Mine Drainage Technology Initiative (MDTI)

ABA is an important method for predicting post-mining 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 post-mining and reclamation water quality (Skousen et al., 2002). Overburden analyses, permit maps, and predictions of post-mining 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 post-mining 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 post-mining 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 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.

MDTI 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[.] 

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 MDTI 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.