City of Afton Large Subsurface Sewage Treatment System
The City of Afton used to be one of over 100 small communities in Minnesota that are still unsewered – discharging partially settled and untreated sewage effluent into surface waters, on the ground surface, or directly into groundwater – a major pollution concern for both public health and the environment. Historically when faced with a mature, unsewered community infrastructure problem, the engineer defaults to regionalization to a larger treatment facility, or in more rural areas, just building a wastewater stabilization pond. Those solutions are no longer an option when the nearest sewer interceptor is miles away and a suitable location for a multi-acre pond does is nonexistent.
Wenck was the lead design engineer for the City of Afton Large Subsurface Sewage Treatment System (LSTS). The LSTS provides sanitary service to Afton’s “Old Village” along the St. Croix River in Washington County. The LSTS, designed to treat 50,550 gallons per day (gpd) of wastewater, is the largest soil-based subsurface treatment system (septic system) in Minnesota. As the ultimate treated effluent is dispersed to the native soil, stringent limits are in-place to ensure the protection of the environment and public heath prior to groundwater recharge. Specifically, the Minnesota Pollution Control Agency (MPCA) State Disposal System permit includes a 10 mg/L total nitrogen limit at the end-of-pipe prior to soil dispersal. To achieve this level of treatment, the LSTS includes complex treatment components and processes.
Wenck provided a reliable, long term wastewater solution, designing a decentralized, soil based dispersal system like none other in the upper Midwest in size or complexity. The City of Afton benefited from 10 years of experience in similar communities from a team brought together from an array of multidisciplinary fields to deliver not only a safer wastewater treatment system, but also a sense of communal resiliency and an improved quality of life.
"Bringing Wenck in to the project was what the City needed to come up with a cost-effective wastewater treatment solution. Their practical approach to a complex problem helped assure the City that these projects could move forward."
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