July 2013 - June 2014 annual report on collection, treatment and recycling of wastewater and biosolids (expanded version)

Links to sections below:   Highlights  Improvements at our Wastewater Treatment Plant  Causes of overflows from sewers  Our work to prevent overflows  Please help prevent wastewater overflows  Safe disposal of medication  Wastewater treatment  Quality of our treated wastewater  Sewer system  Biosolids treatment and recycling  Our reclaimed water system  Questions or comments? 


We surpassed the water quality standards for our Mason Farm Wastewater Treatment Plant (WWTP). The phosphorus level in our treated wastewater was 13% below the regulatory limit and nitrogen was 60% below the limit. Limiting phosphorus and nitrogen is important for water quality because they promote the growth of algae, which reduce water quality and make lake water harder to treat for drinking purposes.

We treated and recycled an average of 3.5 tons dry tons of wastewater biosolids per day. Our Class A biosolids 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 are making $10 million of improvements at our WWTP to reduce electricity use by about 20% ($120,000 annual savings), enhance our treated water quality and further eliminate off-site odor. We expect the improvements will be complete in the fall of 2014, in advance of the December 31, 2014 deadline to which OWASA committed in 2009.

There were 6 overflows from our sanitary sewers. The overflows totaled an estimated 17,013 gallons or a fraction of one percent of total wastewater volume (2.237 billion gallons).

Below: Installation of improvements in one of our biological treatment tanks. The "bubble diffusers"  provide oxygen needed by microorganisms in the tank when it is full of wastewater in normal operation. The mixer distributes air in the tank when full of wastewater.

Improvements at our Mason Farm WWTP

In April 2013, we began a $10 million project at our Mason Farm plant which will:

  • Reduce electricity use at the plant by about 20% through more efficient biological treatment equipment. The energy efficiencies will save about $120,000 annually and reduce greenhouse gas emissions from generating electricity for OWASA’s use.
  • The NC Clean Water Revolving Fund is providing a 20-year no-interest loan of about $6.5 million to support the energy efficiency improvements. Compared to issuing bonds, the no-interest loan will save about $1.7 million in interest costs, or an average of $85,000 annually.
  • Minimize off-site odor from the WWTP. The contractor will cover additional treatment tanks at the WWTP and add equipment to clean up foul air from the tanks. The improvements are the latest phase of work needed to meet OWASA’s goal of eliminating off-site odor from the WWTP.

In late August, we resumed providing tours at the WWTP. To arrange a tour or get more information, please contact us at 919-537-4289 or aradcliffe@owasa.org

The wastewater collection (sewer) system

We maintain 338 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. We maintain about 10,500 manholes.

In 2013-14, our sewer maintenance work included:

  • 24 sewer repairs
  • 80 manhole repairs
  • Cleaning 116 miles of sewers
  • Inspecting 38 miles of sewers with a videocamera
  • Mowing 100 miles of easements

Causes of overflows from sewers

When a sewer is damaged, when the 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 and towels.

In 2013-14, our wastewater system handled about 2.237 billion gallons, so the estimated volume of wastewater spills (17,013 gallons) was a small fraction of one per cent of total wastewater.

Our work to prevent wastewater overflows

We inspect the inside of our sewers with video cameras to find blockages, damage and leaks. When leaks allow stormwater and/or groundwater to get into a sewer, the extra water can exceed the pipe’s capacity and result in an overflow from manhole(s).

In some places, we test for leaks and cracks in our sewers by putting non-toxic smoke into the pipes to see where the smoke comes out.

We periodically clean sewers to remove blockages by fat, oil, grease, roots, debris, etc.

We fix cracks in our sewers to keep rainwater and groundwater from getting in and wastewater from leaking out.

We put special dishes under manhole covers to help keep out stormwater.

In some places, we reseal the inside of a sewer with a special plastic that hardens after it is put inside a sewer pipe.

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.  In 2013-14, we did not replace or renew any sewers but began the planning and design of projects planned for the coming year. A contractor hired by OWASA checked the condition of 16.1 miles of sewers in 2013-14. 

Please help prevent wastewater overflows


Residents can help prevent overflows and protect the environment and public health by properly disposing of routine amounts 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 recycling@county.orange.nc.us.)

Restaurants and related businesses are required to install and maintain grease traps. 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.

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 to do 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, send an e-mail to info@owasa.org and/or click here for information about our off-street sewer lines and easements, and where we may allow some kinds of trees and other plants in the outer part of an easement.


Our sanitary sewer system is not designed to handle trash and debris, which can cause blockages and overflows. For example, baby wipes and other hygienic wipes 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 at 919-968-4421 (24-hour phone line).


If you notice an overflow from OWASA sewer or a private sewer service line, please contact us 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.

Safe disposal of medication

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. 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 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.

Wastewater treatment

Our wastewater treatment process includes:

  • Removing solids (which are separated treated and recycled, as discussed below) in settling tanks;
  • A biological process, in which bacteria and other microorganisms consume pollutants;
  • Filtration to remove very small particles not removed in settling tanks;
  • Using ultraviolet light to kill pathogens; and
  • Adding oxygen, which is important for fish and amphibians in waterways that receive our treated wastewater.

Quality of our treated wastewater (results from laboratory testing)

What do we test for?

Phosphorus and nitrogen are fertilizers which promote the growth of algae. Algae in a lake will use up oxygen when they die and decompose, and excessive algae 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-blood animals, but some strains of these bacteria may cause serious illness.

Carbonaceous biological oxygen demand refers to the extent to which organic matter consumes oxygen in water, thus reducing the oxygen available to fish and amphibians in a creek, stream, lake, etc.

Oxygen dissolved in water is essential for fish in water such as a creek, stream or lake.

Ammonia (like chlorine) is poisonous to fish and amphibians, which can absorb 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 may be harmful to fish, etc.

Notes about the table below:

  • PPM means parts per million: ppm. One part per million is like a penny in $10,000.
  • CFU/100 ml means Colony Forming Units 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 2013-14 (average unless otherwise noted)



Maximum of 10,188 lbs.

8,887 lbs. (total)

13% below the limit


Maximum of 409,448 lbs.

162,855 lbs. (total)

60% below the limit

Fecal coliform bacteria

Maximum of

200 CFU/100 ml

2 CFU/100 ml

99% below the limit

Dissolved oxygen

Minimum of 6 ppm

8.7 ppm

43% above the minimum

Carbonaceous biological oxygen demand


summer: 4 ppm

winter: 8 ppm


Less than 2 ppm

Less than 2 ppm


50% below the limit

75% below the limit



summer: 1 ppm

winter: 2 ppm


Less than 0.1 ppm

0.47 ppm


90% below the limit

76% below the limit

Suspended solids

Maximum of 30 ppm

Less than 2.5 ppm

92% below the limit


Range of 6 to 9

Range of 6.4 – 7.5

Meets standard

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. OWASA has a State-approved allocation of Jordan Lake water which we can use in severe droughts and operational emergencies

Biosolids treatment and recycling

What are biosolids and why are they recycled?

Biosolids are the solids produced in wastewater treatment processes. Biosolids can be recycled as a soil additive because they include nutrients such as phosphorus and nitrogen, which improve the fertility of soil; and other organic matter which holds moisture in the soil and improves its structure.

Our WWTP produces an average of 3.5 “dry tons” of biosolids per day.  (A dry ton is the weight of solids without considering the weight of water that remains with biosolids after they are partly dewatered.)

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 30 days.

How are biosolids recycled?

Most of our biosolids are recycled in liquid form on local farmlands approved by the State. Biosolids include nitrogen and phosphorus (the key ingredients in fertilizers), so they are a resource for farmers growing crops for non-human consumption. We do not charge farmers for bringing biosolids to an approved farm site.

We have never recycled biosolids on farmland in watershed critical areas designated by the State. In June 2008, we stopped biosolids recycling on two farm properties designated by Orange County as watershed critical areas in the Eno River watershed in north Orange County.

Some of our biosolids are dewatered to the consistency of moist soil and mixed with other organic material at a composting facility in Chatham County. The composting facility produces a soil additive used in landscaping. 

What State and Federal regulations apply to biosolids?

Federal and State regulations limit the levels of various metals in biosolids, and the rates at which biosolids can be put on farmland to help grow crops for animal consumption. The amount of biosolids that can be applied to a field depends on the nitrogen level in the biosolids and ability of a crop to use nitrogen. 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

Our Class A biosolids 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 2013– June 2014); average unless otherwise noted

Difference between EPA limit and OWASA

Fecal coliform bacteria

1,000 CFU per gram

133 CFU (maximum)

- 87%


17 ppm

0.45 ppm

- 97%


39 ppm

0.59 ppm

- 98%


41 ppm

less than 2 ppm

- 95%


300 ppm

9 ppm



1,500 ppm

273 ppm



2,800 ppm

713 ppm



420 ppm

13 ppm




9 ppm



36 ppm

3 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 affects our revenues and is a factor in our water rates. However, conservation 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 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 of rcw service. In June 2010, St. Thomas More School and Church began using RCW to irrigate athletic fields.

From July 2013 through June 2014, the University and UNC Health Care used about 236 million gallons of RCW, or about 29% of the University’s overall water use.

Questions or comments?

If you have questions or comments about wastewater or biosolids collection, treatment and recycling, please contact us at 919-968-4421 or info@owasa.org.