New Analytical Tools for Determination of Water Quality Parameters in the Unsaturated Zone: The Shafdan Soil Aquifer Treatment as a Case Study

Alexander Sopilniak, Environmental analytical chemistry, The Hebrew University, Jerusalem, Israel
Roy Elkayam, Modelling And Water Resources, Mekorot Ltd., Rishon Lezion, Israel
Guy Gasser, Soil And Water, Volcani Center, Beit Dagan, Israel
Irena Pankratov, Soil And Water, Volcani Center, Beit Dagan, Israel
Ovadia Lev, Environmental analytical chemistry, The Hebrew University, Jerusalem, Israel

Water scarcity intensifies in semi/arid countries and calls for the use alternative, high quality water sources. Therefore, there is an increased need for water reuse, and aquifer recharge by treated wastewater effluents is one of the cheapest ways to increase water availability.  The effluent percolates through an unsaturated zone, reaches the aquifer, and the treated water is then reclaimed for unlimited irrigation. This process is called Soil-Aquifer Treatment (SAT). More than 90% of dissolved organic matter (DOC) and 99% of ammonia are removed and excellent disinfection is achieved by optimized SATs. However, to this day, there are no analytical tools to allow determination of pore water quality parameters in the unsaturated zone with high depth resolution. Particularly, high resolution depth profiles of dissolved oxygen, DOC and refractory organic contaminant are still unavailable. 

We devised a set of methods to determine depth profiles of water quality parameters in the unsaturated zone and use the data to gain better insight into SAT processes. The methods are based on extraction of undisturbed soil cores from the unsaturated zone by direct push drilling (a.k.a. “Geoprobe”). 

For dissolved oxygen, a modified push liner was used which allows determination of the local oxygen tension by a miniature optode. For organic matter, a method based on positive displacement of pore water by distilled water was developed.  A similar methodology was used to sample local pore water for determination of the concentration of emerging organic contaminants in the pore water. The metrological characteristics and range of applicability of each of these methods were evaluated, and the methods were validated by controlled laboratory tests under a wide range of soil parameters.  Finally, depth profiles of the different parameters were evaluated throughout the unsaturated zone of the Shafdan SAT.