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• r geotogkfil TecAaks uc. Page 3 Groundwater Monitoring Report Project No.750.2 November 10,2004 The groundwater at this site is free of petroleum hydrocarbon contamination and possibly as much as 600 gallons of gasoline may remain in the vadose zone. On March 28, 2003, GTI submitted the Work Plan for Additional Site Characterization. The work plan was approved, with reservation,by Lori Duncan in a letter dated April 8, 2003. On June 6, 2003, GTI prepared and submitted the Work Plan — Treatment System Feasibility Study. In a letter dated June 23, 2003, Ms Duncan requested that SCJEHD be notified once a decision was made on the method to be employed at the site. The letter requested that remediation should resume as soon as possible. On September 4 and 5, 2003, GTI and Gregg Drilling & Testing Inc. (Gregg) staff arrived at the site and advanced two soil borings per the March 28, 2003 work plan. Details of the event are discussed in GTI's Interim Soil Investigation Report dated October 2, 2003. GTI obtained Fund approval and an Authority to Construct permit to reinstall and operate the Internal Combustion System (IC) at the COE site. The IC was switched on, inspected by the San Joaquin Valley Air Pollution Control District (SJVAPCD) on December 9, 2003, and operated until January 14, 2004. -�.- On February 12, 2004, GTI prepared and submitted the Work Plan — Modified Vapor Extraction Treatment System. The work plan was approved by Ms Duncan in a letter dated February 20, 2004. A budget for the project was submitted on March 29, 2004. The old equipment was removed and the new system with the required utilities has been installed. 2.0 HYDROGEOLOGIC SYSTEM 2.1 Regional Structure The COE site is located in the northwest quarter, of the northwest quarter of Section 4, T2S, R9E, related to the Mount Diablo B&M, on the United States Geological Survey (USGS) topographic map, Escalon Quadrangle, California, 7.5 minutes series. A review of the USGS Topographic Map reveals that the elevation of this site is approximately 115-feet 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