Hydrogeology of a Buried Valley Aquifer at Dayton, Ohio
There is a classic buried valley running beneath the city of Dayton, Ohio. One of the factors promoting the growth of Dayton has been the ready availability of a source of highquality ground water (Norris & Spieker 1966). Permeable layers of glacial drift in the bedrock valley furnish water in large quantities to wells. In turn, these are recharged by infiltration of precipitation, as well as by water from the Miami River and its tributaries.
The bedrock in the area is the Richmond Shale of Ordovician age. During the Tertiary, an erosional surface developed, which was cleft by deeply incised rivers. During the late Tertiary, the main river draining the area was the Teays. This drainage system cut a number of valleys in the bedrock. Early Pleistocene glaciation dammed the rivers, so that lacustrine silts are found filling many parts of the Teays system. During the Kansan-Illinosian interglacial period, a radically different drainage system, the Deep Stage, prevailed in southwestern Ohio. Bedrock valleys were deeply entrenched during this time. The Deep Stage Valley passed through the present site of Dayton. Glacial processes of Illinosian and Wisconsinan age filled the Deep Stage Valley with layers of till and outwash. The character of the sediment is quite heterogeneous, as revealed by a test hole in the bedrock valley south of Dayton (Figure 3). The valley-train gravel aquifers alternate with confining till sheets. The aquifer layers beneath the till sheets are recharged where the till is missing because of either nondeposition or river-channel erosion. A cross section of the valley just south of Dayton shows the upper and lower aquifers separated by a discontinuous till sheet (Figure 4). The potentiometric surface in the lower aquifer lies below the bed of the Miami River. The potentiometric surface rises sharply near the river when the discharge and stage of the Miami River rise. This indicates a good hydraulic connection between the river and the aquifer.
The Rohrers Island Well Field is located on an island in the Mad River, a tributary of the Miami River. The upper sand and gravel aquifer yields up to 90 million gallons per day (3940 L/s). The upper aquifer, which is up to 65 ft (20 m) thick, is artificially recharged with river water that floods onto about 20 ac (8 ha) of infiltration lagoons during periods when the river turbidity is low. The lagoon bottoms are annually cleaned of silt and clay. This is a classic example of induced stream infiltration used as a water resource management technique. Virtually all of the water pumped from this aquifer comes indirectly from the river. The filtration through the sediments reduces turbidity and removes pathogens.