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s1 } southwest The Santa Clara Valley is a large structural depression and the valley floor consists mainly of unconsolidated alluvial and fluvial deposits from the adjacent mountains. Thesite geology is consistent with that of the surrounding valley, with surface elevation contours sloping to the north at an approximate grade of 0.005. 5. The upper 3.5 to 8 feet of soils consists of silty clay, underlain by a 3.5 to 7.5 foot thick zone of sandy silty to silty sand with occasional clay interbeds. An interbedded clay layer is present at a depth from 12 to 15 feet bgs, and ranges in thickness from 2 to 5 feet. The interbedded clay layer separates two saturated permeable zones of the A-level agifer. The A-level aquifer is unconfined and ranges from 7 to 10 feet thick. Fifty feet of clay with occasional thin silt and sand interbeds separate the A Level aquifer from the underlying B-level aquifer. Groundwater elevations in the B- level aquifer are consistently higher thart lev-4tions measured in the A-level aquifer. This indicates an upward vertical hydraulic Zradient between the A- and B-level aquifers. Normal groundwater flow is to the northwest at a gradient from 0.002 to 0.004 ft/ft. 6. Water is not withdrawn from the shallow alluvium for any use other than VOC removal and monitoring at or in the vicinity of the Site. One active domestic well has been documented within a 1-mile radius of the site. This well penetrates to 85 feet or deeper and is located approximately 5,000 feet away at an angle of 30 degrees east of the predominant local groundwater flow direction SITE 1NVESTIGATI NS 7. On August 15, 1984, a leak developed in the piping which transported TCA from an outside storage tank to a degreasing area inside the building. Approximately 10 to 20 gallons of TCA was spilled on the ground just outside the building. On the same day, Varian excavated approximately 22 cubic feet of soil containing visual evidence of TCA. Based on analyses of soil samples collected from the sides of the excavation, Varian excavated an additional 13 cubic feet of soil on October 10, 1984. 8 From January to August 1986, Varian conducted soil and groundwater investigations at the site Varian installed ten soil borings and ten monitoring wells TCA was found in groundwater in concentrations up to 11,000 parts per billion (ppb) 9 The maximum concentrations of VOCs detected on-site in groundwater have been TCA at 11,000 s ug/l, I,l-DCE at 53 ug/l, and 1,1-DCA at 54 ug/l. All these wells are completed in the shallow aquifer 10 Varian has currently identified one shallow-groundwater pollutant plume A small TCA plume extends northeastward from the source area to the northeast edge of the property boundary TCA has not been detected at concentrations above the 200 ug/l State and Federal maximum contaminant level (MCL) at wells north of the property boundary Current monitoring results show the plume still to be present and moving slowly towards the downgradient site boundary The extent of the TCA plume and existing wells are shown on Figure 2 12 Sample results from monitoring well E-13 show DCE and DCA concentrations consistently above State and Federal MCLS 2