This report describes the results of a reconnaissance of the sources, location, quantity, and quality of ground water in the proposed irrigation project area called the "Crofton Unit," an area of approximately 350 square miles in northeastern Nebraska.
Precambrian Sioux Quartzite underlies the entire study area. Throughout most of the area, the Sioux is overlain by undifferentiated Paleozoic rocks. The Sioux and, where present, the Paleozoic rocks are overlain unconformably by Cretaceous formations, including both the Dakota and Niobrara Formations. Surface strata are Pleistocene and Holocene deposits of sand and gravel and Pleistocene deposits of glacial till.
The Dakota and Niobrara Formations are each capable of yielding sufficient water for irrigation in parts of the area. Pleistocene and Holocene deposits yield adequate water for irrigation in the southern part of the area where saturated thicknesses range from 25 to 176 feet and along the flood plain of the Missouri River where saturated thicknesses range from 40 to 101 feet. Reported yields of 13 Pleistocene irrigation wells sampled for water-quality analyses averaged 857 gallons per minute.
Water from wells developed in the Dakota Formation is a calcium sulfate type. Use of this water for successful long-term irrigation would necessitate burdensome salinity-control measures because of the salinity of the water. Water from wells developed in the Niobrara Formation is a calcium bicarbonate type and is suitable for irrigation of most crops. Water from wells developed in both Niobrara and Pleistocene deposits generally is a calcium sulfate type and may be used for irrigation of salt-tolerant crops with special measures for salinity control. The quality of water from Pleistocene and Holocene deposits is highly variable. In both the southern part of the area and along the Missouri River, water from these deposits is a calcium bicarbonate type and generally suitable for irrigation.
