Anaerobic Compost Constructed Wetlands at the Clear Creek/Central City Superfund site, Burleigh Tunnel, Silver Plume, Colorado

Site Name:

Clear Creek/Central City Superfund site

Location:

Silver Plume, Colorado

Period of
Operation:

Fall 1994 - Fall 1997

Cleanup
Type:

Field demonstration

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

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.