Page 304 - Advances In Productive, Safe, and Responsible Coal Mining

280 Advances in Productive, Safe, and Responsible Coal Mining

14.3.6 Surface and mine-soil construction

A “mine soil” is a soil-like material that is placed on the reclaimed mine surface and
that often develops form and properties similar to natural soil over time [35]. Mine-
soil construction involves selection of disturbed materials, and placement of those
materials on the reclaimed land surface. Ideally, materials are selected with the intent
of establishing a mine soil that is suitable for the proposed land use. Disturbed mate-
rials can vary widely in physical and chemical properties; and hence, in their suitabil-
ity for soil construction [31].
Soil contains organic matter and is often the most favorable material if natural
ecosystems are to be restored. Moving soil materials directly from the excavation area
to the reclamation area is a recommended practice that can maintain beneficial micro-
organisms, and the viability of seeds and propagules from plant species that were
present prior to mining disturbance. Soils are recommended for salvage and use in
mine-soil construction in Appalachia [32] and in other world regions [36–42].The
term “soil” (as used in the Appalachian Region) refers to all surface soil material
to a depth of broken bedrock that can be removed with a dozer.
Weathered spoils are the rock materials that occur directly below the soil [32]. Gen-
erally, weathered spoils will have more favorable chemical properties for native veg-
etation and will break down into soil-like materials more easily than unweathered
parent rock. Weathered spoils will generally have less capacity to generate TDS than
unweathered rock materials [22]. However, weathered spoil will lack organic matter
and plant nutrients that are present in salvaged soil.
Unweathered spoils occur below the zone of environmental weathering (generally
deeper than 10m below the premining surface). Unweathered spoils can vary widely
in physical and chemical properties. For example, Roberts et al. [43] describe
siltstone-derived mine soils that declined in pH from 7.5 to 6.3 within 2 years. Con-
versely, Emerson et al. [44] describe soils constructed from gray unweathered sand-
stones that retained soil pH levels >8 over a similar time period. Some unweathered
spoils break down easily into soil-like fragments and maintain soil pHs that are favor-
able for pasture grasses and legumes [45]. If unweathered spoils are to be used for soil
construction, it is necessary to select certain strata that have both physical and chem-
ical properties that will be favorable for the postmining land use as initially placed
and as they weather. When re-establishing natural ecosystems, use of natural soils
and weathered spoils for mine-soil construction is recommended when available
[31,32]. If such materials are not available, unweathered spoils should be selected
based on capacity to achieve pHs that are similar to those of natural soils
(e.g., moderately acidic in Appalachia) and relatively low-soluble salt levels.
Respreading of native topsoil is important when establishing unmanaged post-
mining land uses for many reasons. First, viable seeds and propagules contained in
the soil (called a seed bank) enable restoration of native species. Second, organic mat-
ter in the native soil contains soil nutrients, such as nitrogen and phosphorus, not read-
ily available to plants in mine overburden materials, but essential for plant growth.
Third, use of native soils, with organic materials salvaged from the premining land-
scape, promotes favorable hydrologic properties. Finally, soil-dwelling animals and