Comparison of Water Chemistry in Spring and Well Samples from Selected Carbonate Aquifers in the United States

Water chemistry in samples from 226 wells and 176 springs were assessed to determine if samples from springs and wells have similar concentrations of selected properties such as dissolved solids, dissolved oxy- gen, nitrate, and calcite and dolomite saturation indices. Samples were collected in seven carbonate aqui- fers-Edwards-Trinity, Floridan, Mississippian, Basin and Range, Valley and Ridge, Springfield Plateau, and Ozark. Comparisons were made between concentrations of inorganic constituents in water samples from springs and from wells within the same aquifer. Results were variable, but showed that concentrations were not significantly different between samples from springs and wells for most properties. Nitrate and dis- solved solids concentrations were only significantly different between spring and well samples in one or two of the seven aquifers; however, dissolved oxygen concentrations were significantly different between well and spring samples in four of the seven aquifers. Median calcite and dolomite saturation index values were significantly different between well and spring samples in three of the seven aquifers. Spring samples prob- ably represent water from shallower parts of the aquifer flow systems and thus represent parts of the flow system that are most susceptible to contamination from land-use practices. These results indicate that the collection of water from springs should be considered critical to adequately characterize water quality in carbonate aquifers.