U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5090
Vertical Distribution of Trace-Element Concentrations and Occurrence of Metallurgical Slag Particles in Accumulated Bed Sediments of Lake Roosevelt, Washington, September 2002
Introduction
Trace-element contamination is known to be widespread throughout surficial bed sediments of Franklin D. Roosevelt Lake, the reservoir created by the impoundment of the Columbia River behind Grand Coulee Dam. Franklin D. Roosevelt Lake, better known as Lake Roosevelt, was completed in 1941 and has developed into a major economic and recreational resource for the region attracting from 1 to 1.5 million visitors each year. Lake Roosevelt also is a vital cultural resource for The Confederated Tribes of the Colville Reservation (CCT) and The Spokane Tribe of Indians whose combined tribal lands extend along more than one-half of the reservoir's length. The reservoir is used extensively by many tribal members who live near the reservoir.
Trace-element contamination of reservoir sediments was first reported in the mid-1980s (Lowe and others, 1985; Johnson and others, 1988, 1990). Trace elements of concern include arsenic, cadmium, copper, lead, mercury, and zinc. Subsequent studies have shown that trace-element contamination of surficial sediments in the lake and adjacent beach deposits is widespread and follows a general pattern in which concentrations of trace elements typically are larger in the upstream reaches of the reservoir compared to concentrations in downstream reaches (Johnson and others, 1990; Bortleson and others, 1994; Majewski and others, 2003; U.S. Environmental Protection Agency, 2003). Trace-element concentrations in bed sediments range from 4 to 220 times larger than concentrations in background reference sediments. In addition, contamination of sport fish with mercury and other trace elements has resulted in the issuance of a health advisory on the human consumption of several species of popular sport fish (Munn and others, 1995), although the level of sport fish contamination has decreased for some constituents (Munn, 2000).
The primary source of elevated trace-element concentrations in bed sediments of Lake Roosevelt is attributed to the transport of metallurgical wastes discharged to the Columbia River by a smelter at Trail, British Columbia, located 21 km upstream of the International Boundary (Bortleson and others, 1994). The smelter has been in operation since the 1890s and historically has discharged wastes to the Columbia River, much of which are transported and deposited in the quiescent waters of Lake Roosevelt. Although waste discharges have occurred nearly continuously throughout most of Lake Roosevelt's 60 plus years of existence, efforts have been underway at the smelter over the last several decades to reduce trace-element loading to the Columbia River. The reduction in effluent discharges may be reflected in the variations in the concentrations of trace elements present in the accumulated sedimentary record of Lake Roosevelt. Previous information on variations in the vertical distribution of trace elements in the accumulated sediments of Lake Roosevelt is limited. Additional information on variations in concentrations of trace elements in the accumulated sediments could provide a useful record of trace elements entering Lake Roosevelt.
Purpose and Scope
The purpose of this report is to present the results of a study (1) to evaluate the trace-element concentrations within the accumulated bed sediments of Lake Roosevelt; (2) to determine if the potential exists for remobilization of trace elements within the buried sediments; and (3) to evaluate sediment from selected core intervals for the occurrence of metallurgical slag. The study was conducted by the U.S. Geological Survey (USGS) in cooperation with the Confederated Tribes of the Colville Reservation. Sediment cores were collected for the determination of trace-element profiles at six widely spaced locations in Lake Roosevelt in September 2002; with additional sediments collected in July 2003 for analysis of trace elements in pore water. Sediment cores were sectioned and concentrations of trace elements were analyzed for the individual sections, generating a profile of trace-element concentrations. Selected sediment intervals also were examined for either the occurrence of metallurgical slag particles or the concentration of trace elements in pore water.
Description of Study Area
Lake Roosevelt is in north-central Washington and is the largest reservoir in the State of Washington (fig. 1). The lake was formed by the impoundment of the Columbia River behind Grand Coulee Dam and, when filled to capacity, the reservoir extends upstream more than 237 km such that back-water conditions extend to near the International Boundary (Ray Smith, U.S. Geological Survey, oral commun., 2004). The entire reservoir covers about 32,700 ha and has a storage volume of about 12.8 billion m3. The maximum water depth in the reservoir is more than 115 m (377 ft), and averages about 35 m (115 ft). Flow from the Columbia River makes up the majority (90 percent) of the inflow to Lake Roosevelt; with another 7 percent of inflow from the Spokane River. Flow in these rivers is highly regulated and depleted of suspended sediment by the numerous dams and reservoirs that have been constructed on upstream reaches. Other sources of river inflow to Lake Roosevelt include the Colville, Kettle, and Sanpoil Rivers and the numerous creeks that drain the uplands surrounding the reservoir.
Bed sediments of Lake Roosevelt vary from armored boulders to silts and clay. To provide a framework for interpreting the sediment chemistry data, Bortleson and others (1994) divided the reservoir along the length of the pre-reservoir river channel into several reaches based predominantly on the physical characteristic and depositional environment. The lower reach extends from Grand Coulee Dam to the confluence of the Spokane River and is characterized by a deep wide channel with slowing flowing water covering extensive pre-reservoir shorelands and containing lacustrine sediments, which are influenced by inputs from the Spokane River. The mid-reach of the reservoir extends from the confluence of the Spokane River to Marcus Island and is characterized by deep-slowing moving water in a wide irregular channel containing lacustrine sediments. The upper reach of the reservoir extends from Marcus Island to about RM 730, which is characterized by a narrowing and shallowing channel with fewer embayments and flooded areas generally lacking lacustrine sediments from the swifter flowing reservoir conditions in the pre-reservoir channel. The transitional reach (Northport Reach) that extends from RM 730 to near the International Boundary where flow conditions transition from impounded slack water of the upper reach of the reservoir to the swift river environment of the free flowing Columbia River contain primarily a cobbly-boulder streambed with sand-size sediments deposited only in protected areas.
Figure 1. Location of study area and sediment-core collection sites on Lake Roosevelt and the upper Columbia River, Washington.
Sediments deposited in Lake Roosevelt are derived from the upper basin of the Columbia River, tributary streams and rivers, and from landslides and erosion of unconsolidated sediments along the margin of the reservoir. Granulated slag discharged to the Columbia River from the smelter upstream of Lake Roosevelt is a component of sediment that is transported and deposited in Lake Roosevelt. Numerous landslides have occurred along the shores of Lake Roosevelt, primarily in the unconsolidated Pleistocene terrace sediments that occur along 80 to 90 percent of reservoir shoreline (Jones and others, 1961; Kiver and Stradling, 1995; and U.S. Bureau of Reclamation, 2001). Large landslides on the order of 765,000 m3 of material occurred more frequently in the past, particularly in the early years following completion of the reservoir. Between 1941 and 1954, there were more than 500 landslides along the reservoir shoreline that related to the initial filling of the reservoir and the fluctuating water level in the reservoir (Jones and others, 1961). Landslides continue to occur up to the present (U.S. Bureau of Reclamation, 2001), although they typically are smaller in magnitude and the severity has greatly diminished. Concentrations of trace elements in bank sediments prone to landslides are on the order of western continental averages reported by Shacklette and Boerngen (1984).
Trace-element concentrations in bank material typically were much smaller than concentrations measured in suspended sediment flowing into Lake Roosevelt (Bortleson and others, 1994; Kelly and others, 2001). A comparison of trace-element concentrations in bank sediments adjacent to Lake Roosevelt to trace-element concentrations reported in Columbia River suspended sediment is shown in figure 2. The reported concentrations of trace elements in suspended sediment were determined from 22 discharge-weighted samples collected between 1995 and 2000 at Northport (Kelly and others, 2001). For the trace elements of concern, the greatest difference was in the concentration for zinc, which was roughly 30 times larger in suspended sediment than in bank sediments. Concentrations of cadmium, copper, and lead were about 10 times larger in suspended-sediment samples than concentrations in samples of bank sediments. The concentrations of arsenic were the most similar; the concentration in suspended sediment was only about two times as large as arsenic concentrations in samples of bank sediments. Mercury concentrations in suspended sediment were not reported by Kelly and others (2001), however, Bortleson and others (1994) reported a median concentration of mercury in five discharge-weighted suspended-sediment samples of 1.7 mg/kg, which is roughly 30 times larger than the concentrations in typical bank deposits (<0.05 mg/kg). From these data, the episodic addition of bank sediments to relatively consistent input of suspended sediment transported to Lake Roosevelt by the Columbia River will dilute the concentration of trace elements in the resulting bed sediments. Thus landslides, particularly in the upper part of the reservoir, tend to dilute concentrations of arsenic, copper, cadmium, lead, mercury, and zinc in sediments carried to the reservoir by the Columbia River.
Figure 2. Concentrations of selected trace elements in suspended sediment from the Columbia River at Northport, Washington, and in Lake Roosevelt shoreline bank materials.
Most of Lake Roosevelt is situated within the Okanogan Highland of north-central Washington, an area that extends about 250 km north into British Columbia, in which extensive geologic processes have resulted in a mountainous and highly mineralized region containing many precious and base metal deposits (Washington State Department of Natural Resources, 2003). Geologically, this region is composed of some of the oldest and most mineralized geologic units in Washington. In the area east of Lake Roosevelt, the repeated folded metasedimentary rocks of the Kootenay Arc contain hydrothermal ore deposits, particularly lead and zinc, many of which have been developed. Lead and zinc ores typically occur as the minerals galena and sphalerite that were deposited in veins, open space fillings, or as replacement bodies in limestone and dolomite deposits. Mills (1977) describes 98 separate deposits in Stevens County alone, many of which also were reported to contain minor amounts of silver. Numerous similar sites also occur in the Kootenay Arc region of British Columbia although the Sullivan Mine that produced much of the ore for the Trail smelter was characterized as a sedimentary-exhalative deposit (Lydon, 2000). Other trace elements often associated with lead deposits composed of galena include antimony, copper, arsenic, and bismuth; elements associated with zinc deposits composed primarily of sphalerite include copper, tin, arsenic, silver, mercury, iron, manganese, and cadmium (Levinson, 1974). Precious metal deposits to the west of Lake Roosevelt also have been developed particularly in the area around Republic. In addition to gold and silver, there are deposits containing copper, cobalt, bismuth, and molybdenum.
Metallurgical and mining wastes have been discharged to streams of the upper Columbia River (Orlob and Saxton, 1950). The Trail smelter was originally built as a copper smelter in 1896 and was converted to smelt lead and zinc in 1909 (G3 Consulting, Ltd., 2001). Lead and zinc production have been nearly continuous since that time and the facility has developed into one of the worlds largest integrated metallurgical complexes. Annual production in 2000 was 273,000 metric tonnes of refined zinc and 91,000 tonnes of refined lead, with smaller quantities of silver, gold, cadmium, bismuth, and many other associated metal products (Teck-Cominco, 2002). Historically, waste materials from this facility, including slag and process waste water, were discharged directly to the Columbia River. Between the late 1970s and late 1990, the metallurgical complex was extensively modernized to improve production efficiency and reduce the discharge of slag and effluent to the Columbia River. Effluent treatment was installed in 1981 and was upgraded through the 1990s. The operation of the phosphate fertilizer plant was discontinued in 1994. The routine discharge of slag to the Columbia River was discontinued in 1995 after which time reported slag discharge has been limited to periods when disruption in the smelting process have resulted in upset conditions at the smelter when the release of waste material has occurred.
Previous Studies of Trace Elements in Lake Roosevelt Bed Sediments
Initial assessment of the extent of trace-element contamination in Lake Roosevelt bed sediment (Johnson and others, 1988, 1990) showed that elevated concentrations of trace elements were widespread throughout Lake Roosevelt and that the concentrations of trace elements decreased along the longitudinal axis from upstream to downstream. They attributed the source of the elevated trace elements to the discharge of smelter wastes to the Columbia River at Trail. This source had been previously identified by British Columbia Ministry of Environment (1976, 1979) and Environment Canada (Sheehan and Lamb, 1987; Sigma Engineering Ltd., 1987; and Smith, 1987; NORECOL Environmental Consultants Ltd., 1989,) as a source of metals contamination of water, sediment, and biota in the reach of the Columbia River immediately upstream of the International Border.
A comprehensive follow-up study was conducted in 1992 by the U.S. Geological Survey (Bortleson and others, 1994) that determined trace-element concentrations in sediment from Lake Roosevelt and its tributaries, including the upstream reach of the Columbia River extending to reservoirs in Canada. The results of that study confirmed and greatly extended previous findings and conclusions. The overarching conclusion was that although other possible sources of trace elements were present within the region and may have a localized influence on trace-element concentrations in the sediments of Lake Roosevelt, the primary source of the widespread elevated trace-element concentrations in the bed sediments of Lake Roosevelt was the waste discharged to the Columbia River from the Trail smelter. This conclusion, based on the distribution of elevated trace-element concentrations in bed sediments and the hydrology of the reservoir-river system, was the only adequate explanation of the persistent and widespread distribution of trace elements in the bed sediments throughout Lake Roosevelt and the upstream reach of the Columbia River and the differences in the patterns of specific trace-element concentrations.
All trace elements of concern, including arsenic, cadmium, copper, lead, mercury, and zinc, are known to be components of the liquid effluent or slag discharged to the Columbia River by the Trail smelter (British Columbia Ministry of Environment, 1976; 1979). The concentrations of these trace elements in bed sediments were all highly elevated at locations downstream of the area of smelter waste discharge, however, the distributional pattern of elevated trace elements in the sediments of Lake Roosevelt varied among trace elements reflecting depositional grain-size and mode of trace-element input. The most notable pattern was simultaneous presence of slag particles and very large concentrations of copper and zinc in bed sediments of the upper and transitional reaches of Lake Roosevelt and the upstream reach of the Columbia River. Slag, which was reported to contain 0.5 to 1 percent copper and 2 to 3 percent zinc, could be easily identified in sand-size fractions by its unique morphology and physical characteristics. In sediment samples from the International Boundary, in which slag was estimated to compose 48 percent of sediment grains, the concentrations of copper and zinc were 3,000 and 15,000 mg/kg, respectively, while slag in bed sediments 24 km farther downstream was estimated to comprise 5 percent of the sand-sized fraction and the concentrations of copper and zinc were 670 and 4,100 mg/kg, respectively. In the transitional reach of the reservoir near Northport, bed sediments contained substantial percentages of sand-sized particles and the very large concentrations of copper and zinc were attributed to the presence of slag particles in these sediments. Other trace elements noted to follow distributional patterns similar to slag were antimony, arsenic, barium, chromium, iron, and manganese.
Bortleson and others (1994) also reported that concentrations of cadmium, lead, and mercury were larger in bed sediments farther downstream in the mid and lower reaches of the reservoir where depositional areas are predominated by silt-size particles. Cadmium, lead, and particularly mercury are present in slag in very small concentrations compared to copper and zinc but are prevalent in the liquid effluent discharged by the Trail smelter. The presence of these trace elements in bed sediments of Lake Roosevelt was attributed to the sorption of trace elements from the water column onto suspended-sediment particles, which are subsequently deposited in the downstream quiescent waters of the mid and lower reaches of Lake Roosevelt. Because sorption is related to the surface area of particles, a proportionally greater mass of trace elements is sorbed to smaller sized sediment particles. Thus, concentrations of these trace elements were larger in the downstream reaches of Lake Roosevelt that were dominated by fine colloidal silt and clay sized lacustrine sediments.
Additional information on previous studies of the water quality of Lake Roosevelt and trace-element contamination of bed sediments in Lake Roosevelt have been reviewed and summarized in Derewetzky and others (1994) and U.S. Environmental Protection Agency (2000; 2003).
The effects of the Trail-smelter discharge on water, sediment, and biota in the Columbia River receiving water was evaluated in a study conducted by the smelter between 1995 and 1999 (G3 Consulting, Ltd., 2001). The intent of that study was to document the effects from modernization of the smelter process and improved waste-management practices implemented in the mid-1990s on trace-element loading to the Columbia River from the Trail smelter effluent discharge. This study examined trace-element concentrations in water, sediment, and biota at locations upstream and downstream of the effluent discharge zone of the Trail-smelter complex in the spring and autumn of 1995 and 1999 (G3 Consulting, Ltd., 2001). Results from this study clearly demonstrated the large influence that slag and liquid effluent discharges have had on the trace-element concentrations in water and sediment of the Columbia River, and thus Lake Roosevelt.
Very large increases in trace-element concentration in sediment immediately downstream of the effluent and slag discharge from the smelter were observed during the 1995 sampling prior to completion of the last phases of an extensive modernization of the lead smelting facility. As shown in table 1, the measured concentrations of nearly all 29 trace elements measured were often many fold higher in bed-sediment samples collected downstream of the smelter complex than the concentrations measured in samples of similar material collected from a background reference site 8 km upstream of the smelter complex. Although the measured concentrations of trace elements in sediment collected at the upstream reference site did not change substantially between 1995 and 1999, except for iron, the trace-element concentrations in sediments at sites downstream of the metallurgical complex were much smaller in 1999 than in 1995. These decreases in concentrations were attributed to implementation of the new lead smelter and discontinuing the practice of discharging slag to the Columbia River (G3 Consulting, Ltd., 2001). Considering that historical discharges of slag and liquid effluent were substantially larger than occurred in 1995, these results demonstrate a minimum level of influence that Trail smelter discharge had on sediment chemistry in the Columbia River down stream of smelter and subsequently Lake Roosevelt throughout most of its existence.
[Modified from Appendix 3.1.4, G3 Consulting Ltd., 2001. mg/kg, milligram per kilogram]
| Element | Upstream reference site |
Downstream monitoring site |
||
|---|---|---|---|---|
| 1995 | 1999 | 1995 | 1999 | |
| Major element (mg/kg) | ||||
| Aluminum | 2,820 | 3,290 | 15,700 | 8,600 |
| Calcium | 1,690 | 1,840 | 49,800 | 21,800 |
| Iron | 5,160 | 14,900 | 181,000 | 80,000 |
| Magnesium | 2,020 | 1,850 | 5,700 | 3,580 |
| Manganese | 129 | 146 | 4,840 | 1,870 |
| Titanium | 281 | 298 | 1,230 | 641 |
| Trace elements (mg/kg) | ||||
| Antimony | 0.15 | 0.187 | 56 | 87.2 |
| Arsenic | 1.14 | 1 | 41.8 | 23.5 |
| Barium | 29.4 | 24.6 | 3,260 | 920 |
| Berylium | <.2 | .14 | 1.4 | 4 |
| Bismuth | .05 | .055 | .838 | .218 |
| Boron | 6.47 | 5 | 147 | 24 |
| Cadmium | .17 | .147 | 4.1 | 1.19 |
| Chromium | 8.73 | 16.6 | 265 | 58.6 |
| Cobalt | 2.43 | 2.51 | 192 | 35.6 |
| Copper | 10.1 | 13.2 | 3,740 | 1,100 |
| Germanium | <.1 | .09 | 34.5 | 9.6 |
| Gallium | 1.55 | 2.22 | 35.3 | 10.2 |
| Indium | <.05 | .02 | 23.9 | 9.23 |
| Lead | 8.48 | 8.29 | 312 | 237 |
| Lithium | 7.72 | 5.21 | 21.3 | 7.67 |
| Mercury | <.05 | <.02 | .05 | .02 |
| Molybdenum | .21 | .15 | 68.8 | 16.1 |
| Nickel | 7.05 | 7.3 | 26.4 | 12.9 |
| Selenium | <1 | <.05 | 1.3 | 1 |
| Silver | .12 | .076 | 12.7 | 5.48 |
| Strontium | 22.5 | 22.8 | 732 | 195 |
| Tellerium | <.2 | <.01 | .261 | .06 |
| Thalium | <.05 | .04 | .353 | .215 |
| Thorium | 4.04 | 8.81 | 4.38 | 4.22 |
| Tin | .24 | .248 | 44 | 68.7 |
| Tungsten | .59 | .24 | 20 | 4.16 |
| Uranium | .49 | .68 | 7.16 | 2.34 |
| Vanadium | 13.3 | 28.7 | 54.5 | 28 |
| Zinc | 58.1 | 40.3 | 21,400 | 5,660 |
Acknowledgments
This study was conducted with the assistance of many individuals and organizations. We thank Patti Bailey and the Confederated Tribes of the Colville Indian Reservation for their assistance in planning and conducting this study; Greg Behrans of the U.S. Bureau of Reclamation at Grand Coulee Dam for map coverages and information on landslides; Brian Hicks of the Colville Tribe and Louis Wynn of the Spokane Tribe for archaeological support of field activities; Rick Sanzalone of the U.S. Geological Survey, Geologic Materials Laboratory for conducting the partial extraction of trace-element experiment and oversight of laboratory analysis. Technical review of previous drafts of this report were provided by Don Hurst of the Confederated Tribes of the Colville Indian Reservation and Lauri Balistrieri, Gilbert Bortleson (retired), Anthony Paulson, and Gary Turney of the U.S. Geological Survey.
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