Withdrawals of ground water in the central Mill Creek Valley near Evendale, Ohio, caused water-level declines of more than 100 feet by the 1950s. Since the 1950s, management practices have changed to reduce the withdrawals of ground water, and recovery of water levels in long-term monitoring wells in the valley has been documented. Changing conditions such as these prompted a survey of water use, streamflow conditions, and water levels in several aquifers in the central Mill Creek Valley, Hamilton and Butler Counties, Ohio. Geohydrologic information, water use, and water levels were compiled from historical records and collected during the regional survey. Data collected during the survey are presented in terms of updated geohydrologic information, water use in the study area, water levels in the aquifers, and interactions between ground water and surface water. Some of the data are concentrated at former Air Force Plant 36 (AFP36), which is collocated with the General Electric Aircraft Engines (GEAE) plant, and these data are used to describe geohydrology and water levels on a more local scale at and near the plant.

A comparison of past and current ground-water use and levels indicates that the demand for ground water is decreasing and water levels are rising. Before 1955, most of the major industrial ground-water users had their own wells, ground water was mined from a confined surficial (lower) aquifer, and water levels were more than 100 feet below their predevelopment level. Since 1955, however, these users have been purchasing their water from the city of Cincinnati or a private water purveyor. The cities of Reading and Lockland, both producers of municipal ground-water supplies in the area, shut down their well fields within their city limits. Because the demand for ground-water supplies in the valley has lessened greatly since the 1950s, withdrawals have decreased, and, consequently, water levels in the lower aquifer are 65 to 105 feet higher than they were in 1955.

During the time of the water-level survey (November 2000), ground water was being pumped from four locations in the lower aquifer, including three municipalities and one remediation site. Effects of pumping in those four areas were evident from the regional water-level data. Overall, the direction of ground-water flow in the lower aquifer is from northeast to southwest along the primary orientation of the Mill Creek Valley in the study area.

Water levels in shallower surficial aquifers were mapped at local scales centered on GEAE. Examination of well logs indicated that these aquifers (called shallow and water-table) are discontinuous and, on a regional scale, few wells were completed in these aquifers. Water levels in the shallow aquifer indicated that flow was from northeast to southwest except in areas where pumping in the lower aquifer or the proximity of Mill Creek may have been affecting water levels in the shallow aquifer. Water levels in the water-table aquifer indicated flow toward Mill Creek from GEAE.