Laserfiche WebLink
\ \\ <br />Unconsolidated sediments present at the site generally consist ofeither areddish-brown clayey sand <br />that occurs to depths of eight to 15 feet or a layer of terrace gravel that outcrop; beneath the <br />impoundments and suberops beneath the clayey. sand. Thickness of the gravel deposit is variable, <br />ranging from two to 16 ft. <br />Immediately beneath the unconsolidated sediments of the Uravan terrace is the Kayenta Formation. <br />This formation also forms the bed of the San Miguel River. ht the study area, the Kayenta <br />Formation is between 130 and 200 ft thick, as observed in well logs from [he area. The formation is <br />predominately a very fine- to medium-grained, subangular to subrounded quartz sandstone. The <br />sandstone is well to poorly cemented with dolomite cement and exhibits fair to good intergranular <br />porosity. Trough crossbedding and the lenticular nature of sandstone units within this formation <br />suggest a predominantly fluvial depositional envirorunent. <br />Below the Kayenta Formation is the Wingate Sandstone, a massive cliff-forming unit, consisting of <br />well sorted, very fine- to fine-grained sandstone. This formation is approximately 250 ft thick in the <br />Uravan area. Based on the available data, the porosity of the Wingate Sandstone is similar to the <br />Kayenta Formation; however, the hydraulic conductivity of the Wingate Sandstone in the vicinity of <br />the Club Ranch Ponds area is relatively low. The contact between the Kayenta Formation and the <br />underlying Wingate Sandstone dips gently to the north and outcrops along the San Miguel River <br />approximately 5000 feet downstream from the Chtb Ranch Ponds. The aquifer recharges the river in <br />this area. <br />The most significant aquifer, with respect to the groundwater plume beneath the Club Ranch Ponds <br />area, i.s the Kayenta Formation. In the Uravan area, the Kayenta Formation has been documented as <br />having relatively high permeability (700 ft per year) and high porosity (27 percent). Recharge to <br />the Kayenta probably occurs west and northeast of Uravan, where the formation is exposed, from <br />the San Miguel River, from infiltration through the overlying unconsolidated sediments and <br />potentially from the underlying Wingate Sandstone. An extensive network of extraction wells and <br />monitoring wells have been emplaced at the Club Ranch Ponds area. Aquifer pumping test and slug <br />test data from these wells indicate highly variable hydraulic conductivity within the Kayenta <br />Formation. <br />The water table typically is located near the contact between the Kayenta Formation and the. <br />overlying unconsolidated sediments, indicating tharmost of the entire section of the Kayenta <br />Formation is saturated. Water-level data from 1997, considered representative of steady state <br />nonpumping conditions at the site, indicate horizontal hydraulic gradients from Club Ranch Ponds <br />area to the San Miguel River range from 0.025 it/ft to 0.007 ft/fr. <br />6.0 WASTE REPOSITORY DESIGN CONSIDERATIONS <br />There are two tailings repositories that have been completed or are near completion. Construction of <br />the Burbank Repository has also been completed. The Burbank Repository facility is a below grade <br />repository on three sides with a I.5 meter thick clay cover and a rock protection layer on top of the <br />clay. The one exposed out slope has a S1I:1V slope. The tailings repositories are nearly completed, <br />with the'remaining work involving placement of the final top covers. Tailings Pile 1-2 and Tailings <br />Pile 3 are above grade structures and have 3 meter thick clay covers and a rock protection cover. <br />Three meters was the minimum acceptable thickness under the regulations promulgated in the early <br />Umetco-Uravan DA February 1 I, 2000 <br />i <br />ET/Ei 39dd <br />t7l~f1N d210D b3110~ <br />lG <br />L8ZLb980L6 9L~TT L00L/5T/90 <br />