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Combined Sewer Overflow Long-Term Control Plan Design-Phase Services

Minimizing long-term combined sewer overflows to achieve compliance with federal regulations.
  • 16-inch force main in downtown Monessen, Pa.-Gannett Fleming

    The project includes more than 1 mile of 16-inch, horizontal-directional-drilled force main.

  • Vortex grit separator at the WWTP in Donora, Pa.-Gannett Fleming

    Upgrades at the headworks of the existing WWTP include a new 15.0 mgd grit facility.

  • Mechanically cleaned bar screen at the WWTP in Donora, Pa.-Gannett Fleming

    Upgrades at the headworks of the existing WWTP include a new 15.0 mgd mechanically cleaned bar screen.

  • Equalization tank at the WWTP in Donora, Pa.-Gannett Fleming

    The WWTP's 3 mgal equalization tank receives wet weather flows in excess of the plant capacity.

Mon Valley Sewage Authority

Monessen and Donora, Pennsylvania

Our Role
Long-Term Control Planning, Surveying, Permitting, Design, Construction Management, Construction Observation.

10,000 LF of sanitary gravity sewer, 12,000 LF of sanitary force main, and a 3 mgal equalization tankĀ 
Construction Cost
$9 million
New Construction
5 Years
  • Maximized flows to the WWTP and reduced the inflow and infiltration of wet weather into the Mon Valley Sewage Authority (Authority) system

  • Eliminated or minimized 17 combined sewer overflows (CSO) in the Authority's service area

  • Ensured that improvements and designs comply with federal CSO regulations.

Mon Valley Sewage Authority (Authority) worked with Gannett Fleming to implement the projects and recommendations of their combined sewer overflow (CSO) long-term control plan (LTCP) that the Pennsylvania Department of Environmental Protection approved in May 2008. The LTCP is intended to improve water quality for the community by limiting CSO.

The LTCP outlined three phases of work to be implemented during a 12-year period, with an estimated total project cost exceeding $50 million. Phase I construction comprises two stream separations, interceptor and force main upgrades, five pump station upgrades, and a 3.0-mgal equalization facility. Phases II and III comprise sewer separation and nine satellite treatment facilities.

What We Did

Gannett Fleming completed design, surveying, permitting, and construction management services associated with the final design and construction of facilities for Phase I of the Authority's LTCP. The design of the equalization tank and WWTP upgrades was completed with Revit building information modeling (BIM) software. The fully functional, three-dimensional model includes all mechanical, electrical, and plumbing; structural; and architectural aspects of the facility.

Construction included approximately 10,000 LF of sanitary gravity sewer, 12,000 LF of sanitary force main, a 3 mgal equalization tank with a wet-weather pump station and valve vault, upgrades to the WWTP headworks including screening and grit removal, upgrades at 5 pump stations, manholes, restoration, and incidental work. Challenging aspects of the project included more than 1 mile of 16-inch, horizontal-directional-drilled force main adjacent to a highway in downtown Monessen, as well as multiple bores with diameters as large as 72 inches.

Key Features

  • CSO LTCP development

  • Treatment facility design

  • Sewer separation design

  • Pump station and WWTP upgrades

  • Surveying and permitting.

Sustainability Features & Outcomes

  • More efficient pumps and variable-frequency drives included in the pump station upgrades reduce electrical usage

  • Increased flow to the WWTP improves water quality by reducing CSO volumes

  • Removal of streams from the combined sewer system reduces the clean water conveyed to the WWTP, reducing combined sewer overflow volumes and treatment costs

  • The equalization tank design included a reinforced grass driveway around the perimeter of the tank, which allows access to the tank while decreasing stormwater runoff.

Similar Projects: Information Technology: Building Information Modeling & Visualization, Engineering, Environmental Management & Remediation, Geotechnical: Foundations, Geotechnical, Information Technology, Wastewater: Interceptors, Force Mains, & Collection Systems, Environmental Management & Remediation: Permitting, Wastewater: Planning, Wastewater: Pumping, Water/Wastewater: Wastewater, Wastewater: Wastewater Treatment Plants, Water/Wastewater, Engineering: Water/Wastewater