Defining the Extent of Mine-Influenced Groundwater in a Mineralized and Agricultural Area Using Multiple Lines of Evidence

Abstract

Mine-influenced groundwater (MIW) at a former copper mine site has affected an alluvial aquifer that also contains groundwater with solutes characteristic of natural mineralization and agricultural activities. Many of the solutes are common to at least two of three potential sources, and some solutes (e.g., sulfate and uranium) are common to all three. This precludes the conventional use of one, or several, characteristic solutes to identify the extent of MIW. So, we used five independent lines of evidence (LOE) to define the extent of MIW in the alluvial aquifer. The five LOE are multivariate statistical analysis of an extensive groundwater analyte suite, groundwater sulfur isotope (δ34SSO4) data, probabilistic calculations of groundwater velocity and flow distance, isotopic (3H/3He) estimates of groundwater age, and extent of nitrate in groundwater originating from agricultural activities.