Technology:
Constructed wetlands systems (CWS)
- Excavated pits filled with organic matter; two cells constructed
- Cells constructed below grade in both upflow and downflow mode
- Both cells consisted of a 0.05-acre cell (pit) filled 4 feet deep with a mixture of an organic-rich compost (96 percent) and alfalfa hay (4 percent)
- Base of each cell made up of a gravel subgrade, a 16-ounce geofabric, a sand layer, a clay liner, and a high-density polyethylene liner
- Base separated from influent or effluent piping by a geonet
- Each cell designed for a flow of 7 gpm
- Metals removed through a combination of sorption, precipitation, and biological sulfate reduction
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Cleanup Authority:
Not identified
Contacts:
EPA Work Assignment Manager
Edward Bates
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Office of Research and Development
26 West Martin Luther King Drive
Cincinnati, Ohio 45268
(513) 569-7774 (phone)
E-mail: bates.edward@epa.gov |
Contaminants:
Zinc |
Waste Source:
Drainage from mine operations |
Type/Quantity of Media Treated:
Mine drainage |
Purpose/Significance of Application:
Use of constructed wetlands for treatment of zinc in acid mine drainage |
Regulatory Requirements/Cleanup Goals:
Not identified |
Results:
- Upflow cell removed an average of 93 percent of zinc during the first year of operation, and 49 and 43 percent during the second and third years
- Downflow cell removed an average of 77 percent of zinc during the first year and 70 percent during the second year. During the final 6 months of operation, loss of permeability in the cell caused an increase in the retention time of the mine drainage in the cell. This resulted in a higher percentage (82 percent) of zinc removal |
Cost Factors:
No information was provided about the cost of this application. |
Description:
As part of the Superfund Innovative Technology Evaluation (SITE) Program, EPA evaluated CWS for removing high concentrations of zinc from mine drainage at Burleigh Tunnel in Silver Plume, Colorado. The system operated for three years and treated zinc in the mine drainage through sorption, sulfate reduction, and precipitation of zinc oxides, hydroxides, and carbonates. Organic-rich compost and alfalfa hay were placed two 0.05-acre, 4 ft deep cells (one upflow and one downflow). The cells were designed for a flow of 7 gpm.
Results from the upflow cell showed that the constructed wetlands system removed an average of 93 percent of zinc during the first year of operation, and 49 and 43 percent during the second and third years. The downflow cell removed an average of 77 percent of zinc during the first year and 70 percent during the second year. During the final 6 months of operation, the cell showed 82 percent zinc removal. No information was provided about the cost of this application. During the demonstration, it was noted that the cells can sometimes develop visibly obvious preferential pathways of flow. This was observed in the upflow cell in 1997, and was addressed by terminating flow to the preferred section, excavating the wetland substrate, and allowing installation of a cap on the influent line. |
