GENERAL33376

• Permit No: C1982057
• IBM Index Class Name: General Documents
• Doc Date: 9/4/1991
• Doc Name: PROPOSED DECISION & FINDINGS OF COMPLIANCE FOR PR1
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

The alluvium is thin or absent in dregs 'Nhere streams cross the resistant
Sandstones of the Mesaverde Group. Thz alluvial aquifers are wider where the
Streams Cro55 1255 r2515tdnt rOCk Units Or the L2'N15 and IMancoS ShdleS.
B. Ground Water
Ground Wdter OCCUri t0 d llmlted ext?nt in 311 the S2d'mentdry rocks Of
Ubper Cretaceous age in the region. The only identifies strata cabable of
regionally storing and transmitting 'Mater are the low creek, the Trout Creek,
and the Twentymile Sandstones. Lecaliy the lenticular and interbedded
sanestene5 or the three coal greucs as weal as tr.e mater coal seams will also
store and transmit limited amounts of ',vatar.
Wells Completed in the .Mancos Shale gen2.'dlly vleld 5mdil CU3n tl t~2s Of 'Ndt2r,
less than 5 gal/min. Tne water is pr2dcminantiv a caic~um-bicarbonate type
(Brogden and Giles, 1977). Total Dissolved Solids (TDS) concentration ranges
from 338 to 2,590 mg/l, and the water ma! contain concentrations of chloride,
fluoride, iron and manganese in excess of U.S. ?ublic Health Service (1962)
drinking water standards (Brogden and Giles, i977>. ,although the Mancos Shale
contains limited ground water that may be suitable for domestic and stock use,
the extensive shales in the upper part of the formation act as relatively
imeermeable barriers to the subsurface movement Of wdter. The Mancos Shale
can be considered as an impermeab~e, confining layer underlying the Mesa/erde
Group, and could be classifies as an acuiclude.
The major bedrock aqui•"er; in the Mesaverde Group occur within the massive,
regional sandstone units of the Ile<. anc 'Williams Fork Formations. dells
completed in the Tow Creek Sandstone and Trout Creek Sandstcne of the
Iles Formation and the Twentvmiie Sandstcne ;~ the Williams Fork Formation are
used primarily for domestic and stock purposes. Weil yields from these
sandstone dpUife'S d:"2 USUdlly less than 10 gal/min (Brogden and ;ills,
1971). Higher yields generally occur at great=r deaths Nn2re water in the
Sandstcne is under artesian pres>ur2, anc where the sandstones have been
fractured extensively. Hydraulic conductivity values for fractured sandstones
of the Iles and Williams Fork Formations range from 3.7 to 26 feet/day
(Brogden and Giles, 1977).
Limited ground water also occurs in coal seams and disccntinueus, lenticular
sandstones 'Nithin the Mesaverde Grcub. The perme3bilities of these water
be of ing Unl is dre Quit? 1CW, gener3'.ly an order of magnitude 125; than the
fractured sandstone 3•CUif2r,. Ground water Nithin the Iles and Williams rock
rcrmdtion5 i5 Oredemin3fl tly talCium 3nC 5eC"Jm-pi G3rbend C? In Cn3rdC ter.
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