The movement of water from the surface through the soil and into groundwater governs many ecological functions critical to ensuring the health of lakes and rivers. Water inflow and outflow, or flux, affects the type of microbes in the soil and the nutrients present. Surface water flux is also key to understanding contaminant transport through soil and groundwater. However, traditional methods for monitoring this flux do not provide sufficient information to track movements with confidence. For example, currently used flux chambers determine the total mass flux, but they do not provide any information on pore velocity or residence time, which are needed to track contaminants. Another common method, vertical temperature arrays, provide information on pore velocity and residence time but not on total mass flux, preventing accurate calculations of water movement.

The Thermo-Electric Water Flux Detection Probe (TEFLUX), developed by researchers at Pacific Northwest National Laboratory, identifies the interactions between groundwater and surface water. When inserted into the sediment at the lower boundary of a water body (e.g., stream, river, lake, or tidal zone), TEFLUX determines pressure over time, fluid electrical conductivity (EC), temperature, and bulk conductivity for a more complete picture of water flux. These data are sufficient to estimate the vertical distribution of porosity and permeability. From all of these geophysical measurements, the calibrated flow model that comes with the probe computes the corresponding Darcy flux and pore velocity time-series. The only requirement is that a contrast in temperature and/or fluid conductivity exists between surface water and groundwater.

The probe comprises a non-metallic conduit approximately 2 to 5 cm in diameter and 50 to 300 cm long, which includes a series of ring electrodes that can be used to monitor the bulk EC time-series of the sediment along the longitudinal axis. It can also be equipped with miniature sensors that monitor pressure, temperature, and fluid conductivity along the vertical axis of the probe.

All time-series data from TEFLUX can be simulated using the PNNL-developed PFLOTRAN-E4D, an open-source parallel multi-physics code that simulates reactive flow and transport in porous materials. The combination of data time-series available through TEFLUX and corresponding analysis using PFLOTRAN-E4D offers a unique perspective not available with any other tool or approach, for faster, more thorough results. 

APPLICABILITY

TEFLUX can be configured to assess the vertical movement of surface water and groundwater even under conditions when flow is transient and sediments vary highly. The data it provides can be used to

• Inform river corridor flux models
• Determine movement of water between surface water and groundwater
• Monitor interactions between surface water and groundwater for a variety of regulatory needs.

This information is of key importance to research organizations, subsurface monitoring companies, and state and federal regulators.