Scientific Investigations Report 2006-5056
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5056
Chlorinated volatile organic compounds (CVOCs) have migrated to ground water beneath a former 9-acre landfill at Operable Unit 1 (OU-1) of the Naval Undersea Warfare Center (NUWC), Division Keyport, Washington (fig. 1). The predominant ground-water contaminants are the chloroethene compounds—trichloroethene (TCE), cis 1,2 dichloroethene (cis-DCE), and vinyl chloride (VC). Less predominant contaminants include tetrachloroethene (PCE), trans-1,2 dichloroethene (trans-DCE), 1,1-dichloroethene (1,1 DCE) 1,1,1-trichloroethane (TCA), 1,1-dichloroethane (1,1-DCA), and 1,2-dichloroethane (1,2-DCA). A need for remedial action was identified because some of the contaminants present a potential risk to humans, primarily through drinking contaminated ground water or through ingesting seafood harvested from contaminated surface water (URS Consultants, Inc., 1998).
The Navy began a cooperative effort with the U.S. Geological Survey (USGS) in 1995 to evaluate the effectiveness of natural attenuation processes for removing and controlling the migration of CVOCs in ground water at OU-1. Field and laboratory studies from 1996 through 2000 demonstrated that natural attenuation and biodegradation of CVOCs in shallow ground water at OU-1 is substantial (URS Consultants, Inc., 1997a; Bradley and others, 1998; Dinicola and others, 2002). In 1998, a remedy was developed for contaminated ground water at OU-1 that includes phytoremediation and on-going natural attenuation processes to remove and control the migration of CVOCs in shallow ground water (URS Consultants, Inc., 1998). In 1999, the Navy planted two hybrid poplar plantations in two areas on the landfill where contaminant concentrations in ground water were exceptionally high (fig. 2) (URS Greiner, Inc., 1999). The Navy regularly monitored contaminant concentrations in ground and surface water, along with tree health and water levels, to determine the effectiveness of phytoremediation (CH2M Hill Constructors, Inc., 2002, 2003, 2004, and 2005). The USGS monitored geochemistry and contaminant concentrations in ground and surface water annually from 2001 through 2004 to evaluate reduction-oxidation (redox) conditions and CVOC biodegradation.
This report presents ground-water geochemical and selected CVOC data collected by the USGS at OU-1 during June and July 2004, and evaluates evidence for continued biodegradation of chloroethenes in ground water at OU 1. Biodegradation of chloroethanes was not specifically evaluated because those contaminants are greatly limited in extent at the site. Data used for the evaluation included CVOC and geochemical data collected during 2001–04 by the USGS (Dinicola, 2003; 2004; Dinicola and Huffman, 2004) and the Navy (CH2M Hill Constructors, Inc., 2002, 2003, 2004, and 2005) in addition to data presented in a prior evaluation of natural attenuation (Dinicola and others, 2002).
In June 2004, the USGS collected water samples from 19 wells and 9 piezometers (table 1, fig. 2) to determine volatile organic compound (VOC) and geochemical concentrations. The USGS also sampled VOCs in shallow ground water directly beneath the marsh stream and pond (fig. 2) using passive-diffusion samplers. Samplers were deployed in the same locations that were sampled by the USGS in June 2000.
NUWC, Division Keyport is on a small peninsula in Kitsap County, Washington, in an extension of Puget Sound called Liberty Bay (fig. 1). The 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 marshland. The landfill was the primary disposal area for domestic and industrial wastes generated by NUWC, Division 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 (fig. 2).
CVOCs are present in the upper and intermediate aquifers and in surface water at OU-1. Ground water beneath OU-1 occurs in a series of aquifers composed of permeable sand, gravel, or fill materials separated by fine-grained silt or clay layers. Contamination at OU-1 occurs only in about the top 60 ft of the unconsolidated deposits in the hydrogeologic units referred to locally as the unsaturated zone, the upper aquifer, the middle confining unit, and the intermediate aquifer.
The unsaturated zone primarily consists of fill materials including a mix of silt, sand, gravel, clay, and trash debris. The unit also includes organic-rich silt or silty-sand marsh deposits and silt or silty-sand estuary and tide flats deposits. The unit ranges from 0- to about 20-ft thick. The permeability of the unsaturated zone is highly variable due to its heterogeneity.
The upper aquifer consists primarily of sand or silty-sand and gravel with localized zones of marsh, estuary, and tide flat deposits. The unit is nearly continuous across OU-1 and ranges from about 4- to 22-ft thick. The permeability of the upper aquifer is variable and scattered deposits of finer grained materials indicate that preferential flow pathways are likely over short distances. Estimated hydraulic conductivity for the upper aquifer ranges from 0.2 to 4.1 ft/d (URS Consultants, Inc., 1997a).
The middle confining unit separates the upper and intermediate aquifers and consists primarily of silt, clay, and fine sand with localized peat. The unit is nearly continuous across OU-1 and ranges from about 1- to 40-ft thick. The middle confining unit is notably absent beneath the central part of the landfill; an eroded window of about 1 acre extends northwest for about 500 ft from the southeastern edge of the landfill (fig. 2). The permeability of the middle confining unit is mostly low, with an estimated vertical hydraulic conductivity of 0.0001 ft/d (URS Consultants, Inc., 1993).
The intermediate aquifer consists primarily of sand and gravel with localized silt and glacial-till lenses. The unit is continuous across OU-1 except near well MW1-7 (southwest of the marsh pond), where it is truncated by fine-grained glaciolacustrine clay and silt deposits. The intermediate aquifer thins to less than 1 ft and is indistinct near the northwestern margin of the landfill, and it increases to about 30–40 ft in thickness upgradient (south) and downgradient (northwest) of the landfill. Beneath the tide flats and in the vicinity of State Highway 308 causeway, the aquifer is divided into an upper and lower permeable zone by as much as 16 ft of a compacted glacial till deposit. Estimated hydraulic conductivity for the intermediate aquifer is 3.3 ft/d (URS Consultants, Inc., 1997a).
The Clover Park confining unit is a regionally extensive unit consisting of hard silt, peat, and clay that lies beneath the intermediate aquifer. The unit is continuous beneath OU-1 and ranges from 100- to 200-ft thick. The estimated vertical hydraulic conductivity of the Clover Park confining unit is 0.01–0.0001 ft/d (URS Consultants, Inc., 1993).
Water in the unconfined upper aquifer generally flows from east to west beneath the landfill toward Dogfish Bay (fig. 3). Water in the predominately confined intermediate aquifer flows from the south and west toward the landfill, and then northwest from the landfill toward Dogfish Bay (fig. 4). Some ground water in the contaminated portion of the upper aquifer flows downward into the intermediate aquifer. Measured water levels indicate that a downward gradient for ground-water flow is between the upper and intermediate aquifers beneath the northeastern one-third of the landfill, and that an upward gradient is beneath the remainder of the landfill and perhaps the entire marsh (URS Consultants, Ins., 1997a). Although upper-aquifer water levels and flow directions beneath the northwestern part of the landfill are influenced by tidal changes, ground-water salinity and water-levels frequently measured by the Navy indicated little seawater flux entered the upper aquifer during high tides (URS Consultants Inc., 1997a). Ground-water levels and flow directions in the intermediate aquifer beneath and adjacent to the tide flats also are influenced by tidal changes, but the seawater flux into and out of the aquifer beneath OU-1 during the tidal cycle was negligible (URS Consultants Inc., 1997a). More detailed descriptions of study area hydrogeology and contamination are available in URS Consultants Inc., (1997a) and Dinicola and others (2002).
The entire area bordered by Bradley, Shapely, and Keys Roads, and the former landfill is referred to as the marsh in this report (fig. 2). Two creeks flow into the perennial pond in the marsh, and a single perennial creek drains the marsh and discharges into the tide flats of Dogfish Bay (fig. 2). The outlet creek flows through a culvert and tide gate and into the tide flats. During periods of no runoff, freshwater inflow into the marsh is entirely ground-water discharge. Seawater flows into the marsh due to the 10–12 ft diurnal tidal fluctuations in Dogfish Bay. During high tides, water levels in the tide flats are at the same water-level altitude as Dogfish Bay. However, the tide gate at the marsh outlet automatically closes during high tide cycles and prevents seawater from flowing upstream beyond the marsh pond.
The landfill was constructed on a tidal marsh and was the primary disposal area for domestic and industrial wastes generated by NUWC, Division Keyport from the 1930s through 1973. The bottom of the landfill was unlined, and the top was kept covered with a thin veneer of soil as filling progressed. The Navy burned mixed trash and demolition debris in the northern part of the landfill, and disposed of unburned materials including paints, thinners, solvents, acids, dried sludge from a wastewater-treatment plant, and other industrial wastes at various locations in the landfill from the 1930s through 1973. The most concentrated area for waste paint and solvent disposal was at the southern end of the landfill (fig. 2). Few, if any, intact and full drums of waste were thought to be buried in the landfill. Instead, most drum contents were emptied into the landfill and the drums were reused or crushed and buried. After closure, the southern two-thirds of the landfill was covered with asphalt, while the northern one-third was covered with gravel, fine-grained soils, and grass.
Preparation for phytoremediation began in February 1999 at the two plantation sites, referred to as the “northern plantation” and the “southern plantation.” Asphalt, which covered all of the northern plantation site and the south 25 percent of southern plantation, was removed and the top 18-in. of the plantation sites were cultivated using agricultural equipment and amended with about 0.5–1.5 ft of clean topsoil (URS Greiner, Inc., 1999). The Navy planted the two hybrid poplar plantations on the landfill in April and May 1999. The plantations were irrigated when the trees showed sign of stress during the latter part of most summers. Test pits by the Navy confirmed that tree roots reached the water table during the 2002 growing season (URS Greiner, Inc., 2002), and the plantation canopies closed during the 2003 growing season (URS Greiner, Inc., 2003).
The authors thank the many people and agencies for their significant contributions to the study. Douglas Thelin and Matthew Butler of the Naval Facilities Engineering Command, Engineering Field Activity, Northwest (EFANW) provided guidance and funding for the investigation. Gene Ellis of NUWC, Division Keyport and Mick Butterfield of EFANW provided logistic support for field activities. Michael Meyer of URS Corporation and Bernard Wong of CH2M Hill Constructors, Inc., provided logistic support and additional data.
For more information about USGS activities in Washington, visit the USGS Washington Water Science Center home page.
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