Mass Flux of Agricultural Nonpoint-Source Pollutants in a Conduit-Flow-Dominated Karst Aquifer, Logan County, Kentucky
Creators: name: Currens, James C.
Publisher: name: Kentucky Geological Survey, University of Kentucky
Year: 1999

description: Abstract:
Changes in water quality in a karst ground-water basin used intensively for agriculture are being measured before, during, and after the implementation of best management practices (BMP’s) and other management practices, to determine the success of such programs in protecting ground water. The study was divided into three phases. The results of the first two phases are included in this report and cover research conducted between August 1990 and October 1994. During phase I of the study the overall ground-water quality of the basin and its hydrogeology were investigated. Phase II began monitoring the water quality at Pleasant Grove Spring before BMP implementation. 
The Pleasant Grove Spring Basin in southern Logan County, Ky., was selected for study because it is largely free of nonagricultural pollution sources. About 70 percent of the watershed is in crop production and 22 percent is pasture. The area of the karst drainage basin is approximately 10,054 acres (4,069 hectares), as determined by ground-water dye tracing. Ground-water flow in the basin is divided into a diffuse (slow) flow regime and a conduit (fast) flow regime. The diffuse and conduit flow regimes have a major influence on the timing of contaminant peaks and valleys during storms. 
Nitrate is the most widespread, persistent contaminant in the basin, but concentrations average 5.2 mg/L basinwide and generally do not exceed maximum contaminant levels (MCL’s) set by the U.S. Environmental Protection Agency for drinking water. Atrazine has been consistently detected in low concentrations, and other pesticides occasionally are detected. Concentrations of triazines (including atrazine) and alachlor have exceeded drinking-water MCL’s during spring flooding. Maximum concentrations of triazines, carbofuran, metolachlor, and alachlor in samples from Pleasant Grove Spring were 44.0, 7.4, 9.6, and 6.1 µg/L, respectively. Flow-weighted average concentrations for 1992–93 were 4.91 µg/L for atrazine-equivalent triazines and 5.0 mg/L for nitrate-nitrogen. Averages for 1993–94 were 0.97 µg/L and 5.7 mg/L, respectively. The difference in atrazine-equivalent triazine concentration between the 2 years may be either the result of weather conditions or crop patterns. 
Bacteria counts always exceed standards for drinking water and occasionally exceed standards for drinking-water supplies. Basinwide, samples averaged 465 fecal coliform colony-forming units per 100 ml (col/100 ml) and 1,891 fecal streptococci col/100 ml; maximum counts were 14,000 and 24,000 col/100 ml, respectively. Bacteriological speciation failed to identify the source of high bacteria counts at Pleasant Grove Spring, but showed that the bacteria are not indigenous to the natural environment of the basin. 
Suspended sediment discharging from Pleasant Grove Spring has had an adverse impact on aquatic biota downstream. 
In the Pleasant Grove Spring Basin, ground water for human consumption is adversely affected by contamination from triazines and bacteria. Implemented BMP’s should focus on reduction of runoff, disposal of animal waste, and efficient application of nutrients. A public education program on ground-water protection would also be beneficial.