Water levels have declined about 30 ft from 1940 to 1980 in part of the Equus beds aquifer in south-central Kansas where the city of Wichita operates a well field. A three-dimensional, finite-difference, groundwater flow model was developed to: (1) Reproduce hydrologic conditions in the flow system between the Equus beds aquifer and the underlying Wellington aquifer from 1940 to 1980, and (2) simulate the effect that future withdrawals could have on water supply in the Equus beds aquifer and on relationships between water levels in the Equus beds aquifer and the Wellington aquifer from 1980 to 2020. The model favorably reproduced both measured water levels and streamflow gains in the Equus beds aquifer for 1971 and 1980, and measured water levels in the Wellington aquifer. The flow model then was used to simulate the effects of five pumping alternatives based on rates of withdrawal by wells from 1971-79. For the first alternative, withdrawal rates were decreased by one-half. Projected saturated thickness in the aquifer and streamflow gain were the greatest among the five alternatives. For the second alternative, withdrawal rates for 1971-79 were continued. Compared to results from the first alternative, saturated thickness was projected to decline from 10 to 40 ft in some areas, and streamflow gains were maintained for the Arkansas and Little Arkansas Rivers. A two-dimensional, finite-difference, solute-transport model was developed to: (1) Reproduce the movement of chloride ion in part of the Equus beds aquifer, including the Wichita municipal well field, from 1940 to 1980, and (2) simulate the effect that future withdrawal rates could have on the concentration of chloride ion from 1980 to 2020. Sources of the chloride ion were oilfield brine disposed from 1932-43 that is moving toward the well field and water in the Arkansas River. Each simulation projected an increase in the concentration of chloride ion in the Wichita well field. The projections indicated that a continuous 1,000 mg/L source of chloride ion in streamflow losses from the Arkansas River had a greater effect on increasing chloride-ion concentrations in the Wichita well field than did the movement of residual oilfield brine. (Author 's abstract)