Laserfiche WebLink
Morrison Formation—Brushy Basin Member <br /> The Brushy Basin Member of the Morrison Formation is composed dominantly of variegated <br /> mudstone with lesser amounts of sandstone, conglomeratic sandstone, and limestone. This <br /> unit is considered to be an aquitard for the underlying water-bearing zone in the Salt Wash <br /> Member. Packer tests in the upper part of the Brushy Basin showed permeabilities ranging <br /> from 0.62 to less than 0.01 foot/year. (EPA, 2017) <br /> Morrison Formation—Salt Wash Member <br /> The Salt Wash member of the Morrison Formation is comprised of alternating beds or lenses <br /> of siltstone or mudstone and highly lenticular sandstone, and near the base, a few thin <br /> limestone beds. The sandstone beds, which are the dominant lithology, consist mostly of fine, <br /> medium, and coarse-grained quartz sand. <br /> Because of the lithology and lenticular nature of the Salt Wash Member,permeabilities tend <br /> to be relatively low and water availability highly variable. Flow tests on wells in the region <br /> completed in the Salt Wash yield a transmissivity and storativity of 47 gpd/ft and 3 x 10-5, <br /> respectively. (EPA. 2017) <br /> Salt Wash groundwater tends to be sodium bicarbonate-sodium sulfate water of relatively <br /> good quality. Pyrite is suspected as the source of the sulfate. High sodium levels suggest <br /> water in the Salt Wash has undergone more natural base exchange than water in any other <br /> water-bearing units. <br /> The Salt Wash Member is exposed over a wide area southwest of Uravan and is probably one <br /> area of recharge.As are the other formations,this member is also exposed along the flanks of <br /> the Uncompahgre Uplift and receives water at that location. The San Miguel River Canyon <br /> and Atkinson Creek are areas of natural discharge. <br /> Summerville Formation <br /> The thinly bedded Summerville Formation consists mainly of alternating beds of siltstone <br /> and sandstone with shale and mudstone near the top. It is considered by the EPA to be an <br /> aquitard in this region, and to effectively confine water in the Entrada and lower units. This <br /> formation generally does not yield water to wells, due to its lower permeability. <br /> Formation Position in Permeabilit ft/ r Storativity Reference <br /> formation Horizontal Vertical <br /> Dakota No data <br /> Sandstone <br /> Burro 827 2 <br /> Canyon <br /> Morrison Brushy Basin 0.62-0.01 2 <br /> Member <br /> Slick Rock Project Groundwater Sampling and Analysis Plan-2025 <br /> Slick Rock NOI Modification July 2025 <br /> Appendix C Page 7 of 35 <br />