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clakgiul Technicsinc. Page 2 Sinclair Trucking Project No.: 1030.2 November 1,2005 C buildings are covered in compacted base rock material or native soil. As of January 20, 2005, groundwater bearing and gradient have historically averaged N49°E and 0.0037 ft/ft, respectively(Table 1 of Appendix A). f ST is located in the southeast quarter of the northwest quarter of Section 7, T3S, R6E, related IL to the Mount Diablo B&M, on the United States Geological Survey (USGS) topographic map, Vernalis Quadrangle, California, 7.5 minutes series. A review of the USGS Topographic Map reveals that the elevation of this site is approximately 75 feet above mean sea level (AMSL). The site is located on the gradually sloped floor of the northern San Joaquin Valley. The geologic composition of the area is characterized as fluvial deposits of the San Joaquin - Sacramento River delta system that overlay continental rocks and deposits derived from erosion of the Sierra Nevada Mountain Range located approximately 50 miles northeast of Modesto. The southwest tilting Sierra Nevada fault block underlies the northern San Joaquin Valley area. Overlying the consolidated rocks are unconsolidated sediments. The lower consolidated batholithic and metamorphic rocks are poorly transmissive, however the overlying sedimentary layers are often quite permeable. These unconsolidated layers include j f Pliocene/Pleistocene age continental deposits, Pleistocene age lacustrine and marsh deposits, and Holocene older and younger alluviums and flood-basin deposits. 1.2 Site Background On March 31, 1989, one steel 250-gallon underground storage tank (UST), used to supply leaded gasoline, was removed from the site. The SJCEHD inspection report indicated that corrosion was present on the UST and a petroleum odor was noticeable in the area of the tank removal. Subsequent laboratory soil analyses indicated the presence of petroleum hydrocarbons at the site. A limited over excavation to a depth of 18-feet bgs was conducted in the general area of the UST and was backfilled with native soil. fOn June 14, 1995, Geological Technics Inc. (GTI) installed three monitoring wells and advanced one soil boring in order to evaluate the vertical and lateral extent of gasoline range petroleum hydrocarbons. On February 16, 1999, GTI personnel supervised the installation of one groundwater monitoring well down gradient of the former UST to further define the lateral extent of - - =gasoline contamination in the soil and groundwater. This well showed low levels of gasoline - --- range hydrocarbons. In response to a request by Mr. Ron Rowe of SJCEHD,GTI prepared a work plan on January 18, 2000, to define the lateral extent of the soil and groundwater contamination at the site. On April 20, 2000, Ms Lori Duncan, SJCEHD, issued a letter denying the approval of the work plan. During phone conversations in May of 2000, Ms Duncan requested that a work