SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

David Stavarek, SLIC Unit Central Valley- California Regional Water Quality Control Board April 17, 1998 Page 2 Ground-water samples collected from the main down-gradient monitoring well(MW-7)have consistently had little or no nitrates. Several years of laboratory testing indicate that molasses feed product constituents present in soils beneath the Washington Street facility have had little or no deleterious effect on shallow ground-water resources. In fact, extremely low nitrate concentrations detected at MW-7 support Sierra-Pacific's contention that molasses-based feed products enhance the viability of organisms which are denitrifying saturated sediments beneath the facility. Elevated Total Dissolved Solids(TDS)concentrations, including chlorides,detected in ground-water samples from MW-3, MW-4, and MW-7 indicate that brackish(connate) ground-water pervades near-surface deltaic sediments of the Port of Stockton. The localized infiltration of relatively fresh storm water flushes saline components from near-surface soils. Stratigraphy and Hydrology The sequence of beds intercepted in dozens of shallow soil borings at the site show a consistent stratigraphic pattern. Sediments beneath the site consist largely of greenish-brown deltaic(brackish)sediments. The upper three feet of undisturbed deltaic sediment(below the pavement layers)consists of light-brown sand with minor amounts of pea gravel, silt,and clay. The sediments are generally porous and permeable.. A laterally continuous bed of silty-clay was intercepted in several borings at 4.5 feet to 5.5 feet below surface grade. Although somewhat variable, the upper six inches is generally dark-green to black smectite clay, whereas the lower six inches is greenish-black clayey silt. A dark-gray clay bed intercepted in the east tank farm area appears to thicken to the east and pinch-out towards the west side of the tank farm. Thin-bedded, laterally discontinuous,clay beds could serve as effective barriers to migration of nitrogen-rich feed products. Uniform, olive-green, fine-grained sand with silt and traces of clay is present from 5.5 feet to 12.0 feet throughout the site. Although the olive-green sand is generally uniform and well-sorted, a thin-bedded clay was intercepted at 8.0 feet. Elevated ammonium and TKN concentrations were detected within this porous and permeable formation, but dark-colored, feed products were seldom observed deeper than six feet below the surface.