ARCHIVED REPORTS_ANNUAL 2014 GRAOUNDWATER MONITORING AND SAMPLING REPORT

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i Mr.C.Dean Hubbard—Central Valley RWQCB J Annual 2014 Groundwater Monitoring and Sampling Report April 29,2014 ! Alden Park Page 2 of 7 The fuel oil was loaded onto railroad tank cars for distribution as steam-locomotive fuel throughout the western United States (U.S.). The facility consisted of one 750,000-barrel, concrete-lined reservoir. The reservoir was approximately 632 feet in diameter and 25 feet deep(about 17 feet above the ground surface, and 8 feet below ground surface [bgs]), and was surrounded by a dirt firewall. An estimated 30,000 barrels of Bunker C oil were received at the reservoir daily. The reservoir was emptied, cleaned, and decommissioned after operations ceased in 1957. The area was sold and used for farming throughout the 1960s. Residential demand in Tracy increased, and the area was developed by Renown Enterprises into the Rancho Pacifica, Westchester Green(in the 1970s), and Tennis Villa(in the 1980s)housing developments. The present park(Alden Park)was constructed during the development of Rancho Pacifica. REGIONAL/LOCAL HYDROGEOLOGY The Site is within the Tracy Sub-basin(Groundwater Basin Number 5-22.15) and is defined by the areal extent of unconsolidated to semi-consolidated sedimentary deposits ' bounded by the Diablo Range on the west, the Mokelumne and San Joaquin rivers on the north,the San Joaquin River on the east, and the San Joaquin-Stanislaus county line on the south. The Tracy Sub-basin is located adjacent to the eastern San Joaquin Sub-basin to the east and the Delta-Mendota Sub-basin to the south.1 These sub-basins are located ' within the larger San Joaquin Valley Groundwater Basin. The Tracy Sub-basin consists of continental deposits of Late Tertiary to Quaternary age, ' which include the Tulare Formation, Older Alluvium, Flood Basin Deposits, and Younger Alluvium. The thickness of these formations ranges from a few hundred feet in the western foothills to about 3,000 feet near the eastern margin of the basin. The Tulare ' Formation is comprised of semi-consolidated,poorly sorted, discontinuous deposits of clay, silt, and gravel. The Corcoran Clay is situated near the top of the Tulare Formation, separating groundwater in the basin in what has been reported as two primary aquifers. ' The upper aquifer is reported to range in thickness from 15 to 250 feet bgs, and the lower aquifer is reported at 600 feet bgs. Generally, depth to groundwater in the Tracy Sub- basin varies from 5 to 10 feet bgsl. Groundwater flow at the Site remains relatively consistent to the north to north-northwest at a gradient of approximately 0.003 feet per , foot(ft/ft). PETROLEUM DISTRIBUTION IN GROUNDWATER ' The petroleum in the groundwater is highly degraded Bunker C oil in both the separate and dissolved phases. The presence of dissolved-phase Bunker C oil is indicated by total petroleum hydrocarbons (TPH) quantified as diesel(TPHd) analyses. The extent of SPO , is limited to the area of Alden Park and, historically, dissolved-phase hydrocarbons extend down gradient in the direction of monitoring well MW-7. The constituents at the Site are TPHd and polynuclear aromatic hydrocarbons(PAHs). Low concentrations of ' several PAHs(primarily naphthalene)have been detected in Site wells. The distribution 1. California Department of Water Resources,2003. California's Groundwater Bulletin 118,2003 Update.