GENERAL30588

• Permit No: C1981026
• IBM Index Class Name: General Documents
• Doc Date: 3/30/1987
• Doc Name: Proposed Decision & Findings of Compliance for RN1
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

Upon completion of the backfilling operations at pit No. 1, a spoils aquifer
will develop. The sources of the water suppling this aquifer are:
(1) infiltration of overland flow from upslope drainage;
(2) inflow from undisturbed Sudduth Coal to the south, and from the
adjacent under/overburden.
Upon completion of reclamation activities, some amount of surface drainage
will infiltrate the backfilled pit. Initially, the amount of infiltration
will be fairly large due to the depression formed by the pit reclamation. As
the vegetative cover in the reclaimed area becomes established, it is thought
that a large percentage of the summer surface runoff will be used by the
vegetation, and eventually lost to evapotranspiration processes. Spring
snowmelt runoff will always add some amount of recharge to the spoils aquifer.
As documented during the previous permit term, the volume of ground water
inflow to pit No. 1 stabilizes over time. There is no reason to expect that
any inflow conditions will change upon backfillling the open pit. Therefore,
the amount and rate of inflow from adjacent units will not exceed
approximately two gallons per minute. Inflow will stabilize when an
equilibrium is reached between the spoil aquifer and the source of inflow, the
most significant of which is the undisturbed Sudduth Coal seam.
It is expected that the equilibrium between the spoils aquifer and the Sudduth
Coal seam will be exceeded for some period of time each year following spring
snowmelt runoff. The snowmelt runoff will cause the spoils aquifer water
table to rise to a point where the aquifer will recharge the Sudduth Coal to
the south. As the coal accepts the recharge, the spoil aquifer water table
will be depleted until equilibrium is again established.
Using water quality data collected at the Canadian Strip Mine, it is not
thought that the spoil recharge will adversely affect the quality of either
the coal, underburden or overburden. Based upon total dissolved solids (TDS)
concentrations measured at Well No. 7, a spoils completion well in the north
pit area, and compared to TDS concentrations measured in underburden, coal and
overburden wells, the spoil aquifer quality is equal to or better than that of
the other three units. Furthermore, it is not thought that the quantity of
spoils water which will recharge these units, due to the limited area of
impact, is significant.
Based upon water level data obtained from well No. 7, spoils aquifer
establishment may take up to four (4) years. To monitor the aquifer
development, as well as water quality, Wyoming Fuel Company has committed to
establishing a spoils monitoring welt in the backfilled portion of pit No. ].
As spoil aquifer development is expected to be limited, it is thought that the
potential for future surface discharges is slight. If surface discharge in
the form of springs or seeps do occur in the future the quantity of the
discharge should be limited and the quality acceptable for the purpose of
livestock use. If a discharge is to occur in the future, it will be into the
drainage being established per the proposed reclamation plan.
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