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Unweathered overburden and coal processing wastes in southwestern Virginia contain varying amounts of carbonates and pyrite which affect water quality as spoil and refuse materials weather and leach. In addition to pH effects, these materials can input significant total dissolved solids (TDS) loads to drainage waters under both low and circumneutral pH conditions. The objective of this study was to evaluate acid-base interactions and overall TDS elution (as measured by electrical conductivity/EC) in leachates from a variety of spoil and refuse materials. Ten spoils and three pairs of coarse/fine refuse samples were characterized and subjected to leaching in columns for five months (2 leaching events per week) under saturated and unsaturated conditions. Leachates were analyzed for pH, EC, and cations and oxyanions of concern. The pH of the bulk samples (prior to leaching) were typically near-neutral to alkaline. Bulk EC produced by fresh spoils was relatively low (< 1.0 dS m-1), although a few values ranged up to 3.5 dS m-1. Relatively low total S (< 0.25%) in conjunction with calcium carbonate equivalence (CCE) levels of 1.3-6% resulted in low (3.6 Mg CaCO 3 per 1000 Mg material or less net acid) peroxide potential acidity (PPA) levels. For refuse samples, total S was slightly higher (0.27-1.25%), CCE ranged from 5.0 to 6.9%, and PPA ranged up to 31.2 Mg CaCO 3 per 1000 Mg material of net acidity. Leachate pH increased noticeably for most materials over the first few leachings, but after approximately one month, the majority of samples showed no major changes. Electrical conductivity decreased over the first several leachings and most samples achieved a relatively steady state with relatively low levels (< 1.0 dS m-1) within two months. Leachate pH, EC, bicarbonate, Ca, Fe, Mn and sulfate elution were directly related to internal acidbase reactions and water saturation regime. Surprisingly, no major significant or consistent differences were apparent between coarse and fine refuse materials for any parameter of long term leaching concern.

Abstract:Research on the beneficial utilization of coal combustion products (CCPs) as surface amendments in mining environments has focused upon bulk acid-base balances and heavy metal (Cu, Zn, Fe, Al, Mn, etc.) mobility to local groundwater. Currently, the public and regulatory communities are placing greater focus on the potential of As, B and Se mobility from CCP utilization. Five CCPs were selected from a regional set of 28 materials following complete chemical characterization for greenhouse bioassay trials. Acidic sandstone mine spoil was amended at 0, 10, and 20% (v:v) with the CCPs. The bioassay trial was designed to test the presumed effectiveness of CCPs as surface-applied amendments to mine soils for improving pH and water holding capacity. The procedures were modified to include a "pour-through" protocol where we leached greenhouse pots with excess water starting one month after establishment of the trial, and then collected leachates for analyses of pH, EC, As, B, Se and other parameters. The trial was conducted using soybean (Glycine max) as an indicator plant sensitive to substrate chemical conditions (EC, pH, elemental toxicity) and tall fescue (Festuca arundinaceae) as a species exhibiting relative tolerance to low pH, metals, and salts. Tall fescue dry matter yield tended to increase with increasing CCP rate as long as the bulk soil pH remained at pH 8.0 or less. Depending on the liming capacity (as measured by calcium carbonate equivalence -CCE) of the CCP applied, the 20% application had the greatest positive effect on plant yield (e.g. at CCE = 7.7). However, in case of a CCP with a high liming potential (CCE = 47.7), a 5% application was most beneficial to dry matter yield. The EC and pH from various mixes related well to CCE of the respective CCP and the loading rate. Leaching of oxyanion forming elements (As, Mo, Se) under these soil conditions and loading rates does not appear to be a concern, although some Se was observed in the first leachates. As expected, B along with S (as SO 4 2-) were the two elements at highest concentration in the leachates. However, correlation and stepwise regression analysis of yield data with the elemental concentrations from the pour-through solutions indicated these two elements did not negatively affect fescue yield. However, stepwise regression analysis did show that fescue yield was affected by pH (p > 0.0034). Our combined results indicate that a few relatively simple lab measurements (pH, EC, CCE) coupled with a simple soybean bioassay such as reported here can readily predict both the relative effectiveness and potential toxicity of a given CCP when used as either a bulk mine soil amendment or an alkaline additive for mine soil acidity control.Additional Key Words: Fly ash, flue gas desulfurization sludge, beneficial use, phytotoxicity.