Aquifer Characterization Using Fiber Bragg Grating Multi‐Level Monitoring System

Abstract

Groundwater responses measured from multiple wells at different depths are essential for delineating the aquifer heterogeneity using hydraulic tomography (HT). In general, conducting HT requires many wells because traditional well monitoring is usually partially open at a specific depth interval or is fully penetrating. Accordingly, conducting an HT survey is typically costly and time-consuming. To tackle these issues, a new multi-level monitoring system (MLMS) for the HT survey was developed using the fiber Bragg grating (FBG) technique. This FBG MLMS could collect the depth-discrete groundwater observations from a fully penetrated 2-inch well. Three field campaigns were conducted to validate the capability of the FBG MLMS for HT surveys. The results show that the accuracy and stability of this MLMS are reliable and that FBG MLMS is beneficial for conducting an HT survey. Specifically, compared to the traditional monitoring well in an injection event, this FBG MLMS can concurrently cause an increase in the number of cross-hole tests several times and collect many more head observations than the standard methods, resulting in the observed flow fields efficiently reaching ergodic conditions and effectively improving the accuracy of the estimated hydraulic heterogeneity. Therefore, the FBG MLMS could be an alternative MLMS for efficiently and economically conducting an HT survey.

Replies to Comments on “Aquifer Characterization Using Fiber Bragg Grating Multi‐Level Monitoring System” by Leven and Barrash

“…The injections of heated remediation agents, chemical reactions, biochemical reactions, and many other factors affect subsurface and aquifer temperature variations. For example, we observed noticeable groundwater temperature variations in our study site (figure 4b in Wang et al 2022). We understand that the temperature change may not be an important issue in other areas, but it is a factor we should consider at our sites.…”

“…Many thanks for the comments by Leven and Barrash on our article (Wang et al 2022). We briefly reply to the comments in a point-by-point fashion:…”

“…Reply to comment 1: Leven and Barrash (2022) have presented the specifications (e.g., accuracy and resolution) of fiber optic pressure (FP) sensors they used in Table 2 of their work. The discussion of whether the resolution is a reasonable indicator is interesting, but out of the scope of our article (Wang et al 2022).…”

Characterize Basin‐Scale Subsurface Using Rocket‐Triggered Lightning

“…An adjoint state approach (e.g., Sun & Yeh, 1990; Sykes et al., 1985) is adopted here to determine the sensitivity matrix of n th order temporal moments to parameters $$\sigma $$ and $$\varepsilon $$. The approach’s computational efficiency has been proven in many real‐world applications of hydraulic tomography (Cardiff et al., 2020; Wang et al., 2022; Zha et al., 2016; Zhao & Illman, 2022).…”

Comment on “Aquifer Characterization Using Fiber Bragg Grating Multi‐Level Monitoring System”

“…We appreciate the work by Wang et al (2022) to present an additional option for groundwater pressure measurements using fiber-optic sensors (in this case FBG transducers), especially for applications such as HT that require high-resolution data from multiple discrete measurement locations in multiple wells. This Comment addresses details we believe are important for clarifying or correcting generalized statements by Wang et al (2022) about a type of alternative FP fiber-optic pressure transducer used in HT studies.…”