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The dominant cations in Dry Creek water are magnesium, calcium and sodium. The dominant <br /> anion is sulfate. The pH is generally around 8.2. The concentrations of the major cations, total <br /> dissolved solids, and nitrate (possibly due to agricultural return flow) increase during periods of <br /> low flow(baseflow). Total suspended solids (TSS), aluminum and total iron increase during <br /> high flows. Average values for total dissolved solids (TDS) are higher downstream than <br /> upstream of the loadout, with average values of 2,439 and 3,175 mg/l (milligrams per liter), <br /> respectively. <br /> Please see Section B, Item III of this document for a discussion of the probable hydrologic <br /> consequences (PHC) of the Loadout on surface water quantity and quality and for a further <br /> discussion of the surface water monitoring plan. Alluvial valley floors (AVF's) are discussed in <br /> Section B, Item XIV of this document. <br /> Ground Water <br /> Ground water information is located in Tabs 7, 13, 14 and 15 of the PAP. A summary of this <br /> information can be found in Section B, Item III of this document, along with specific findings <br /> related to ground water hydrology. <br /> The reclaimed coal storage and tipple area of the Loadout was situated on alluvial and colluvial <br /> materials overlying the Lewis shale. Waters from the Lewis shale are primarily calcium or <br /> sodium bicarbonate type although sulfate type water also occurs in the Lewis shale. The source <br /> of sulfate is the reduction of sulfide minerals and organic materials in the shales. <br /> The Lewis shale has low hydraulic conductivity. It is generally considered to be an aquitard that <br /> retards transmission of surface water to the underlying regional aquifer, the Twentymile <br /> Sandstone. This low conductivity results in low well yields which, along with poor water quality <br /> characteristics,preclude the use of Lewis shale waters for use other than stock watering (Seneca <br /> II-W Permit Application, HGTI application Attachment 7-1). <br /> The alluvial material also has relatively low hydraulic conductivity (approximately 0.1 to 0.01 <br /> feet/day) due to its high composition of silts and clays. These alluvial waters are of poor quality <br /> due to the proximity of the Lewis shale, contributions from agriculture, and the ephemeral nature <br /> of Dry Creek(although the applicant reports that water is taken from Dry Creek below the <br /> Loadout and used for irrigation). <br /> Please see Section B, Item III of this document for discussion of the probable hydrologic <br /> consequences (PHC) of the Loadout and railroad loop on ground water quantity and quality and <br /> for a further discussion of the ground water monitoring plan. <br /> Climate <br /> The region is characterized by a semi-arid steppe climatic regime with cold winters and mild to <br /> cool summers. The prevailing wind is from the northwest(reversing at night due to <br /> southeasterly upslope winds). Average annual precipitation is 16 inches and the growing season <br /> 7 <br />