Non-invasive flow path characterization in a mining-impacted wetland

Abstract

Time-lapse electrical resistivity (ER) is used in this study to capture the annual pulse of acid mine drainage (AMD) contamination, the so-called 'first-flush' driven by spring snowmelt, through the subsurface of a wetland downgradient of the abandoned Pennsylvania Mine workings in Central Colorado. Data were collected from mid-July to late October of 2013, with an additional dataset collected in June of 2014. ER provides a distributed measurement of changes in subsurface electrical properties at high spatial resolution. Inversion of the data shows the development through time of multiple resistive anomalies in the subsurface, which corroborating data suggest are driven by changes in total dissolved solids (TDS) localized in preferential flow pathways. Because of the non-uniqueness inherent to deterministic inversion, the exact geometry and magnitude of the anomalies is unknown, but sensitivity analyses on synthetic data taken to mimic the site suggest that the anomalies would need to be at least several meters in diameter to be adequately resolved by the inversions. Preferential flow path existence would have a critical impact on the extent of attenuation mechanisms at the site, and their further characterization could be used to parameterize reactive transport models in developing quantitative predictions of remediation strategies.