EVALUATION OF GROUND WATER IN THE ARKANSAS RIVER ALLUVIAL AND TERRACE AQUIFERS, OSAGE RESERVATION, OKLAHOMA 2002

Increasing demand for water on the Osage Reservation led to an evaluation of shallow ground water resources contained within alluvial and terrace deposits along the Arkansas River. The Osage Reservation is located in north-central Oklahoma and covers about 2,350 square miles (6,090 square kilometers). The Arkansas River valley forms the southern and western boundaries of the reservation.

The thickness of the alluvium and terrace deposits ranged from 20 to 93 feet (6 to 28 meters). The alluvial deposits were composed of sand, silt, clay, and gravel, and all alluvial boreholes produced water. The terrace deposits were predominantly sand, but most terrace boreholes were dry. A direct push tool was used to drive an electrical conductivity probe and extract cores. Data from 20 cores and 75 electrical conductivity logs were used to determine sediment types and thickness of the alluvium and terrace deposits along the Arkansas River. The cores were collected from the surface to total depth of the borehole. Electrical conductivity measurements taken in boreholes were calibrated to cores and used to estimate sediment compositions in non-cored boreholes.

Water samples were collected using the direct push tool with a slotted screen. Water quality was determined through field measurements of pH, specific conductivity, dissolved oxygen, and nitrates. Several specific conductivity values were greater in areas near oilfield production facilities. Nitrate concentration decreased with depth. Several greater nitrate concentrations occurred in areas near cultivated crops. Dissolved oxygen and pH measurements were relatively homogeneous in the alluvial aquifer.

Water quality in the Arkansas River alluvium is variable and concentrations of dissolved constituents may be locally influenced by land use. This research is part of a joint study of the U.S. Geological Survey, Bureau of Indian Affairs, and Osage Tribe.