Vadose-zone Monitoring Systemkey to groundwater protection and

optimization of remediation strategies

Dr. Ofer Dahan Ben-Gurion UniversityE-mail: odahan@bgu.ac.il Phone: (+972) 52 8795888

Shuki BonesE-Mail: shuki.bones@ametis.co.ilPhone: (+972) 50 5316637

Minimization subsurface pollution and optimization of remediation efficiency depend on reliable and effective monitoring tools that provide real-time information on the chemical and hydrological state of the percolating water. Today, most monitoring programs are based on observation wells that samples groundwater. As such, identification of pollution in well water is clear evidence that the contaminants already crossed the vadose-zone and accumulated in groundwater. Unfortunately, only little can be done to fully remediate contaminated aquifers. Accordingly, effective monitoring program that aims at protecting groundwater from potential pollution must include vadose-zone monitoring technologies that provide real-time information on the hydrological and chemical properties of the percolating water, long before contaminants reach the water table. Hence, efficient and cost effective vadose-zone monitoring system provides "early warning" for potential contamination that may risk groundwater. Moreover, implementation of the vadose zone monitoring system in the vadose-zone of a site that undergoes active remediation operation provides real time information on the actual chemical and hydrological conditions in the vadose zone. Such information is critical for proper assessment of the remediation strategies.

Monitoring Concept

*Patents pending

Dynamics of flood-water infiltration and groundwater recharge in hyper-arid desert

Vadose zone Monitoring systems which were installed under stream bed of the rivers and reservoirs allowed continuous monitoring of water infiltration during flood events. Each individual flood initiated an infiltration event which was recognized as a measurable wetting front propagation along deep sections vadose zone followed by a rise in water table. The data that was collected by the VMS during the flood events enabled direct calculation of the percolation flow velocities and infiltration fluxes. Dahan et al., 2007. Journal of Hydrology. Dahan et al., 2008. Groundwater.

VMS installation Monitored process

Surface, vadose zone and groundwater hydrographs

Dahan, O., Shani, Y., Enzel, Y., Yechieli, Y. and Yakirevich, A. 2007: Direct measurements of floodwater infiltration into shallow alluvial aquifers. Journal of Hydrology.

Infiltration from stream channels and reservoirs

Flood & groundwater hydrographs

Vadose zone water Content Profile

Tzukim Reservoir

In-situ monitoring of water percolation and tracers migration through the vadose zone

Experimental setup Tracer breakthrough

Water percolation and tracer migration through the vadose zone were studied through a multi-tracer experiment. Frequent sampling of the vadose zone pore-water at multiple points by the VMS allowed establishment of tracer breakthrough curves at various depths.

Dahan et al., 2009. In-situ monitoring of water percolation in layered soils using a vadose-zone monitoring system. Vadose zone Journal.

Water percolation through the deep vadose zone

Temporal variation in water content of deep vadose zone

Chloride concentration in the vadose zone as obtained by the VMS, sediment

water extracts and groundwater

Water percolation and solute transport through a 21m thick vadose zone were studied in a sand dune area. A vadose zone monitoring system which was installed in the site allowed continuous tracing of the wetting and drainage cycles in the deep section of the vadose zone in response to seasonal rain events. In addition, frequent sampling of the vadose zone pore water by the VSPs allowed continuous tracking of the chemical properties of the percolating water. It has been shown that the chemical composition of the infiltrating water is significantly different from that obtained from standard sediment sampling methods.

Rimon et al., 2007: Water percolation through the deep vadose zone and groundwater recharge: preliminary results based on a new vadose-zone monitoring system. Water Resources Research.

Bioremediation of polluted vadose zone

Temporal variation of VOC concentration in the vadose zone pore water during remediation process

Potential monitoring application

• Leaches under LANDFILLS

• Fuel leaks from GAS STATIONS

• Leaks HAZARDOUS WASTE from tanks, storage lagoons and sensitive factories of potential pollution

• On line monitoring and control of REMRDIATION efficiency

* The monitoring system may be installed under existing active facilities with minimal disturbance