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' S v � Zrdk d. Y\ A S S Q C I A 7 E S I N C 221 UndLr=und Storage Tanks According to information previously supplied by the Department of Public Works, the following USTs were removed from the site on the given dates, and the excavations backfdled T-1 550-gallon Diesel Removed 10/28/93 T-2 1,000-gallon Regular Unleaded Removed 10/28/93 T-3 1,000-gallon Unleaded Removed 04/01/87 ' T4 350-gallon Waste Oil Removed 04/23/92 T-5 550-gallon Diesel Removed 10/28/93 T-6 1,000-gallon Gasohne/Water Removed 08/07/87 ' According to the information given to ATC, no USTs remain at the site 2_2 ReLvional Geolmy and H droeolo The site is underlain by the Modesto Formation, which is divided into nonmar ne basun deposits, fan ' deposits, and stream channel deposits consisting of clay, silt, and sand (Rogers, 1966) Basin deposits are dominant at this site The Modesto Formation dips gently to the west(Wagner, et al , 198 1) The site is in the Eastern San Joaquin County Groundwater Basin (California Department of Water 4 Resources, 1980) According to personnel of the San Joaquin County Public Works Department and the City of Stockton Municipal Utilities Department, the direction of regional groundwater flow is to ' the east-southeast and the depth to groundwater ranges from approximately 40 to 42 feet below surface grade (bsg) The groundwater basin has been developed for intensive irrigation, domestic, industrial, municipal, and stock use ' There are two surface streams near the site Mormon Slough approximately 500 feet to the southwest and the eastward extension of the Stockton Deep Water Channel (including MacLeod Lake) ' approximately 2,000 feet to the north-northwest Both bodies of water empty into the San Joaquin River approximately 2 miles downstream from the site ' 223 Site Geology and H dro eolo Based on information obtained from previous borings at the site, sediments underlying the site consist ' primarily of silt from ground surface to approximately 12 to 20 feet bsg From 12 to 20 feet to approximately 30 feet bsg, the sediments consist predominantly of sand and silty sand, with silt lenses ' varying in thickness from approximately 2 to 5 feet Geologic cross sections depicting the interpreted subsurface conditions are included presented on Figures 3 and 4 and in Appendix A During on-site drilling activities, groundwater was encountered at approximately 37 feet bsg From December 1988 to December 1999, static water levels have fluctuated from approximately 19 to 45 feet bsg, variations in depth to water between the wells during each monitoring event are apparently due to seasonal fluctuations and possible hydraulic influence caused by the Stockton Deep Water Channel which is iocated approximately 2,000 feet to the north-northwest W 162574 011CAP report doe 2