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C Zone <br /> The C Zone is composed of sand units that may exceed 25 feet in thickness. The <br /> top of the C Zone is typically encountered between 45 and 50 feet bgs, but may <br /> occur at depths as shallow as 40 feet bgs beneath the northwest part of the site. <br /> C Zone sands beneath the STTC facilities appear to be laterally continuous, and <br /> trend north-northwest. The C Zone sands appear to be thickest in an area <br /> extending to the south and southeast. <br /> Stratigraphic data from cone penetrometer testing (CPT) profiles suggest that <br /> C Zone sands are continuous from north to south; however,the sands appear to be <br /> a series of individual lenses that grade laterally into silts and clays. C Zone sands <br /> are underlain by low-permeability silt and clay deposits typically encountered <br /> between approximately 75 to 85 feet bgs, and the contact between the C and <br /> D Zones is not well defined. Groundwater within the C Zone generally flows to <br /> the east with a hydraulic gradient ranging from approximately 0.001 to 0.003 ft/ft. <br /> C/D Aquitard <br /> During SECOR's off-site assessment east of the STTC facilities,the C Zone sands <br /> were underlain by low permeability silts and clays at depths ranging from <br /> approximately 67 feet to 77 feet bgs. The low-permeability silts and clays <br /> extended to depths ranging from approximately 80 to 84 feet bgs. The thickness <br /> of the silts and clays ranged from approximately 4 feet to 17 feet bgs and appeared <br /> to be continuous during the investigation (SECOR, 2002). <br /> D Zone <br /> Typical D Zone strata consist of isolated sand units 2 to 5 feet thick, interbedded <br /> with sandy silts, silts, and clays. The sands are encountered at depths below <br /> 80 feet bgs. The lateral extent of the D Zone sands has not been established; <br /> however, the sands are less than 5 feet thick, and occur at varying stratigraphic <br /> intervals, suggesting that the sands are not laterally continuous in the interval <br /> explored. <br /> 2.3 Historical Releases <br /> Information regarding known historic releases at the former Time Oil terminal is <br /> summarized below. Approximate spill locations are shown on Figure 3. <br /> 1981 Unleaded Gasoline Spill: A spill of approximately 74,760 gallons (1,780 barrels) <br /> of regular unleaded gasoline occurred in November 1981 during a product transfer at <br /> Tank 10004 (Time Oil, 1988). The majority of the spilled gasoline was reportedly <br /> recovered using a vacuum truck. The volume of product recovered is unknown. <br /> Site Characterization Work Plan,Final, May 18,2012 <br /> 1007-012.002 2-5 <br />