Practical strategies for identifying groundwater discharges into sediment and surface water with fiber optic temperature measurement

Abstract

Identifying or ruling out groundwater discharges into sediment and surface waters is often critical for evaluating impacts and for planning remedial actions. Information about subsurface structure and groundwater can be helpful, but imperfect information, heterogeneous materials, and the likelihood of preferential pathways make it difficult to locate seeps without direct seep monitoring. We present the practical application of a method that uses fiber optic temperature measurement to provide high-resolution, sensitive, and dynamic monitoring of seepage from sediments over large areas: distributed temperature sensing to identify groundwater discharge (DTSID). First, we introduce a stochastic Monte Carlo method for designing DTSID installation based on site characteristics and the required probability of detecting particular size seeps. We then present practical methods for analysing DTSID results to prioritize locations for further investigation used at three industrial locations. Summer conditions generally presented greater difficulty in the method due to stronger environmentally-driven temperature fluctuations and thermal stratification of surface water. Tidal fluctuations were shown to be helpful in seepage detection at some locations by creating a dynamic temperature pattern that likely reflects changing seepage with varying water levels. At locations with suitable conditions for the application of DTSID, it can provide unique information regarding likely seep locations, enhancing an integrated site investigation.

Four‐dimensional electrical conductivity monitoring of stage‐driven river water intrusion: Accounting for water table effects using a transient mesh boundary and conditional inversion constraints

“…Numerous techniques have been used to study GW‐SW interaction at a range of scales, from point‐scale measurements of flux using flux meters or piezometer tubes, to large‐scale integrated mass balance measurements of stream loss [ Kalbus et al ., ]. The temperature contrast between surface water and groundwater in many systems has been utilized extensively to estimate flux rates and locate zones of active exchange at the GW‐SW interface [ Anibas et al ., ; Henderson et al ., ; Keery et al ., ; Keshari and Koo , ; Mamer and Lowry , ; McCallum et al ., ; Mwakanyamale et al ., ; Rau et al ., ; Rau et al ., ; Selker et al ., ; Slater et al ., ]. Chemical tracers, both natural and engineered, have also been used extensively to study groundwater flow paths through aquifer systems influenced by GW‐SW interactions [ Hoehn and Santschi , ; Jones et al ., ; Massmann et al ., ; Meigs and Bahr , ; Rodgers et al ., ; Schmidt and Schubert , ].…”

Spreadsheet Tools for Quantifying Seepage Flux Across the GW‐SW Interface

“…Identifying the spatial distribution and magnitude of seepage flux into surface water is critical for assessing potential impairments and restoration alternatives for water bodies adjacent to sites with groundwater contamination (Conant, 2004; Conant et al, 2004; Duncan et al, 2007; Kalbus et al, 2007; Rønde et al, 2017; Selker et al, 2014; Zachara et al, 2016). While there are several alternative methods for characterizing water exchange across the groundwater‐surface water (GW‐SW) interface (Rosenberry & LaBaugh, 2008), use of temperature‐based methods for reconnaissance surveys and quantitative assessments at the site scale provides cost‐effective options that are relatively easy to implement (Kurylyk et al, 2019).…”