Sanitary Sewer System Improvements


  • Local Governments
  • Public Utilities


  • Construction
  • Wastewater


  • McHenry, Illinois

This work consisted of improvements to the City’s sanitary sewer system to optimize performance of the City’s two waste water treatment plants, Central and South, while operating within the current limits to the NPDES permits. The project generally consisted of pump station improvements at the Central Plant, force main construction between Central and South Plants, and the addition of a raw sewage screen unit and solids handling upgrades at the South Plant.

Since the South plant currently has excess capacity and the Central plant is nearing the end of its design life, the installation of 6,980 linear feet of 14” force main allowed raw sewage to be pumped from the Central plant directly to the South Plant. Construction of the forcemains utilized both open trench and directional drilling methods. Directional drilling was used to facilitate forcemain installation across the following sensitive areas:

  • 1.) River
  • 2.) Golf course
  • 3.) Wetland
  • 4.) High point of a hill to eliminate air release stations in farm field

A new primary transfer pump and VFD was also installed at the raw sewage pump station at the Central Plant to replace an existing pump and VFD. The raw sewage pump flow rate will be controlled by the operators at the South Plant through monitoring equipment and the existing SCADA system.

In addition to the proposed conveyance system employing the 14” diameter force main, approximately 3,206 linear feet of 24” diameter forcemain for future use was installed in all open cut areas. When put into service, the 24” force main will connect to an entirely new pump station constructed as a part of the FPA long term plan to completely retire the Central Plant.

Improvements included 7,360 linear feet of 6” diameter sludge main that will transfer sludge from the aeration basins at the Central plant to the South Plant. The improvements also eliminated the primary clarifiers at the Central Plant and now all sludge stabilization and dewatering will take place at the South Plant. The improvements to the City’s South Plant to treat the sludge consisted of new WAS transfer pumps, new gravity belt thickener (GBT), GBT feed pumps, thickened sludge pumps, belt filter press (BFP), and BFP feed pumps, installation of a GBT that was relocated from the Central plant, upgrades to existing BFP’s at South Plant, addition of thickened sludge discharge piping to existing digesters and other miscellaneous pump and piping upgrades.

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