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Geology and ground-water resources of Ogden Valley, Utah
Ogden Valley, in Weber County, is a fault trough or graben. It is known as one of the ”back valleys” of the Wasatch Range. Consolidated rocks of pre-Tertiary age, unconsolidated and poorly consolidated rocks of Tertiary age, and unconsolidated rocks of Quaternary age constitute the rocks of Ogden Valley and its watershed. The pre-Tertiary rocks are exposed in the mountains surrounding the valley. These rocks range in age from Precambrian to late Paleozoic. Several stratigraphic gaps exclude the rocks of Ordovician, Silurian, much of the Devonian, and the Permian systems from the area. The pre- Tertiary rocks are not very significant as water bearers in the area. The Tertiary rocks include Knight Formation, Norwood Tuff, and upper Pliocene (?) Fanglomerate and range in age from early (?) Eocene to late Pliocene(?). Miocene rocks are missing. The Knight Formation sup¬ plies about 860 acre-feet of water annually to Bennett Spring. The Norwood Tuff has a low permeability and acts as an underlying confining bed in Ogden Valley. The upper Pliocene (?) Fanglomerate is unconsolidated and unsorted. The formation has a relatively low permeability; therefore, it will not receive much recharge from precipitation. The Quaternary rocks include more than 400 feet of unconsolidated sediments of the Pleistocene and Recent epochs deposited within the graben. The Pleistocene sediments consist of pre-Lake Bonneville and Lake Bonneville gravels, sands, silts, and clays. The Recent deposits are fan gravels, flood-plain gravel, sand, and silt, landslide deposits, and slope wash deposits. Pre-Lake Bonneville deposits include fan gravels and stream-laid deposits of gravel, sand, silt, and clay; they make up the artesian aquifer, whose waters are confined by the over¬ lying silt and clay of the Alpine Formation of Lake Bonneville age and by the relatively impermeable underlying Norwood Tuff. Overlying the Alpine Formation are the sands and gravels of the Bonneville Formation which, together with Recent sands and gravels, contain perched water bodies. In the recharge area these Bonneville and Recent deposits are hydraulically connected with the artesian and water-table aquifer. Ogden Valley is drained by three forks of Ogden River, and the flow of this river is regulated by the earth-fill dam which impounds the water of Pineview Reservoir. Recharge to the ground-water reservoirs is by seepage from waterways and irrigated lands, and infiltration of precipitation. The estimated minimum recharge in 1970 was 34,300 acre-feet. The greatest contribution to this recharge is from seepage waters from the waterways and irrigated land. Discharge from the ground-water reservoirs is by (1) wells, (2) evapotranspiration,and (3) springs. The estimated minimum discharge in 1970 was 34,000 acre-feet, of which 20,000 acre-feet was discharged by evapotranspiration. The most important causes of water-level fluctuations in the artesian wells are discharge from the wells and loading by Pineview Reservoir. Since November 1936, Pineview Reservoir has created a unique situation in Ogden Valley by adding a load on the underlying artesian aquifer. Thus, with an increase in the storage of the surface reservoir, the artesian aquifer is compressed and the water levels in the wells start to rise. An increase of about 4,800 acre-feet in the storage of Pineview Reservoir corresponds to a rise of water level in the test well, (A-6-2) 18 bab-1, of one foot. The chemical quality of the ground water in Ogden Valley is good and the water is suitable for household and irrigation purposes. The results of bacteriological analyses of water samples from ten wells indicate that the water in six wells is satisfactory, but the water in four wells around Eden may be classed as unsatisfactory for drinking purposes. The artesian aquifer in Ogden Valley probably could be developed further if the present users would be willing to accept a reduction in pres¬ sure in exchange for the additional water. The water-table aquifer probably could be developed to yield five times its present yield of 100 acre-feet per year.