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<br />formations would generally rank as havinu poor dom<stic well potential (Bureau of
<br />Reclamation, 1977}. however, although the thrr_e units do not possess significant
<br />aquifer characteristics, the presence of water in the units indicates that pit-water
<br />inflow will be expected to occur. The limited gcouncl water contained in the overburden
<br />bedrocl; units beneath the site would be expected, under undisturbed conditions, to be
<br />recharged by vertical infiltration of precipitation into the outcrops near the eastern
<br />edge of the permit boundary, move doe,~ndip in a westerly direction, and discharge into
<br />the alluvium of Trout Creek. This entire flow path essentially represents a separate
<br />system in which water moves a distance of less than two miles from recharge to discharge)
<br />The Trout Creek Sandstone, a 100' thick sandstone unit which is persistent throughout
<br />much of northwestern Colorado, underlies the wed-pit bottoms by approximately
<br />150-225 feet. This regionally significant sandstone ,.i..,,~r sill not be physically
<br />disturbed by the p~e¢esF>31 mining plan. Because of the interbedded nature and low
<br />permea2rilities ( of the rock units located
<br />stratigraphically between the [•ladge Coal and the Trout CreeF: Sandstone, little hydro-
<br />logic interconnection is expected.
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<br />In~i xhe alluviaxa f ^..~-m,'~g Trout CreeY. and Oak
<br />Creek i-s~also water bearing. Th^ bedrock formations generally plunge beneath or sub-
<br />crop iNto the Trout Creek alluvium. However, folloi,ring mining and the disruption of
<br />the overburden, it ~s+-r~be possible for water percolating through the spoils to enter
<br />the Trout Creek alluvial aquifer. The alluvium a_'ong Trout and Oak. Creeks is in direct
<br />hydrologic connection with the stream channels.
<br />A large portion of the permit area has been in~,d roviousli Ffininq has disrupted
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<br />the natural sequence of strata do~,m to thegcoal seam, and the overbu mlen has been re-
<br />placed with spoil. An increase .in vertical continuity has been realizer], such thct the
<br />percolation rate of the spoil is greater than the rates r:•hich existed prior to distur-
<br />bance, R ep percolation of precipitation through the spoils ,has created a perched
<br />water table aquifer which abuts against the now buried highwall of the box cut near
<br />the foct of the slope (see Figure 2, p. 8, of h[c!t'horter, et a1. , 1975) . Numerous springs
<br />have been formed as a result. T!;ese springs, s;;cwn on Ytap 2.5-2I, emanate From the
<br />relatively steep face which exists above the eastside Trout Creek alluvium.
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<br />Ground water quality in the bedrock pones (overbuy<!en and [J<7dge) generally decreases
<br />in the dor.~ndip direction; the up-dip monitorrnq Incntinns inriicate that the ~,mter is
<br />of moderately good qual i.ty, chnractr_ri rc!i fn! tom sn,ii um Absorption Ratio (SAR) val u:a
<br />and moderate levels of Total Dissnlvcrl Solid; (Ti)S). 7'h r_ rloi:~rdip monitoring ~.:~lls,
<br />however, show increasingly higher levels of TDS. This trend applies primarily to the
<br />Moffat area, where undisturbed conditions now exist.
<br />The average pre-mining value of TDS
<br />in the undisturbed portions of [Lest
<br />(AfdJhorte r, et al., 19791. The TDS
<br />water) in the [Jest Ridge area is on
<br />with the measure TDS levels of satu
<br />which were found to have TDS levels
<br />in the Ploffat area ground water is 570 mg/1, while
<br />Ridge area, the value was reported as 960 my/1
<br />level measure for areas already reined (e.g., spoil
<br />the order of )030 mg/1. This corresponds ~~iell
<br />ration extracts prepared from drill cuttings,
<br />of around 3000 mg/1 (~L1c[Jhorter, et al. , 1979) .
<br />Background water quality data From t}re alluvial ground water of Trout Creek indicates
<br />that the quality of the alluvial ground water is suitable for agricultural purposes.
<br />The water is moderately low in TAi levels (less than 350 mg/1) and is low in SAR. The
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