Employees at the City of Hendersonville strive to provide excellent customer service to citizens, visitors and businesses. During employee orientation, new hires are introduced to nine principles that guide the organizations’ actions that form the acronym PROACTIVE.
A department that has been exhibiting proactive steps to improve the service provided to customers, minimize impact to the environment and improve aging infrastructure is the Hendersonville Water and Sewer Department. This department is responsible for treating approximately 2.5 billion gallons of consumable water and 1.1 billion gallons of wastewater each year. In Hendersonville and Henderson County, more than 65,000 residents and businesses receive water service and more than 21,000 residents and businesses receive sewer service. Operating a utility of this size presents many opportunities to not only provide service for today’s water and sewer demand, but plan for long term growth and system improvements.
The City of Hendersonville was awarded a $150,000 North Carolina Department of Environmental Quality, Division of Water Infrastructure Grant to fund a portion of a Sanitary Sewer Asset Inventory and Assessment (SSAIA) project in 2016. The goals of this SSAIA conducted by Black & Veatch were to develop a well-documented, data-driven and forward-looking master plan. Additional objectives included conducting an overall assessment of the sewer system’s condition, providing guidance for future repairs and maintenance, prioritizing system improvements, adding data to the GIS database and providing an interactive planning tool for city staff. The SSAIA can be found at https://www.hendersonvillenc.gov/sanitary-sewer-asset-inventory-and-assessment-master-plan.
“Back in the 1920’s, in the beginning of the system, terracotta was used for sewer lines,” said Utilities Director Lee Smith. “It was a great material because sewer gasses don’t effect it.” Smith explained that the City of Hendersonville Sewer System currently uses PVC or ductile iron epoxy coated pipe when they are installing new lines, but much of the system is still the originally installed terracotta. The age of a system plays a big factor in the challenges it presents a utility, and it is one of the factors considered in a sewer system master plan.
Beyond the creation of a sewer system master plan that will guide future projects and improve the reliability of the system, staff has also taken the initiative to reduce the occurrences of sanitary sewer overflows (SSO).
SSOs are a release of untreated or partially treated sewage from a municipal sanitary sewer. The Environmental Protection Agency (EPA) states that SSOs occasionally occur in almost every sewer system across the nation, and they estimate there are at least 23,000 – 75,000 SSOs per year in the U.S. SSOs can be caused by a variety of factors such as sewer line blockages caused by fats, oils and grease (FOG), tree roots, sediment or other material buildup; excessive stormwater entering sewer lines during periods of heavy rainfall or flooding, referred to as inflow; equipment or power failures; and broken sewer lines or deteriorating sewer systems that are either installed improperly or poorly maintained.
SSOs occur infrequently in the area, but if they do, Hendersonville Water and Sewer is required to notify the North Carolina Department of Environmental Quality (NCDEQ) in accordance with NC General Statute Article 21 Chapter 143.215.1C. The EPA has acknowledged that a few SSOs may be unavoidable; those occurring from unpreventable acts of vandalism, some types of blockages, extreme rainstorms and acts of nature like earthquakes or floods. Knowing that a system can never be completely immune to SSOs, staff at Hendersonville Water and Sewer are taking steps to reduce their likelihood and improve the system as a whole.
Inflow and Infiltration Reduction
Sanitary sewer systems are designed to carry wastewater from toilets, sinks, dishwashers, and showers, but that is not the only water that enters systems. Inflow is stormwater that enters a sanitary sewer system through improper connections like downspouts, drains from driveways or basement sump pumps. Periods of heavy rains and floodwaters can also flow into the system contributing to high inflow levels. Infiltration occurs when groundwater enters the system through cracks or leaks in the sewer pipes. Reducing the amount of Inflow and Infiltration (I&I) is one of the most effective methods in reducing SSOs and reduces the amount of wastewater needed to be treated at the wastewater treatment plant.
Flow Meters and Monitoring
“We actively pursue sources of I&I,” said Andy Brogden, Water and Sewer Operations Manager, “and part of that process comes from monitoring the system levels.” Andy explained that crew members check flow monitors that have been installed in each of the eight sewer sheds. Data is compiled to get a baseline so that when spikes occur, staff knows there may be a problem that needs to be investigated. Beyond using flow metering data to address current issues, levels are tracked during dry weather and wet weather to help predict future flow levels and infrastructure needs.
“We also have a SCADA (Supervisory Control and Data Acquisition) system that allows facilities maintenance workers and the Wastewater Treatment plant to monitor the pumping stations,” said Brogden. “If we get a high level alarm we get someone headed that way to try and head it off before we have an issue.” Sewer pumping stations are inspected at least weekly in addition to the continuous monitoring.
Andy Brogden mentioned an example where staff noticed an anomaly that led to the discovery of an issue before it led to bigger problems. On Friday, December 28, 2018, our area experienced a large rain event that resulted in flooding across the county. After floodwaters had subsided, Garrett DeMoss, the Facilities Manager at the Wastewater Treatment Plant (WWTP), noticed the levels were not returning to normal as they typically would following a flooding event. Garrett alerted staff and crews began looking for issues. A manhole adjacent to Mud Creek had been compromised and creek water was pouring into the system. Crews were able to fill the manhole, stop the inflow of creek water and reroute the wastewater into an adjacent sewer line.
“When it was all said and done, this repair reduced about 2.5 million gallons of creek water from entering the sewer system each day,” said Brogden. Had the issue not been located and remedied, the large amount of inflow could have led to SSOs further down the system or overwhelmed the WWTP.
Additional I&I Reduction Methods
Finding I&I in over 180 miles of sanitary sewer lines can seem like finding needles in a massive haystack, but the crews have employed methods to strategically locate issues. Tim Sexton is the Utility Systems Supervisor in charge of preventative maintenance. Beyond making sure that at least 10% of the system is cleaned every year using a vacuum/jetting truck, Tim’s staff locate I&I using some fascinating methods.
One method is smoke testing. Non-toxic smoke is forced into the sewer pipes and the smoke that is observed in between manholes can identify cracks and holes in the sewer system. Regular inspections of manholes and lift stations are another way staff identify problems.
Another method is using portable iTracker sensors. These small, battery operated sensors are strategically placed in areas of the sewer system to record volumetric changes in wastewater between dry and wet weather events. The devices are Wi-Fi enabled and take readings every thirty minutes. Before the city began using these flow meters, measurements would have to be taken manually by visual inspections which were not as accurate and much more time consuming.
The city also utilizes closed-circuit television (CCTV) to inspect the internal condition of sewer lines. When there is an area that is suspect, or a potential problem has been identified using the aforementioned methods, the vacuum/jetting truck and CCTV crew are assigned to inspect the areas to see what is causing the blockage or leak. Once identified, repairs can be planned.
Wastewater Treatment Plant Upgrades
The City’s Wastewater Treatment Plant (WWTP) is permitted to treat 4.8 million gallons of sewage daily. Garrett DeMoss, WWTP Facilities Manager and Operator in Responsible Charge (ORC), reports that the plant averages 3 million gallons a day, but stormwater and the results of I&I during times of heavy rain raise the total. Beyond looking at ways to prevent SSOs from occurring on the collections side of the system, the City is also looking at improvements to the WWTP.
The City has purchased a generator that will be installed later this year to provide back-up power to the WWTP in the event of an outage. Additional upgrades include improvements to the SCADA monitoring system and replacing one of the two sand filters with an Aqua Aerobics Aqua-Diamond cloth media filter that can treat up to fifteen million gallons a day, far exceeding the capacity of what it took both sand filters to do. The remaining sand filter will be utilized when the Aqua-Diamond filter undergoes routine maintenance.
Also, funding has been set aside to evaluate the need for an equalization (EQ) basin. An EQ basin would allow the plant to store wastewater in a tank, slowing the system down and allowing the plant to take on more flow during periods of heavy rains. This could be a potential method on the WWTP side to help reduce SSOs.
“The City sees the big picture and is being proactive instead of reactive,” said Garrett DeMoss with regard to the generator and other upgrades. “We are an older plant—about twenty years old and a lot of the equipment is original. Much of it, like the blowers, run 24 hours a day.”
Excessive rainfall has an undeniable impact on sanitary sewer systems. Hendersonville’s sewer system, like so many other municipal sewer systems, are faced with challenges to handle large amounts of rain, fund system improvements and replace lines, some of which date back a century. 2018’s record setting rain totals further support the City’s decision to commission a sewer master plan and continue efforts to reduce I&I in the system.
“The Mayor and City Council have directed City staff to identify ways to reduce the number of SSOs within the sewer system,” said City Manager John Connet. “Our wastewater treatment plant upgrades, preventative maintenance programs and Sewer Asset Inventory and Assessment are just the first steps in meeting this directive.”
Sanitary sewer system improvements video
Photo: Inflow and Infiltration Technician Kenneth Page installs an iTracker flow monitoring sensor in a manhole as Line Maintenance Mechanic directs traffic