The Use of Acid-Base Accounting to Predict Post-mining Drainage Quality On West Virginia Surface Mines

Abstract

Acid-Base Accounting (ABA) is an analytical tool to determine the acid-or alkalineproducing potential of overburden rocks prior to coal mining. This procedure was developed by Dr. Richard M. Smith and associates at West Virginia University in the late 1960s. After the passage of laws requiring an assessment of mining on water quality, ABA became the preferred method to predict post-mining water quality, and many permitting decisions for surface mines were and are based on the values determined by ABA. As a post-mining water quality predictor, ABA is best used as a qualitative assessment of the site's potential to produce acid mine drainage. Several studies have attempted to adapt ABA to a quantitative assessment of the site's post-mining water quality. By this approach, the mass of acid-producing rock is compared to the mass of alkaline-producing rock and a prediction of the water quality (amount of acidity or alkalinity) is obtained. Such analyses have given variable prediction success. We gathered information for 28 sites in West Virginia and estimated overburden amounts and ABA parameters on each site based on ABA data and topographic maps. Maximum potential acidity (MPA), neutralization potential (NP), net neutralization potential (NNP), and NP/MPA ratios were determined for each site based on ABA and correlated to post-mining water quality from springs or seeps on the mined property. On our 28 sites, total NNP varied from -12.7 to I 06 tons per thousand tons (t/1000 t) and NP/MPA ratios varied from 0.2 to 21. We found no relationship between MPA with post-mining water quality, while NNP and NP/MPA ratio showed the best correlation. Six sites.gave NP/MPA ratios of <I; four of them (67%) gave net acid post-mining water quality, while the other two sites were only slightly net alkaline. Five sites had NP/MPA ratios of I.I to 1.6, and only one of these sites had net acid water quality and only slightly so. The remaining 17 sites had NP/MPA ratios >2.2 (all of which should produce alkaline water) and three of the 17 sites produced acid drainage. Two sites with NP/MPA ratios of<! gave net alkaline water, while 18 out of22 sites (82%) with NP/MPA ratios >I gave net alkaline water quality. ABA is a good tool to assess overburden quality before mining and to predict post-mining drainage quality after mining. Most sites followed the prescribed patterns of prediction.Additional

Using Minesoil and Overburden Analyses to Locate a Highway in West Virginia

“…The MPA is the maximum amount of sulfuric acid that can be produced from the oxidation of sulfur in the coal and overburden and is determined by multiplying the total sulfur by 31.25. The value of 31.25 is used because it represents the amount of CaCO 3 in tons that it would take to neutralize 1000 tons of material that contains 1% pyritic sulfur (Skousen et al, 2001;Sobek et al, 2000). The NP is a measure of the amount of neutralizing materials within the soil, coal, and overburden.…”

“…This is determined by subtracting the MPA from the NP. Negative NNP values indicate potentially acid producing materials, where positive numbers indicate potentially acidneutralizing materials (Skousen et al, 1987;2001). When the NNP values are below -5 tons CaCO 3 /1000 tons, materials are expected to produce significant amounts of acidic drainage and the more negative the number, the higher the potential.…”

Environmental geochemistry of the abandoned Mamut Copper Mine (Sabah) Malaysia

“…This is confirmed by acid-base accounting (ABA) tests by Jopony and Tongkul (2009) concluding that the tailings has negligible AMD potential. They used the procedures formulated by Skousen et al (2002), O'Shay et al (1990) and Sobek et al (1978).…”