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CSO Separation Projects Protect Rivers

Wright-Pierce assisted the City of Lebanon in developing a plan acceptable to city, state, and federal agencies to abate the negative effects of combined sewer overflows (CSOs), which allow untreated wastewater flows to be discharged to the Mascoma and Connecticut rivers, and to Great Brook.

A study of the sewer system and the aquatic environment was performed to evaluate the nature and effects of the overflows, and to develop alternative solutions to the CSO problem. The CSO and interceptor systems were modeled and calibrated to reflect the study data. The models were then used to predict discharge frequency, duration and volume for a design storm in order to evaluate the solution options.

The alternatives included partial sewer separation, full-scale sewer separation, and the use of satellite treatment facilities to provide partial treatment and disinfection prior to discharge. The study concluded that the most cost effective solution to the CSO discharges was to separate the sewer system.  The report was submitted and approved by both the NHDES and the US EPA and is now being implemented in phases.

Wright-Pierce will assess existing water, sewer, drainage, traffic patterns, street alignments, curbs, sidewalks, pavement condition, ADA compliance, signage, traffic patterns, bike and pedestrian access, parking and above ground utilities for each design. Upgrades, replacements and new construction are included in the final design for each phase. As a result of Lebanon’s commitment, the City is developing its reputation as one of New England’s most desirable places to live.

The City's long-range planning allows its phased CSO separation implementation to optimize funding and scheduling of the projects. The CSO projects are being funded through a combination of grants from NHDES, USEPA, CDBG, the US Army Corps of Engineers, and from its own resources. The entire investment over the next 12 years is estimated to be $40 million.

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Project Highlights

Background

The City of Lebanon is under an EPA Administrative Order to evaluate solutions to address the combined sewer overflows (CSO) problem.

Challenges

There were seven relief points known to be CSOs in the City’s sewer system, which allowed untreated combined flows to be discharged to the Mascoma and Connecticut rivers and to Great Brook.

Solutions

  • Wright-Pierce determined the most cost-effective method to comply with the Administrative Order.
  • The City made a major commitment to improving its infrastructure as part of the sewer separation projects
  • The project is funded through a combination of grants from NHDES, USEPA, CDBG, the US Army Corps of Engineers, and from the City's own resources.
  • The entire investment over the next 12 years is estimated to be $40 million.