Water resources of the central Powder River area of southeastern Montana

Abstract

Water for domestic, stock, and public use is available from the Fox Hills-lower Hell Creek aquifer of Late Cretaceous age. Water for domestic and stock use is available from the upper part of the Hell Creek Formation of Late Cretaceous age and the lower part of the Fort Union Formation of Paleocene age. Water for irrigation can be obtained from alluvium of Holocene and Pleistocene age along the Powder River. The Fox Hills-lower Hell Creek aquifer yields as much as 188 gallons per minute to wells as deep as 999 feet, but most well yields are 20 gallons per minute or less. The upper part of the Hell Creek Formation yields as much as 12 gallons per minute to wells as deep as 465 feet. The lower part of the Fort Union Formation yields a maximum of 25 gallons per minute to wells as deep as 373 feet. The alluvium of the Powder River yields 600 gallons per minute to the only known irrigation well, which is 40 feet deep. Water from the Fox Hills-lower Hell Creek aquifer generally contains sodium and bicarbonate or sulfate as the major ions; dissolved-solids concentration is as much as 1,700 milligrams per liter. Sodium, bicarbonate, and sulfate were the major ions in two samples from the upper part of the Hell Creek Formation; the dissolved-solids concentration was 840 milligrams per liter in both samples. Water from the Fort Union Formation contains principally sodium, sulfate, and bicarbonate ions; the dissolved-solids concentration ranges from 780 to 2,300 milligrams per liter. One water sample from the alluvium contained principally sodium and sulfate ions and had a dissolved-solids concentration of 2,300 milligrams per liter. The Powder River is the only perennial stream in the study area. The average annual discharge of the Powder River near Locate for the period of record, 1938-69, was 601 cubic feet per second. instantaneous discharge ranged from 0 to 31,000 cubic feet per second. Dissolved-solids concentration of water from the Powder River for the period of record, 1949-63, ranged from 278 to 5,430 milligrams per liter. Calcium, sodium, and sulfate were the major ions.