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U-Haul#709-50 Preliminary Site Conceptual Model Blaes Environmental December 15,2006 The local subsurface sediments of the site consist of poorly sorted sands and silty sands with interbedded silts, clayey sands, and clay The occurrence of these near surface sediments are characteristic of fluvial and over-bank flood deposits, which are typical of the San Joaquin Valley The nearest fluvial system to the site is the Calaveras River, located approximately a mile north of the site The nearest water body is the Stockton Diverting Canal, which is approximately one-half rrule north of the site Based on the exploratory soil boring logs generated from soil sampling activities conducted at the site, soil beneath the site consists of silty sand, silt, sand, clayey sand, and clay Based on the soil descriptions, interpretation, and the correlation between the sample points, it appears that more clayey soil is present on the eastern portion of the site Soil sample collection and field observations during drilling, indicate that the soils beneath the site vary Clearly defined soil horizons were not apparent 2,4 SITE HYDROGEOLOGY Based on soil sample descriptions, the aquifer (saturated sediment) beneath the site is composed of sand and silty sand with interbedded silt, clayey sand, and clay Drilling and soil sample collection indicate that the shallow aquifer appears unconfined Well development activities conducted at the monitor wells have indicated that the saturated sediments can yield approximately two to three gallons per minute In addition, groundwater measurements taken at the existing on-site monitor wells indicate that there is little or no difference in groundwater levels across different screened horizons This suggests that the saturated zone, across which the monitor wells are screened in multiple horizons, is likely hydraulically connected Blaes Environmental last performed groundwater monitoring at the site in September 2006 Groundwater depth measurements collected in September 2006 indicated groundwater depths ranging between approximately 48 5 and 52 feet bgs The apparent groundwater flow direction in September 2006 appeared to radiate outward from a high point near the center of the site at an average of 0 014 feet per foot across the site 2 5 DETECTION OF HYDROCARBON RELEASE According to a 1990 ETS Environmental & Associates (ETS) report, four USTs and associated fuel dispensers were removed from the site in 1990 The four USTs included three unleaded gasoline tanks including one 10,000-gallon, one 8,000-gallon, and one 6,000-gallon capacity tanks, and included one 250- Page 3