SAN LUIS VALLEY - The Environmental Protection Agency is creating a new office in Lakewood that will focus on cleaning up abandoned hard rock mining sites west of the Mississippi River, including the Bonita Peak Mining District where the Gold King Mine disaster originated in 2015.
Abandoned mine lands (AML) are those lands, waters, and surrounding watersheds contaminated or scarred by the extraction, beneficiation or processing of coal, ores and minerals. Abandoned mine lands include areas where mining or processing activity is determined to have ceased.
Colorado’s abundant mineral wealth helped drive the economic development of the state and contributed to the development of the United States as a whole. Unfortunately, the mines that hosted these minerals have left a legacy of hazards ranging from environmental issues like water quality degradation and increased sedimentation, to physical hazards associated with the mines themselves.
Across the state, there are an estimated 23,000 abandoned mine sites on both public and private land.
The CGS has been involved in characterizing and understanding various aspects of abandoned mine lands in Colorado. An inventory of environmental degradation and physical hazards associated with abandoned mines on United States Forest Service property was conducted by CGS from 1991 to 1998.
In all, 18,382 mine-related features were identified during this program and helped to identify sites that warranted further investigation and characterization.
Environmental Degradation - During the summer of 1993, the Colorado Geological Survey (CGS) inventoried mines in the upper Alamosa River basin of the Conejos Peak Ranger District, Rio Grande National Forest. This project was part of an eight-year, statewide inventory of abandoned mines on National Forest System (NFS) lands in Colorado. Not all of the mines were on NFS lands; in some instances, the forest boundary or mine locations were incorrectly located on Primary Base Series (PBS) maps. Some mines on private land close to NFS lands were inventoried, as were mines that potentially impacted NFS lands.
In 1998 and 1999, the Forest Service requested more detailed studies on selected mines in five inventory areas in the upper Alamosa River drainage basin. All of the selected mines had received Environmental Degradation Ratings (EDRs) of 3 (potentially significant) or worse from CGS. This study presents the results of the additional investigation (field work or historic records searches) requested on mines in the upper Alamosa River watershed.
Many of the smaller mines in the upper Alamosa River watershed were worked in the late 1800s and early 1900s. Some of the mines may have shipped very small quantities of ore, if any. Very little historical information was available regarding these mines. Without a formal mine or claim name, historical research is difficult. Defining geographical locations of mining claims from older county records can be difficult or impossible. Mining district or mining camp names vary depending on the reference source and time period. Some of the district or camp names used in the upper Alamosa River include Summitville, Jasper, Stunner, Decatur and Gilmore.
These early surveys and reports have been credited with stronger and more thorough examinations of the sites, leading to the new agency.
It is unknown if any of them have been remediated or if they end up on the list.
Acid mine drainage (AMD) is water that is discharged from mining or mine-related operations, which contains high levels of dissolved metals and sulfates in conjunction with pH values less than 4.5 (acidic). AMD is formed from the reaction of various minerals (principally pyrite) with oxygen and water. AMD can degrade the water quality of streams and water supplies, often to the point of causing harmful effects to the aquatic life of the stream.
Sedimentation and Sediment Contamination - Surface runoff can carry AMD-originated silt and debris down-stream, eventually leading to stream clogging. Sedimentation results in the blockage of the stream and can cause flooding of roads and/or residences and pose a danger to the public.
Sedimentation may also cause adverse impacts on fish.
Air Pollution - Air pollution can occur from piles of earth materials left at an abandoned mine. Windblown dust can have significant impacts on nearby residents and wildlife. The toxicity of the dust depends on the proximity of environmental receptors and the composition of the material. In particular, arsenic and lead are contaminants of concern.
Physical Hazards - Various physical hazards may exist at abandoned mine sites. Mine openings such as tunnels and shafts are imminent hazards because they present an opportunity for falls as well as the potential for collapse onto adjacent areas. Dangerous gases may exist in mine workings and can quickly overcome an unsuspecting visitor. Historic structures and equipment can present a hazard as these features are often unstable and prone to collapse.