Page 317 - Advances In Productive, Safe, and Responsible Coal Mining

Sustainable reclamation and water management practices 293

enhance the introduction of surface water with dissolved solids into shallow and then
deeper groundwater systems through fractures or other conduits. The type and nature
of the mining activity, the disturbed geologic strata, and alteration of surface and sub-
surface materials will determine how groundwater supplies will be impacted.
Because mining activities can result in impacted ground waters, enforcement of
regulations is needed to minimize and/or eliminate potential problems. The SMCRA
identifies policies and practices for mining and reclamation to minimize water-quality
impacts. It requires that specific actions be taken to protect the quantity and quality of
both on- and off-site ground waters. All mines are required to meet either state or fed-
eral groundwater guidelines, which are generally related to priority pollutant stan-
dards described in the CWA and Safe Drinking Water Act (SDWA). As water
comes into contact and interacts with disturbed geologic materials, constituents such
as salts, metals, trace elements, and organic compounds become mobilized [89]. Dis-
solved substances can leach into deep aquifers and cause groundwater-quality impacts
[90]. In addition to concerns related to naturally occurring contaminants from distur-
bance activities, mining operations may also contribute to groundwater pollution from
leaking underground storage tanks, improper disposal of lubricants and solvents, and
contaminant spills. Blasting and hydraulic fracking activities can provide additional
connection to surface water inputs, and underground injection of wastes can also occur
during these operations.
The chemistry of ground waters in mined lands and potential levels of naturally
occurring contaminants are related to the following: (i) groundwater hydrologic con-
ditions; (ii) mineralogy of the mined and locally impacted geological materials;
(iii) mining operations (e.g., extent of disturbed materials and its exposure to atmo-
spheric conditions); and (iv) time. Movement of metal contaminants in ground waters
varies depending on the chemical of concern. Solubility considerations include metals
such as cobalt, copper, nickel, and zinc being more mobile than silver and lead, and
gold and tin being even less mobile [89]. As conditions such as pH, redox, and ionic
strength change over time, dissolved constituents in ground waters may decrease
owing to adsorption, precipitation, and chemical speciation reactions and
transformations.
Acid mine drainage (AMD) is one of the most prevalent groundwater-quality con-
cerns at active and abandoned underground mine sites. If geologic strata containing
reduced S minerals [e.g., pyrite (FeS2)] are exposed to weathering conditions, high
concentrations of sulfuric acid can develop and form acid waters with pH levels below
2. Neutralization of some or all of the acidity produced during the oxidation of reduced
S compounds can occur when carbonate minerals in proximity to the acid-producing
materials dissolve [34]. Neutralization can also occur when silicate minerals dissolve,
but sometimes, high levels of potentially toxic metals such as Al, Cu, Cd, Fe, Mn, Ni,
Pb, and Zn may be released. For example, coal mining in the Toms Run area of north-
western Pennsylvania resulted in groundwater contamination by AMD containing
high concentrations of Fe and sulfate that leached into the underlying aquifer through
joints, fractures, and abandoned oil and gas wells [91].
Extensive underground mining has taken place in West Virginia since the late
1800s, and Bennett [92] estimated an area of about 610,000ha with underground min-
ing beneath the surface in West Virginia alone. This legacy of mining has changed