The St. Charles County well field consists of 8 wells that penetrate the entire thickness of the Missouri River alluvial aquifer. The wells range from 98 to 116 ft deep. The lower 40 ft of each well is screened and open to the aquifer. The specific capacities of the wells calculated soon after well completion ranged from 115 to 248 gal/min/ft of drawdown. Transmissivities range from 900 to 60,200 sq ft/day. Hydraulic conductivities range from 23 to 602 ft/day. Storage coefficients range from 0.005 to 0.2. A tracer test determined effective porosity ranging from 0.21 to 0.32. A point dilution test determined a groundwater velocity of 0.83 ft/day. From 1985-91, the average daily water supply from the St. Charles County well field and water- treatment plant increased from 5.76 to 10.23 Mgal/day, an increase from 36.2 to 42.2 percent of the total quantity of water supplied by major public-water suppliers in St. Charles County. The average daily water supply from the well field and water-treatment plant is projected to increase to 11.0 Mgal/day during 1995 and 12.2 Mgal/day during 2000. The St. Charles County Water Department's projections of peak daily demands from customers indicate that these demands will exceed the capacity of the water-treatment plant during 1995 and will exceed the capacities of both the well field and water-treatment plant during 2000.