An innovative tool for groundwater velocity measurement compared with other tools in laboratory and field tests

An innovative solution for groundwater velocity measurement in wells, the Direct Velocity Tool (DVT), is developed and tested. The DVT allows measurement of Darcy flux at centimeter scale vertical resolution requiring only a few minutes for each measurement (typically 5-10 min). Results are generated in real time through the use of an equation. The theoretical functional Darcy flux range is between 1 and 40 cm.day (1) for an aquifer with a hydraulic conductivity, K, less than 10 (3) m.s (1). Laboratory tests showed a linear response between Darcy flux imposed and Darcy flux measured with the DVT, with a high correlation coefficient (R-2 = 0.99). The DVT was tested for velocities ranging from 5 to 30 cm.day (1) where a higher standard deviation was observed for higher velocity (+/- 6.46 cm.day 1 for 30 cm.day (1)). At a hydraulically controlled field site, tracer tests, borehole dilutions, Passive Flux Meter (PFM) and DVT were tested under constant flow conditions. The PFM, tracer test and DVT technologies measured similar Darcy flux ranging from 10 to 17 cm.day (1). The DVT and PFM had uncertainties of 2.70 cm.day (1) and 2.50 cm.day (1), respectively. At a contaminated field site, velocities measured with the PFM range between 5 and 9 cm.day (1), while the DVT provided velocities of 4 to 8 cm.day (1). Velocity measurement showed similar results at the contaminated field site between PFM and DVT. The DVT offers an innovative solution for Darcy flux measurement and can be deployed easily. It provides the capability to characterize the vertical distribution of the horizontal velocity for a well in a period of 1-2 h. (C) 2018 The Author(s). Published by Elsevier B.V.