The Ozark Plateaus aquifer system generally is characterized as a carbonate aquifer with numerous karst features throughout (Imes and Emmett, 1994). Five geohydrologic units have been identified in the Ozark Plateaus aquifer system according to differences in permeability and well yields (fig. 1). The St. Francois aquifer, the St. Francois confining unit, the Ozark aquifer, the Ozark confining unit, and the Springfield Plateau aquifer collectively comprise the Ozark Plateaus aquifer system, the principal source of fresh ground water in central and southern Missouri. The most important source of water for public supplies is the Ozark aquifer, both where it is unconfined and where it is confined by the Ozark confining unit and Springfield Plateau aquifer in southwest Missouri. To a much lesser extent, the St. Francois aquifer is used for public-water supplies where it is unconfined. These aquifers consist primarily of limestone and dolomite strata that have been weathered to form karst features such as caves, sinkholes, and springs. Karst aquifers are characterized as having relatively free exchange of surface and ground water with limited geologic restrictions on water movement, which makes the aquifers susceptible to surface contamination. Microbiological activity in ground water can be affected by the presence of fractures, faults, and karst features such as losing streams, sinkholes, or solution channels in ground-water recharge areas that can affect the ability of viruses and bacteria to enter and move rapidly through the aquifers. The unconfined Ozark aquifer in south-central Missouri has the most mature karst features (fig. 2) and is considered most vulnerable to viral and bacterial contamination. These features were mapped by Harvey (1980) and have been categorized into primary and secondary karst areas. Primary karst areas are characterized as having sinkhole densities greater than 10 per 100 square miles, whereas secondary karst areas are characterized as having sinkhole densities of 1 to 10 per 100 square miles. The unconfined Ozark aquifer in central Missouri has less developed karst features and is considered somewhat less vulnerable, and the confined Ozark aquifer in |
in southwest Missouri is considered the least vulnerable. However, the proximity of the aquifers to the land surface and the land-use practices in the areas where the aquifers crop out may greatly affect the presence of microbiological activity in ground water. Land use in southern Missouri (fig. 3; U.S. Geological Survey, 1990) is primarily forest and agriculture, including pasture, cropland, and confined animal operations. Second-growth, deciduous forest mixed with evergreen forest is predominant in the eastern two-thirds of the Ozark Plateaus, and agricultural land use is predominant in the southwestern part of the Ozark Plateaus. Agricultural land use in the study area consists primarily of the raising of |
livestock, including beef
and dairy cattle, poultry, and swine. Numerous confined poultry
operations are present in southwest Missouri. Waste generated by
cattle, poultry, and swine operations is a major source of
nutrients and fecal bacteria. Much of the manure is applied to
local pastures as fertilizer (Davis and others, 1995).
Excluding the St. Louis metropolitan area, the 1990 population within the Ozark Plateaus was approximately 1.6 million. Springfield, Missouri, is the largest city with a 1990 population of about 140,000. Cape Girardeau, Jefferson City, and Joplin, Missouri, are the only other cities with populations exceeding 30,000. Recreational activities in the Lake of the Ozarks and the Table Rock Lake-Lake Taneycomo areas have attracted many tourists and year-round residents. The populations of these areas have increased by more than 90 percent since 1970 (Adamski and others, 1995). Waste from private septic systems and municipal wastewater-treatment plants can contaminate ground water. The USGS and MDNR-PDWP selected a total of 109 PWS wells of which 105 PWS wells are located within the Ozark Plateaus aquifer system to represent ground water in the confined and unconfined |
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