GROUNDWATER - SURFACE WATER INTERACTION CAUSED BY PUMPING FROM A RIVERBANK INDUCEMENT WELL FIELD

A municipal well field consisting of 3 wells completed in a shallow sand and gravel aquifer in southeast Wisconsin has been monitored since December 2006. Two of the wells are immediately adjacent to a river and behave as riverbank inducement (RBI) wells. The third well is distal from the river and pumps pristine groundwater. Movement of river water into the RBI wells was studied using multiple geochemical tracers. Tracers include major ions, boron, bromide, lithium, gadolinium, δ¹⁸O, δD, emerging contaminants, qPCR and bacterial RNA. This data, in conjunction with numeric modelling of the site performed by the USGS, has yielded a clear picture of the interaction between river and well field. Key findings include presence of ~40% river water in the RBI wells; induced river water is a function of the relative pumping between RBI and pristine wells; an apparent lack of bacterial transport from river to well; and retarded movement of the sweetener sucralose. The study is a good example of the coordinated use of geochemical data and numeric modelling.