MANAGING GROUND WATER RESOURCES TO MEET FUTURE WATER SUPPLY DEMANDS IN A RURAL SETTING IN NORTHWESTERN KENTUCKY

Numerical simulations were performed to characterize ground water flow trends in the Ohio River alluvial aquifer in the vicinity of Westport, in Oldham County, Kentucky. The objective was to evaluate the potential of increasing withdrawal rates in high-yield wells to meet future demands in water supply. Also, the water quality implications of such increases were analyzed. The impact of future expansion of residential developments and sewage disposal systems on the migration of contaminants into the aquifer was considered. The aquifer is composed of sand and gravel overlain by clay and silt sediments. Well log data and ground water measurements indicated that the aquifer is semi-confined and can be as thick as 80 feet in most areas. The U.S. Geological Survey computer codes MODFLOW and MODPATH were used for all the model simulations. The Ohio River formed the western boundary of the model area with the bluffs in the eastern part being modeled as a flux boundary. An unconfined conceptual model and a two-layer unconfined/semi-confined model were considered. The observed field ground water levels matched the latter model better. However, the model was sensitive to the conductance within the Ohio River.

The ten-year capture zone covered about a third of the model area. Withdrawal rates within the aquifer were increased to meet future increase in water demand. The resulting increase in drawdown did not cause excessive decrease in ground water storage, even under persistent drought conditions. Also, there was a little but insignificant increase in the capture zone as a result of the increase in the withdrawal rates. Under excessive recharge conditions (flooding), the rise of ground water was at 15-30 feet below ground surface. This may increase the probability of ground water contamination in areas where the overburden is sandy rather than silt or clay. This is particularly important at locations where new subdivisions could introduce contamination via septic systems. It must be noted that the eastern portion of the aquifer was characterized by deducing ground water levels from a very limited data base. A better understanding of the model area requires test wells that run along, at least, three east-west transects.