C) i SITE HYDROGEOLOGY r Table 2 - Depth to Ground Water, contains ground water data for the i" site. As part of a previous assessment at this site, SGD advanced four drill holes and converted one into MW-1 (total depth 80 feet) in October of 1990. The logs of these drill holes are included in the SGD report listed above, dated February 1990. During the drilling of MW-1, no ground water table was ' encountered. However, a wet -zone was noted between 64 and 67 feet below ground surface (bgs). This interval was not perched above a clay layer, rather it is the top of a medium- to coarse-grained sand layer that is overlain by a clayey I.A fine- to medium-grained sand. The accumulation of moisture at the top of a sand layer just beneath a clayey layer is common in unsaturated soils. In this type of situation, the effects of capillary forces on the hydraulic gradient are greater than gravitational forces. It is possible that the ground water i3 encountered at 90 feet bgs in DH-2 is another example of this phenomenon, as a clayey sand layer was observed directly above the sand layer at 90 feet bgs. The County of San Joaquin Flood Control and Water Conservation t District (District) data for water levels in wells in the fall of 1990 indicate that depth to ground water at this site at that time was approximately 85 feet T _ bgs- In the fall of 1990, the local ground water flow direction at the site, according to the District data, was to the southeast toward the Pixlew Slough about 6,500 feet away. Current data from the District were not available at the time of the writing of this letter-report. The depth to ground water in MW-1 was measured by SGD on May 22, 1991, at 74.5 feet bgs. There are six known water wells within 1,000 feet of the former UST location, as shown on Figure 2. Two of the wells are reported to be abandoned and two ae not owned by Color Spot, Inc. Of the two not owned by Color Spot, Inc., well No. 3N/7E-19B (located about 50 feet west of MW-1) has a total depth of 112 feet. Color Spot management reports that these two are in use by the adjacent residences, but the pumping rates or pumping schedules are not known. Color Spot Well No. 1, about 300 feet south of the former UST location, reportedly discharges approximately 3 hours per day at rates between 50 and 80 gallons per minute (gpm) or between 9,000 and 14,000 gallons per day (gpd). Color Spot Well No. 4, about 500 feet northwest of the former. UST, reportedly discharges at a rate of 280 gpm for approximately 6 hours per cay (100,800 gpd). Perforated casing intervals, wellhead elevations, pumping water levels, and static water levels in the above-mentioned wells are not available at this time. Nine driller's reports supplied by the State of California Department of Wates Resources (DWR) for water wells located within 1,000 feet of the outer boundaries of the Color Spot facility were reviewed for construction details. These driller's reports have been provided to EHD for their reference. The wells were drilled between 1950 and 1975 and the total depths of the wells range between 72 and 184 feet. Static water levels at the time of drilling ranged --- --- _ -�'— . ._._._._-between-49 -and-68 feet-bgs.-.... _.___