GENERAL46203

• Permit No: C1981028
• IBM Index Class Name: General Documents
• Doc Date: 10/8/1981
• Doc Name: Draft Copy of Revised Decision Documents
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

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contain the 10-year event plus three years of sediment s~orage. Sediment
production estimates were made using the Universal Soii Loss Eouation consider-
ing a worst-case area of disturbance.
Based on runoff studies submitted in the application, the applicant has
requested a variance from sediment control on certain reclaimed areas. The
request is for the reclaimed area south of the initial spoil pile to the active
unreclaimed spoil and bound bu t~,e haul road ramps in each pit area. The
Division hereby grants the variance in accordance with section 4.C5.2(3) based
on the finding that runoff will not be generated from the area and therefore,
sediment ponds are not needed to meet the e°fluent limitations of sectior, 9.05.2
or applicable State and Federal water quality requirements.
The applicant also requests a variance from the dewatering device requirement
of section 4.05.6(3)(c). The reason for the request is that the ponds are built
on blow sands which are very permeable and should allow the water to percolate
through the bottom and sides of the pond. Although this appears to be an
acceptable method of dewatering, the Division feels that the permeability of
the sands on the bottom of the ponds may be reduced by the buildup of sediment
in the ponds. Because of this concern the Division will approve of the de-
watering method with the following stipulation:
IF, DURING AN INSPECTION BY MLRD IT IS FOUND THAT A POND IS NO LONGER
DEWATERING~PROPERLY DUE TO THE ACCUN.ULATIO?1 OF SEDIMENT, THE DIVISION
MAY REQUIRE THE OPERATOR TO REMOVE THE SEDIMENT FP.ON. TXE POND TO
RESTORE THE DEWATERING CAPABILITY.
The applicant has been found to be in compliance with NPDES and Receiving Stream
Standards that are regulated by the Colorado Department of Health, Water Quality
Division. This is verified in the approved NPDES permit number C)-0037-52.
VI. Hydrologic Balance: Ground Water (2.09.5, 2.09.7, 2.05.6, 9.05)
Baseline Discussion:
The applicant has determined the probable hydrologic corseguences of the proposed
surface coal mining operations on four aquifers identified in or adjacent to
the operator (Appendix I-2 and Volume 1 page 38-44).
The lowest aquifer is the Foxhills Sandstone 69-100 feet thick. This is a
confined aquifer exhibiting good water quality characteristics. The operator
has two wells completed in this aquifer for use as potable and irrigation water.
However, since this aquifer is confined and is located more than 200 feet below
the coal seam to be mined the operation should not significantly affect the
quality or quantity of water in this aquifer.
The second aquifer studied was the Larimie coal. This aquifer is the No. 7
coal seam proposed to be extracted by the operation. This aquifer is not known
to provide a water supply for any purpose in the study area. Ten wells were
drilled into the coal seam to determine its physical and chemical properties.
Recovery tests showed a transmissivity of 7.3 to 9.7 x 10-Sft.2/min. Flow through
this 2-8 foot aquifer in the permit area is northeast yielding an estiffated dis-
charge of only 0.1 acre-feet/year. A comparison of the water quality and
piezometric data of-the coal seam and the Laramie overburden aquifer indicates
that the coal seam is a confined aquifer and has very Tittle hydrologic communi-
cation with the overburden. Because the coal aquifer has a low transmissivitg
and is not used as a source of water, impacts should be negligible.