High Resolution Groundwater and Contaminant Characterization in Karst Boreholes in Central Florida, USA
Abstract
A municipal supply well drawing from the karstic Floridan Aquifer System reduced pumping beginning in 2017 due to detection of low concentrations of 1,4-dioxane (1,4D). The well is located in an industrial area. Given the heterogeneity of preferential flow paths and transport behavior of 1,4D in the underlying aquifer, determining the primary 1,4D contributor to the municipal well is challenging. At this site, low hydraulic gradient, high transmissivity, and short distance to the municipal well strip confidence from conventional Darcy's law-based flux calculations given imperceptible hydraulic gradients. Therefore, we propose direct mass flux measurements as the preferred characterization method at this site to avoid multiple measurement uncertainties. Discrete, high resolution rock core contaminant profiles and conventional borehole geophysical logs are collected. Physical caliper profiles capture the significant variability in borehole diameter thus locating zones that could be sealed using FLUTe ™ flexible, impermeable borehole liners. Nominal and oversized liners are installed to recreate natural gradient flow conditions, with the oversized liner inflating to seal more of the borehole length. Hydraulically active features under natural gradient conditions are qualitatively identified using fiber optic active distributed temperature sensing (A-DTS) in lined boreholes. Each independent dataset combines to inform the placement of vertical arrays of eight passive flux meters in discrete, one to two-meter-long zones in each hole near hydraulically active features to quantify water and contaminant flux. PFMs are sealed in each borehole for six weeks to quantify groundwater and contaminant mass fluxes. Vertical arrays of 30 pressure and temperature sensors are co-deployed with the PFMs to capture transient conditions and confirm vertical intervals captured by each PFM. Uniting A-DTS, PFM, and depth discrete pressure and temperature sensor data sets in mature karst boreholes is novel. Preliminary results for groundwater and contaminant flux measurements are presented helping establish site contributions in support of remediation and risk decision-making.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H53L1735J
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGYDE: 1831 Groundwater quality;
- HYDROLOGYDE: 1832 Groundwater transport;
- HYDROLOGYDE: 1880 Water management;
- HYDROLOGY