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2018-01-31_REVISION - C2009087 (30)
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2018-01-31_REVISION - C2009087 (30)
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Last modified
2/1/2018 10:24:04 AM
Creation date
2/1/2018 8:38:18 AM
Metadata
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Template:
DRMS Permit Index
Permit No
C2009087
IBM Index Class Name
Revision
Doc Date
1/31/2018
Doc Name
Proposed Decision and Findings of Compliance
From
DRMS
To
Peabody Sage Creek
Type & Sequence
RN1
Email Name
TNL
DIH
Media Type
D
Archive
No
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inflow from surface mine pits that are up dip from the underground workings. <br />Section 2.05 .6(3)(b)(iii) of the permit application contains an analytic <br />simulation of the drawdown for three points in time after commencement of <br />underground mining: 2 years, 5 years (end of first permit term), and 35 years <br />(30 years after first permit term), with no mining beyond the current non -treat <br />room and pillar proposal. Figure 2.05.6-F4.2 in the permit application shows <br />predicted drawdown contours for the Wadge coal potentiometric surface. The <br />contours indicate drawdown at the location of the seam's outcrop on the <br />northeast flank of the Fish Creek Anticline will exceed 50 feet during the <br />initial five-year permit term, and then will recover to a drawdown of less than <br />5 feet after mining ceases. The Wadge coal seam at this location is within the <br />Trout Creek Sandstone- Twentymile Sandstone outcrop belt that has been <br />reported as contributing to Grassy Creek flows (page 38 of U. S. Geological <br />Survey publication titled Evaluation of the upper part of the Mesaverde <br />Group, Northwestern Colorado, Water -Resources Investigations Report 90- <br />4020, by S.G. Robson and Michael Stewart). Seepage out of the outcrop belt <br />was reported as contributing approximately 20% of Grassy Creek's instream <br />flow when sampled in July and September in 1986. The Wadge coal seam <br />comprises roughly 5% of the aggregate thickness of likely permeable units in <br />the outcrop belt, assuming the seam is 10 feet thick and the Trout Creek and <br />Twentymile Sandstones are in aggregate 200 feet thick. If the coal seam's <br />contributions to Grassy Creek flows are eliminated by PSCM's drawdown <br />(which PSCM's analysis indicates is possible), and assuming the Wadge coal <br />seam contributes 5% of the outcrop belt's total contribution to Grassy Creek <br />flows, then PSCM's drawdown could reduce Grassy Creeks' flows by 1% (a <br />5% reduction of 20% of Grassy Creek's flow). A 1% reduction in flow in <br />Grassy Creek will not be enough to impair the use of Grassy Creek water. <br />There currently are no users of surface water on Grassy Creek. <br />Underground mine water that accumulates in the down dip end of <br />underground mine workings will seep into the unmined rock in the walls, roof, <br />and floor of the workings. The quality of this leachate is expected to be <br />similar to native ground water in the Wadge coal seam and the roof and floor <br />rock because large amounts of gob (waste rock) are not expected to be <br />produced during non -retreat room and pillar mining. SCCC predicts that a <br />plume of the mine water will advance outward from the workings at a <br />maximum velocity of 11 feet per year, a slower velocity than predicted for the <br />nearby Foidel Creek Mine in the previously mentioned U.S. Geological <br />Survey report of Robson and Stewart. SCCC predicts that seepage of <br />underground mine water from the workings up dip into Grassy Creek <br />alluvium after postmining recovery of the Wadge seam potentiometric surface <br />will be less than 1 gallon per minute and will be too small to have a significant <br />effect on alluvial ground water quality. <br />Section 2.03.5 of the PSCM permit provides updated information in relation <br />to selenium both naturally occurring and in the reclaimed mine spoils from the <br />
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