Odor elimination program at the Mason Farm Wastewater Treatment Plant

In March 2004, the Chapel Hill Town Council approved a Special Use Permit (SUP) Modification for the upgrade and expansion (from 12 to 14.5 million gallons per day) of the Mason Farm Wastewater Treatment Plant (WWTP).

The OWASA Board of Directors also adopted in 2004 a resolution reaffirming OWASA’s goal of having no off-site objectionable odors from the WWTP. 

The SUP Modification requires that OWASA eliminate off-site odor from the WWTP to the satisfaction of the Council and regularly report to the Council on the progress of the off-site odor elimination program.  

Here is a link to our most recent quarterly report to the Town of Chapel Hill. Information on the odor elimination program begins on page 7 of the report.

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

Completed improvements                           Clarifier After Odor Filter Install

Since 2000, the community has invested about $9 million in  odor elimination improvements. Annual operating and maintenance costs for odor elimination are about $200,000.

Major completed projects 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 the "headworks" (where wastewater enters our plant) and treating exhaust air from the headworks;
  • Covering and treating exhaust air (with carbon filters) at the influent and effluent splitter boxes leading to and from the primary settling tanks ("clarifiers"), tanks at the intermediate pump station, aeration basin influent channel, and all three primary settling tanks.
  • Covering and treating exhaust air from 10 of the plant’s 16 biological treatment tanks. This project began in the spring of 2013 and was completed in August 2014. The cost was about $2 million.