Introduction

Chlorinated volatile organic compounds (VOCs) are in groundwater 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 former landfill is on the narrow strip of land connecting the peninsula to the mainland and is adjacent to tidal flats that are an extension of Liberty and Dogfish Bays. The OU 1 landfill was constructed in a former marshland and is unlined at the bottom. The landfill was the primary disposal area for domestic and industrial wastes generated by NUWC Division Keyport from the 1930s through 1973. The landfill received paints, thinners, solvents, acids, dried sludge from a wastewater-treatment plant, and other industrial wastes. The most concentrated disposal area for waste paints and solvents was at the southern end of the landfill.

Groundwater beneath OU 1 is within a series of aquifers that are composed of permeable sand, gravel, or fill materials separated by finer grained silt or clay layers. Volatile organic compound contamination at OU 1 is only in about the top 60 ft of the unconsolidated deposits in the four hydrogeologic units: the unsaturated zone, the upper aquifer, the middle aquitard, and the intermediate aquifer. Groundwater in the unconfined upper aquifer generally flows from the east to the west toward Dogfish Bay. Groundwater in the predominately confined intermediate aquifer flows toward the landfill from the south and from the west, and then flows northwest beneath the landfill toward Dogfish Bay (Dinicola and others, 2002). Two perennial freshwater creeks drain the marsh adjacent to the landfill and discharge into the tide flats of Dogfish Bay.

Chlorinated VOCs are in the upper and intermediate aquifers and in surface water at OU 1. The predominant contaminants in groundwater beneath OU 1 are trichloroethene (TCE) and degradation byproducts cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). The compound 1,1,1-trichloroethane (TCA) and 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 these hazardous compounds are a potential risk to humans (URS Consultants, Inc., 1998). Phytoremediation combined with on-going natural attenuation processes was the preferred remedy selected by the Navy, as specified in the Record of Decision for the site (URS Consultants, Inc., 1998). The Navy planted two hybrid poplar plantations on the landfill (fig. 2) in spring 1999 to remove and control the migration of chlorinated VOCs in shallow groundwater (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 from 1996 through 2000 showed that natural attenuation and biodegradation of chlorinated VOCs in shallow groundwater 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 groundwater to ensure that conditions remain favorable for contaminant biodegradation. Annual monitoring from 2001 through 2006 confirmed biodegradation (Dinicola and Huffman, 2007). USGS data collected from 1996 through 2006 are in Dinicola and others (2002), Dinicola (2003, 2004, 2006), and Dinicola and Huffman (2004, 2006, 2007).

This report presents two sets of groundwater chemical and selected VOC data collected by the USGS at OU 1 during June 18–21, 2007 and June 16–18, 2008, in support of the long-term monitoring for natural attenuation. The USGS collected groundwater samples from 14 wells and 9 piezometers in 2007 and 2008 (table 1 and fig. 2), and concentrations of various geochemical constituents used to evaluate groundwater redox conditions were determined in all samples. Concentrations of VOCs also were determined by the USGS in samples collected from seven of nine piezometers in 2007, and in samples from all nine piezometers and three intermediate aquifer wells in 2008. The Navy determined VOC concentrations in samples they collected from other OU 1 monitoring wells during June 2007 and 2008; some of those data are discussed in this report.