CRAPTfRFIVE Draft E!S Relrlsions
<br />• Tertiary Uinta Formation sandstones and mazlstones. The alluvial material is generally
<br />permeable; however, clay lenses may create azeas of low permeability or even impermeable
<br />intervals. Alluvium thicknesses at the Piceance Site aze variable. , '
<br />American Soda's alluvial aquifer monitoring well 21-2, which is located in
<br />the alluvium of a tributary drainage to Piceance Creek, penetrated 95 feet of alluvium. The depth
<br />to groundwater in well 21-2 is approximately 70 feet bgs, indicating a saturated thickness of
<br />about 25 feet at this location. in contrast. test holes drilled at the confluence of Piceance Creek
<br />and Rvan Gulch. iust south of theproiect site, penetrated 70 feet of dense organic clay (Welder
<br />1987). Groundwater flow within the alluvial aquifers is controlled by topographic slopes and
<br />stream flow directions. Therefore, groundwater flow in alluvium at well 21-2 is expected to be
<br />to the east.
<br />Alluvial groundwater at the Piceance Site is represented by analvses from American Soda well
<br />21-2 (fable 3.4-2) and is classified as a sodium bicazbonate type. TDS values measured in 11
<br />samples collected during 1997 and 1998 range from 634 to 2,292 meJl, with a mean of 1,680
<br />m_g/I•
<br />~, ~ ...,... , cAn ..,,,n ~s These TDS values falls within the range observed over the entire
<br />1
<br />basin of 470 mg/I to 6,720 mg/I (Weeks and Welder 1974). The mean values for TDS (1.680
<br />m~/1), sulfate (616 mgR), iron (2.11 mg[I), and manganese (0.18 mgLl) exceed Colorado
<br />i~roundwater standazds. A single analysis performed for aluminum suggests that this parameter
<br />exceeds the aericultural standazd. The standazd for chloride was exceeded by one reported value
<br />of 1.047 me/l. However, this value is more than 12 times hieher than the next hiehest
<br />• concentration recorded for chloride in this well (87 mQ/I) and is, therefore, considered to be
<br />suspect. The standazds for chromium and lead were also exceeded in 1 of 19 sam~es each.
<br />A search of the USGS database was conducted to obtain water quality information for the
<br />alluvium and other water-bearing units neaz the Piceance Site, alone the pipeline route, and neaz
<br />the Pazachute Site. Table 3.4-3 provides a summary of the analytical results for wells neaz the
<br />Piceance Site. and the raw analytical data for these wells are included in Appendix K. TDS
<br />values from three wells completed in the alluvium ranged from 990 to 6.710 me/1. Mean
<br />concentrations of TDS (3,080 me/l), sulfate (357 mpJl). fluoride (11.5 meA), and manganese
<br />(0.09 mg/1) exceed Colorado groundwater standazds for these wells. ,
<br />Paee 3-19
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<br />Upper Aquifer
<br />• The Upper Aquifer is generally defined as the saturated wne that includes the lower, saturated
<br />portion of the Uinta Formation and the upper Parachute Creek Member of the Green River
<br />5-11
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