Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1973. Department of Geology.
Hall County, an area of 540 square miles, is in south-central Nebraska. The Platte River flows east-northeasterly across the county from its southwest corner; the Wood River, which is tributary to the Platte within Hall County, enters the county about 6 miles north of the southwest corner. Analysis of streamflow data indicates that the Platte and Wood Rivers are losing streams in Hall County. Based on an 18-year period, October 1953 through September 1971, the average annual losses between gaging stations were 48,100 and 1,940 acre-feet, respectively.
The county is underlain by unconsolidated deposits of Quaternary age. These deposits mantle an irregular, eroded bedrock surface of Cretaceous and Tertiary age. Sands and gravels of Quaternary age constitute a highly productive aquifer throughout much of the county. In the northwestern part of the county, where deposits of Quaternary age are thin or not saturated, the Ogallala Formation of Tertiary age is the primary aquifer.
The unsaturated zone ranges in thickness from less than 1 foot in the Platte River valley to more than 120 feet in the upland in the northwestern part of the county. Total thickness of silts and clays in the unsaturated zone ranges from 0 to more than 100 feet and correlates fairly closely with the total thickness of the unsaturated zone.
The configuration of the water table indicates that groundwater moves generally to the east-northeast with an average gradient of 7 feet per mile. Calculated velocity values range from 29 to 44 feet per year.
The groundwater from both aquifers is the calcium bicarbonate type and is hard. Total dissolved-solids content is variable, ranging from about 100 to 1,500 mg/l, and is controlled, to a large extent, by the following factors: chemical and physical character of soils, thickness of silts and clays in the unsaturated zone, transmissivity, evapotranspiration, and seepage from the Platte and Wood Rivers.
Chloride content is low, ranging from about 1 to 70 mg/l, and sulfate content ranges from about 1 to 1,180 mg/l. The concentrations of both anions correlate positively with total dissolved-solids content.
Phosphate concentration is generally low, although two areas of moderate concentration are present. An area of generally greater than 0.5 mg/l along the Wood River west of Alda is associated with seepage of phosphate derived from municipal waste effluent discharged into the stream. An area of generally greater than 1.0 mg/l of phosphate in the extreme north-central part of the county is related to acid sandy soils.
Plates 1-12 are attached (below) as Related Files.