PERMFILE133316

• Permit No: C1980003
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Previous Findings and Conclusions
• Section_Exhibit Name: 1996 Appendix F
• Media Type: D
• Archive: No

- The lower and upper coals of the upper Williams Fork formation produce
marginally potable water of limited quantity. Hydraulic conductivity values
range from 1.6-115 ft3/day. The excavation of the recharge area will change
its physical properties and the quality of water which can be recharged. AS
there are no users of the aquifer downdip of the Hayden Gulch Mine, any
impacts will be insignificant.
The Twentymile Sandstone lies below the Lower Coal of Hayden Gulch and is
separated by 200-300 feet of interbedded sandstones and shales. The
Twentymile Sandstone stratigraphically lies 525 feet above the Wadge Coal (the
principal seam to be mined at Seneca II-W ), but it has been eroded over much
of the Seneca II-W area. This regional aquifer will not be disturbed by
either mining operation, and hence its water quality and quantity will not be
affected.
The sediments associated with the Lennox and Wadge coal seams may contain
perched aquifers as Wadge Coal. The strata does not contain or transport
significant volumes of water in this area, although it has been known to in
other locations.
The Wolf Creek coal seam, which lies 150 to 170 feet below the Wadge coal
seem, is the first significant aquifer below the mined seam at Seneca II-W.
This seam, which is up to twelve (12) feet thick, appears to be saturated in
this area. Due to the dip of the unit and the confining nature of the over
and underburden, the Wolf Creek has as much as 770 feet of artesian head in a
well. It should be noted that the amount of head is aerially variable as the
aquifer's conditions change from water table (unconfined) near outcrops to
• confined conditions at depth.
The aquifer characteristics of the Wolf Creek (low transmissivity and
storativity values) indicate that very little water is available for upward
movement. Due to mining methods and the thickness and type of interburden
between the Wolf Creek and 4ladge, pit inflows at Seneca II-W, from upward
movement of the Wolf Creek, are not expected.
About 200 feet below the Wadge coal lies the Trout Creek Sandstone. The
relatively impermeable interburden between the Wadge coal and the Trout Creek
Sandstone (which includes the Wolf Creek coal) and the stratigraphic distance
between them will preclude impacts to the Trout Creek Sandstone from mining.
The Tow Creek Sandstone lies more than 1300 feet below the Wadge coal. Due to
the thickness of the interburden between the Tow Creek and Wadge, it is not
likely that hydraulic pressures capable of affecting this aquifer will develop.
On summary, there is little likelihood of cumulative impacts to bedrock
aquifers from mining by the Hayden Gulch Mine and Seneca II-W Mine for several
reasons. The transmissivity and storativity values of the tdiddle and upper
Mesaverde formations are low. There are only three regional aquifers, and
they are hydrologically separated from mining impacts by sediments of
considerable thickness and low permeability. There are few reported faults in
the region and low vertical permeabilities.
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