Overview of the Field Test of Innovative On-Site Wastewater Treatment Systems during the La Pine National Demonstration Project

This paper presents an overview of the field test results of the La Pine National Decentralized Wastewater Treatment Demonstration Project (La Pine Project). The main objective of the field test was to identify innovative on-site wastewater treatment systems that reduce the amount of nitrogen discharged to groundwater. The aquifer underlying the La Pine subbasin of the upper Deschutes River Watershed is shallow and unconfined and provides the drinking water source for the region’s population. The project also evaluated septic tank and sand filter performance in order to provide baseline information on the impacts of conventional systems on the aquifer. The performance of nitrogen reducing treatment technologies are compared to septic tank and sand filter performance, the State of Oregon’s residential waste strength definition, and La Pine Project performance criteria. The study found that several systems can effectively reduce typical water quality parameters (5-day biochemical oxygen demand, total suspended solids, and fecal coliform) but that nitrogen reduction can be more difficult to achieve in the field. Several systems that showed high levels of nitrogen reduction in test centers did not perform as well in the field and nitrogen reduction below $10\mathrm{mg}∕\mathrm{L}$ appears to be difficult to achieve consistently without a secondary carbon source.