SITE INFORMATION AND CORRESPONDENCE_2

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Del Monte Stockton Property Assessment and Remediation RFP Section III, Page 1 III. DISCO SITE HISTORY A. Background Del Monte Foods currently owns the Disco site. Parmaceast owned the site from the mid-1960s until 1976 and operated the USTs that were associated with a former gasoline station. Del Monte purchased the property from Parmaceast in 1976 and never operated or used the USTs. In October 1985, Del Monte removed the USTs under the supervision of the San Joaquin County Public Health Services (SJCPHS). The tanks contained water at the time of removal, and soil beneath the tanks contained gasoline constituents. An interim cleanup was conducted by excavating as much soil beneath the tanks as possible by a backhoe. The soil was aerated on site to reduce the levels of volatile hydrocarbons below 1,000 mg/kg. The aerated soil was then backfilled into the excavation. In 1991, under the direction of the SJCPHS, Del Monte conducted a soil and groundwater investigation in the vicinity of the old gas station that included a soil-gas survey, soil borings, and eight monitoring wells. The results indicated gasoline constituents in the soil at depths between 55 and 75 feet below ground surface (bgs) and in the groundwater. The site is underlain by unconsolidated alluvial sediments. The soil types include clay, silt, sand, and gravel. The predominant soil types are interbedded sandy clay and silty sand. Historic water levels in this area were as low as 100 feet to 105 feet bgs between 1972 and 1977. The groundwater rose to approximately 47 feet bgs in 2000 and has started to drop again. It currently is around 48 feet bgs. Since 1991, groundwater levels beneath the site have risen approximately 29 feet (from 77 feet bgs to 48 feet bgs), and the groundwater flow changed direction by almost 180 degrees. The rise in groundwater level can be attributed to numerous city water supply wells being shut down as well as three production wells at the Del Monte cannery. PCE was found in two of the Del Monte wells during the annual water testing, and the wells were disconnected in 1994. The three Del Monte wells are located approximately 100 to 150 yards from the former gas station location. Collectively,the three wells were capable of supplying 2,000 gallons per minute. Between 1991 and July 1994, the groundwater flow direction was predominately toward the northwest. From October 1995 to the present,the groundwater now direction has been consistently toward the southeast.