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Page 20 <br /> Key Design Features <br /> ■Performs anaerobic digestion; >40% Primary sewage treatment(STEP/STEG effluent BOD5/TSS typically <br /> 150/40 mg/L and organic matter digests within the tank at about 80% annually.) <br /> ■24 hour emergency storage (>200 gallons), eliminates need for immediate operator response requirements <br /> ■Average 7-12 year pump out frequency, less than$2.50/month/EDU at$250/pumpout(under contract, it could <br /> be less Glide is$160±, homeowner education with respect to organic vs. inorganic discharge practices greatly <br /> extends the length between pumpout events.) <br /> ■Caustic chemicals and other system abuses are limited to interceptor tanks and easily identified <br /> ■Conflicts with other utilities during installation are easily avoided at little to no cost, particularly with directional <br /> boring <br /> ■Low pump repair and replacement costs, less than $1.50/month/EDU. Long pump life of 20 to 30 years. Pumps <br /> come with a standard 5 yr warranty but can be extended with capital. <br /> ■Pumps are lightweight, typically 30 lbs. <br /> ■If terrain permits, gravity(STEG) connections are allowed. <br /> ■ 1"dia service laterals. <br /> ■Less than $1.50/month/EDU for energy costs to operate residential pumps. <br /> ■Small diameter conveyance system, typically 2-4 inch diameter. <br /> ■Force-mains follow the contour of the land and installed at shallow burial depths. <br /> ■Minimum velocities are not required.. <br /> ■Watertight collection system, largely immune to 1/I. <br /> ■Inexpensive cleanouts replace expensive manholes, but only where cleanouts are needed (terminal end of <br /> mainlines). <br /> ■Lift stations are not required (typically). <br /> ■Eliminates need for influence screening and grit removal. <br /> ■Reduces solids management requirement of the secondary treatment facility due to low influent TSS <br /> concentration. <br /> Extended Power Outages <br /> Following a power outage the hydraulics of the system will balance so that even the most remote pumps will still <br /> discharge 1 or 2 gpm into the collection system. The reserve storage in the tanks is normally about 150 gallons, <br /> which allows 24 hours of normal water usage. Power outages of 9 to 12 hours are infrequent and generally <br /> considered the worst condition to allow for; most disruptions last no longer than a couple of hours. Turbine <br /> effluent pumps are constructed with a 1/8"diameter by-pass orifice in the discharge head that allows 3 gpm to <br /> circulate when the pump is operating near its shut-off head. These pumps are capable of operating at shut-off, <br /> continuously,for several days without damage to the motor or liquid end. In extreme conditions, the most <br /> effective way to allow for extended power outage is to substitute 1,500-gallon tanks for the standard 1,000-gallon <br /> tanks. . <br /> Freezing <br /> During extended periods of cold weather, exposed portions of the sewer system may be subject to freeze <br /> damage. Underground components are normally buried below the frost line. In extremely cold climates where <br /> frost depth is great, underground components may be protected by insulation or heating tape. Risers should be <br /> backfilled with pea gravel to prevent frost heave from separating the riser from the tank. Bridge crossings and air <br /> release valve locations are especially susceptible to freezing. Continuous water movement inhibits the freezing <br /> process, so as long as the system maintains even a slight flow, mainlines shouldn't freeze. If for any reason, <br />