|
,~
<br />~~ `
<br />~~
<br />~~'
<br />CHAPTERTHREE
<br />Affected Enuironmem
<br />Ii
<br />from Uinta wells (20-5 and 20-8) and the A-Groove portion of the solution mining well (20-3) a~ur Oa.~+,-*
<br />' indicate that only the Uinta Formation portion of the Upper Aquifer would be considered a . ~ ~ ~''~
<br />j. _ ~• .
<br />Il USDW. ~ ~"' ~ I
<br />,~ J using drilling and subsequent sampling of mho ~Oring-well 20-5-~3inta Formation), t
<br />;fro - concentrations of fluoride (5 to 8.3 mg/I), c ohl ride (769 mg/1), st~tate (290 to 390 mg/1), nitrite vra
<br />`i? ~. ~ ,+ (2.5 mg/l), chromium (0.066 mg/1), iron (0.5 to 13.3 mg/I), manganese (0.0)S 1 tq 0.405 mg/I), d' ts~ ~,
<br />~' ~F' f ~ zinc (13.3 mg/1), and pH (8.8) exceeded Colorado groundwater standards. /11 (. le-4' '
<br />~ ~
<br />Mahogany Zone
<br />The Mahogany Zone is a kerogen-rich oil shale zone that sepazates the Upper Aquifer from the
<br />Lower Aquifer spatially, but not entirely hydrologically. The Mahogany Zone is considered a
<br />semi-confining layer and it is approximately 180 feet thick at American Soda well 20-1.
<br />~x~The vertical hydraulic conductivity which controls the verticai exchange of water between the
<br />~~~ tyS' Upper Aquifer and the Lower Aquifer. varies throughout the rock formation. There are
<br />,~~.~'~ : ~ ~ insufficient data available at the Piceance Site to evaluate vertical gradients. However, published
<br />~~~r~ o\y data indicate that downward vertical gradienu probably exist in the upland azeas of the project
<br />\~e° ~ and upwazd gradients may occur near Piceance Creek (Robson and Saulnier 1980).
<br />~~ LowerAquifer
<br />The Lower Aquifer consists of the Leached Zone of the Parachute Creek Member. The Leached
<br />Zone is generally located below the Mahogany Zone and above the Dissolution Surface.
<br />
<br />Based on geologic information from American Soda boreholes, the thickness of the Lower C~„~
<br />~~, v ry
<br />°
<br />Aquifer ranges from 342 feet bgs in we1129-2 to the south to 440 feet bgs in well 19-2 in the ~~ ~
<br />northwestern part of the Project Area. In the wells in section 20 at the project site, the thickness
<br />1 ~ `~-~~
<br />~
<br />l ranges from approximately 367 to 405 feet bgs. The Dissolution Surface (i.e., base of the Lower ~~ ~~
<br />\ Aquifer) is located at an approximate elevation of 4,700 to 4,800 feet msl within the project
<br />boundary.
<br />a
<br />' t~` ~ Based on static water elevations measured on September 21, 1998, in well 20-1 (6,087.69 feet
<br />`a ~,'; msl), well 29-2 (6,119.84 feet msl), welt 20-4 (6,138.25 feet msl), and well 20-9 (6,108.63 feet
<br />~+ ,,~tsl), groundwater flow in the Lower Aquifer below the Piceance Site is generally to the east-
<br />,,' ct ,, ~f
<br />~
<br />emu' . southeast at 100 degrees azimuth, and the horizontal hydraulic gradient is approximately 0.014 ~ Ply
<br />:'~ ~-~~
<br />~ Sty+~ .Meet per foot. ,'' '
<br />«
<br />o`.+''} (~
<br />~~ I a 7-day pump test of the Lower Aquifer conducted at the adjacent lease property to the west of
<br />~
<br />~,~ ti ~ e Piceance Site, transmissivity vaned from 280 to 350 square feet per day in fora observation
<br />~~~ wells. However, transmissivity has not been determined for American Soda wells completed in , y
<br />~~~ the Lower Aquifer. Storage coefficient data from a 7-day pump test conducted on the adjacent ,~~=' ~ n
<br />;o~ lease property to the west of the Piceance Site ranged from 2x10-5 to 7x10-5 (Cole et al. 1995).
<br />CS
<br />i Lower Aquifer water is generally classified as a sodium bicarbonate-c ride type.
<br />~ ~ concentrations of the Lower Aquifer range from about 500 mg/1 to greater than 6 g/1 and
<br />~'?L are dependent on depth and location. Data indicate that the salinity of the Lo r gwfer
<br />~ h
<br />3-20 Groundwater
<br />
|