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Wetland Symposium

Variations in Water Quality and Detection of Agricultural Chemicals in Small Lakes and Wetlands Associated with the Warwick Aquifer on the Fort Totten Indian Reservation, North Dakota


ROBERT M. LENT, MICHAEL L. STROBEL, AND OLIVER S. GOURD

U.S. Geological Survey, Water Resources Division, 821 East Interstate Avenue, Bismarck, ND 58501; U.S. Geological Survey, Water Resources Division, 821 East Interstate Avenue, Bismarck, ND 58501; Fort Totten, ND 58335

In 1993, the U.S. Geological Survey, in cooperation with the Devils Lake Sioux Tribe, is conducting a study to evaluate water quality of the Warwick aquifer on the Fort Totten Indian Reservation. The Warwick aquifer is a shallow, unconfined glacial-outwash aquifer that is susceptible to contamination by surface sources. Numerous small lakes and wetlands are located in topographic depressions that are hydrologically connected to the Warwick aquifer. These lakes and wetlands are located along ground-water flow paths and can act as recharge, flow-through, or discharge points in the Warwick aquifer. Therefore, they may be point sources of contamination to the aquifer.

The objectives of the study include: (1) document the water quality of small lakes and wetlands associated with the Warwick aquifer and of the Warwick aquifer; (2) determine the chemical interactions between surface water and the Warwick aquifer; (3) determine the chemical evolution of water in surface water and the Warwick aquifer; (4) determine detectable concentration of agricultural chemicals (nutrients and pesticides) in small lakes and wetlands associated with the Warwick aquifer and in the Warwick aquifer; and (5) evaluate the potential for nonpoint-source contamination of the Warwick aquifer by agricultural chemicals. The purpose of this paper is to present data and preliminary interpretations resulting from the study.

A preliminary water-quality sampling of 15 lakes and wetlands on or adjacent to the Warwick aquifer was completed in August 1992. One sample was collected from each location and analyzed for major-ion, nutrient, 2,4-D, and atrazine concentrations. A single sample was collected from Warwick Springs, a natural surface-water discharge of the Warwick aquifer. On the basis of the sample from Warwick Springs, along with published data, ground-water in the Warwick aquifer can be characterized as calcium bicarbonate water that has relatively small dissolved-solids concentrations (about 300 to 500 mg/l). Major-ion data were plotted on Piper diagrams to identify water type. On the basis of these data, four types of surface water were identified; calcium bicarbonate water (dissolved solids about 300 to 500 mg/l), magnesium bicarbonate water (dissolved solids about 400 to 1,400 mg/l), sodium bicarbonate water (dissolved solids about 1,500 to 4,000 mg/l), and sodium sulfate water (dissolved solids about 6,000 to 10,000 mg/l).

Concentrations of orthophosphate and dissolved nitrite, nitrite plus nitrate, and ammonia were small. Concentrations of 2,4-D and atrazine generally were small and, in all cases, well below water-quality standards. However, 2,4-D was detected in 4 of 14 surface-water samples, and atrazine was detected in 8 of 14 samples.


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