4/26/2011 SEWER COMMISSION Minutes

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Page 38 Frequently Asked Questions 1) Does every residence in an Orenco effluent sewer require a Septic Tank Effluent Pumping (STEP) system? Depending upon the elevation of the interceptor tank and the pressure in the collection main, certain connections, referred to as Septic Tank Effluent Gravity(STEG) systems, can gravity flow into main lines. Relatively simple hydraulic analyses are required to determine which connections require STEP systems and which permit STEG systems. Orenco effluent sewers can be entirely STEP or STEG, or any combination thereof, depending upon the results of the hydraulic analyses. 2) Gravity sewer systems, and at times grinder sewer systems, frequently require lift/pump stations to convey wastewater to the point of discharge. Do Orenco effluent sewer systems require lift stations? Lift stations are generally not required with Orenco effluent sewers, even when the point of discharge is located miles away from the point of wastewater generation. Main lines are normally sized to allow communities to standardize on a single high-head effluent pump, typically 10 gal/min, 1/2Hp, throughout. 3) In existing neighborhoods, conventional gravity sewers are normally installed under existing roads, often-requiring road removal, replacement, and closures. Where are Orenco effluent sewers typically installed and are road closures common? Orenco effluent sewer mains are generally installed in the right-of-way next to the road, thus avoiding road removal, replacement, and closures. Main lines are typically small diameter,often times two inches, follow the contour of the land, and are installed at shallow burial depths, below frost depth, much like water lines.As a result, small open trench installation is common, as well as directional boring, a trenchless method for installing small diameter pressure pipe. Directional boring significantly reduces construction trauma and elevated costs associated with avoiding existing utilities and driveways in existing communities. 4) Do I need to replace my interceptor tank if an Orenco effluent sewer system is installed? Although rare, some communities have used existing tanks in an Orenco effluent sewer. Existing tanks, however, require thorough evaluation to confirm watertightness and structural integrity. Leaky and structurally inadequate tanks,a common theme among old tanks, often translates to increased infiltration, higher maintenance costs, less efficient solids digestion, and compromised secondary treatment processes. Existing tanks, as a result, require a detailed evaluation before utilization. Recently installed tanks with watertight and satisfactory specifications, nonetheless, are worth investigating. 5) Do Orenco effluent sewer systems require an AdvanTex Treatment process? Although AdvanTex Treatment Systems are manufactured and designed specifically to process effluent sewer wastewater affordably and reliably, several other secondary treatment processes can be paired with Orenco effluent sewers. Plus, nearly all types of secondary treatment processes can be downsized with effluent sewers, as they are the only technology that provides primary treatment. 6) Septic tanks are normally pumped out at intervals of three years or less. How often do Orenco effluent sewers require solids removal? Septic tank pump-out intervals are generally mandated by local health departments and based upon short-term solids accumulation studies that fail to take into account long-term solids decomposition in interceptor tanks. The microbial activity that affects optimal decomposition takes up to three years to develop fully.When a management program is in place, pump-outs are scheduled based on inspections and monitoring records so that costs are controlled. Onsite regulations and manuals may encourage frequent pump-outs as a precautionary measure when an inspection program is not in effect; however, longer intervals are usually justified, particularly if an effluent screening device is in place. At 95% level