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Passive Treatment Technologies for Reducing Metal Loading
Primary Issue Addressed: Acid Drainage/Water Treatment
Secondary Issue Addressed: Passive Treatment
Project Site: Primary focus is Canyon Creek, tributary of South Fork of Coeur d’Alene River and largest zinc load to South Fork
Collaborating Entities: EPA Region 10 and Coeur d’Alene Basin Project Focus Team meeting
Cost Share: None
Project Description
Historical mining practices and the naturally occurring geochemistry in the Coeur d’Alene Basin have resulted in contamination of soil, sediment, surface water, and groundwater. The purpose of this project is to evaluate passive treatment systems side-by-side while treating similar contaminated source water(s). The proposed work will: 1) evaluate new/promising materials for reactive bed-type application to remove zinc from neutral pH water; 2) start development of a chemistry based framework for matching media to contaminated water sources; and 3) provide performance data to support scale-up and economic evaluation of technologies. The information generated in this study will aid the U.S. Environment Protection Agency Region 10, Coeur d’Alene Basin Commission, and Idaho Department of Environmental Quality to evaluate and select passive treatment system designs for future implementation in the Coeur d’Alene Basin.
The Record of Decision for the Bunker Hill Operable Unit 3 Superfund site states that the goal is to reduce the zinc load to Canyon Creek by 50%. Figure 7 illustrates the dissolved zinc concentrations in the Canyon Creek groundwater. The Canyon Creek site is shown in Figure 8. Currently, Region 10/CH2MHill are considering treating a lower volume of higher zinc concentration groundwater in lower Canyon Creek rather than surface water. A hydrogeological evaluation must be conducted to evaluate feasibility of this alternative. Region 10/CH2M Hill are performing pilot testing of a lime high density sludge (HDS) system and a sulfate-reducing bacteria (SRB) bioreactor system. The Mine Waste Technology Program (MWTP) work complements this effort by focusing on new materials and passive treatment, as directed in the Record of Decision. The original project approach included bench-scale testing of materials followed by extensive on-site pilot testing of an unknown number of materials. The present approach will be to conduct bench-scale testing, evaluate technical and economic aspects, and conduct pilot testing only if it makes sense and fits within the MWTP budget and program priorities. High iron, low pH water was not sufficiently prevalent in Coeur d’Alene basin to warrant inclusion as a selected water; however, an effort is ongoing to identify a higher-hardness water to include in the study if such a water is deemed sufficiently different from the Canyon Creek groundwater that is currently the focus of this study. The likely media to be tested are listed below:
- Bauxsol;
- Apatite II™
- juniper bark (U.S. Forest Service-developed material);
- ferrihydrite or ferrihydrite-coated sand;
- aluminum-modified ferrihydrite;
- granular ferric hydroxide;
- manganese dioxide-coated sand;
- ferrous sulfide;
- limestone/MgO;
- activated carbon/apatite; and
- zeolites (if available locally).
Status
A literature search was performed for potentially suitable materials. We
had difficulties obtaining access from Hecla Mining for the Canyon Creek
site selected for Region 10/CH2M Hill pilot testing.
Figure 7. Dissolved zinc concentrations in the Canyon creek groundwater.
Figure 8. Canyon Creek site.
Region 10 obtained access mid-September, and two wells were installed to provide groundwater for testing. Region 10 decided to perform lime HDS and SRB pilot testing at the Bunker Hill water treatment plant in Kellogg and transport water there for testing. Additional materials were identified for testing, and high iron, low pH water not sufficiently prevalent in Coeur d’Alene basin to warrant inclusion. Personnel are searching OU3 RI for higher-hardness waters to include, which must be sufficiently different from Canyon Creek
We also plan to finalize a list of materials, prepare QA test plan (may include small batch contacts as well as small columns), transport test waters to MSE Technology Applications, Inc., for testing, and execute test plan.