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According to the Groundwater Branch of the Kentucky Division of Water, "Groundwater is a vital, renewable natural resource that is widely used throughout Kentucky. Wells and springs provide approximately one-third of public domestic water supplies in the state. Surface streams, the major source of Kentucky's water supply, are primarily sustained during base flow by groundwater discharge from adjacent aquifers. This resource is susceptible to contamination from a variety of activities at the land surface. Once contaminated, groundwater can be difficult or impossible to remediate." Quality of Groundwater in the CountyThe quality of groundwater in the Mississippian Plateau Region varies considerably from place to place and is determined by the geologic source of the water and the length of time the water has been in contact with the rocks. Generally, deeper wells produce more mineralized water; however, deeper wells are generally less likely to become polluted by human activities. In Logan County, groundwater obtained from most wells drilled into limestone aquifers is considered hard. Common salt and hydrogen sulfide are the two naturally occurring constituents most often encountered in objectionable amounts in groundwater. Water obtained from wells and springs in many limestone aquifers is subject to pollution, and at a minimum, should be treated to eliminate bacterial contamination. It is a good practice to have any residential water source tested once a year, or as often as possible. At a time when surprisingly little information is available on groundwater quality, groundwater contamination has become a major environmental issue. Reliable information about water quality is necessary in order to develop plans for protecting groundwater. The absence of accurate and broad perspectives on groundwater quality may lead to inappropriate and ineffective regulatory policies. Because groundwater supplies a large percentage of rural drinking water and water for agricultural use, rural landowners have become increasingly concerned about the quality of groundwater. The Kentucky Farm Bureau, Kentucky Division of Conservation, University of Kentucky Cooperative Extension Service, and the Kentucky Geological Survey conducted a water-quality survey of nearly 5,000 rural domestic wells. The results are discussed in "Quality of Private Ground-Water Supplies in Kentucky." Additional references are contained in the Water Research Library on the Kentucky Geological Survey's Web site. Salt WaterSalt water (saline water) is found below fresh groundwater at variable depths throughout the entire state of Kentucky. Depths to the saline groundwater range from 50 feet or less down to 2,000 feet below land surface in Kentucky. "Salinity" is defined as a measure of the quantity of dissolved mineral matter or total dissolved solids (TDS) in water, reported in parts per million (parts per million) or milligrams per liter (mg/L); the two forms of measurement are usually equivalent. The term "salt" or "table salt" as used by most people is pure sodium chloride. Sodium and chloride are generally the major component of saline waters in Kentucky, but are not the only constituents. Water having a TDS concentration of less than 1,000 parts per million is classified as fresh and water having a TDS concentration of 1,000 parts per million or more is classified as saline. Recommendations by the U.S. Public Health Service for drinking water suggest that total dissolved solids should not exceed 500 parts per million, but less than 1,000 parts per million may be used. In agriculture, the recommended TDS levels vary with uses, as shown in the following table, which was taken in part from "Fresh-Saline Water Interface Map of Kentucky" (Hopkins, 1966).
Being aware of the depth to saline groundwater is valuable when planning a water-supply well. Drilling a well too deep through the freshwater interval may cause a good well to be unsuitable for various uses. Care must be taken to prevent contamination of the freshwater zones by the deeper saline waters. Properly constructed water wells will screen the production zone in the targeted aquifer and isolate all other zones by casing and properly grouting and cementing of the space outside the casings in the boreholes. In Logan County, the elevation of the fresh-saline interface ranges from 500 feet msl in the southeastern part of the county to 300 feet msl in the western and northern parts of the county. This corresponds to a total depth from land surface of greater than 100 feet in the river bottoms and greater than 150 feet in the uplands. Sensitivity of Groundwater to PollutionAccording to the Kentucky Division of Water, Groundwater
Branch, Logan County has areas of |
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