POTENTIAL IMPACTS OF PAST LAND USE AND RECHARGE RATES ON THE OGALLALA AQUIFER: WATER QUALITY ISSUES IN KANSAS

Quantification of available water and the rate of recharge to the High Plains aquifer in western Kansas are much discussed but little agreed upon topics. The usable lifetime of the aquifer is under investigation, but thus far studies have focused largely on the quantity of water and ignored the quality. The quality of the remaining water for agricultural and water supply uses is an issue that deserves attention and further research.

Land use in the High Plains aquifer area is dominated by irrigated agriculture. Water levels and water quality in the Ogallala portion of the High Plains aquifer continue to be impacted by past land uses. KGS site studies and USGS National Water Quality Assessment (NAWQA) program regional studies show that irrigation recharge enhances the movement of contaminants to the water table.

Overall increase of nitrate-N (20% - 80%), specific conductance (3% - 30%), chloride (11% - 50%), and sulfate (4% - 90%) concentrations measured at the same irrigation wells in the 1970's and 1990's indicate movement of contaminants to the water table. The USGS NAWQA study has observed atrazine and its metabolites in soil water and at the water table at monitoring sites. Nitrogen-15 analyses of soil water and ground water indicate that row crop and feedlot agriculture are major sources of contamination.

Recharge estimates and calculated fluxes by both KGS and USGS show that recharge from flood irrigation return flows moves contaminants faster than does natural recharge or center pivot or drip irrigation. Still, the amount of recharge is only a fraction of the amount of water pumped for irrigation. Although irrigation efficiency improvements could result in slower downward movement of contaminated water in the distant future, the current problem is to determine (1) the quantity of contaminated water in transit to the aquifer within the next few decades, and (2) will the quality of water sustain current and future demands in the area.