Olsson Associates

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Olsson helps city address wastewater challenges with bypass elimination plan

Monday, May 13, 2013

Nancy Wichmer, Marketing

The City of Republic, Missouri, is a very proactive, expanding community whose population grew over 75 percent between 2000 and 2010. Given the city’s location, available transportation resources, and existing utility infrastructure, continued residential, commercial, and industrial growth is expected in the future. However, this growth has brought wastewater capacity challenges at its wastewater treatment plant (WWTP), which Olsson has helped address.

The City of Republic experiences very high flows at its WWTP during and after wet-weather events because of excessive inflow and infiltration (I&I) into the collection system. Over the past two decades, the city has undertaken several sewer system rehabilitation efforts in an attempt to mitigate the high I&I volumes and has also constructed a stormwater clarifier to treat flows that exceed the peak capacity of the WWTP’s biological treatment system. On average, the daily flow received at the WWTP is well below the hydraulic capacity of the biological treatment system. However, several times a year, wet-weather conditions result in flows that exceed the hydraulic capacity of the WWTP’s biological system, and this excess flow must then be diverted to the stormwater clarifier. 

The stormwater clarifier is initially used as a holding basin for peak flows until biological treatment capacity is available, but excessive wet-weather flows can result in the need to discharge from the stormwater clarifier through the WWTP’s previously permitted Outfall #002. Recent federal regulations, however, no longer permit discharges from stormwater clarifiers because these discharges bypass secondary treatment, which is a requirement of the Clean Water Act and associated federal regulations. Accordingly, in 2011, the City of Republic and the Missouri Department of Natural Resources (MoDNR) entered into a Peak Flow Voluntary Compliance Agreement that requires the city to develop a Bypass Elimination Plan to evaluate the city’s wastewater collection and treatment systems and to identify improvements to eliminate discharges from the city’s stormwater clarifier over the next 10 years. 

As city engineer for the City of Republic, Olsson Associates was contracted to analyze the city’s wastewater system and develop a bypass elimination plan report to satisfy the requirements of the city’s Compliance Agreement.

Flow monitoring in manholes. Data was incorporated into the BEP report and allowed Olsson to develop recommendations.After extensively evaluating the city’s wastewater system, including analyzing data collected from 11 flow meters installed within the city’s largest drainage basin, Olsson provided the city and MoDNR with a detailed bypass elimination plan engineering report to guide the city’s I&I reduction efforts over the next 10 years. This engineering report included analyzing the existing collection system flows, capacity, and physical integrity. It also analyzed the treatment system’s hydraulic and organic loading capacity. The report recommended prioritized improvements to the city’s wastewater collection and treatment systems with the goal of reducing and handling peak flows to eliminate any unauthorized discharges through its stormwater clarifier. Jerry Jesky, PE, project engineer for Olsson’s Public Infrastructure team, wrote the report, and it was approved by the MoDNR in February 2013 for full implementation. Applying the carefully planned and budgeted improvements outlined in the bypass elimination plan report will allow the city to sustain its wastewater system for many years to come.

For more information, please contact Jerry Jesky at 417.890.8802 or jjesky@olssonassociates.com.

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