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<br />CHAPTERTHREE "'S1• Attected Environment
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<br />In a grab sample collected at 95 feet bgs doling drilling oftalluvial monitoring well 21-2, Erb {~ 1 ~ s ~- i~
<br />concentrations of sulfate (335 mgil), iron (4.50 mg/l), and r4tanganese (0.910 mg/1) exceeded d, ~ • ~. ,r ,r.~
<br />Colorado groundwater standazds. j ce~,~ ~'`''
<br />I
<br />Subsequent sampling of monitoring we1121-2 shows that several chemtcaLparameters exceeded
<br />Colorado groundwater standazds. These include chloride (1,047 mg/1), sulfate (550 to 900 mg/1),
<br />chromium (0.061 to 0.102 mg/I), iron (0.5 to ] 0 mgil), and manganese (0.065 to 0.91 mg/1).
<br />Upper Aquifer
<br />The Upper Aquifer is generally defined as the saturated zone that includes the lower, saturated
<br />portion of the Uinta Formation and the upper Pazachute Creek Member of the Green River
<br />Formation down to the top of the Mahogany Zone. The depth to groundwater in two American
<br />Soda monitoring wells (20-5 and 20-8) completed in the Uinta Formation was about 105 and 158
<br />feet bgs, respectively. Although wells 20-5 and 20-8 did not penetrate the entire Upper Aquifer
<br />sequence. the total saturated thickness of the Upper Aquifer at the Piceance Site, based on
<br />information from neazby wells (i.e., we1120-1) and core holes, is approximately 650 feet. It
<br />should be noted that most of American Soda's wells aze located close to each other on the side
<br />slope (i.e., elevations of approximately 6,200 feet msl) of a tributary drainage to Piceance Creek.
<br />Depth to groundwater in upland areas of the lease block at elevations of about 6,500 feet msl is
<br />expected to be 350 to 450 feet bgs.
<br />Based on static groundwater elevations measured on September 21, 1998, in well 19-2 (6,145.86
<br />feet msl), well 29-3 (6,103.66 feet msl), well 20-5 (6,098.52 feet msl), an we112-10
<br />feet msl), the potentiometric surface is located in the upper portion of the Uinta Formatton a e
<br />Piceance Site. Groundwater flow in the Upper Aquifer below the Piceance Site is generally to
<br />the east northeast at 80 degrees azimuth (Daub 1996). The horizontal hydraulic gradient "s 2
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<br />approximately 0.0096 feet per foot. ~ ~j ~+ •r++" h"P ~ ~ `` fi/,,.,-;,Ps vc -~~/f'~-
<br />American Soda conducted a pumping test on well 20-8 (Upper Aquifet) at a maximum sustained
<br />rate of 150 gpm with an associated drawdown of 266 feet. Agapito's analysis of the test
<br />indicated a transmissivity of 1,500 gallons per day (gpd/ft) (Agapito 1997).
<br />Much of the groundwater in the Upper Aquifer system is classified as a sodium bicazbonate type, ~ tyy,~,}.
<br />with sulfate as a major anion. Generally, concentrations of dissolved solids increase with aquifer ", K' •
<br />depth and in a northerly direction. TDS content ranges from 400 to 2,000 mg/l. Calcium, \•r!
<br />magnesium, and sulfate concentrations aze generally greater in the Upper Aquifer than in the > ~ ~ ' ~
<br />Lower Aquifer, while sodium, bicazbonate, and fluoride aze higher in the Lower Aquifer. d ?
<br />Groundwater quality data collected during drilling of American Soda solution mining well 20-3, yF
<br />monitoring well 20-5, and water supply well 20-8, indicate TDS concentrations in the Uinta y.~'
<br />Formation ranged from 944 to 2,980 mg/1 at depths from 357 to 650 feet bgs in the Uinta S
<br />Formation._ Vic----'"-- -_
<br />Salinity increases rapidly as the A-Groove is approached, with TDS concentrations in e e s of ~ ~ ~,
<br />10,000 mg/I in the lowest parts of the Upper Aquifer (Steigers 1997x, Steigers 1997b). A wa~er ~ dr a~ l
<br />quality sample taken just above the A-Groove at a depth of 811 feet bgs at solution mining well ~~'~' ,t,~
<br />20-3 had a TDS concentration of 15,900 mg/1(Steigers 1997x, Steigers 1997b). The TDS dat~ c~~\ ~i
<br />~~5 h pf a ~l ('e~ w ~'rt~+ aw a -+ ~~~^ Groundwater 3-19
<br />mar wC1 S oU-~ ~O/J- 1~'L
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