SEWER: Pressure Relief

The Western Carolina Regional Sewer Authority deploys innovative pumping technology to replace an old pump station and build capacity for growth.

For more than eight decades, the Western Carolina Regional Sewer Authority has protected the public health and provided infrastructure to support economic growth in South Carolina, even as state and federal environmental regulations grew tighter.

A population surge over the past 15 to 20 years challenged the authority with rebuilding the Tubbs Mountain Road No.1 pump station, one of the oldest in the wastewater network. Installed in the 1960s, the pump station was operating at maximum duty cycle and showing telltale signs of aging.

In the end, rather than rebuild the old pump station, the authority decided to build one that uses the latest in high-head, high- efficiency pump technology. The newly configured pump station delivers more capacity in a smaller footprint. Besides fulfilling the authority’s immediate needs, it provides capacity to accommodate growth.

Facing constraints

Celebrating 80 years of environmental stewardship, WCRSA aims to be a world-class organization and to have zero violations, while enhancing the caliber of life in its service area with high quality wastewater treatment services.

Founded in 1925 and based in Greenville in northwestern South Carolina, the authority is a special purpose district, serving more than 400,000 customers in Greenville County and parts of Anderson, Spartanburg and Laurens counties. Some 300 miles of major sewer trunk lines serve a 296-square-mile area. WCRSA maintains those lines and operates nine major wastewater treatment facilities.

As a participant in the U.S. EPA Capacity Management, Operation and Maintenance (CMOM) program, the authority’s in-house Inflow and Infiltration Abatement Program identified Tubbs Mountain Road No.1 pump station as its leading offender for sanitary sewer overflows (SSO) during rain events exceeding 1.5 inches in 24 hours. The pump station serves two sub-basins through 10-inch gravity trunk sewers and one sub-basin through an additional pump station with a 6-inch force main.

The authority made a commitment to correct the station’s problems within two years, while operating the site during rebuilding to minimize community inconvenience. “This process is very difficult — and can be very expensive,” says Tony Walton, collection system manager.

Trent Bowles, pump station supervisor, noted that space was a critical issue. “We’re in a developed area, so we had a very small footprint within which to work,” he says. “The site was already very compact, and the redesign imposed even tighter restrictions.”

Change of plans

Rogers & Callcott, the Green-ville-based engineering firm charged with addressing the challenge, originally drafted the new design to incorporate two 7- by 10-foot Gorman-Rupp pump stations, but that larger footprint didn’t use space in the most efficient manner. Reducing that footprint required a creative solution.

Rogers & Callcott found that in addition to aging, the Tubbs Mountain Road No.1 station was capacity-limited by the facilities that received its discharge. There-fore, rather than build a force main to the original discharge point, the engineers decided to reroute the 10-inch ductile iron pipe to a remote destination about two miles away, where the flow could discharge into a 20-mile-long gravity trunk sewer feeding the 29 mgd Mauldin Road wastewater treatment plant.

“The day that decision was made was a big day in western South Carolina, says Bowles. “This new pump station has removed a load from a regional pump station, and that is an additional benefit to the sewer authority.”

Proceeding with the plan, the team determined that the pump station needed a yield of 800 gpm based on current wastewater flow, projected growth, and projected infiltration and inflow. Calcula-tions showed that a total of 160 feet of dynamic head had to be overcome in the force main, plus the friction loss created at 800 gpm.

Because the required volume and pressure would push a single pump to the extreme, the original plan incorporated two T-series pumps. They would split the horsepower, enabling them to operate at a more efficient point on the pump curve and achieve the required head.

Next generation

However, while planning, the engineers learned of a new pumping technology that could maximize the station’s efficiency and performance, delivering up to 30 percent more capacity than the team previously expected. They chose an Ultra V Series pump, a new-generation solids-handling, self-priming centrifugal trash pump manufactured by the ­Gorman-Rupp Co.

The V6 can reach 1,950 gpm or 325 feet of head. Its 8-inch suction/6-inch discharge handles 3-inch solids. The pump is capable of 60 percent increased pressure and 40 percent increased flow over self-priming trash pumps of the same size, while substantially increasing overall pumping efficiency.

By using the V Series, WCRSA still has two pumps in effect, but each has a higher efficiency range and therefore uses less horsepower. Besides allowing more expansion capabilities for the same dollar, they also reduced the size requirements for the onsite generator.

Also key in the decision process was the ability to reduce the pump footprint, freeing space to enable the equipment to be positioned for safer, more comfortable routine maintenance, such as cleaning of the wet well.

“To integrate the new technology required a quick redirect and redesign, but we went to work, modifying drawings to accommodate the change in technology,” recalls Walton. The pump installed by WCRSA was the first of its kind in the state. The design allows more room to install equipment and do the work needed to keep the station functioning for 20 to 40 years.

System monitoring

The application incorporates a custom level controller, integrating air-release value technology. WCRSA uses a level control system integrated with the pump’s control panel. To communicate that data, WCRSA relies on a RACO dialer, used on all the authority’s pump stations for data monitoring.

“We also have an internal polling system,” adds Walton. “We use land lines at our facilities, and we poll the stations twice an hour to ensure communications. If we don’t receive a signal, then we know we’re experiencing a disruption on the system, and someone is dispatched instantly to rectify the failure.”

To WCRSA, the ability to monitor the pump stations is extremely important, as that allows the engineering team to focus on the repairs and line work associated with the pump stations and collection system.

With the new system, authority staff can diagnose problems whenever they occur simply by using gauge readings. WCRSA provides all personnel with ongoing courses on the basics of centrifugal pumps, operation and maintenance, safety, and troubleshooting, enabling them to diagnose problems before they become acute.

Maintenance is a top priority. The pump station has one supervisor and three teams of an electrician and a mechanic. They are responsible for inspection, operation, and repair of 21 pump stations on each of three routes.

Added insurance

In all, the authority uses pumps from nine manufacturers throughout its collection system and 63 pump stations. To help ensure that any repairs are streamlined, WCRSA stocks critical spare parts. “Due to the inventory of parts available within 24-hours, our staff can quickly rectify any problem with simple maintenance in the field,” says Walton.

More than half the pump stations use Gorman-Rupp pumps. “By having that amount of experience with the Gorman-Rupp pumps and pump stations, we benefit from our familiarity with the technology and the company, and troubleshooting and service are easier,” Walton says.

Diligent maintenance helps ensure that WCRSA provides reliable, cost-effective service to its customer. And the creative design of the replacement pump station will help the authority accommodate growth cost-effectively for years to come.

About the Author

Barry Harms, P.E., is a sales engineer with Tencarva Machinery Co., a regional pump and compressor distributor in Greensboro, N.C.



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