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San Joaquin County of Public Works January 15, 1999 Workplan for Site Assessment In addition, two (2) hand auger borings will be advanced to depths 15 feet in the piping area where diesel contamination was previously detected. Soil samples will be taken at five-foot intervals. See Figure 1. AREA 3 TEM proposes to advance one (1) boring by Tanks # 6-8 until 20 feet of uncontaminated soil is encountered or groundwater is detected. If groundwater is identified, the boring will be advanced an additional 15 feet for the installation of a monitoring well. Soil samples will be taken at five-foot intervals. A mobile lab will be used to analyze the soil samples. See Figure 1. AREA 4 The County of San Joaquin would like to remove the waste-oil UST and associated piping with bottom soil samples. The UST and associated piping will he triple rinsed & cleaned prior to removal. Confirmation samples will be taken at the bottom of the UST cavity. The excavation will be backfilled and compacted and the concrete will be resurfaced. One additional 1,000 gal UST discovered recently will be abandoned in place. Work includes triple rinse and fill with slurry. The boring for Area 3 will act as the confirmation boring for this UST. REGIONAL GEOLOGY & HYDROGEOLOGY The SITE is centrally located within the Great Valley physiographic province of California. The SITE occurs near the boundary between the San Joaquin Valley to the south, and the Sacramento Valley to the north, which together form the Central Valley of California. The SITE is underlain by a veneer of Quaternary fine-grained flood-basin deposits which are underlain by more than 3,000 feet of a heterogeneous mix of generally poorly sorted clay, silt, sand, and gravel, with some beds of claystone, siltstone, sandstone, and conglomerate which range in age from Oligocene to Holocene. These rocks and sediments are continental in origin and at depth include Oligocene to Miocene age material of the Valley Springs Formation, and Miocene and Pliocene age Mehrten Formation deposits. The shallow and surficial fine-grained sediments reflect flood stage deposits from major streams which emptied into the Central Valley from the west. Based on data provided by the City of Stockton Department of Public Works, and the California Water Company, groundwater in the vicinity of the SITE is estimated to range between 50 and 60 feet below ground surface (bgs). Groundwater movement beneath the SITE is approximately westerly, towards the San Joaquin Delta region. Based on data provided by the City of Stockton Department of Public Works, the groundwater gradient in the vicinity of the SITE is relatively flat, with a shallow gradient similar to the land surface gradient. According to Mr. Ebner Fowler with the California 2