Temporal and spatial variation of water quality in the upper Cibolo Creek watershed, Kendall County, TX

Waters from the Edwards Aquifer contain slightly elevated concentrations of nitrate with occasional measured concentrations higher than the 44 mg/L (as NO₃) maximum contaminant level (MCL) set by the Environmental Protection Agency. Well water samples that contain elevated levels of nitrate are generally widely dispersed throughout the aquifer and the nitrate does not appear to be from any single source. These elevated nitrate levels are generally attributed to anthropogenic sources, but the exact source is unknown. The goal of this project is to characterize the waters from the upper Cibolo Creek watershed, specifically from the segment located within the Cibolo Preserve, to determine if the discharge from Cibolo Creek may account for a portion of the elevated nitrates in the Edwards Aquifer.

Evaporation, photosynthesis, and changes in input from the two wastewater treatment plants appear to be the dominant controls on the evolution of water quality over time. Overall, waters in this section of the creek have a distinct signature with elevated concentrations of sodium, nitrate, and chloride. The average nitrate concentration was 55.2 mg/L (as NO₃) and all values measured were consistently higher than previously reported values. The results from this study may be used to trace possible groundwater flow paths.