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<br />
<br />The Alluvial Aquifers, which are a primary source of stream
<br />recharoe, are limited to the valley bottoms along major creeks.
<br />The degree of saturation within the alluvium is highly variable
<br />and is dependent on seasonal recharge from precipitation,
<br />snowmelt runoff, and localized discharge from underlying bedrock
<br />aquifers. Generally, the aquifers are less than 0.5 mile in
<br />width, and the alluvium is less than 190 feet thick. At the
<br />project site, the alluvial aquifers are generally about 80 feet
<br />thick. Generally, the Alluvial Aquifer is under unconfined
<br />conditions; however, locally confined conditions could exist
<br />depending on the cccurrence of clay beds.
<br />Upper Aquifer: water samples from the recently completed
<br />American Soda water supply well (20-8) and solution mining well
<br />(20-3) exhibit total dissolved solids (TDS) concentrations in the
<br />Uinta Formation portion of the Upper Aquifer ranging from 944 to
<br />1,260 ma/1. at depths of 357 to 560 feet. The data indicates that ~,,~''o,~
<br />~ n
<br />USDWs are probably confined to the Uinta portion of the Upper ,. y+V~~,
<br />Aquifer. TDS concentrations indicate that the TDS increases tY^9{ `~
<br />dramatically with depth in the Green River Formation (Parachute~~~ L
<br />Creek Member) portion of the Upper Aquifer, with the water sample yfto
<br />from B11 feet, immediately above the Mahogany Zone, yielding a D^~'~~~ ~
<br />TDS concentration of 15, 90 mq/ 11~i zooo
<br />J o_~,`„~uJa, nlw~v-+l..tn boon e~Zn~ ~7FtF'Me ~y„~ d. ~1-
<br />o~ Lower Aquifer: TDS concentrations ranging from 38,000 ~~ ~"
<br />to 60, 000 mg/1 have been reported in the Lower Aquifer. A water r~`~,~~a~,,,,~~,
<br />sample taken from the lower part of the Lower Aquifer at the ''`s•,.•~'~~''P~,~
<br />American Soda monitoring well 20-1 in June 1997 exhibited a TDS ~~ `~ s'r~
<br />concentration of 61,600 mq/1 at a depth of approximately 1,400 ~~~°,.~j•^~
<br />feet near the Dissolution Surface. The base of the Lower Aquifer ~`~~C~•„M.
<br />occurs at the Dissolution Surface, which is coincident with the iwb•`E,~s,~y
<br />top cf the Saline Zone. There have been some questions regarding.~;r.,~~~tt~"
<br />the construction of this well and the resulting long term !~
<br />reliability of the well for the purpose of monitoring. As a
<br />result, anew well shall be installed prior to commencement of
<br />this project.
<br />~ e
<br />The upper confining zone of the Lower Aquifer is referred to v~ai~ ~,!
<br />as the Mahogany Zone which is approximately 223 feet thick. This SO ~1'^•';r
<br />confining zone is adequate to provide an effective barrier to A'~.~a'~jOi
<br />upward movement of fluids from the injection zone. The Mahogany `~;''~,~'~'
<br />Zone, however, is probably the principal semi-confining layer. ~i0yf"
<br />Even though the rich oil shale composing the Mahogany Zone is _
<br />itself quite impermeable, the presence of fractures and ,~d'~+:cL
<br />dissolution features within this zone may permit some vertical-~^~S.^ ~ ~
<br />exchange of water between the two aquifer systems. The lower y n ~~~
<br />confining zone of the Lower Aquifer in the area of the proposed
<br />disposal well (20-6) is the unsaturated, low permeability zone
<br />known as the Saline zone. The upper contact of this confining
<br />bed is referred to as the Dissolution Surface.
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