The main objective of this demonstration is to develop and validate a multi-scale thermal and electromagnetic technologies toolbox for mapping and monitoring the interactions between contaminated groundwater (GW) and surface water (SW). Specific objectives include the following:

1. Demonstrate and validate an integrated approach to mapping and monitoring of GW/SW exchange at one freshwater (e.g. lake, river) and one saline (e.g. estuarine/coastal) Department of Defense (DoD) site using the following technologies:
   • fiberoptic distributed temperature sensing (FO-DTS),
   • vertical temperature profiling (VTP),
   • thermal infrared (IR) from an unmanned aircraft system (UAS), and
   • waterborne frequency domain electromagnetics (EM);
2. Obtain and/or measure GW contaminant concentration in nearby boreholes as well as at the detected GW/SW interaction location; and
3. Determine the mass flux of contamination from GW to SW.

Accomplishing the objectives will allow the project team to develop a decision matrix/tool that DoD site managers can use to select the appropriate technique(s) to investigate GW/SW interactions at their sites.

The technological solution combines FO-DTS, VTP, IR-UAS and EM to provide semi-continuous information on the location of GW discharges into surface water bodies. Temperature and electrical conductivity (EC) are excellent tracers of discharge. FO-DTS, VTP and IR-UAS exploit the temperature contrast between GW and SW whereas EM senses the EC contrast between GW and SW. Thermal cameras deployed by UAS measure infrared radiation emitted by objects as a function of their temperature. FO-DTS uses back-scattering of transmitted light to provide continuous temperature measurements over km scales with meter scale resolution. VTPs are a low-cost alternative to established methods (e.g., Trident probe and seepage meters) for assessing GW flux (at point locations only) and provide high temporal resolution data on variations in flux with time. EM non-invasively senses the EC of sediments by recording induced magnetic fields in conductors.

The benefits of using the technologies relative to traditional point measurements (e.g., Trident and UltraSeep) include:

1. improved spatial coverage of characterization (orders of magnitude) from EM and thermal imaging,
2. cost reductions (perhaps an order of magnitude) from inexpensive VTPs, and
3. reduced remediation costs resulting from improved conceptual site models (CSMs) for seep locations and fluxes.

The multi-scale technologies toolbox would benefit characterization and monitoring at many DoD installations. Indeed, GW seepage to surface water has been recorded to be occurring at 75% of the Resource Conservation and Recovery Act and the Comprehensive Environmental Response, Compensation, and Liability Act sites including DoD installations located within 0.8 km of a surface water body. Forty three percent of the 67 Navy installations on the National Priority List are located in coastal areas of CA, FL, VA, and WA. Twenty-five of 32 sites (78%) evaluated by the Navy in 2015 were found to discharge contaminated GW to surface water. However, these discharge zones were rarely included in the CSMs or even quantified. Traditional point-measurement methods have been applied at a minimum of 17 Navy coastal sites but questions remain regarding the number of seeps that went undetected. The toolbox would dramatically reduce such uncertainty regarding localized contaminant discharges from DoD sites. (Anticipated Project Completion - 2024)

Briggs, M.A., D. Rey, C. Johnson, H. Moore, K. Marble, L. Slater, and R. Iery. 2023. Fiber-Optic Distributed Temperature Sensing Data Collected for Improved Mapping and Monitoring of Contaminated Groundwater Discharges Along the Upper Quashnet River, Mashpee and Falmouth, Massachusetts, USA 2020. U.S. Geological Survey Data Release. doi.org/10.5066/P96KF0L2.