Core-Flooding Experimental Set-up and Mineralogical Assessment of Aquifers Proposed for Managed Aquifer Recharge

Abstract

In response to PFAS plumes in aquifers that supply drinking water to residents near the Twin Cities Metro area, Managed Aquifer Recharge (MAR) is being considered as a potential remediation strategy. MAR would be used to extract PFAS contaminated groundwater for treatment and filtration at the surface before reinjection into the subsurface. One major concern associated with this strategy is the release of geogenic contaminants due to the reintroduction of water that varies chemically from the native groundwater. Therefore, data about possible outcomes including geogenic contaminant release from sediments and changes to permeability are needed to determine the viability of MAR. Core-flooding experiments can be used to gather this data and predict how aquifers may respond to MAR. Two core-flooding experiments were conducted on samples from the Prosser Formation and the Shakopee Formation to determine permeability. Both cores demonstrated permeability that was too low for exact values to be found due to equipment limitations, but estimates for the upper limits of permeability were calculated to be 1.17*10-6 mD for the Prosser and 6.51*10-7 mD for the Shakopee. In addition to core-flooding, X-ray Diffraction (XRD) analysis was performed on samples from the Shakopee Dolomite and Jordan Sandstone to determine lithology and mineralogy within an aquifer being considered for MAR. XRD analysis showed that the Shakopee was almost pure dolomite while the Jordan was mostly quartz with some dolomite components included, likely as a form of cement between sand grains. Additionally, iron-bearing concretions were found throughout the Jordan samples. XRD analysis revealed that these concretions are composed of quartz, hematite, and goethite.