Design of Soil Cover Systems
S.E.T. employs an approach for developing optimal cover designs
that is initiated by evaluating the performance of the most simple
and economical design, and adding complexity as necessary based
on the performance evaluation.
The approach assesses cover performance based on predetermined
performance criteria such as allowable net infiltration through
the cover. Comprehensive field and laboratory testing is conducted
to determine the necessary parameters for computer modeling to
quantify net infiltration. Empirical-based modeling techniques
are employed (i.e., U.S. EPA's HELP MODEL) as a screening level
tool, and physical-based model techniques (i.e., SOILCOVER, UNSATH
or OPUS) optimize the cover thickness. Cover material volume-accounting
is used to assess the availability of suitable cover materials.
As a final stage in the cover design optimization process, a cost
analysis is performed to evaluate the economical feasibility of
the cover designs. .
This approach was used by S.E.T. at mines in the Western United
States to develop optimal cover designs for several waste rock
and tailings facilities, using multiple cover material sources.
The projects involved development of cover designs of optimal thickness
for limiting net infiltration and utilization of various cover
material. S.E.T.'s approach saved millions of dollars in capping
cost for the mining clients.
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Liner and Leak Detection System Design
S.E.T. can design leachate collection and
removal systems (LCRS) for containment pond facilities. At a
mine in Arizona, S.E.T. estimated leakage rates through the upper
line as a function of pond depth to establish realistic alert
levels and to determine the capacity of the LCRS. The seepage
rate through the liner system and travel time to groundwater
was also required by the state agency. S.E.T. performed these
calculations based on unsaturated zone flow theory and other
published methods.
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Design and Analysis of Waste Rock Facilities
In the permitting of new waste rock facilities,
S.E.T. combines acide-base accounting data with geologic data
and the excavation plan for the mine to characterize the waste
rock during each year of proposed mining.
This characterization is then used to develop a waste rock handling
plan that routes either net acid-generating or net acid-neutralization
waste, or a combination of both to a specific facility. Tne end
result is a design that provides long-term environmental stability.
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Site Assessment and Remediation
In conducting site assessments and remediation
activities, S.E.T. can perform all phases including geochemical
characterization, volume classification, regulatory representation,
supervision of cleanup activities and development and execution
of monitoring plans.
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Channel Improvements
S.E.T.'s technical approach for coordinating
the design of engineered improvements leaves the channel in as
natural a condition as possible and uses natural materials where
possible to minimize costs and maximize aesthetics. Replacement
of the channels with reinforced concrete walls or stabilization
with gunnite or shotcrete is considered only where the use of
natural materials is not technically feasible.
S.E.T. applied this approach to a stormwater channel in the Southwestern
United States that has been impacted by historical mining activities.
The end result of this project ensured that stormwater runoff would
not contact historic mining materials and degrade water quality;
it was also aesthetically pleasing and effectively minimized costs.
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Design of ARD Containment Systems
The containment of acid rock drainage (ARD)
from mine facilities is a critical component of any permit or
closure design. S.E.T. has designed systems to contain runoff
and seepage originating from tailing, waste rock, and heap leach
facilities.
For example, a system of diversion channels and containment ponds
were designed to contain surface water runoff from impacted areas
at a mine in the Southwestern United States. Contributing watersheds
were defined and the HEC-1 model was used to calculate the channel
and reservoir capacities for design storm events. A number of alternative
designs were considered and a cost vs. benefit analysis was conducted
to identify the most effective and economical design.
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Design of ARD Treatment Systems
In-situ treament of ARD and release to the
environment is a common, but costly design for the operational
life and closure of a mine waste facility. S.E.T. develops effective,
economical, and defensible design alternatives for ARD that incorporate
neutralization and metal removal systems or bio-reactor tecnologies.
For example, S.E.T. performed an alternative analysis of treatment
systems for ARD originating from a historic audit system in Arizona.
the base design that was developed included conveyance channels
and retention cells designed to neutralize and remove metals of
concern prior to release to the native watershed.
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