Page 301 - Advances In Productive, Safe, and Responsible Coal Mining

Sustainable reclamation and water management practices 277

14.3.2 Landform design

Postmining land use and SMCRA’s AOC requirements are essential considerations in
landform design. Geologic materials expand upon disturbance; hence, in the eastern
USA where coal seams are thin relative to overburden strata, postdisturbance spoil
volumes typically exceed the volume of material prior to mining. Overburden expan-
sion or “swell” factors can range from 15% to 40%, depending on rock type and degree
of fracture. Historically, mine operators disposed of excess spoils in “valley fill” struc-
tures placed in topographic depressions below the mining operations. In recent years,
however, valley fill construction has been discouraged by regulatory policies due to
water-quality concerns, as valley fills often give rise to waters with TDS concentra-
tions that are elevated relative to natural background levels [23,24]. In response, mine
operators have been developing alternative excess-spoil disposal strategies, including
placement in abandoned pre-SMCRA mine sites for use in mitigating long-standing
environmental problems.
In the western USA, coal seams are often thick relative to overburden. Therefore,
even though overburden swells during disturbance, postmining landforms often
occupy smaller volumes than the undisturbed landforms present before coal removal
and postmining elevations can be much lower than premining elevations.
Prior to mining, the process of designing landforms, and methods that will be used to
construct such landforms, may consider the existence of problematic spoils, if such are
expected to be disturbed by the mining operation. Historically, spoils have been con-
sidered as problematic if containing significant concentrations ( 0.5%) of sulfur
(S) and lacking alkaline neutralizers sufficient to offset the S-oxidation-generated
acids. Under current environmental policies, spoils are considered problematic if they
havehighTDSgenerationpotential,and/orahighpotentialtoreleaseelevatedSe.Inthe
Appalachians, these problems can coexist with spoil materials exhibiting high concen-
trations of S (i.e., potential highly acidic spoils) and thus the capacity to generate high
levels of TDS [21], because S oxidation generates TDS as well as acidity. Given the
tendencyofSe tosubstituteforSincertainmineralforms,such spoilsmayalso beprone
to release of high quantities of Se. Premining overburden testing procedures can iden-
tifyproblematicspoilsinadvanceofmining,suchthattheminingplancanbedeveloped
to manage those spoils in a manner that is both cost effective and protective of the envi-
ronment. Some of these methods are described in the remainder of this section.

14.3.3 Geomorphic reclamation and hydrologic concerns

The term “geomorphic reclamation” describes reconstruction of mined landscapes
that resemble premining landscape forms and restore water drainage patterns similar
to those present before mining. The outcome of geomorphic reclamation is a more
natural look and more intricate drainage patterns than typical engineered structures
with linear features. Similarly, geomorphic reclamation landscapes are intended to
remain more stable over the long term than nongeomorphic land configurations pro-
duced by conventional reclamation and characterized by linear features. That
enhanced stability, if successfully achieved, will minimize movement of sediments