Hydrogeology of The Buffalo Aquifer, Clay and Wilkin Counties, West-Central Minnesota

Increasing demands on the water resources near Moorhead, Minnesota, have led to conflicting opinions on the availability and quality of water. Results of this study indicate that large water supplies are available in the western part of the Buffalo River watershed. The Precambrian bedrock surface, which ranges in depth from 200 to 1,000 feet below land surface, forms the lower boundary of ground-water supplies. Above this boundary, several aquifers are generally present in the drift and possibly in sandstone of Cretaceous age. Some wells in the deeper aquifers may have initial yields of 1,000 gallons per minute, but these yields cannot generally be sustained for periods of several months or longer. The Buffalo aquifer is the principal source of ground-water supplies in the area. The aquifer is an elongate deposit of sand and gravel that locally contains water under confined conditions. Lake sediments overlie more than half the aquifer and are 20 to 120 feet thick. Its most permeable part is a deep, narrow trough along the axis of the 32-mile long aquifer. The average hydraulic conductivity ranges from about 20 feet per day along the outer edges to about 300 feet per day along the axis. Its saturated thickness ranges from 0 at the edges to about 200 feet in the center. The general direction of flow is northward and toward the adjacent stream. Seepage runs along the South Branch Buffalo River indicate the river loses water near the Moorhead well field and in a 22-mile reach upstream from Sabin. Although the Buffalo aquifer contains about 270 billion gallons of water in storage, only about 120 billion gallons could be withdrawn. Well yields are greatest along the narrow, deep trough along the axis of the aquifer. Induced streambed infiltration is possible in certain areas where the stream overlies the aquifer, if the intervening lake sediments are thin or absent. The aquifer could be artificially recharged through properly constructed and maintained recharge .ponds where it is most permeable and most storage space is available. A numerical model designed for aquifer evaluation has shown that a considerable amount of ground water is discharged through the confining bed to the stream or leaves the area as underflow to the west. The model indicates the need for more data on (1) vertical hydraulic conductivity, head, and thickness of the confining bed; (2) head differences between the aquifer, confining beds and the stream; and (3) long-term water levels, recharge, and pumpage. Water from the Buffalo aquifer is generally very hard and of the calcium bicarbonate type. Dissolved solids range from about 300 to 1,900 milligrams per liter. The water is well suited for municipal supplies except for hardness and, in some places, high concentrations of iron and sulfate. The water is well suited for irrigation in terms of low sodium hazard and low concentrations of boron. The average discharge of the Buffalo River during the base period 1946- 78 ranged from 0.229 cubic foot per second per square mile near Hawley to 0.108 cubic foot per second per square mile at Sabin. Flow-duration and low-flow-frequency curves indicate a persistent low flow for the Buffalo River near Hawley and long periods of low or no flow for the South Branch Buffalo River at Sabin. Approximately 90 percent of the flood peaks on the Buffalo River system occur from March through July, with the greatest number of peaks in April. Estimated average sediment yields of the Buffalo River near Hawley and near Dilworth and of the South Branch Buffalo River at Sabin are 14.2, 9.7, and 3.9 tons per square mile per year, respectively, Surface water in the Buffalo River drainage system is a calcium bicarbonate type similar to the water in the Buffalo aquifer, especially at low flow in the upper reaches of the tributaries. The Buffalo River generally contains lower concentrations of dissolved solids and of specific ions (except sodium and chloride) than the South Branch Buffalo River. Mean monthly stream temperatures range from 0° to 23° Celsius.