GENERAL46787

• Permit No: C1983059
• IBM Index Class Name: General Documents
• Doc Date: 8/15/1988
• Doc Name: PROPOSED DECISION & FINDINGS OF COMPLIANCE FOR RN1
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

The replacement of 10 inches of topsoil rather than the 13 inch depth which
existed prior to disturbance will reduce the amount of water stored within the
rooting zone by approximately .33 inches. However, the reconstructed root
zone (10 inches of soil and 34 inches of colluvium) would hold 3.51 inches of
water at field capacity, which is comparable to orchard soils adjacent to the
permit area.
SUMMARY OF CUMULATIVE HYDROLOGIC IMPACT ASSESSMENT
DESCRIPTION OF GROUND WATER STUDY AREA
Four categories of potential aquifers occur in the Somerset Coal Field. These
are: the alluvial and terrace deposits associated with the North Fork of the
Gunnison River; the local shallow alluvium along creeks tributary to the North
Fork; the discontinuous, lenticular and laminar sandstone of the Mesa Verde
Formation; and the Rollins Sandstone.
The most significant aquifer in the area is the alluvium of the North Fork of
the Gunnison River. Thicknesses of alluvial sand and gravel range from
30'-80' thick. Numerous wells are developed in the alluvium with an average
yield of 17.4 gpm. A pump test performed on an alluvial well at Bear Mine
yielded a transmissivity of 806.5 g/ft/d and a storativity of 0.2.
One mine draws water from the alluvium of tributaries to the North Fork; the
Orchard Valley Mine withdraws water from the alluvium of Stevens Gulch. CWI
pumping tests suggest that this alluvium could support a pumping rate of
28 gpm. Transmissivity ranges from 187-230 ft2/day. Both Hubbard and
Terror Creek have deposits which could be similarly developed, but have not
been to date.
Observations made underground by the Division staff at Blue Ribbon, Hawk's
Nest, Mt. Gunnison, Somerset and Orchard Valley Mines indicate the coal seams
in the region are poor aquifers with low transmissivities. The "B-2", "E",
and "F" seams were observed to weep slightly at fresh cut faces, while mine
entry faces a short distance away were dry. Coal seam water typology
generally consists of a sodium bicarbonate or sodium sulfate type water with
salinities ranging from 750-7,560 umhos/cm (E.C.).
The Rollins Sandstone is a poorly recharged aquifer in this area due to the
steep, immature topography of the area and its outcrops as cliffs. Water
quality is marginal due to high salinity.
The ground water system in the Paonia and Somerset area is divided by the
North Fork of the Gunnison River into two separate systems. The strata in the
general area dip shallowly in a northerly direction. The North Fork of the
Gunnison River cagyon isolates the coal beds and aquifers of the Mesa Verde
group north and south of the river. The ground water systems on either side
of the river are isolated from each other and will only be impacted by
operations on one side of the valley.
The mines north of the North fork of the Gunnison River are Hawk's Nest,
Somerset, Blue Ribbon, and Orchard Yalley. The Terror Creek Loadout is also
on the north side of the river. Mines south of the river include Mt.
Gunnison, Bear Mines 1, 2, and 3, and the Hawk's Nest Landfill.
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