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M.D. Unthank

Publications and source records attributed to M.D. Unthank.

4 recordsLinked to original sources
USGS1997

Geohydrology and simulation of ground-water flow for the Ohio River alluvial aquifer near Owensboro, northwestern Kentucky

The Ohio River alluvial aquifer is the primary source of drinking water for the residents of Owensboro and Daviess County and adjacent counties in Kentucky. The aquifer consists of sand and gravel deposits that partly fill a bedrock-valley system consisting of shales of Pennsylvanian age. The valley is a result of dissection by the Ohio River during the Pleistocene epoch. The sand and gravel deposits in the bedrock valley are glacial-outwash deposits of Illinoian and Wisconsin age. The thickness of the alluvium ranges from just a few feet near the bedrock-valley walls to nearly 150 feet in the Bon Harbor Hills area west of Owensboro. Estimates of transmissivity of the alluvium near the Ohio River are in excess of 50,000 gallons per day per foot. A two-dimensional, steady-state ground-water-flow model was developed to estimate the hydraulic properties, the rate of recharge, and the contributing areas to discharge boundaries for the Ohio River alluvial aquifer near Owensboro. Results from previous studies, available geohydrologic data, and observations of water levels from area ground-water wells were compiled to conceptualize the ground-water-flow system and construct the numerical model. Ground water enters the modeled area primarily by infiltration from precipitation and river leakage towards nearby wells and exits the modeled area primarily by withdrawal wells, flow through the valley across model boundaries, and discharge to the Ohio River. A sensitivity analysis of the model indicates the model is most sensitive to changes in horizontal hydraulic conductivity, especially near the Ohio River boundary. Particle tracking was used to compute the contributing areas to discharge boundaries. Contributing areas for withdrawal wells at Owensboro Municipal Utilities extended south and east toward the valley walls and model boundaries and toward the Ohio River, where most of the water withdrawn by the wells is from induced flow from the river.

Water-Resources Investigations Report↗
USGS1996

Hydrogeology and simulation of ground-water flow in the alluvial aquifer at Louisville, Kentucky

The alluvial aquifer at Louisville, Ky., lies in a valley eroded by glacial meltwater that was later partly filled with outwash sand and gravel deposits. The aquifer is primarily unconfined, and the direction of flow is from the adjacent limestone and shale valley wall toward the Ohio River and major pumping centers. Pumpage and water-level data indicate that the alluvial aquifer was in a steady-state condition in November 1962 and again in November 1983. Between these two dates, water-level data indicate a general rise in the water table. A two-dimensional finite-element ground-water-flow model of the alluvial aquifer was calibrated for both the steady-state and the transient-state period of 1962-83. The year 1962 represented a period in time when pumping was nearly three times that in 1983. The simulated steady-state water budget for 1962 indicated that of the total recharge to the aquifer of 5.19 million feet per day, 37.2 percent was flow from the river to pumped wells, 28.3 percent was recharge from rainfall, 19.7 percent was flow across the eastern valley wall, and 14.8 percent was upward flow from the bedrock. Discharge from the aquifer was to wells (68.9 percent) and to the Ohio River (31.1 percent). The simulated steady-state water budget for 1983 indicated that of the total recharge to the aquifer of 4.11 million feet per day, 42.6 percent was recharge from rainfall, 18.2 percent was flow across the eastern valley wall, 17.8 percent was flow from the river to pumped wells, 15.6 percent was upward flow from the bedrock, and 5.8 percent was flow from septic systems. The transient simulation resulted in an acceptable match between measured and simulated hydrographs. This gave additional confidence to the model calibration, choice of boundary conditions, and published values of specific yield. Both steady-state and transient-state models demonstrated that the main source of water needed to meet increased pumping requirements was induced flow from the Ohio River.

Water-Resources Investigations Report↗
USGS1988

Assessment of ground-water contamination in the alluvial aquifer near West Point, Kentucky

Well inventories, water level measurements, groundwater quality samples, surface geophysical techniques (specifically, electromagnetic techniques), and test drilling were used to investigate the extent and sources of groundwater contamination in the alluvial aquifer near West Point, Kentucky. This aquifer serves as the principal source of drinking water for over 50,000 people. Groundwater flow in the alluvial aquifer is generally unconfined and moves in a northerly direction toward the Ohio River. Two large public supply well fields and numerous domestic wells are located in this natural flow path. High concentrations of chloride in groundwater have resulted in the abandonment of several public supply wells in the West Point areas. Chloride concentrations in water samples collected for this study were as high as 11,000 mg/L. Electromagnetic techniques indicated and test drilling later confirmed that the source of chloride in well waters was probably improperly plugged or unplugged, abandoned oil and gas exploration wells. The potential for chloride contamination of wells exists in the study area and is related to proximity to improperly abandoned oil and gas exploration wells and to gradients established by drawdowns associated with pumped wells. Periodic use of surface geophysical methods, in combination with added observation wells , could be used to monitor significant changes in groundwater quality related to chloride contamination. (USGS)

Water-Resources Investigations Report↗