Overview
Jan. 12, 2005
The Town of Cary leads the state in preserving and protecting our natural resources – from wastewater facility operations and stream buffers to open space preservation, water conservation, reuse of water for irrigation, and wastewater treatment sludge handling.
In this regard,
Town staff responded to a
request from the U.S. Environmental Protection Agency for public
comment on proposed rulemaking regarding the use of “blending”
in the wastewater treatment process.
Read more on what the EPA says about blending of effluent at publicly-owned sewage treatment plants.
While the Cary Town Council has not adopted a policy on blending, the Town’s wastewater operations staff did file comment with the EPA. This comment gave the technical, practical opinion of professionals tasked with handling the complex, system-wide issues that can develop during extreme wet weather – from raw sewage backups and overflows to loss of plant treatment capacity from overwhelming storm water flows.
Operations Guiding Principles
With regard to wastewater treatment practices, the Town of Cary does not support the release of untreated waste into waters or onto land. The Town of Cary is committed to continuing to meet all requirements of its discharge permit, including those that set safe release levels for bacteria and pathogens back into streams and creeks following the wastewater treatment process.
The Town of Cary also supports using flow equalization as a primary mechanism for dealing with wet weather situations and does so at its North Cary and South Cary Water Reclamation facilities.
However, if given the choice in an emergency of (1) having raw sewage back up, overflow our sanitary sewer system, and go into our rivers and creeks, or (2) removing the solids and disinfecting the remaining water to meet all requirements of our discharge permits before the treated water is released (commonly referred to as blending), the Town of Cary chooses the latter.
Protecting Public Health
The discharge permit at each of Cary's wastewater facilities allows no more than a monthly average of 200 colony counts per 100 milliliters of fecal coliform bacteria. The fecal coliform bacteria are selected by water quality regulators as the indicator organism for disinfecting treated wastewater because they are the most persistent and most harmful of such organisms within the water environment.
The disinfection step of the treatment process is responsible for killing bacteria and pathogens. It is never skipped in Cary under any circumstances, including extreme wet weather. Cary treatment plants always meet required disinfection levels, whether there are normal plant operations or wet weather related peak flow operations. The process always ensures that the proper disinfection is achieved.
Treatment Process at a Glance
Step 1 – Coarse
screening to remove large solids
Step 2 – Grit and grease removal
Step 3 – Biological nutrient removal
Step 4 – Settling of solid residuals from biological treatment
Step 5 – Filtration of fine solids
Step 6 – Disinfection with ultraviolet light to kill remaining
bacteria and viruses
Read more about
Town
of Cary wastewater treatment operations.