IMPACTS OF HIGH-FREQUENCY INTERMITTENT PUMPING ON GROUNDWATER AND SURFACE WATER INTERACTIONS ALONG THE REGULATED STREAMS

The role of high-frequency intermittent pumping (HFIP) on groundwater/surface water interaction was studied for alluvial aquifers along the Ohio River. Datasets include two and a half-year long hydrographs, thermographs, and water chemistry of the river and wells. The purpose of the study was to determine source water(s) for pumping wells and to determine the hydraulic connectivity of aquifers with the river. Wells are pumped simultaneously and intermittently with 8–10 minute breaks in between pumping. Such HFIP induces a year-round quasi-steady state potentiometric depression beneath the well field, always at least >1 m below stream stage. This is a strong evidence that groundwater is under surface water influence throughout the year. In periods of non-pumping, however, groundwater level rises in a Theisian fashion but never fully recovers to the inferred water level that predates the well field operation. Spatial variability in water chemistry supports the interpretation that HFIP induces stream infiltration and is a primary source of groundwater to the pumping wells close to the stream. Stream stage fluctuations displayed as a primary control over groundwater levels than recharge, especially during high-flow periods. Dam operations locally altered groundwater flow paths, velocity, and bank storage capacity. Generally, groundwater is warmer than surface water in winter and colder in summer. However, HFIP reversed the thermal signature of those wells. Potentiometric, chemical, and thermal results support the claim that the aquifers induced infiltration from the stream during pumping and at high-stream stages. Numerical modeling depicts an extent of the cone of depression and confirms the hypothesis. The results suggest human and climate interferences could exacerbate groundwater quality in case of surface water contamination. The findings of this study has consequences on policymaking with respect to public health protection as well as potential financial, operational, and compliance implications for public water supply systems that lie next to a surface water body.