A Spreadsheet Tool for Reconstruction of Vertical Groundwater Concentration Profiles

This methods brief introduces FLARE (Flow-Log Analysis with Radial Exchange), a spreadsheet-based inverse modeling tool for reconstruction of the vertical concentration profile (VCP) around long-screened wells or open boreholes affected by borehole flow. In such wells, vertical flow and radial exchange can mix water from multiple aquifer intervals, causing sampled concentrations to differ from true aquifer conditions. FLARE uses flow logs and sampled concentrations to construct a forward flow-and-mixing model and formulate a regularized inverse problem to reconstruct the VCP in the aquifer surrounding the well. Implemented entirely in Excel without macros, the tool provides accessible calculations, traceable formulas, and diagnostic outputs that quantify sensitivity, model resolution, and estimation uncertainty (i.e., posterior covariance). These diagnostics help distinguish well-constrained intervals from those where limited information or unfavorable flow conditions reduce interpretive confidence. An example application demonstrates how flow-controlled mixing can cause sampled concentrations to misrepresent local aquifer conditions and documents the use and interpretation of FLARE's inversion and diagnostic results. FLARE enables practitioners to evaluate borehole-flow impacts, extract more information from existing wells, and better target additional depth-discrete characterization or focus remediation efforts where needed.