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

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.