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2.04.7(1) (a) (i) (ii) <br />ARCO's investigations of the lithology, stratigraphy and <br />structure indicates that the aquifers in the area are <br />confined to limited aquifers consisting of the sandstones <br />and the alluvium in Sylvester Gulch. The sandstones have <br />a negligible contribution as aquifers due .to the existence <br />of many shales acting as aquicludes. <br />Following is an excerpt from ARCO's t•1 5 F. Plan of August, 197E:. <br />Recharge to the springs appears to come from snow melt. The <br />Mesaverde sandstones and the fracture system within these <br />sandstones is the apparent aquifer. The outcropping rocks <br />consist of interbedded lenticular sandstones and shales of <br />stream channel and floodplain origin. The sandstones, which <br />• have law permeability, (refer to page 46a) act as the aqu~.fers, while the shale <br />There is a rather even distribution of a number of springs <br />through the 400' interval above the F seam with a significant <br />increase in the number of springs occurring between 450'-500' <br />and 550'-600' above the F seam. This latter distribution <br />suggests a significant shale or aquiclude layer at these <br />two points. One of the above groups of springs occurs within <br />Poison Gulch, a tributary of the Dry Fork of the Minnesota <br />Creek. The valley bottom parallels the dip, thus giving <br />rise to this stratigraphic zonation of springs. In addition, <br />the spring waters are dominantly low solids (500 ppm, TDS) <br />sodium bicarbonate waters. There is no marked change in water <br />quality with distance above the F seam. <br />layers act as barriers to vertical migration of waters. Thus, <br />each sandstone is a potential aquifer which may or may not <br />be perched by the underlying shale members. Perched water <br />tables or aquifers appear to be the rule. <br />5-9 <br />