Acid Drainage Technology Initiative (ADTI)
Acid mine drainage (AMD) has been a detrimental by-product of coal mining for many years. At present, acid mine drainage continues to pose a potential problem in some areas, despite improved prediction and prevention techniques.
Acid Mine Drainage
The ADTI was formed as a partnership of technical experts from industry, state and federal agencies and academia who have joined together to combat the pervasive problem of AMD.
AMD is a long-term water pollution impact of mining in the coal fields of Appalachia and other areas of coal and metal mining. At right is a typical acid mine drainage discharge from an abandoned underground coal mine.
To combat this problem, the ADTI was formed as a partnership of technical experts from industry, state and federal agencies and academia who have joined together to combat AMD and related water-quality problems from mining and seek solutions to them.
ADTI members include, the Office of Surface Mining Reclamation and Enforcement (OSMRE), the U.S. Geological Survey (USGS), the Bureau of Land Management (BLM), the Environmental Protection Agency (EPA), the Department of Energy (DOE), the U.S. Army Corps of Engineers (USACE), the Interstate Mining Compact Commission (IMCC) representing coal mining States, the National Mining Association (NMA) representing mining companies, and the National Mine Land Reclamation Center and associated universities (West Virginia University, Pennsylvania State University and others) and the Colorado School of Mines (and associated universities), representing the academic community.
ADTI provides a forum for collaboration and information exchange on the following goals:
- Develop innovative solutions to AMD and related water-quality problems
- Identify, evaluate, and develop “best science” practices to predict AMD prior to mining
- Identify successful remediation practices for existing sources of AMD and describe the best technology for AMD prevention
- Work cooperatively to develop understanding and applications of proven and innovative technologies to predict, avoid, monitor, and remediate mine drainage
- Promote transfer of information on mine drainage prediction, monitoring, avoidance and remediation
ADTI members have developed a Statement of Mutual Intent as a mechanism to allow agencies, organizations, academic institutions, and others to participate in ADTI. Multiple bureaus of the Department of the Interior (DOI), including OSMRE, the BLM, the National Park Service (NPS), Bureau of Reclamation (BOR) and USGS, have participated in the activities of ADTI to this point.
Organization of ADTI
- Two major units: Coal Mining Sector (CMS) and Metal Mining Sector (MMS).
- Working groups in each sector focus on Prediction and Avoidance/Remediation.
Initially, the ADTI Operations Committee initially set up Working Groups on Prediction and Avoidance/Remediation in 1996 to address these issues, focusing primarily on coal mining in the Eastern U.S. In 1999, a Metal Mining Sector (MMS) was formed to better address these issues for hard rock mining in the Western U.S.
Coal Mining Sector (CMS)
The key points of the history and development of the CMS are given below.
CMS - Funding
Funding for CMS has been provided from a relatively few sources. OSMRE has provided the majority of the funding. OSMRE has provided $100-250,000 per year over the last 15 years (FY99–FY15). Other past funding has come from EPA, WVU and the mining industry.
CMS - Projects
A wide variety of mine drainage projects have been and are being undertaken by ADTI CMS members. West Virginia University and National Mined Land Reclamation Center (NMLRC) are studying flooded underground mine pools and their potential for contributing new sources of AMD. OSMRE funded projects include assessments of abandoned coal mine drainage treatment sites, selenium in coal mine overburden and surface and ground water, field verification of Acid-Base Accounting method to predict AMD and development of standardized lab-based kinetic test methods to evaluate AMD potential using leaching columns and humidity cells to predict the quality of drainage from geologic materials associated with coal mines.
CMS - Published Reports
Prediction of Water Quality at Surface Coal Mines (2000).
This technical manual, prepared by the ADTI Coal Mining Sector Prediction Working Group, provides an overview of the various options available to predict water quality resulting from coal mining and provides guidelines and recommendations on the best science and technology to predict AMD potential at surface coal mines in the Appalachian region.
A Handbook of Technologies for Avoidance and Remediation of Acid Mine Drainage (1998).
The ADTI Coal Mining Sector’s Avoidance/Remediation Working Group prepared this user oriented handbook on AMD Remediation Methods for coal mining in the Appalachian region that includes case studies. It is a compilation of previously conducted AMD remediation technology experiments and technology , including those that did not succeed. The anticipated outcome will be a higher success rate in remediating existing sources of AMD and more cost effective stream cleanup.
OSMRE and the National Mining Association provided funding for these publications, which were published by the NMLRC.
Printed copies of both reports are also available at no cost. To obtain a printed copy, contact the West Virginia Water Resources Institute, West Virginia University, 202 NRCCE Building PO Box 6064 Morgantown, WV 26506-6064, Attention: Terry Polce. Email: Terry.Polce@mail.wvu.edu ; Phone: (304) 293-2867 x 5450; Fax: (304) 293-7822
CMS - Continuing and Future Work
Continuing support of ADTI CMS activities has been through OSMRE funding of a series of cooperative agreements with West Virginia University. This OSMRE funding constitutes an important component of support to ADTI CMS. Following is a detailed summary of some of the tasks funded under these cooperative agreements.
Technical Support for Watershed Projects and Follow Up Evaluations
In order to obtain on-the-ground experience with the effectiveness and applicability of AMD remediation technologies at a variety of sites, the coal mining sector of ADTI works closely with watershed groups and others working to clean up streams and watersheds affected by abandoned mines under the Appalachian Clean Streams Program. OSMRE and the NMLRC at West Virginia University has worked through a series of annual cooperative funding agreements to:
- Provide technical assistance to watershed groups and others in the design, construction and maintenance of remediation technologies, and
- Evaluate the site conditions, technologies applied, cost of remediation and the resulting quality of water from affected sites.
As part of this task, NMLRC has conducted an ongoing evaluation of the performance of different methods of passive treatment (e.g., aerobic and anaerobic wetlands, anoxic limestone drains, open limestone channels, limestone leach beds) used for remediation of AMD from abandoned mines. Ziemkiewicz et al., (2003), reported on the results of a comparative evaluation of nine methods. Based on this work, three methods were found to give the best performance, in terms of unit treatment cost, effectiveness of acid load removal and reliability. These were: limestone beds, anoxic limestone drains and open limestone channels (Ziemkiewicz et al., 2003).
Acid Base Accounting (ABA) for Prediction of Postmining and Reclamation Water Quality
ABA is an important method for predicting postmining and reclamation water quality and evaluating the potential for production of acid mine drainage. The method, developed in the 1960’s and 1970’s and continuously refined since (Perry, 1998), assesses the potential for the production of acidic drainage at a mine site by balancing the acid-producing and the acid-neutralizing potential of materials at a site to predict the net water quality that can be expected. (Skousen et al., 2002)
The NMLRC has been studying the effectiveness of acid base accounting for predicting postmining and reclamation water quality (Skousen et al., 2002). Overburden analyses, permit maps, and predictions of postmining and reclamation water quality data were collected from regulatory agency permit files from several states in the Appalachian coal region. Data collected from these files was used to calculate mass-weighted acid base accounting for each site. Neutralization potential (NP), maximum potential acidity (MPA) and NP/MPA ratio from each ABA were compared to alkalinity levels in postmining and reclamation water quality data. The results of the ABA analyses were found to be correct in 82% of the cases using the NP/MPA parameter; this indicates that ABA is a good way to predict postmining and reclamation water quality at a mine site (Skousen et al., 2002). More work is planned or is underway to refine this useful analytical tool.
In-Situ Underground Mine AMD Treatment Technology
In-situ neutralization is a relatively new concept in the field of passive AMD treatment. The addition of alkaline materials into underground mine voids and ground-water recharge areas may provide an attractive alternative to current treatment practices. These systems require limited land area and, because many of these systems are installed in areas that exclude or limit oxygen, may permit the neutralization of acid without the precipitation of metals in the system. Under this task, three in-situ treatment systems were installed in north-central West Virginia. These sites include a deep mine alkaline injection project, an in-situ limestone portal drain, and ground water alkaline recharge trenches. The performance of these systems with respect to acidity neutralized and metal removed from the discharge is being monitored. The final report on this project is pending.
Kinetic Test Methods
ADTI is following up on the recommendations by Geidel et al., (2000) and Perry (2000) to find a consensus on the establishment of kinetic testing protocol for evaluating potentially acid-generating materials. There are several humidity cell methods and numerous leaching column methods that have been used to predict the quality of drainage from coal and metal mines. However, there are currently no standard methods that are widely used and accepted as accurate predictors of coal mine drainage quality by state and federal regulatory agencies or the coal mining industry. Hornberger and Brady (1998, page 7-5) state — "A tremendous amount of kinetic test information now exists, but the variety of test apparatus and procedures in use is so great that it is very difficult to interpret the results and make meaningful comparisons of data from different studies in similar or different lithologic settings[.] *** [I]t should be no wonder that mine operator and consultants new to the subject of AMD prediction would shy away from kinetic tests because they don't know which apparatus or procedure to use, nor how to interpret the results." In order to rectify this problem, OSMRE funded a project to:
- Develop standard procedures for a humidity cell test and a leaching column test that will meet the U.S. EPA requirements for performance-based measurement systems (PBMS) methods specifications, and
- Improve existing humidity cell and leaching column test methods by maintaining a carbon dioxide enriched gas environment throughout the test to simulate the partial pressure of CO2 normally found in soils and spoil gas environments. This is needed to optimize carbonate mineral dissolution and the production of significant alkalinity concentrations in ground water, mine drainage discharges, or leachate in laboratory tests used to predict mine drainage quality.
Selenium is a naturally occurring widely distributed element, which shows an affinity for sulfide minerals. It combines with metals and non-metals and may form both organic and inorganic compounds. Selenium is the most strongly enriched trace metal in coal, and can occur in several forms in solution. Selenium discharges that exceed water quality standards have been identified in several coal mine watersheds in southern West Virginia. It is suspected that these Se concentrations are the result of leaching of selenium compounds in coal and overburden exposed to oxidizing conditions during mining activities in this region.
OSMRE is currently funding an ADTI cooperative agreement with West Virginia University to determine sorption-desorption parameters for selenite as a function of temperature to iron oxides formed during mine drainage treatment and other common minerals found in acid and alkaline mine drainage impacted waters.
What is acid mine drainage?
AMD or acid rock drainage (ARD), collectively called acid drainage (AD), is acidic water (pH < 5.0), laden with iron, sulfate and other metals, that forms when geologic strata containing sulfide minerals such as pyrite are exposed to the atmosphere or oxidizing environments. AMD can form from coal mining, both in surface and in underground mines, but AD can also result from metal mining, or under natural conditions where sulfides in geologic materials are encountered in highway construction, and other deep excavations. Iron sulfides common in coal regions are predominately pyrite and marcasite (FeS2), but other metals may be combined with sulfide in the form of chalcopyrite (CuFeS2), covellite (CuS), and arsenopyrite (FeAsS). Pyrite commonly occurs with other metal sulfides, potential causing AD.
What is the Acid Drainage Technology Initiative?
To combat the long-term water pollution impacts of mining in the coal fields of Appalachia and other areas of coal and metal mining, the ADTI was formed as a partnership of technical experts from industry, state and federal agencies and academia who have joined together to combat AMD and related water-quality problems from mining and seek solutions to them. There are two major units: a CMS and a Metal Mining Sector (MMS). Working groups in each sector focus on Prediction and Avoidance /Remediation. An Operations Committee provides overall direction.