OVERVIEW OF ANTHROPOGENIC AND NATURAL CONTAMINANT IMPACTS ON THE HIGH PLAINS AQUIFER IN KANSAS, USA

Ground-water quantity is of a major concern in western Kansas where the Ogallala portion of the High Plains aquifer system is heavily utilized for agriculture, municipal, and domestic use. Areas of western Kansas are currently being evaluated to define subunits of the aquifer that need monitoring to prevent extensive water-level declines. Although the quantity issue is of major concern to the users of the aquifer, quality issues will soon become the next issue of concern. Data from the Kansas Geological Survey, USGS, and EPA Storet databases for the area strongly indicate that contamination particularly by salinity and nitrate may impair the usability of the water source in the future.

Recharge to the Ogallala aquifer is approximately 0.6 cm/yr in western Kansas. However, nitrate-N and herbicide contamination has reached the aquifer in portions of the state as shown by both KGS and USGS studies. Salinity from a variety of sources has impacted the aquifer, particularly in areas of stream flow recharge. Recharge by high salinity water from Colorado in the Arkansas River will eventually impact the aquifer at large, possibly rendering portions unusable.

Total dissolved solids (TDS) and nitrate-N data indicate that certain areas of the aquifer have been impacted by both anthropogenic and natural sources such as evapotranspiration, oil brine disposal, agricultural practices, brine intrusion, and waste disposal. TDS values frequently are above the secondary drinking water standards for chloride and sulfate. Increasing TDS generally occurs with depth and also in areas where high evapotranspiration water has impacted the High Plains aquifer. Increased TDS also correlates with nitrate-N concentration in areas of high evapoconcentration.

Median nitrate-N values for area studies in Kansas are generally above the 2-mg/L-background level obtained from USGS NAWQA studies. δ¹⁵N values of ground water throughout the aquifer region indicate both fertilizer and animal waste as sources for the nitrate. Comparison of nitrogen budgets for two counties will illustrate the volume of potentially available nitrogen in the unsaturated zone: one in an area that utilizes the deep Ogallala and the other that uses the shallower Quaternary High Plains portion of the aquifer.