Wastewater and biosolids management report for July 2014 - June 2015 (expanded version)

Links to sections below:


  • We surpassed the water quality standards for our Mason Farm Wastewater Treatment Plant (WWTP). The phosphorus level in our treated wastewater was 57% below the limit and nitrogen was 71% below the limit. Limiting phosphorus and nitrogen is important for water quality because they promote excessive growth of algae, which reduces water quality and makes water more difficult and expensive to treat for drinking purposes.
  • We treated and recycled 1,597 dry tons of wastewater biosolids. Biosolids are solids which we separate from wastewater and treat so that they can be recycled in agriculture or landscaping. Our Class A biosolids continue to meet the U.S. Environmental Protection Agency’s (EPA’s) standards for Exceptional Quality.
  • In September 2014, we completed $10.4 million of improvements at our WWTP which reduced electricity use per gallon of wastewater by about 30% ($250,000 annual savings); will help us meet future standards for treated wastewater; and further eliminated off-site odor.
  • There were two overflows from our sanitary sewers. The overflows totaled an estimated 1,100 gallons or a fraction of one percent of total wastewater volume (2.95 billion gallons).
  • In 2014, we began a review of opportunities to reduce biosolids management costs while ensuring sustainable use of biosolids. A key issue in this study is whether OWASA should continue applying liquid biosolids to approved farmlands.

Our Wastewater Treatment and Biosolids Recycling team at the Mason Farm Wastewater Treatment Plant. Top row, left to right: Jed Clark, Rod Dail, Johnny Johnson, Ken Bailey, Greg Monschein, Alex Braxton, Jay Lowe, Michael Wolfgang, John Kiviniemi, Nathan Barnhardt, James Dodson. Bottom row: Ronnie Williams, Sandra Bradshaw, Emily Caperton, Dirk Cartner, Ronnie Weed and David Hartshorn. Not pictured: Todd Norman, Cory Kirkland, Stephen Long and Charles Williams.

Preventing wastewater overflows

Causes of Overflows from Sewers

When a sewer is damaged, the flow in a sewer is blocked or if the flow in a sewer exceeds pipe capacity, the result is an overflow of untreated wastewater.

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.

What we do to prevent overflows

  • We clean sewers to remove blockages by fat, grease, roots, etc. In 2014-15, we cleaned about 86 miles of sewers, or one fourth of the system.
  • We inspect sewers to find blockages, damage, cracks and leaks. In 2014-15 we inspected about 11 miles of sewers.
  • We test for leaks, cracks and unauthorized connections to our sewers by putting non-toxic smoke into the pipes to see where smoke comes out.
  • We fix cracks in sewers to keep out rainwater and groundwater.
  • We mow and clear our “easements” to help keep tree and shrub roots from growing into and blocking sewers, and to maintain safe, timely access. A sewer easement is an area where we can install and improve sewer lines; inspect, maintain and repair them; and keep clear access. For more information about easements, please click here.
  • To ensure adequate capacity, structural integrity and reliable operation, we rehabilitate or replace sewers and manholes where needed.

In 2014-15, we spent about $1.7 million to replace or renew 2.7 miles of sewers and related manholes to help prevent wastewater overflows, etc. In the photo above, a contractor is resealing the inside of a sewer by putting a special kind of liner into the sewer via manholes. The liner inside the pipe is then hardened or "cured" with steam heat.

Proper disposal of fat, oil and grease

Please dispose of household fat and grease with trash that goes to a landfill. Please recycle used cooking oil at the:

Orange County Household Hazardous Waste Program

1514 Eubanks Road (north side of Chapel Hill), Chapel Hill, NC 27516 

919.932.2989 or recycling@orangecountync.gov

Restaurants and related businesses are required to install grease traps and to have them pumped out on a regular basis.

Tree and shrub roots can grow into sewers and cause overflows

As noted above, tree and shrub roots can grow into cracks in sewers and form a dense mass which blocks the flow of wastewater.

Please help us keep roots out of sewers and maintain clear access through our easements so we can work safely and efficiently in maintaining, repairing, inspecting, etc. our sewers. 

Before planting trees or shrubs, installing a fence, etc. in an OWASA easement, and to find out whether there is an OWASA sewer or easement on your property, please contact us at 919.537.4292 or info@owasa.org. We may allow some kinds of plantings in the outer part of an easement. We would need to receive a planting plan from you as the first step. 

Keeping trash and debris out of sewers

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, even those called “flushable,” should not be flushed. 

For information about disposal of personal hygiene wipes and pet litter bags, please click here.

For information about what should and should not go into our sewer system, please click here.

Reporting wastewater overflows and odor

If you notice 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.

Randy Horton was promoted to Manager of our Wastewater Collection and Water Distribution Systems in April 2015. Randy has worked at OWASA since we began serving the community in 1977, and he had also worked at the University’s water utility starting in 1975.

Biosolids Treatment and Recycling

What are biosolids and why are they recycled?

Biosolids are the solids separated from wastewater then treated at our WWTP. Biosolids can be recycled to improve soil because biosolids include 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 about 4.4 “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?

We break down biosolids in a biological process (“digestion”) and heat them to about 140 degrees to kill pathogens.

How are biosolids recycled?

We apply about half of our biosolids in liquid form on farmlands approved by the State. Biosolids include nitrogen and phosphorus (the key ingredients in fertilizers), so they are a resource for farmers. The other half of our biosolids are dewatered and mixed with other organic material at a private composting facility.

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, phosphorus, nitrogen, metals, etc. 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.

In the table below, PPM means parts per million. One part per million is like a penny in $10,000. CFU means colony forming units.

Substances we tested for in biosolids EPA Limit for Exceptional Quality Biosolids OWASA average except as noted
Fecal coliform bacteria 1,000 CFU per gram 121 CFU (max.)
Mercury 17 ppm 0.7 ppm
Cadmium 39 ppm 0.5 ppm
Arsenic 41 ppm under 2.4 ppm
Lead 300 ppm 4.3 ppm
Copper 1,500 ppm 260 ppm
Zinc 2,800 ppm 771 ppm
Nickel  420 ppm 13.9 ppm
Molybdenum n/a 7.7 ppm
Selenium  36 2.5 ppm


Our Wastewater Treatment Process

  • Solids are removed in settling tanks;
  • Bacteria and other microorganisms consume pollutants;
  • We use filters to remove very small particles not removed in settling tanks;
  • Ultraviolet light disinfects the wastewater; and
  • We add oxygen to benefit fish and amphibians in waterways receiving treated wastewater.
  • In treating wastewater for reuse in our Reclaimed Water System, we also add chlorine in the form of bleach to minimize bacteria.

Some treated wastewater is used for non-drinking purposes via our reclaimed water system. Most treated wastewater is recycled at Morgan Creek near Finley Golf Course. Morgan Creek flows to Jordan Lake, a water supply for several communities in the region. OWASA has a State allocation of Jordan Lake water for severe droughts and operational emergencies.

Quality of our treated wastewater

In the table below, PPM means parts per million. (One part per million is like a penny in $10,000). CFU means colony forming units (the required reporting unit for the bacteria item below).

In the table below, PPM means parts per million. (One part per million is like a penny in $10,000). CFU means colony forming units (the required reporting unit for the bacteria item below).
Measure of treated wastewater quality  Limit (maximum level unless otherwise noted)  OWASA average (except as noted)
Phosphorus -- total pounds for the year 10188 lbs. 4388 lbs.
Nitrogen -- total pounds for the year 409448 lbs. 119900 lbs.
Ammonia                                                  summer 1 PPM <0.10 PPM
Ammonia                                                  winter 2 PPM 0.33 PPM
Carbonaceous biological oxygen demand     summer 4 PPM <2 PPM
Carbonaceous biological oxygen demand     winter 8 PPM <2 PPM
Dissolved oxygen 6 PPM (minimum) 8.7 PPM
pH (measure of alkalinity/acidity on scale of 1 to 14) between 6 and 9 range of 6.8 to 7.4
Fecal coliform bacteria --CFU per 100 milliliters 200 CFU 2 CFU

Our Wastewater Collection (Sewer) System

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

Our sanitary sewer system is separate from stormwater facilities, which handle rainwater which has fallen on streets, buildings, other paved areas, landscaped areas, etc.

Our Reclaimed Water System

Reclaimed water (RCW) is highly treated wastewater which can be used for various non-drinking purposes. Using reclaimed water reduces the need to use water from our reservoirs. From July 2014 - June 2015, the University and UNC Healthcare used about 239 million gallons of RCW, or about 30% of the University’s overall water purchases from OWASA.

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; drop box days and hours: Monday-Friday, 9 AM to 5 PM. For more information: 919.968.2760.
  • Carrboro Police Department: 100 North Greensboro Street (at the Town of Carrboro's Century Center); drop box days and hours: Monday-Friday, 8:30 AM to 5 PM. For more information: 919.918.7397.

For a Tour of Our Mason Farm WWTP

We would appreciate the opportunity to provide a tour of our WWTP for your neighborhood or civic group, class, etc. Please contact us at 919.537.4289 or info@owasa.org to arrange a time and date.

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.