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Soil Salvage
Topsoil is of paramount importance to reclamation success. Once
waste materials have been excavated or treated, the surface of the
site is regraded to a topography similar to that before mining activities
were initiated. After regrading, topsoil is placed overtop of the
surface to provide a growth medium for vegetation. Topsoil is the
most fertile portion of soil and contains important nutrients, microorganisms,
seeds, and roots for enhancing vegetation growth. It is in high
demand during reclamation activities and there is often a shortage
for covering regraded areas. For this reason it is important to
salvage topsoil when the site is first disturbed. Topsoil should
be scraped off the surface and stockpiled before excavation of overburden
initiates.
Salvaged soils are either stockpiled and stored for future use
or they are immediately used for covering regraded surfaces in a
different location. Immediate placement of salvaged soils is most
desirable since the soil microbes, bacteria, viable seeds, and plants
that can take root are most abundant at this time, and would lead
to better revegetation. Stockpiling of soils for long periods results
in loss or elimination of these beneficial characteristics. If soils
must be stockpiled and stored for long periods of time, it is important
to protect the soils from erosion and weed invasion by positioning
stockpiles to minimize exposure to wind and by immediately seeding
the piles with wheatgrass or other low cost perennial cover crop.
Vegetation of the stockpiled soil helps maintain viability of soil
fungi and microbial communities. For more information on weed control,
click here. For more information
on soil health and its importance to topsoil quality for revegetation,
click here.
Once soils are stockpiled and seeded, it is important not to disturb
the soils again until they used to cover regraded areas. Compaction
and/or excessive disturbance can affect the soil
structure. Compaction results in loss of pore spaces in the
soil and an increase in bulk density which have adverse affects
on plant rooting, nutrient transport, etc. Excessive moisture or
dryness can also have adverse affects on topsoil quality and, subsequently,
on revegetation success. Soils that are too wet become compacted
and soils that are too dry turn to powder and are difficult to handle.
For recommendations on soil handling, stockpiling, replacement,
see The Practical
Guide to Reclamation in Utah. In addition, attempts should be
made to segregate the A and B horizons of the topsoil. Where possible,
stockpile the B horizon separately from the overlying A horizon.
When the soils are replaced, lay the B horizon first, followed by
the A horizon. This effort will result in higher productivity and
better revegetation success at the reclamation site. For more information
on revegetation strategies, click
here.
Different geographic areas have varying depths and quality of topsoil.
Sometimes, an area may have only a few inches of salvageable soil
while other areas may have a few feet of salvageable soil. It is
important to assess the thickness and quality of topsoil before
mining activities initiate. A soil survey or inventory is important
for determining the kind, extent, depth, location, and quality of
soils in the survey area. This information can be used to assess
whether the soil is suitable for salvage and how much can be salvaged.
Each soil survey should follow the methods, standards, and procedures
described in Title 430-VI of the National Soils Handbook (USDA-NRCS,
1993), Soil Survey Manual (USDA-NRCS, 1993), and Keys to Soil Taxonomy,
7th ed. (USDA-NRCS, 1998). It is recommended that a certified soil
scientist conduct the soil survey investigation. Information for
the survey is collected from samples taken from soil pits and supplemental
auger holes. The samples are analyzed for pH, electrical conductivity
(EC), texture, percent organic matter (%OM), available water holding
capacity, calcium carbonate (CaCO3), soluble potassium, magnesium,
calcium, sodium, total nitrogen, available phosphorous, and the
sodium adsorption ratio (SAR). Results from sampling and analysis
will be used to evaluate soil types and the desirability of the
soil for salvage. For more information on soil sampling methods,
click here. For more information
on analytical methods, click
here.
From the survey, a soil map can be created which provides information
on individual soil units; their extent, depth, location, and type
of plant communities adapted to different types of soil. If the
volume of soil salvaged from upper layers of overburden are not
enough to adequately cover the regraded surfaces, subsoils or strata
deeper within the overburden with suitable characteristics for plant
growth can be used.
When the stockpiled soils are laid over the regraded areas, it
is recommended that 6-12 inches of topsoil be used to ensure successful
plant growth. Because roots will extend into the graded overburden,
it is also important to prepare the overburden to a depth of at
least one foot.
For more information on soil salvage, see the following documents:
Problem | Compliance
| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
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