Direct Mass Flux Measurements for 1,4-Dioxane From an Industrial Site in a Karst Aquifer
Tuesday, September 24, 2019: 10:50 a.m.
Several sites are possible contributors to trace 1,4-dioxane detections in a municipal supply well in the karstic Upper Floridan aquifer. Efforts are underway to assess potential contribution from one nearby industrial site; however, high aquifer transmissivity and site dimensions create uncertainty in hydraulic gradients, thus stripping confidence from conventional Darcy’s law-based mass flux calculations. To avoid multiple measurement uncertainties, we advanced direct mass flux measurement techniques in two cored holes to characterize this site. Depth-discrete, high resolution rock core contaminant profiles were developed, and borehole geophysical and hydrophysical logs were collected. Physical caliper profiles captured the significant variability in borehole diameter, locating zones that could be sealed using FLUTe™ borehole liners. Hydraulically active features under natural hydraulic conditions were qualitatively identified using active distributed temperature sensing (A-DTS). These datasets informed placement of modified, fractured rock passive flux meters (PFM) in multiple, depth-discrete zones (1-2 m long), to quantify both water and contaminant flux. Vertical arrays of pressure and temperature sensors were co-deployed with the PFMs, external to the FLUTe™ liners, to capture transient hydraulic conditions. This presentation will discuss challenges and adjustments made for karstic boreholes as well as in-situ groundwater and contaminant flux distributions used to estimate mass discharge.