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Geosynte& <br /> consultants <br /> 2. BACKGROUND <br /> ' The WFS Stockton facility is located at 1905 N. Broadway, in Stockton, California, as <br /> shown on Figure 1. Site facilities on the six-acre property include one main office <br /> building, warehouse and maintenance buildings, gasoline and diesel fuel above ground <br /> ' storage tank areas, bulk liquid fertilizer tanks, application trailers, and a vehicle wash <br /> pad. Site operations began approximately 40 years ago and consist of blending and <br /> distributing bulk liquid fertilizers. Pre-packaged containers of fertilizers and pesticides <br /> ' are currently stored in the warehouse and sold to farmers. Prior to 1993, the northern <br /> half of the Site was operated by Brea Agricultural Services, Inc. (Brea), an agricultural <br /> chemical retail company, and the southern half of the Site was operated by PureGro <br /> Company, a Union Oil Company of California(Unocal). Both portions of the Site were <br /> bought by Crop Production Services, Inc. (CPS) in 1993 and then sold to WFS in 1996. <br /> ' 2.1 Pond Operation and Closure <br /> There were two shallow evaporation ponds on-site; the North Pond and South Pond. <br /> From 1965 to 1985, Brea placed diluted fertilizer and pesticide rinseates in the North <br /> ' Pond, now known as the former North Pond Area (Figure 2). Historical reports of past <br /> operations have assumed that the South Pond was operated in the same manner by <br /> Unocal. <br /> Sometime between 1985 and 1993, the North and South Ponds were removed from <br /> operation. The top 2 to 4 feet (ft) of soil were removed from both ponds and <br /> ' excavations were backfilled with an aggregate base material comprised of crushed <br /> gravel and stone. As discussed in the following sections, soil and groundwater near the <br /> ' ponds were investigated from 1993 through 1995. Then in 1995, both former ponds <br /> were excavated to 3 to 4 ft below ground surface (ft bgs) and backfilled with clean <br /> imported fill. In 1996, a low-permeability cap/liner system was installed in the footprint <br /> of each of the two former evaporation ponds to prevent infiltration to the shallow <br /> groundwater (Sierra-Pacific, 2001). The liner/cap system was constructed by first <br /> excavating the top 14 inches of aggregate material and then placing in the order listed, <br /> the following layers over the excavated area: a granulated bentonite liner, 3 inches of <br /> clean sand, 7 inches of base rock, and 4 inches of asphaltic concrete (Sierra-Pacific, <br /> ' 1997). Since installation, routine annual cap inspections and maintenance have been <br /> conducted on this liner/cap system as part of the Site's MRP. <br /> Work Pim-Stockton Pond Inv_01-07-08 2 01.07.08 <br />