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9 I � 9 a , 3.0 HYDROGEOLOGIC SETTING Soil borings at the site have encountered a sequence of silts and sands with varying amounts of clay. Between the surface and 8 feet the sediments are largely elastic (clayey) silts to silty sands. From 8 to 17 feet below grade the section is largely lean clay. In the approximate interval 17 to 25-34 feet below grade a silty-clean sand is present which overlies a lean clay. The stratigraphy of the site is presented on pages 22 and 23 of Appendix I. Logs of soil borings at the site are also contained in Appendix 1. Groundwater is currently approximately 18 feet below grade, however, seasonal high groundwater in the area is approximately 8-10 feet below grade based on the maps of the San Joaquin County Flood Control and Water Conservation District (1975, 1980, 1984, 1987). Generally, the shallow groundwater beneath the site flows through low to moderately permeable silty sands. As groundwater levels rise in the spring, somewhat higher transmissiviti.es may be expected, however, because the sediments from approximately B-17 feet below grade are low permeability lean (silty/sandy) clays this effect may be slight. Thegroundwater gradient at the site is generally to the sou..*heast at .005 ft/ft (Appendix 1, page 18). Estimated groundwater velocities range from approximately .3 to 1.1 _ ft/day (Appendix IV). Approximate shallow aquifer hydraulic parameters have been established for the site using data from a 4 :hour constant: rate pumping test .Performed in December, 1 9 This data was' presented to SJCEH in a letter report dated March 13,31,5:8:9:) A 090 summary of the test and calculations of hydraulic parameters (transmissivity and storativity), groundwater velocity, expected well productivity and anticipated capture zones due to pumping are contained in Appendix IV. 4.0 SOIL REMEDIATION _.. 4.1 Soil Remediation Performed to Date A soil remediation Work Plan was submitted to the SJLHD by Sebastiani Vineyards/Woodbridge Cellars on December 7, 1986. In accordance with the Work Plan, excavation work was begun on April 6, 1989 to remove soils contaminated with petroleum hydrocarbons. The amount of soil to be excavated Was to be determined with field measurements...-(Hsu....-..phooi.�nization -..-..---. -. --detector) Soils with.......... etroleum hydrocarbon concentrations in excess of 100 ppm were to be excavated and stockpiled for aeration. The excavation extended to a depth of 18.5 feet where groundwater began entering the excavation. Excavation J 2