In recent years, constructed wetlands have been used to remediate acid mine drainage which has resulted from both coal and metal mining activities. These wetlands are used in conjunction with other engineered components to create a passive mine drainage treatment system (PMDT). Passive systems are designed to remediate mine drainage using minimum capital expenditures and little to no operational and maintenance costs. The Colorado Division of Minerals and Geology (DMG) is responsible for the design, construction, and operation of constructed wetlands in Colorado. Only 5 systems are in existence at this time, located in terrain varying from gentle foothills to remote, sub-alpine mountains. The design of a wetland system is based on a multitude of factors such as site terrain and access, mine drainage composition, and in the Rocky Mountain region, altitude. The salient design issues associated with each wetland system will be presented and discussed. The impact of altitude, climate, terrain, and other physical site constraints on each wetland design will be discussed. In addition, chemical issues critical to the design of each wetland such as pH and alkalinity will be presented. Finally, the performance of each wetland system will be examined.Additional Key Words: passive mine drainage treatment system, anoxic limestone drain, sulfate reducing wetlands.
A large number of abandoned hard rock mines exist in Colorado and other mountain west states, many on public property. Public pressure and resulting policy changes have become a driving force in the reclamation of these sites. Two of the key reclamation issues for these sites is the occurrence of acid forming materials (AFMs) in mine soils, and acid mine drainage (AMD) issuing from mine adits. An AMD treatment system design project for the Forest Queen mine in Colorado's San Juan mountains raised the need for a simple, useable method for analysis of mine land soils, both for suitability as a construction material, and to determine the AFM content and potential for acid release. We have developed a simple, stepwise, go-no go test for the analysis of mine soils. Samples were collected from a variety of sites in the Silverton, CO area, and subjected to three tiers of tests including: paste pH, Eh, and I 0% HCl fizz test; then total digestion in HNO,IHCl, neutralization •potential, exposure to meteoric water, and toxicity content leaching procedure (TCLP). All elemental analyses were performed with an inductively-coupled plasma (ICP) spectrometer. Elimination of samples via the first two testing tiers left two remaining samples, which were subsequently subjected to column and sequential batch tests, with further elemental analysis by ICP. Based on these tests, one sample was chosen for suitability as a construction material for the Forest Queen treatment system basins. Further simplification, and testing on two pairs of independent soil samples, has resulted in a final analytical method suitable for general use.
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