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Hydrology of the Prairie Dog Creek drainage basin, Rosebud and Big Horn Counties, Montana

January 1, 1982

The Prairie Dog Creek drainage basin in southeastern Montana was investigated during 1978-79 to assess the surface-water and ground-water resources and the quality of water in an area having coal-mining potential. The area, a 24.2-square-mile basin, is located 30 miles southwest of Ash-land, Montana. The principal mineable coal is the 40-to 60-foot-thick Wall and lower Wall coal beds near the middle part of the Tongue River Member of the Fort Union Formation (Paleocene age). Other possibly mineable intervals are the Canyon coal bed lying 200 to 250 feet above the Wall, and the Brewster-Arnold coal bed lying about 220 feet below the base of the Wall coal beds.

The hydrologic regime in the basin is composed of Prairie Dog Creek and sandstone, coal, clinker, and alluvium aquifers. Prairie Dog Creek, which originates from springs and seeps issuing from coal and sandstone layers, maintained perennial flow in its upstream and middle reaches during 1978 and 1979. In its downstream reach, the flow decreased consistently until the channel near the mouth had only standing water or was dry. The dissolved-solids concentration of streamflow during periods of high flow (1 cubic foot per second or more) in the spring months ranged from 700 to about 1,000 milligrams per liter and during periods of lesser flow (0.5 cubic foot per second or less) in the summer ranged from about 1,300 to 1,600 milligrams per liter.

Forty-two cased observation wells were used to obtain data on aquifer characteristics and quality of water. Relatively clean (free of silt or mud) sandstone beds have transmissivities of about 15 feet squared per day; the water was a magnesium sulfate or sodium sulfate type and dissolved-solids concentrations ranged from about 2,170 to 3,260 milligrams per liter. The Wall coal aquifer has transmissivities ranging from 2.5 to 65 feet squared per day; the water was a sodium sulfate type and dissolved-solids concentrations ranged from 1,820 to 4,190 milligrams per liter. The Brewster-Arnold coal aquifer has transmissivities similar to those of the Wall coal but the water was a sodium bicarbonate type; the water contained an excessive concentration of fluoride (more than 10 milligrams per liter) and had a very high sodium-adsorption ratio (more than 60).

The alluvial aquifer in the Prairie Dog Creek valley has transmissivities ranging from about 1,000 to 5,000 feet squared per day in the middle reaches and as much as 9,200 feet squared per day near the mouth of the creek. The water quality changed from a magnesium sulfate type in the middle reaches to a sodium sulfate type near the mouth. The dissolved-solids concentration decreased from about 1,700 milligrams per liter in the middle reaches to about 1,100 milligrams per liter near the mouth as inflow of water from clinker and alluvial deposits beneath terraces diluted the alluvial water.

Publication Year 1982
Title Hydrology of the Prairie Dog Creek drainage basin, Rosebud and Big Horn Counties, Montana
DOI 10.3133/wri8137
Authors N. E. McClymonds
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Water-Resources Investigations Report
Series Number 81-37
Index ID wri8137
Record Source USGS Publications Warehouse