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 Preliminary Evaluation of Cluster System Septic Tank Performance
Sara Christopherson, Dave Gustafson and Jim Anderson
Item Number: NRL2006AC-17
Shipping Weight: 0lbs. 0oz.
Price: $20.00
Over the last decade, the growth of “cluster” developments has lead to the use of wastewater treatment systems that serve entire neighborhoods or small communities. The use of cluster developments is an increasing trend in Minnesota and across the country. The Minnesota Pollution Control Agency (MPCA) reports that the majority of onsite wastewater systems over 10,000 gallons per day (gpd) in the state have been permitted in the last five years. The earlier versions of Minnesota Rule 7080 (Design and Operation Standards for Individual Sewage Treatment Systems) included septic tank sizing criteria that was written before cluster systems were widely adopted. The guidelines were more geared towards smaller systems; specifically, systems that treat flows less than 2,500 gpd. Minnesota Rule 7080 is being revised to reflect the evolution of sewage collection systems and increased use of large (greater than 2,500 gpd) cluster systems in the state. The University of Minnesota Onsite Sewage Treatment Program performed a short-term investigation on the performance of septic tanks for mid- and large-sized sewage treatment sites that were designed and commissioned before the release of the Draft Revision of Rule 7080 and the MPCA’s Design Guidance for Large Subsurface Wastewater Treatment Systems (LSTS). Septic tank performance for 7 gravity-flow collection systems, 6 grinder-pump collection systems, and 4 septic tank effluent pumping (STEP) systems will be presented and discussed. Parameters monitored in the study include biochemical oxygen demand (BOD), total suspended solids (TSS), sludge and scum thickness, liquid depth in the tanks, and average actual flow rates. Several different sludge measuring devices were also evaluated during the project.