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o O'JI n ? e e e changes in the glacial aquifer. Second, seasonal and temporal variations of the water quality of the James River, the treated water, and groundwater were characterized over an approximate 3-year period. Third, the injection well and modifications to the pipeline system were designed and constructed. Fourth, the quality of the injectate and ground- water were monitored during recharge. Finally, the collected data were analyzed and evaluated to derive consistent conclusions regarding the success of the recharge related to geology, aquifer characteristics, and water chemistry. Water Source The approximately 747-mile-long James River is a northern Great Plains prairie stream that originates in North Dakota and empties into the Missouri River near Yankton, South Dakota (figure 2). The river, which drains a total area of 21,116 square miles, is the dominant surface water feature of the James River basin. The James River has one of the flattest slopes of any river of similar length in North America. Channel capacities within South Dakota vary between 200 cubic feet per second (efs) in southern Brown County to 10,000 efs near the mouth. Flooding is common during spring snowmelt on the river. The average mean monthly flow in the James River at Huron from April through June is nearly 800 cfs. Geohydrology Nearly all of the surficial deposits of eastern South Dakota consist of materials that are glacial in origin and are collectively referred to as glacial drift. The two common groups of glacial drift are till and outwash. Till, the most abundant glacial deposit, is a heterogeneous mixture of silt, sand, gravel, and boulders in a clay matrix. Outwash consists of cross- bedded gravel, sand, and silt. The thickness of outwash in eastern South Dakota varies with location in the drift and ranges from 0 to greater than 200 feet. In the project area, the outwash has a thickness of less than 10 to 75 feet. The bedrock immediately underlying the glacial drift in the project area is Pierre Shale of the Cretaceous age. The more sandy and gravelly glacial outwash deposits can yield significant quantities of water to wells. Well yields of 300 gallons per minute (gpm) are common, with potential yields of 1,000 gpm from the coarsest materials. The City of Huron's wells typically yield about 350 gpm. The inherent variability of the glacial drift material over very short distances required extensive site characterization. In 1990, 76 test holes were drilled, driller's logs prepared, and samples of drill cuttings collected. Of the 76 test holes, 70 were cased as observation wells in and around the City of Huron.s well (figure 3) to supplement DENR's 15 existing observation wells (figure 4). These wells were used to monitor water levels in the glacial aquifer and for water sample collection. All water level and water quality data collected for the Huron Recharge Project were entered into the USGS National Water Information System computer database. The data collected about and from these wells are compiled in Carter (1995, 1997). 5