Detailed report on wastewater and biosolids management in 2017-18


  • 2018 was the ninth consecutive year in which we met all standards for the quality of our treated wastewater.
  • The phosphorus level in our treated wastewater was 75% below the regulatory limit and nitrogen was 70% below the limit. Limiting phosphorus and nitrogen is important for water quality because they promote growth of algae, which reduce water quality and make water more difficult and expensive to treat for drinking purposes.
  • There were three overflow events from our sewer system. The estimated volume of 768,740 gallons was a fraction of 1% of the 3.0 billion gallons of wastewater we managed.
  • Biosolids are solids which we separate from wastewater and treat so they can be recycled to enhance soil for agriculture or landscaping. All of our biosolids are Class A and they meet the U.S. Environmental Protection Agency’s (EPA’s) standards for “Exceptional Quality.” Our biosolids have very low levels of pathogens and metals, as shown in this report.
  • We replaced or renewed 2.9 miles of sewers at a cost of  $3,200,000 in 2018-19 to help prevent overflows and maintain adequate capacity and structural soundness.

WASTEWATER TREATMENT (for an expanded view of the graphic below, please click here)


We invite you to watch our educational video on wastewater management. We welcome the opportunity to meet with community organizations and school classes to present the video and other information about our services.


We maintain 340 miles of sanitary sewers and operate 21 facilities where we pump wastewater uphill, but most of our sewers operate with the simple force of gravity.


When a sewer is damaged, when wastewater flow in a sewer is blocked or if the flow in a sewer exceeds the pipe’s capacity, the result is an overflow of untreated wastewater. Usually, overflows occur at a sewer manhole that is uphill or “upstream” of the area where a sewer is blocked. Many of our sewers are in public streets, but some sewers are in off-street areas where we have easements on private or public property.

An easement (please see additional information below) is an area where we have the right to install and maintain water or sewer lines; inspect, maintain and repair them; keep clear access; and do improvements.

What can block a sewer pipe and cause an overflow?

  • accumulations of fat, oil and grease. Fat and grease should be disposed of with refuse taken to a landfill, and used cooking oil should be recycled;
  • tree and shrub roots, which can enter a crack in a pipe then grow inside a sewer; and
  • trash or debris such as clothing, towels and personal hygiene wipes.

In 2018-19, our wastewater system handled about 3.0 billion gallons, an average of 8.2 million gallons per day. The estimated volume of the four wastewater spills (768,740 gallons) was a fraction of one percent of total wastewater we received.


To see our video on why and how we clean sewers, please click here.

  • We inspect the inside of our sewers with video cameras to find blockages, damage, cracks and leaks. If stormwater and/or groundwater enter a sewer, the extra water can exceed the pipe’s capacity and result in an overflow from manhole(s).
  • In 2018-19 we cleaned about 190 miles of sewers, or 54% of the system; and inspected about 30 miles with video cameras. We used a chemical to remove roots in 25 miles of sewers.
  • In some places, we test for leaks, cracks and unauthorized connections in our sewers by putting non-toxic smoke into the pipes to see where the smoke comes out. We fix cracks in our sewers to keep rainwater and groundwater from getting in and wastewater from leaking out.
  • We periodically clean sewers to remove blockages by fat, oil, grease, roots, debris, etc.
  • We put special liners under manhole covers to help keep out stormwater.
  • In some areas, we renew older sewers by relining them to keep out stormwater and groundwater, which otherwise could overload a sewer and result in a wastewater overflow from a manhole(s). Relining a sewer involves inserting a flexible liner through manholes into the sewer, hardening the liner with a special resin and heat, and then cutting holes where needed where private service lines connect to the OWASA pipe. Relining means less disruption to a neighborhood than conventional sewer replacement, which involves digging a trench several feet deep and placing pipes into the trench.
  • We normally mow and clear our easements once a year to help keep tree and shrub roots from growing into and blocking our sewers; and to maintain safe, timely access for normal maintenance and emergency responses to overflows.
  • We repair, renew and replace sewers to ensure adequate capacity, structural integrity and reliable operation. Renewal or replacement is done where repair is impractical or repair costs would be excessive. 



Residents can help prevent overflows and protect the environment and public health by disposing of household fat and grease with trash that goes to a landfill.

Please recycle cooking oil at the Orange County Household Hazardous Waste Program at 1514 Eubanks Road on the north side of Chapel Hill. (The Orange County Department of Solid Waste Management can be reached at 919-968-2788 or

Restaurants and related businesses are required to install grease traps and to have them pumped out on a regular basis. Waste grease is recycled by companies that clean out grease traps.


Before planting trees, shrubs, etc. in an OWASA sewer easement, please contact us about the kinds of shallow-rooted plants that may be allowed in the outer part of an easement, and to request OWASA’s approval of a landscaping plan. In some locations, we allow some shallow-rooted trees and other plants in the outer part of an easement.

Also, it is necessary to keep our easements clear of buildings and other structures so that we can have timely, safe access to our utility systems to do inspections, maintenance and repairs and when it is necessary to respond to a wastewater overflow.

Before you plan to do landscaping, install a fence, shed, etc. or pave an area near or over an OWASA water or sewer line, please contact our Wastewater Collection and Water Distribution System staff at 919-537-4292 or send an e-mail to You can get more information call phone or e-mail or by clicking here.


Our sanitary sewer system is not designed to handle trash and debris, which can cause blockages and overflows. For example, baby wipes and other hygiene wipes, even those called “flushable,” should not be flushed or otherwise put in our sewer system because they may cause blockages and overflows.

If you see someone other than OWASA personnel (or a contractor working for OWASA) opening or entering a sewer manhole, please contact us immediately at 919-968-4421 (24-hour phone line).


If you notice wastewater odor or an overflow from OWASA sewer or a private sewer service line, please contact us immediately at 919-968-4421 at any time so that we can stop the overflow from our sewer, or contact the property owner if a private pipe is leaking.


Pharmaceutical compounds in the water environment are a matter of scientific research regarding how they may affect people, fish, etc. If medications are flushed down a toilet or otherwise get into the sewer system, pharmaceuticals may get into a creek, river or lake that is a water supply or important aquatic habitat. Wastewater treatment plants, septic systems and drinking water treatment plants are not designed to remove pharmaceutical compounds.

Medication should not be flushed down the drain. The Chapel Hill and Carrboro Police Departments have drop boxes for safe disposal of liquid and pill medications that are expired, unused, or unwanted.  Liquid medications must be in the original container. Pills must be in the original container or a zip lock bag. New and used needles are not accepted.

Chapel Hill Police Headquarters: 828 Martin Luther King Jr. Boulevard (north of downtown Chapel Hill); drop box days and hours: Monday-Friday, 9 AM to 5 PM. More information:  919- 968-2760.

Carrboro Police Department: 100 North Greensboro Street (Century Center at the northeast corner of Greensboro and Main Streets in downtown Carrboro); drop box days and hours: Monday-Friday, 8:30 AM to 5 PM. More information: 919-918-7397.

QUALITY OF OUR TREATED WASTEWATER (results from laboratory testing)

What do we test for?

  • Phosphorus and nitrogen are nutrients which promote the growth of algae. Algae use up oxygen in the water when they die and decompose, and excessive algae can increase the cost and difficulty of treating lake water to turn it into drinkable water.
  • Fecal coliform bacteria are naturally present in the intestines of warm-blooded animals, but some strains of these bacteria may cause serious illness.
  • Carbonaceous biological oxygen demand refers to the extent to which organic matter chemically combines with oxygen in water and thus reduces the oxygen available to fish and amphibians in a creek, lake, etc.
  • Oxygen dissolved in water is essential for fish and other aquatic life in streams, lakes, etc.
  • Ammonia (like chlorine) is poisonous to fish and amphibians, which can absorb ammonia and chlorine into their blood via their gills.
  • Suspended solids are small solid particles that are carried (not dissolved) in water.
  • pH is a measure of alkalinity or acidity. Excessive alkalinity or acidity is harmful to aquatic life.

Notes about the table below:

PPM means parts per million. One part per million is like a penny in $10,000 pile of pennies.

CFU/100 ml means Colony Forming Units of fecal coliform bacteria per 100 milliliters of water.

pH is measured on a scale of 0 to 14 with 7 being neutral, 0 being most acidic and 14 being most alkaline.

Water quality measure


OWASA’s results

in 2018-19 (average unless otherwise noted)



Maximum of 10,188 lbs. for the year

2,595 lbs (total)

Full compliance; 75% below the limit


Maximum of 409,448 lbs. for the year

121,135 lbs (total)

Full compliance;

70% below the limit

Fecal coliform bacteria

Maximum of

200 CFU/100 ml

2 CFU/100 ml

Full compliance

Dissolved oxygen

Minimum of 6 ppm

8.2 ppm

Full compliance

Carbonaceous biological oxygen demand


summer: 4 ppm

winter: 8 ppm


Less than  2 ppm



Full compliance




summer: 1 ppm

winter: 2 ppm


0.06 ppm



Full compliance


Suspended solids

Maximum of 30 ppm

Less than 2.5 ppm

Full compliance


Range of 6 to 9

Range of 6.8 – 7.5

Full compliance


Treated wastewater not reused in our Reclaimed Water System is returned to the natural environment at Morgan Creek near Finley Golf Course. Morgan Creek flows to Jordan Lake, which is a water supply for the Towns of Cary, Apex and Morrisville and Chatham County and Durham County. OWASA has a State-approved allocation of Jordan Lake water which we can use in severe droughts and operational emergencies.


What are biosolids and why are they recycled?

Biosolids are the solids separated from wastewater and then treated at out WWTP. Biosolids can be recycled as a soil additive because they include phosphorus and nitrogen, which improve the fertility of soil; and other organic matter which holds moisture in the soil and improves its structure.

How do we treat wastewater solids to convert them to recyclable biosolids?

In the biological, chemical and physical processes for cleaning wastewater, we remove solids. We treat the solids in a biological process called “digestion” in which solids are heated to about 140 degrees to kill pathogens. Biosolids treatment takes about 45 days.

How are biosolids recycled?

Our objective is:

  • to recycle about 75% of our biosolids in liquid form on farms approved by the State (we achieved 75% in 2017), and
  • to dewater and recycle about 25% of the biosolids with other organic material at a private composting facility in Chatham County which produces a soil additive for agriculture and landscaping. 

What State and Federal regulations apply to biosolids?

Federal and State regulations limit the uses of biosolids, the allowable levels of various metals in biosolids and the rates at which biosolids can be recycled on farmland to help grow crops for animal consumption. The amount of biosolids that can be put on a field depends on the nitrogen level in the biosolids, the ability of a crop to use nitrogen, and cumulative metals loading. Our biosolids are tested for bacteria and metals every 60 days. 

At OWASA land where we recycle biosolids, we test the groundwater three times a year.

Testing and quality of our biosolids

All of our biosolids are  Class A and they meet the U.S. Environmental Protection Agency’s (EPA’s) standards for “Exceptional Quality.”  Our biosolids have very low levels of pathogens and metals, as shown below. Notes on the table below:

PPM means parts per million. One part per million is like a penny in $10,000.

CFU means colony forming units.


EPA Limit for Exceptional Quality Biosolids

OWASA (July 2017 -June 2019); average unless otherwise noted

Fecal coliform bacteria

1,000 CFU per gram

117 CFU (maximum)


17 ppm

0.48 ppm


39 ppm

0.91 ppm


41 ppm

2.75 ppm


300 ppm

6.75 ppm


1,500 ppm

302 ppm


2,800 ppm

799 ppm


420 ppm

14.5 ppm



5.8 ppm


36 ppm

3.12 ppm

Our reclaimed water system

Reclaimed water (RCW) is highly treated wastewater which can be used for various non-drinking purposes including cooling tower make-up water at chiller plants, irrigation and flushing non-residential toilets. Using reclaimed water reduces the need to draw water from our reservoirs.

Like other forms of conservation, reclaimed water use reduces the need to use water from our reservoirs, makes us better prepared for future droughts, reduces the future need for and costs of expanding our water system capacities, and reduces greenhouse gas emissions due to the use of conventional energy to pump and treat lake water and drinking water.

Like other wastewater, RCW undergoes biological treatment, filtration and disinfection with ultraviolet light. We also add chlorine to RCW for further disinfection while RCW is stored and carried through the RCW pipe system

Our RCW system went into operation in April 2009, initially to serve certain University facilities which had used drinking water for non-drinking purposes. The University and State and Federal grants funded construction of the RCW system. The University pays monthly fees to cover the costs to maintain and operate the reclaimed water system. In June 2010, St. Thomas More School and Church began using RCW to irrigate athletic fields.

In 2018-19, the University and UNC Healthcare used about 0.8 million gallons of RCW, or about one-third of the University’s overall water use.

For a tour of our Mason Farm Wastewater Treatment Plant (WWTP)

We invite you to contact us and arrange a tour of our WWTP for your neighborhood or civic group, class, etc. Please contact us at 919-537-4205 or to arrange a time and date for a tour, which normally takes an hour or less.

Questions or comments?

If you have questions or comments about wastewater collection and treatment, biosolids treatment and recycling, or reclaimed water, please contact us at 919-968-4421 or .