The Ohio River alluvium is the best source of ground water in the county. Many properly-constructed drilled wells in the alluvium will produce over 1000 gal/min, with most wells producing enough for a domestic supply at depths of less than 100 feet. Water is hard or very hard but otherwise of good quality. In the main sections of the larger creek valleys and on broad ridges in central Jefferson County, most drilled wells will produce enough water for a domestic supply at depths of less than 100 feet. Some wells located in the smaller creek valleys and in some broad ridges in southwestern and central Jefferson County will produce enough water for a domestic supply except during dry weather. In the upland areas of the rest of Jefferson County, 30 percent of the county, most drilled wells will not produce enough water for a dependable domestic supply, unless they are drilled along drainage lines, in which case they may produce enough water except during dry weather. Ground water in these areas is hard or very hard and may contain salt or hydrogen sulfide, especially at depths greater than 100 feet.