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Appalachian USA surface coal mines face public and regulatory pressure to reduce total dissolved solids (TDS) in discharge waters, primarily due to effects on sensitive macroinvertebrates. Specific conductance (SC) is an accurate surrogate for TDS and relatively low levels of SC (300-500 μS cm(-1)) have been proposed as regulatory benchmarks for instream water quality. Discharge levels of TDS from regional coal mines are frequently >1000 μS cm(-1). The primary objectives of this study were to (a) determine the effect of rock type and weathering status on SC leaching potentials for a wide range of regional mine spoils; (b) to relate leachate SC from laboratory columns to actual measured discharge SC from field sites; and (c) determine effective rapid lab analyses for SC prediction of overburden materials. We correlated laboratory unsaturated column leaching results for 39 overburden materials with a range of static lab parameters such as total-S, saturated paste SC, and neutralization potential. We also compared column data with available field leaching and valley fill discharge SC data. Leachate SC is strongly related to rock type and pre-disturbance weathering. Fine-textured and non-weathered strata generally produced higher SC and pose greater TDS risk. High-S black shales produced the highest leachate SC. Lab columns generated similar range and overall SC decay response to field observations within 5-10 leaching cycles, while actual reduction in SC in the field occurs over years to decades. Initial peak SC can be reliably predicted (R(2) > 0.850; p < 0.001) by simple lab saturated paste or 1:2 spoil:water SC procedures, but predictions of longer-term SC levels are less reliable and deserve further study. Overall TDS release risk can be accurately predicted by a combination of rock type + S content, weathering extent, and simple rapid SC lab measurements.

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.

Excavation of sulfidic materials during construction has resulted in acid rock drainage (ARD) problems throughout Virginia. The most extensive documented uncontrolled disturbance at a single location is Stafford Regional Airport (SRAP) in Stafford, Virginia. Beginning in 1998, over 150 ha of sulfidic Coastal Plain sediments were disturbed, including steeply sloping cut surfaces and spoils placed into fills. Acid sulfate soils developed, and ARD generated on-site degraded metal and concrete structures and heavily damaged water quality with effects noted over 1 km downstream. The site was not recognized as sulfidic until 2001 when surface soil sampling revealed pH values ranging from 1.9 to 5.3 and peroxide potential acidity (PPA) values ranging from 1 to 42 Mg CaCO(3) per 1000 Mg material. In February 2002 a water quality program was established in and around the site to monitor baseline pH, EC, NO(3)-N, NH(4)-N, PO(4)-P, Fe, Al, Mn, and SO(4)-S, and initial pH values as low as 2.9 were noted in on-site receiving streams. In the spring and fall of 2002, the site was treated with variable rates of lime-stabilized biosolids, straw-mulch, and acid- and salt-tolerant legumes and grasses. By October 2002, the site was fully revegetated (> or = 90% living cover) with the exception of a few highly acidic outcrops and seepage areas. Surface soil sampling in 2003, 2004, and 2006 revealed pH values typically > 6.0. Water quality responded quickly to treatment, although short-term NH(4)(+) release occurred. Despite heavy loadings, no significant surface water P losses were observed.

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