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Headworks Upgrade at the Easterly WWTF

A 2007 Administrative Consent Order directed the City to construct grit removal facilities and upgrade the screening equipment at the Easterly WWTF. The facility serves all residential and commercial sources including the system’s combined sewer portions. Long-term problems with the lack of grit removal facilities had caused the primary clarifiers to clog during wet weather events, providing less than optimum treatment.  Hilly topography necessitated that the grit removal system be able to handle large grit loads during wet weather events. An aerated grit chamber, with a large grit hopper sized for the projected peak grit loading, and a clamshell and hoist, was selected for grit removal.  

Mahr screens by Headworks, Inc. were selected as the new influent screening equipment. The traveling rake design has a very high screening removal capacity, capable of handling elevated combined sewer loadings.  The 3/8” bar spacing, as compared to the existing screens with 1-1/2" and 3/4" spacing, will substantially reduce downstream problems. In addition, the low headroom requirements of the Mahr screen were a good fit for the existing screening area. 

The upgrade also includes two new septage receiving stations which will include a keypad ID system with an automated ticketing system based on a new flow measurement system.  New odor control facilities are also upgrade components to serve the aerated grit, screening, and septage receiving facilities.

Wright-Pierce and the City have worked closely with the DEP and EPA to expedite the implementation schedule.

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Project Highlights

Background

  • Easterly WWTF treats average flows of 9.4 MGD, maximum monthly flows of 16 MGD, and peak hourly flows of 40 MGD.
  • Combined sewer system set in hilly topography.
  • Serves as regional septage receiving facility.

Challenges

  • Severe grit loading during wet weather conditions that routinely caused primary clarifiers to clog.
  • Mechanical screens with large bar spacing and high maintenance requirements.
  • Limited hydraulic grade to accommodate new facilities.
  • Preferred location requires bypass piping.

Solutions

  • Aerated grit chamber with oversized hopper for grit storage and clamshell and hoist for grit removal.