There are thousands of abandoned mines in Wyoming and Colorado that discharge Acid Mine Drainage (AMD) into rivers and streams. This contaminated drainage often contains high levels of metals that at certain concentrations are toxic to fish and humans. On August 5, 2015 contractors under the direction of the US Environmental Protection Agency were working at the Gold King Mine near Silverton Colorado, and released approximately three million gallons of AMD into the Animas River in Southwestern Colorado. The video footage of an orange river on the evening news brought the problem of historical mine drainage contamination to the public stage.
The Bonanza Mining District was extensively mined from the 1880s until the 1940s, and numerous mines dot the high mountain landscape in Central Colorado. The District is located at an elevation above 10,000 feet where the air is thin and the opportunity to perform construction activities is limited. The Minnie Lynch Mine, located within the Bonanza Mining District, had several horizontal shafts that were discharging AMD and toxic metals into Rawley Gulch Creek, which is tributary to Kerber Creek. The State of Colorado had established Kerber Creek as an impaired waterway with a goal to restore its fishery. To achieve this goal Trout Unlimited (TU) with Wenck’s assistance was hired to address mine reclamation and remediation of AMD.
Wenck evaluated seven alternatives to reduce the metal-loading to Minnie Lynch Gulch, and ultimately to Kerber Creek. The alternatives were prioritized by stakeholders and funding secured through the U.S. Forest Service to complete the first phase of construction work in 2015. Wenck and TU collaborated on the 2015 construction which included AMD stabilization, mitigation, and treatment through a constructed wetland. Contaminated soils and waste material adjacent to Minnie Lynch Gulch were excavated, consolidated, isolated, and stabilized. Log check dams were constructed to mitigate bank and bed erosion of the steep tributary channel, thereby retaining contaminated sediment and allowing the process of fishery restoration in the main channel to continue.
The second phase of construction work was completed in the fall of 2016, and included the reconfiguration and restoration of approximately 640 feet of the Minnie Lynch channel. Additional AMD was stabilized and passively treated downslope with limestone trenches to remove the contamination threat. Wenck is still working on the Minnie Lynch Mine drainage project and supporting efforts to restore the Kerber Creek fishery. Additional engineering controls are being designed to stabilize the waste rock piles and reduce the transport of contaminated sediment downstream with construction continuing in 2017. Wenck helps TU, the State of Colorado, and the U.S. Forest Service ensure that our rivers and streams maintain their natural beauty, water quality, and remain free of AMD.