THE USE OF DISCHARGE BALANCING TO QUANTIFY THE ASSIMILATIVE CAPACITY OF A KARST AQUIFER

A tracer test investigation was performed by the USEPA to delineate groundwater drainage basins in an industrial area located on Ordovician carbonate rocks in the Central Basin of Tennessee. This area has been the focus of State and US EPA investigations and response actions since the early 1980’s. Based on the results of the tracer test, and by using the concepts of discharge balancing from Quinlan and Ray (1995), the percent contribution of groundwater discharging from a karst spring was determined for a site with a surface area that is a fraction of the total footprint of the groundwater basin. The percent contribution was calculated by dividing the area of the site by the area of the groundwater basin. Soil response action levels for site related constituents were then calculated by dividing the product of each constituent’s surface water criterion and its corresponding soil-water partitioning coefficient (Kd) by the estimated percentage of water contribution to the karst spring from the site. The calculations were used to predict water quality at the spring discharge point and to quantify the assimilative capacity of the carbonate aquifer. Monitoring of the spring before, during, and after a storm event by the US EPA indicated that the water quality parameters were not exceeded. The State of Tennessee issued a “no action” Record of Decision for the site