GENERAL54873

• Permit No: C1980007
• IBM Index Class Name: General Documents
• Doc Date: 6/23/1981
• Doc Name: Proposed Decision and Findings of Compliance
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

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SUBMITTED TO THE STATE ENGLNEERS OFFICE AND DITCH COMPANIES SHALL BE
COPIED~TO MLRD AS INCLUSIONS WITHIN THE QUARTERLY REPORT REQUIRED UNDER
1 SECTIbN 4.05.13(2) OF THE RULES AND REGULATIONS.
l\Sfipulations: NEITHER ARCO COAL COMPANY, NOR ANY SUCCEEDING OPERATOR OF
2HE MT. GUNNISON PROJECT'S COAL LEASES AND hEBERVES WILL BE PERMITTED TO
MINE COAL OUTSIDE OF THE FIRST 5-YEAR PERMIT BOUNDARY, UNTIL MLRD HAS
RECEIVED A COPY OF AN ADJUDICATED PLAN OF AUGMENTATION.
IX. Probable Hydrologic Consequences and Cumulative.Impact Assessment
A - General Background - Mine Area
The Mt. Gunnison No. 1 Mine lies on the southeast margin of the Pi ceance
Basin. Sediments ranging from late Cretaceous to early Tertiary age, and
dipping 3-5 degrees north to northeasterly, are exposed in the mine aces.
Structural-Strati graphic cross sections are presented in Exhibits 2.7.2.D. -
2.7.2.C. The structure on top of the F-seam is presented on Exhibit
2.7.S.A and geologic maps are presented in Exhibits 2.7.I.A.A and 2.7.2.D.1.
Coal is to be produced from the Mesa Verde Formation, a 2,500-foot-thick
sequence of beds overlain by the Ohio Creek Conglomerate and underlain
by the Man cos Shale. The Mesa Verde Formation is composed of four members;
the Rollins Sandstone, the Upper and Lower Coal members, and the "Barren"
Member. See generalized stratigraphic column, Figure 2.7.2.A, and
description pages 2-219 through 2-227d.
The lowermost: member of the Mesa Verde Formation, the Rollins Sandstone,
is a white to buff-colored, well-sorted, medium-grained sandstone,
ranging from 150 feet to 300 feet thick in the permit area. The Lower
Coal Member overlies the Rollins Sandstone and consists of interbedded
sandstones, siltstones, coals, and shale. The unit averages 270 feet
thick in the permit area and bears three signigicant coal seams-- the
A, B, and C seams. A massive sandstone 25 feet to 225 feet thick lies at the
top of the Lower Coal Member and separates it from the Upper Coal Member.
The Upper Coal Member is approximately 220 feet thick, containing shales,
siltstones, sandstones, and the D, E, and F coal seams. The Mt.
~~•~~"' Gunnison No. 1 Mine will be located in the upper most seam, the F seam.
Rt the mZflA site, the coal is immediately overlain and underlain by
shale.
Overlying the Upper Coal Member is the Barren Member of the Mesa Verde
Group. This unit consists of interbedded sandstones, siltstones, shales,
and coals. This unit is not thought to be of marine origin and, as a
result, the sandstones and the coals are highly lenticular, discontinuous,
and of limited lateral extent in outcrop. This unit ranges up to 1,500
feet thick and outcrops throughout most of the 5-year permit area.
Ground water occurs in both the sandstones and the coal seams of the Mesa
Venda Formation. Regional ground water movement is northeasterly, down
the dip of continuous stratigraphic units. Local ground water movement
is controlled by topography, faults, fractures, and discontinuous lenticular
sandstones. The most continuous sandstone aquifers of any signigicance