This nationwide study was performed for the Water Environment Research Foundation in Alexandria, Virginia.

CES was the lead firm for a multi-disciplined team of scientists, engineers, and decentralized wastewater systems operations specialists who collected information for and evaluated the performance of large/community scale decentralized wastewater systems nationwide. Systems with design flows ranging from 5,000 to 50,000 gallons per day, and with at least five years of service/operation were evaluated in the study. A wide range of combinations of collection, treatment and dispersal methods were studied in the project.

Only limited information had previously been compiled on the long-term performance of
large-scale decentralized, or community sized wastewater collection and treatment and
disposal systems for use by designers, regulators and decision makers. Due to their age and condition, many of these systems will soon require upgrading or replacement to meet current requirements. Adding to the need to compile good quality performance data for large-scale decentralized systems is the perception that property developers frequently arrange for wastewater service that results in the least short-term investment rather than the lowest life-cycle costs. Such choices are likely based largely on the absence of readily available information that could help with that decision-making process. By contrast, centralized systems are often at least partially planned, funded, and managed by utilities that are ultimately accountable to rate-payers that provides an accompanying driver to minimize life cycle costs. Much more operations and performance data has therefore been compiled and made available to the public for larger centralized systems.

The study covered systems handling domestic waste flows only (residential and commercial facilities) designed and constructed in accordance with regulatory requirements and accepted industry practices applicable to the particular state or region. In addition to data gathered for systems’ treatment performance, information was obtained for operating histories and repairs where available from owners or operators, along with capital and operating costs. Systems relying either on soil based disposition or direct discharge of effluent were included in the study. The results of the project better enable designers, regulators and the industry as a whole to better assess and select decentralized systems used to serve certain types of facilities in various geographic settings.

A paper presented about this study at the National Onsite Wastewater Recycling Association (NOWRA) conference in April 2008 may be downloaded here.