Influence of the vadose zone on groundwater pollution - A review

Abstract

The vadose zone is the geologic profile that lies between the water table and the ground surface. It has low water content relative to the saturated zone and commonly referred as the unsaturated zone. Recharge to the water table passes through the vadose zone and understanding transport through this region is critical in groundwater pollution studies. Groundwater pollution is controlled by a number of physical and chemical processes which may retard or transform contaminants as they pass through the vadose zone. Porous materials hold water under tension as a component of soil structure, ambient fluid pressures and other factors. When vadose zone water content is below saturation, leakage liquid as well as the dissolved materials passed on in it are retained. Hydrologically, the depth of unsaturated zone plays an important role in controlling water movement and contaminant transport from the land surface to the aquifer. The purpose of this study is to present an overview of the principles of fluid flow and moisture retention in the vadose zone and its influence on groundwater pollution. The study is presented in two parts: Part I includes descriptions of zones of soil moisture, basic principles of properties controlling the fluid distribution in pore spaces and how subsurface soil properties can be used to assess the leachate mobility. Part II review the principle of fluid movement in the vadose zone and impact of seepage on groundwater pollution. This study will focus on how vadose zone conditions and soil properties act to control groundwater pollution.

A cost-effective method for assessing groundwater well vulnerability to anthropogenic and natural pollution in the framework of water safety plans

“…Water table depth is usually associated with vulnerability to anthropogenic pollution. Thicker vadose zone delays the infiltration of pollutants to the saturated zone, increasing the self-purifying capacity of the unsaturated zone (Juntakut et al, 2019;Panda and S, 2019;Truex et al, 2015). For each well, the water table depth expressed in meters below ground surface (bgs), was calculated as the maximum groundwater level (m a.s.l.)…”

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.…”

The Geological Characteristics of the Vadose Zone Influence the Impact of Treated Wastewater on the Groundwater Quality (SCA.Re.S. Project 2019–2020)

“…When the water flows relatively slowly through the vadose zone, the pollutants can be removed by chemical reactions and other physical attenuation mechanisms [11]. Because of the characteristics of different aquifer types, an understanding of the processes that occur in the vadose zone is fundamental for preserving the groundwater quality [12,13]. Research is therefore needed on how contaminants move through the unsaturated zone before reaching the water table, particularly in close proximity to waste disposal and treatment facilities [14].…”