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connected by a valve to the city storm sewer system beneath Church Street; the valve is <br /> kept closed to prevent the discharge of unwanted substances to the storm drain. Water col- <br /> lected in the sump is allowed to evaporate; to date, water has not been released from the <br /> sump to the storm drain system. (Latham, 1992). This collection system wa„ installed in <br /> 1989 to comply with SPCC regulations, which required utilities to install a surface water <br /> runoff collection system onsite to prevent runoff from leaving the site. <br /> Surface water runoff from Area III enters the storm grates located within Area III and <br /> eventually drains into lower Mormon Slough west of the site (Figure 4-1). <br /> The depth to groundwater beneath the site (measured at approximately 10 to 15 feet msl) is <br /> between 30 and 40.feet bgs. Monitoring wells in Area I indicate that groundwater gradient <br /> directions are fo the southeast, with a lesser component of flow to the west. The <br /> magnitude of the horizontal gradient ranges from about 0.0044 to 0.016. The slough is <br /> estimated to be 25 feet or more above the groundwater table. There is also a downward <br /> vertical gradient; therefore, groundwater is not expected to discharge into the slough. <br /> 8.3.2 Summary of Nature and Extent of Contamination <br /> COPC were identified from those compounds detected in the media sampled between <br /> December 1991, and September 1992. The RI included offsite sampling to provide <br /> background surface and subsurface soil data for comparison with onsite surface and <br /> subsurface soil data. <br /> Chemicals detected in samples collected from Areas I, II, and III were discussed in <br /> Sections 5.3 and 5.4, and were summarized in Tables 7-1 through 7-6. Chemicals detected <br /> in each area are discussed below. <br /> Area I is completely paved; therefore, only subsurface soil samples and groundwater <br /> samples were collected. PNAs, VOCs, TPH-gasoline, TPH-diesel, and various inorganic <br /> chemicals were detected in soil and groundwater at the site. The highest concentrations of <br /> PNAs were generally detected within the upper 5 to 10 feet of soil. VOCs such as <br /> benzene, chlorobenzene, ethylbenzene, toluene, and xylenes were detected above <br /> background. Benzoic acid was the only semivolatile organic compound detected above <br /> background for Area I. <br /> Area II is gravel covered, and houses many high voltage underground conduits and <br /> aboveground structures that prohibited subsurface drilling; therefore, shallow surface soils <br /> primarily between 0 and 6 inches, with two samples from 2 feet bgs, were collected. Five <br /> PNAs, benzoic acid, and a number of inorganic compounds were detected at or above <br /> background. PCB-1254, 4,4'-DDE, and 4,4'-DDT were also detected in samples collected <br /> from Area II, but background data were not available for these parameters. <br /> 10010427.sFo 8-4 <br />