Onsite wastewater systems (OWS) serve nearly 25% of the U.S. population and are increasingly viewed as a necessary, permanent component of a sustainable water/wastewater infrastructure in the U.S.  Among the science and technology advancements that have been made to enable OWS and decentralized approaches, engineered treatment units have evolved to include various forms of packed bed biofilters, (e.g., sand, foam, and textile filters), tank-based bioreactors, membrane systems, and disinfection units, that offer the potential to dramatically decrease the reliance on natural soils as a critical component to the effective performance of an OWS.  While much is known about effects of high quality effluents on soil pore-clogging and infiltration capacity, there are serious gaps in thecurrent knowledge base regarding the advanced pretreatment effects on the genesis of an in situ biozone and soil system purificaiton efficiency, particularly for pathogens, which determine the overall OWS performance with respect to protecting public health and environmental quality. To further increase the understanding and advance the standard of practice for application of advanced pretreatment for OWS, controlled but representative experimentation  must be completed.  In the proposed project, proven methodologies involving existing research facilities and apparatus will be used to enable detailed characterization of the effluent quality produced by three different levels of pretreatment (septic tank, septic tank with textile filter unit, and a membrane bioreactor) and the effects of these effluent qualities on the genesis of an in situ biozone and the hydraulic and purification performance of a soil treatment system.   The research will also address the matter of performance monitoring of engineered units and soils systems with respect to methods and frequency of measurements. The proposed research will be completed by a team of faculty, staff and students at the Colorado School of Mines (CSM) and will be enabled by CSM's existing facilities and an ongoing research program.  Theresearch will be completed using replicated and instrumented, field pilot-scale unit operations installed at the Mines Park Test Site located on theCSM campus.  The results of the work will directly support guidance regarding when and how to apply increasing levels of pretreamtent to cost-effectively treat wastewater at a given site.