Humid Region Salt Accumulation in Soils At Penn State's Living Filter.

Irrigation reuse of municipal wastewater effluent conserves freshwater resources and avoids direct nutrient discharge to surface waters. Since the early 1960’s the Pennsylvania State University has used effluent from its waste water treatment plant to irrigate agricultural and forested land as its Living Filter site.

Salt accumulation is generally an issue for arid regions. However in the Living Filter, effluent concentrations of sodium (Na⁺), magnesium (Mg²⁺), and calcium (Ca²⁺) have all increased over the years.  It is also significant that concentrations have increased disproportionally due to the installation of water softeners on Penn State’s campus. Sodium has increased to 446% its initial concentration, while Ca²⁺ and Mg²⁺ have increased only 28% and 53% of their initial concentrations respectively. This asymmetric increase of monovalent cations has led to a much higher Sodium Adsorption Ratio (SAR) than was initially present. Application of high SAR water can reduce macroporosity and increase microporosity, resulting in reduced hydraulic conductivity.

This research assessed the present condition of soils at the Living Filter with regards to salt concentrations and hydraulic conductivities. This data will be compared to data collected in 2009 and both sets of data will be modeled with HYDRUS 1-D. This research provides insight into the impact of salt accumulation on the long-term sustainability of the Living Filter system.