Open-File Report 2006-1374

Open-File Report 2006-1374

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Chlorinated volatile organic compounds (VOCs) have migrated to ground water beneath the 9-acre former landfill at Operable Unit 1 (OU-1) at the Naval Undersea Warfare Center (NUWC), Division Keyport. The NUWC is on a small peninsula in Kitsap County, Washington, in an extension of Puget Sound called Liberty Bay (fig. 1). The 9-acre former landfill at OU-1 is on the narrow strip of land connecting the peninsula to the mainland and is adjacent to tidal flats that are an extension of Dogfish and Liberty Bays. The OU-1 landfill is unlined at the bottom and was constructed in a former marshland. The landfill was the primary disposal area for domestic and industrial wastes generated by NUWC Keyport from the 1930s through 1973. Paints, thinners, solvents, acids, dried sludge from a wastewater-treatment plant, and other industrial wastes were disposed in the landfill. The most concentrated disposal area for waste paints and solvents was at the southern end of the landfill.

Chlorinated VOCs are present in the upper and intermediate aquifers and in surface water at OU-1. Ground water beneath OU-1 occurs within a series of aquifers that are composed of permeable sand, gravel, or fill materials separated by finer-grained silt or clay layers. Contamination at OU-1 is known to occur only in about the top 60 feet of the unconsolidated deposits in the hydrogeologic units referred to as the unsaturated zone, the upper aquifer, the middle aquitard, and the intermediate aquifer. Ground water in the unconfined upper aquifer generally flows from east to west towards Dogfish Bay. Ground water in the predominately confined intermediate aquifer flows from the south and west towards the landfill, and then northwest from the landfill towards Dogfish Bay (Dinicola and others, 2002). Two perennial freshwater creeks drain the marsh adjacent to the landfill and discharge into the tideflats of Dogfish Bay.

The predominant contaminants in ground water beneath OU-1 are trichloroethene (TCE) and its degradation byproducts cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). The compound 1,1,1-trichloroethane (TCA) and its degradation byproducts 1,1-dichloroethane (1,1-DCA), 1,1-dichloroethene (1,1-DCE), and chloroethane (CA) have been detected at concentrations of concern at a few locations at OU-1. A need for remedial action was identified because those hazardous compounds present a potential risk to humans (URS Consultants, Inc., 1998). Phytoremediation combined with on-going natural attenuation processes was chosen by the Navy as the preferred remedy (URS Consultants, Inc., 1998). The Navy planted two hybrid poplar plantations on the landfill (fig. 2) in spring of 1999 to remove and control the migration of chlorinated VOCs in shallow ground water (URS Greiner, Inc., 1999). The landfill between the plantations is covered with pavement, although the area north of the northern plantation is permeable.

Purpose and Scope

The Navy began a cooperative effort with the U.S. Geological Survey (USGS) in 1995 to investigate various natural attenuation mechanisms at OU-1. Field and laboratory studies conducted from 1996 through 2000 showed that natural attenuation and biodegradation of chlorinated VOCs in shallow ground water at OU-1 were substantial (URS Consultants, Inc., 1997; Bradley and others, 1998; Dinicola and others, 2002). The USGS has continued to monitor the geochemistry of ground water to assure that conditions remain favorable for contaminant biodegradation, and annual monitoring from 2001 through 2004 confirmed that biodegradation was continuing (Dinicola, 2006).

This report presents ground-water chemical and selected VOC data collected by the USGS at OU-1 during June 21–24, 2005, in support of the long-term monitoring for natural attenuation. USGS data collected from 1996 through 2004 were presented in Dinicola and others (2002), Dinicola (2003, 2004, 2006), and, Dinicola and Huffman (2004). In June 2005, the USGS collected ground-water samples from 13 wells and 9 piezometers (table 1 and fig. 2). Concentrations of various geochemical constituents used to evaluate ground-water redox conditions were determined in all samples from wells and piezometers. Concentrations of VOCs also were determined by the USGS in samples from all piezometers and in samples from 3 of the 13 monitoring wells. The Navy determined VOC concentrations in samples they collected from other OU-1 monitoring wells during April 2005, but those data are not presented in this report. The USGS determined VOC concentrations in shallow ground water directly beneath the southern reach of the marsh stream (fig. 2) using passive-diffusion samplers. Samplers were located closer together than previously done to refine the characterization of contaminant discharge to surface water. The USGS also determined VOC concentrations in surface-water samples collected at the upstream and downstream ends of the reach of the marsh creek where diffusion samplers were deployed.

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