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WEST PAGE SWAMP WETLAND RESTORATION PROJECT
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Introduction: Off the slopes of Bunker Hill, into wetlands
Bunker Hill in the Coeur d'Alene River Basin in Idaho is the second largest Superfund site in the US. Mining and smelting of Zn and Pb took place from 1916 to the 1980's.
West Page Swamp (WPS) is an 11-ha wetland that was used for direct tailings deposition for the Hayes Company Mill from 1918-1929, resulting in Pb, Zn, Cd, and As contamination. The primary ecosystem risk associated with elevated Pb levels in wetlands is to the migratory fowl that use these wetlands as a seasonal feeding and nesting area.
- Lead 30,000 mg/kg
- Zinc 15,000 mg/kg
- Cadmium 100 mg/kg
As part of a closure agreement with Region 10 U.S. EPA, the mining companies involved with the site excavated a 2-ha portion of the swamp. Tailings were removed in 1997 to a depth of 0.7 m to reduce the potential for exposure of wildlife to metal contamination.
Basis for Amendment
Previous work in lead-contaminated soils has shown the potential for soil amendments to reduce the bioaccessibility of lead. This reduction can be achieved in two ways: (1) by altering Pb mineralogy, and (2) through a physical separation of the contaminated sediments from edible plant tissue. By adding approximately 15 cm of fertile surface to WPS, plant species should be able to rapidly reestablish, with rooting concentrated primarily in the compost surface horizon. For waterfowl, this suggests that the bulk of ingested sediment will be from the newly created soil horizon, so that the risk associated with the elevated Pb concentrations in the underlying horizon will be reduced.
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Biosolids composts are fertile, primarily organic materials that are similar in many respects to the organic horizon commonly found on the surface soil of a fully functional wetland. Composts have successfully been used to build wetlands. Wood ash is a high calcium carbonate residual that also provides K for plant growth. Log yard debris is a woody material that is a by-product of the lumber industry. It has a high C:N ratio, and so can limit release of excess N. All of these materials were used to create a new surface horizon at the WS.
Project goal
The goal of this project was to test the feasibility of using biosolids compost in combination with other residuals to accelerate revegetation and to limit the ecosystem impact of metals contaminated wetlands. If successful, this remediation strategy could be used in the approximately 25,000 ha of tailings-affected wetlands downstream of the mining area.
Applications
Application of composts to a pre-existing wetland provides a challenge from an operational perspective. Initially dry, we began operations with a loader and dozer.
However, rising fall groundwater caused standing water and a low bearing capacity after only one day. To gain access to the center of the swamp, logyard debris was used to build a road by dump truck and bulldozer over road fabric. Compost and wood ash were mixed and thrown with an throw spreader from both the constructed road and the county highway. Coverage was up to 25 m with the most extensive occurring between 0-15 m. Initial application was completed in late October 1998.
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Due to limitations in access and throwing
distance, a significant portion was either lightly applied or
not applied at all. In September 2000 the remaining portion was
treated by the use of a blower. |
The wetland has now been closed on the outlet end, so that a water depth of 2 feet will be maintained.
Elements being Monitored
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Physical Changes. Movement and
settling of treatment at 12 and 24 months.
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Effluent Quality. Monthly for suspended solids, pH, total elements, and N species |
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Plant Establishment and metal uptake. |
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C & N Dynamics. Decomposition and N mineralization at 6, 12 and 24 months by porous ceramic tubes filled with treatment mixtures. |
| These cups were filled with mixtures of compost, ash and logyard waste, and innoculated with swamp water. | Then they were buried in the wetland treatment layer. |
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Collection after 12 months |
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Collection site after 24 months - and the uncovered tubes |
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Greenhouse Study
A study was initiated in a greenhouse to understand the effectiveness of our treatments on wetland plants and the chemistry of the soil. Treatments to 10 cm of sediment included 15 cm biosolids compost & wood ash, K2SO4, or nothing, and covered with 5 cm of water. Arrowhead (Sagittaria latifolia) and cattail (Typha latifolia) were grown for 3 months. Some of the measurements included pH, redox potential, pore soluble lead, bioaccessibility of sediment Pb and a physiologically based extraction procedure (PBET), and plant growth and metal uptake.
Cooperators
Sally Brown, Chuck Henry and Pam DeVolder
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Harry Compton and Scott Fredericks
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Earl Liverman
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Dan Sturgill
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Mike Kennedy
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Suppliers: Avista Utilities, Coeur d'Alene, Eko Compost, Abitibi, Crown Pacific, and Malloy Lumber
