Real-time monitoring of the vadose zone as a key to groundwater protection from pollution hazard

Abstract

Minimization subsurface pollution is very dependent on reliable and effective monitoring tools. Today, most monitoring programs are based on observation wells that enable collection of hydrological and chemical information from the saturated part of the subsurface. As a result, identification of pollution in wells is clear evidence that the contaminants already crossed the entire vadose-zone and accumulated in the aquifer. Accordingly, an effective monitoring program must include monitoring means that provide real-time information in the unsaturated zone. Such monitoring programs may provide "early warning" for potential pollution processes that may risk groundwater quality. A vadose-zone monitoring system (VMS), which was developed recently, allows continuous monitoring of the hydrological and chemical properties of percolating water in the deep vadose zone. Data which is collected by the system allows direct measurements of the water percolation fluxes and detects the chemical evolution of the percolating water across the entire unsaturated domain. The VMS is designed for long term continuous operation in a time scale of years to decades. To date, the system has been successfully implemented in several studies on water flow and contaminant transport in various hydrological and geological setups. These include research projects on: (a) floodwater infiltration and groundwater recharge from stream channels and reservoirs, (b) impact of various agricultural regimes on quality and quantity of groundwater recharge, (c) subsurface pollution of dairy farms, (d) chemical evolution of landfill leachates, and (e) control of remediation operations in contaminated sites.

Simulation of Contaminant Transport through the Vadose Zone: A Continuum Mechanical Approach within the Framework of the Extended Theory of Porous Media (eTPM)

“…These contaminants are transferred through the vadose zone, which is partially saturated with air and water. Although the vadose zone functions as a buffer and filter zone, in which attenuation, absorption, screening, degradation as well as chemical and biological transformations of contaminants occur, most of the hazardous contaminants are reactive in soil, and they infiltrate through the vadose zone and permeate unsaturated soil in order to reach the aquifer and continue to migrate in the direction of the groundwater flow [4]. Hence, the contamination of the vadose zone can be considered as a continuous source of contamination for aquifers, and it affects the quality and quantity of groundwater resources [5,6], leading to significant risks for human health and the environment.…”

A comparative aquifer vulnerability study of the Quaternary Sombreiro – Warri Deltaic plain deposits, Western Niger Delta, Nigeria

“…Groundwater contamination usually begins on the ground surface, the contaminants have to travel through the vadose zone before it reaches the water table (Dahan, 2020). The reduced flow rates leading to longer residence time of contaminants and natural attenuation process of the vadose zone protects the aquifer below from contamination (Dahan, 2015;Panda and Sabarathinam, 2019). Longitudinal conductance, which is regarded as proportionate to the capacity of vadose zone to protect the aquifer beneath (Henriet, 1976), has also found wide application in aquifer vulnerability studies in Nigeria (Oladapo et al, 2004;Atakpo and Ayolabi, 2009;Atakpo, 2013;Aweto and Mamah, 2014;Egbai et al, 2015), this method measures vulnerability by incorporating the resistivity and thickness of the overlying vadose zone above aquifers.…”