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Odor Elimination Program


In 2004 OWASA was required to apply for and receive a Special Use Permit (SUP) Modification from the Town of Chapel Hill for the proposed upgrade and expansion (from 12 to 14.5 million gallons per day) of OWASA’s WWTP. In order to gain approval of the SUP, the OWASA Board adopted a Resolution reaffirming OWASA’s goal of no off-site objectionable odors from the WWTP. The SUP Modification was then approved by the Chapel Hill Town Council on March 1, 2004, stipulating a requirement that OWASA eliminate off-site odor from the WWTP to the satisfaction of the Council and that OWASA regularly report to the Council on the progress of its off-site odor elimination program.  Here is a link to our most recent Quarterly Report to the Town of Chapel Hill.

 To report odor from our Mason Farm Wastewater Treatment Plant, please call 919-537-4376 at any time.

Work Already Accomplished                           Clarifier After Odor Filter Install

OWASA has invested extensively in its program to eliminate off-site odors at the WWTP. Capital investment to date totals approximately $6.6 million, and the annual operating and maintenance costs for odor control are currently about $124,000.

Major projects already completed include:

  • Four  studies to assess and determine the appropriate remedial actions for odor sources at the WWTP;
  • Construction of a biofilter to treat exhaust air from the wastewater solids handling facility;
  • Covering the solids storage basins and treating the exhaust air through a scrubber;
  • Establishing an in-house odor monitoring program, including installation of hydrogen sulfide (H2S) monitors at various locations for automated monitoring and an alarm system for odors related to H2S; and
  • Covering and treating exhaust air from the new headworks structure;
  • Covering and treating exhaust air (with carbon filters) at the influent and effluent splitter boxes leading to and from the primary clarifiers, intermediate pump station wet wells (#1 and #2), aeration basin influent channel, and all three primary clarifiers.

Remaining Work

The final capital project identified as necessary to prevent objectionable odors from leaving the perimeter of the WWTP involves covering and treating exhaust air from 10 of the plant’s 16 aeration basins (Phase III odor control improvements). This project began in the spring of 2013. In September 2009, the OWASA Board adopted a resolution committing to complete the Phase III Odor Control Project as soon as practical but no later than December 31, 2014.  

Upon completion of the Phase III project, OWASA’s capital investments in odor control will total about $10.4 million. Annual operating costs are projected to be $204,000.