Fig. 1

Schematic of B-PASS monitoring configurations. (a) Up-hole and cross-hole surveys with illustrations of the conceptual geological layers. Pictures of hydraulic coupling mechanism (b) before locking and (c) after locking inside the borehole. (d) Picture of B-PASS ready for deployment. The Schematic image in (a) was created using Microsoft PowerPoint software in Microsoft 365 (Version 16.0.1; https://www.microsoft.com/en-us/microsoft-365/powerpoint).