The Village of Springville NY operates a wastewater treatment plant (WWTP) with a rated capacityof 1.2 million gallons per day (mgd). Average daily flow is approximately 0.7 mgd with wet weather peak flow ofapproximately 4.0 mgd. Treatment processes include: mechanically cleaned screening; grit collection; primaryclarification; plastic media trickling filtration; secondary clarification; and disinfection prior to discharge to SpringBrook.The WWTP receives 1/2 of its flow from the west through a triple barrel inverted siphon which passes under SpringBrook, a native trout spawning stream. The soil on which the WWTP and siphon were constructed is wet unstableglacial deposits that are susceptible to creep and erosion. During periods of snow melt and heavy rain the creekerodes its bed and banks. Eventually this erosion exposed and undermined the existing siphon causing it to fail anddischarge raw sewage to Spring Brook. The siphon was temporarily repaired and supported until a replacementsiphon could be designed and constructed.Due to existing soil conditions and the small WWTP site (approximately 5.0 acres with less than half dedicated totreatment processes), open cut construction was not practical. The replacement siphon was designed using horizontaldirectional drilling methods. The pipes had to be installed a minimum of 8' below the creek bed and had to passbetween the trickling filter and secondary clarifier tanks with approximately 15' of horizontal separation.Complicating the project was the need to coordinate with other concurrent construction for WWTP site stabilizationdue to bank failure along Spring Brook. The bank failure was encroaching to within 8 feet of the primary clarifierand trickling filter. The design required the installation of rip-rap rock protection at the siphon creek crossing whichwas tied into the bank stabilization. The work was completed on time at a cost of $410,000.
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