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S . � The surface material is predominantly asphalt with some surface concrete in the " vicinity of the gasoline USTs and pump islands. r: u 2.3 Site History Exxon Retail Location Number 7-3330 was constructed in 1968. All underground t storage tanks (USTs) on the property are the original tanks; no tanks have been excavated or replaced to date. Currently, the station is not in service for retail fuel sales; station operations were suspended in late February 1991. A protective chain-link fence E 8 was scheduled to be erected at the property on 4 March 1991. 2.4 Regional Geology/Hydrology and Water Usage The site is located in the San Joaquin Valley portion of the Central Valley of ts comprise the major aquifer known as California, where continental alluvial deposimel, Central Valley Aquifer System. These deposits consist predominantly of sand, gra zt silt, and clay lenses, with the finer-grained sediments making up more than 50 percent of the sequence. The climate is and to semi-arid, with annual precipitation ranging from 5 to 14 inches in the San Joaquin Valley. Prior to groundwater development in the Valley,recharge was " lied primarily by streams entering the Valley from the eastern and northern side. su Most discharge of the aquifer system occurred as evapotranspiration or seepage to streams in the central part of the valley. y art to a high The recent intensive groundwater development has been due in large p i level of agricultural activity sustained by a combination of heavy groundwater pumpage and large imports of surface water. This importation of surface water, primarily into 'he E western part of the valley beginning in 1968, largely replaced the groundwater pumpage• The principle source of recharge is now infiltration and percolation of imported surface waters applied to irrigated lands. Most aquifer discharge is now from pumping wells rather than by natural discharge as streamflow or evapotranspiration- 3.0 PROPOSED WORK 3.1 Introduction The proposed initial site investigation to be performed at Exxon Retail Location Number 7-3330 includes a scope-of-work that consists of the following tasks: permits,utility clearances, and site-access permission; 1. Obtaining all necessary pe Y . 2. Installation of 3 borings to an approximate depth of 40 feet. Fou'-inch monitoring wells will be installed where groundwater is encountered, and the wells will be designed to monitor the free-water table in order to intersect light non-aqueous phase liquids(LNAPLS); 3. Collection of soil samples from each boring at least every 5 feet throughout the unsaturated zone. One or more samples from each boring will be submitted for laboratory analysis for total petroleum hydrocarbons (T-PH), and for the fuel constituents benzene,toluene, xylene, and ethyl benzene (BTX&E); -5- i , + 02-32,R1 318191