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periodically eliminate streamflow in the vicinity of the loadout, while at the same time <br />return flows from surrounding irrigated fields are supplying small amounts of discharge to <br />Dry Creek below the loadout. <br />Water from Dry Creek is dominated by magnesium, calcium and sodium cations and sulfate <br />anions with a mean pH of 8.2. The major cations, total dissolved solids and nitrate (possibly <br />due to agricultural return flow) increase during baseflow. Total suspended solids (TSS), <br />aluminum and total iron increase during high flows. Average values for total dissolved <br />solids (TDS) are higher downstream than upstream of the loadout; with average values of <br />2,439 and 3,175 mg/1 (milligrams per liter), respectively. <br />Please see Section B, Item III of this document for a discussion of the probable hydrologic <br />consequences (PHC) of the loadout and railroad loop on surface water quantity and quality <br />and for a further discussion of the surface water monitoring plan. Alluvial valley floors <br />(AVFs) are discussed in Section B, Item XIV of this document. <br />Ground Water Hydrology <br />Ground water information is located in Tabs 7, 13, 14 and 15 of the permit application. A <br />summary of this information, not discussed here, can be found in Section B, Item III of this <br />document, along with specific findings germane to ground water hydrology. <br />The coal storage and tipple area of the HG Loadout is situated on alluvial and colluvial <br />materials overlying the Lewis shale of upper Cretaceous age. Waters from the Lewis shale <br />are primarily calcium or sodium bicarbonate types; though sulfate type waters, produced <br />from the reduction of sulfide minerals and organic materials in the shales, also occur in <br />these units. <br />The Lewis shale has low conductivity values and is generally considered to be an aquitard <br />that retards transmission of surface water to the underlying regional aquifer, the Twenrymile <br />sandstone. This low conductivity results in low well yields which, along with poor water <br />quality characteristics, precludes the use of its waters for other than stock watering (Seneca <br />II-W Permit Application, HGTI application Attachment 7-1). <br />The alluvial material also has relatively low values for hydrologic conductivity <br />(approximately .1 to .Ol feet/day) due to its high composition of silts and clays. These <br />alluvial waters are of poor quality due to the proximity of the Lewis shale, contributions <br />from agriculture and the ephemeral nature of Dry Creek (although the applicant reports <br />that water is taken from Dry Creek below the loadout and used for irrigation). <br />Two monitoring wells ,HGDALl and HGDAL2, were drilled into a combination of alluvium <br />and Lewis shale in 1987. The former well was drilled into material along Stokes Gulch, <br />while the later well was drilled immediately below the confluence of Stokes Gulch and Dry <br />Creek. Both wells exhibit a Na-Ca-So4 water type. TDS, magnesium and sulfate <br />concentrations exhibited from the Stokes Gulch well (HGDALl) are approximately twice <br />those exhibited from HGDAL2 on Dry Creek; with TDS mean values of 44,106 and 16,292 <br /> <br />