INVESTIGATING GROUNDWATER/SURFACE-WATER INTERACTIONS ALONG A STREAM SECTION INFLUENCED BY MUNICIPAL-WELL WATER PRODUCTION

Understanding the way in which municipal production wells interact with nearby surface water is important in terms of managing sustainable pumping rates, predicting the impact of pumping on surface-water flows and assessing the potential impact of surface-water quality on the quality of produced groundwater.

This study examines the effects of municipal pumping on groundwater/surface-water interaction. The study area is associated with three production wells used by the City of Oxford in the Four Mile Creek buried-valley aquifer in southwest Ohio. Piezometers, seepage meters and streamflow measurements were employed to delineate and quantify the areas of stream that were most influenced by pumping. Surface water, groundwater and production-well water were analyzed biweekly for major ions to help determine the extent of surface water and groundwater in production-well water as well as the extent of groundwater contribution to surface water away from production wells. In addition, the fraction of surface water in the municipally-produced water was investigated using stable isotopes, ¹⁸O and deuterium. Because most groundwater recharges between November and May, the δ ¹⁸O and δ ²H values of groundwater are expected to be less variable and lower compared to the values of surface water which should reflect precipitation throughout the year. We hypothesized that these differences can be used to measure the average contribution of surface water in production-well water.

Oxford’s production wells 1, 2 and 3 are about 200, 26 and 240 m, respectively, from Four Mile Creek. Piezometers and seepage meters indicated losing areas of Four Mile Creek associated with each of the production wells despite the fact that the stream is overall a gaining stream. Cation analyses also showed that the stream took on more of a groundwater chemistry as it moved down stream but did not indicate surface-water contribution to the production-well water. Isotope analyses thus far were only from three samplings between the end of February and the end of March 2012 and did not yet provide enough data to differentiate between surface water, groundwater and production-well water in terms of their variability. Surface and production-well water did, however, became more enriched in ¹⁸O and ²H with time relative to groundwater over the sampling period.