Estimating Surface Water Contribution to Ground Water Recharge in the Verdi Aquifer, Southwest Minnesota

The Minnesota Pollution Control Agency (MPCA) conducted a study in 2000 and 2001 to determine the contribution of Spring Creek to recharge of the Verdi aquifer in southwest Minnesota. The Verdi aquifer is in a designated source water management area. Because the creek may contribute to ground water recharge, the management area includes a large portion of the Spring Creek watershed outside the 10-year aquifer time of travel, which usually defines the wellhead protection zone. Three methods were used to estimate recharge from Spring Creek — water mass balance, chloride mass balance, and distribution of stable isotopes of oxygen and hydrogen. Estimated recharge was about 16 percent with water mass balance, 27 percent with chloride mass balance, and 13 percent using stable isotopes. The large variability in the estimates reflects limitations of the data, but provides evidence that Spring Creek contributes to recharge. The source water management area should therefore include the entire watershed, since management practices in the upper part of the watershed may impact water quality of Spring Creek and, subsequently, the Verdi aquifer. Continued monitoring is recommended, however, to better establish the relationship between the creek and ground water.