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Water: Nonpoint Source Success Stories

Colorado: Mosquito Creek Watershed

London Extension Mine Drainage Treatment Project Removes Heavy Metals

Waterbody | Problem | Project Highlights | Results | Partners & Funding

Waterbody Improved

co_circleSouth Mosquito Creek, in central Colorado, has been plagued for years by toxic metals from an abandoned gold mine. A drainage treatment system was constructed to increase the pH of the water and reduce heavy metal concentrations. The treatment system has reduced zinc levels in the creek to below the chronic toxicity level, on average meeting water quality standards and achieving part of the total maximum daily load (TMDL).


Since the construction of the mine drainage treatment system, monitoring samples show significant decreases in zinc concentrations. Zinc levels in South Mosquito Creek are below the chronic toxicity level and on average meet water quality standards. Additional verification will be required to confirm that the creek is in full compliance with water quality standards.

The treatment system removes approximately 50 percent of the zinc in the drainage, about 26 pounds of zinc per day, and averages a total metal removal of almost 47 pounds per day. On a yearly basis, approximately 8.5 tons of metals that formerly entered South Mosquito Creek are now captured by the treatment system.

Additional investigation and remediation will be required for the main stem Mosquito Creek to attain water quality standards. Since the TMDL includes both segments, goals for Mosquito Creek will need to be attained to meet the overall TMDL. However, the project demonstrates achievement of part of the overall TMDL goal, and South Mosquito Creek should now be able to support a brook trout fishery.

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Partners and Funding

The following partners were involved in this project and provided funding, in-kind services, and technical assistance:

  • Colorado Department of Natural Resources, Division of Minerals and Geology ($21,376)
  • Colorado Department of Public Health and Environment, Water Quality Control Division ($53,118 in section 319 funds)
  • London Mine Limited Liability Company (landowner) ($16,661)
  • Colorado School of Mines ($9,240)

Construction costs for the treatment system were around $100,000, and the cost of system operation and maintenance is estimated to be $10,000 annually, plus labor costs. To date EPA section 319 funding has provided $53,118 for the London Extension Tunnel mine drainage treatment project. With matching funds, the total amount spent was $100,395.

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