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U %'� 4.1 Collection System Wastewater generated at a future development at the Lin Family- Properties will be conveyed to the treatment system by a septic tank effluent pump(STEP)and septic tank effluent gravity (STSG)collection system. A STEP collection system consists of septic tanks equipped with effluent pumps. which pump effluent via small diameter force mains to the treatment and dispersal area STSG collection consists of septic tanks with standard small diameter gravity effluent drains that transport the effluent to the treatment and dispersal area. A STENSTEG collection system can be constructed as clusters of houses are constructed, offering flexibility in the phasing of collection system infrastructure. In addition, construction costs for STEP and STEL installation are less than construction costs for comparable gravity se%ver mains because these smaller diameter pipelines can be installed at shallower depths. Wastewater generated from a group or--cluster"of homes flows through gravity sewer services to a community septic tank. Sizing of STEP and STEG tanks is based on the number and configuration of homes served. For the proposed Lin Family Properties decentralized system, 30 to 50 STEP or STEG tanks ranging in size from 5,000 gallons to 25.000 gallons would be required. Assuming a wastewater generation rate of 250 gallons per day per dwelling unfit(gpd/du), an average of 12 du would be typically served by a STEP or STEG tank_ Septic tanks should be located in easily accessible, public areas for ease of maintenance. Proposed placement of STEP/STSG tanks is below grade in roadways, with access provided by a standard manhole and a traffic-rated cover. Primary treatment in the septic tank is accomplished with removal of settleable solids, oils. greases and floating debris. During the hydraulic residence time, both a sludge layer (on the tank bottom)and a scum laver(on the water surface) form inside the septic tank. The clarified effluent, located between the sludge and scum layers, is filtered by an effluent screen to remove larger solids prior to pumping. This effluent screen prevents the transport of excess solids to the treatment and dispersal systems. STEP systems typically include float switches, which activate the effluent pumps when a preset high water elevation is reached and shut off the pumps when a preset love water elevation is reached. Effluent pumps within the STEP tanks convey the primary-treated wastewater via small diameter force mains to the treatment and dispersal area. Typical force main diameters are two to four inches. If STEG collection is possible, the effluent drains are tv ically four inches in diameter. 4.2 Tivatment System Several onsite treatment methods are available to treat wastewater generated in the development, including activated sludge, membrane bioreactor, sequencing batch reactor, and sand filter technology. For evaluation in this report, wastewater collected in the development is assumed to be treated with a typical recirculating textile media filter prior Decentralized Treatment for Lin Fainily t SAB038100 December 2008 N.1SA80381001Docuncen1a120081219_LinProp%X,'W DraR.doc