Published October 2007

SEWER: Out of Sight, Always In Mind

By Suzan Marie Chin (page 36)

Derry Township Municipal Authority combines inspection and maintenance to keep the pipes flowing freely in the community known as Chocolate Town, USA.

A simple philosophy helps keep Derry Township Municipal Authority on the cutting edge of sewer maintenance technology:

“Just because it’s out of sight, it can’t be out of mind,” says Wayne Schutz, assistant manager of the authority, which serves the community better known as Hershey, Pa., or Chocolate Town, USA. “We’ve got a huge capital investment in our underground structures, and we have to pay attention to them.”

Like many older cities in the Northeastern United States, Hershey has many underground structures that need rehabilitation or replacement. Infrastructure inspection and maintenance is a top priority for Schutz and his team.

They keep the system operating smoothly with a coordinated program of sewer inspection and grouting and regular pipe cleaning. The program also includes an aggressive program of manhole rehabilitation using a spray-applied polyurethane product.

Diligent maintenance

Derry Township — the official name of what most people call Hershey — has a 150-mile wastewater collection system with facilities ranging from modern installations to 1927 vintage lines installed by Milton Hershey, founder of The Hershey Co., producer of chocolate bars, Hershey’s Kisses, and other popular candy and snack items. The system is primarily gravity-based, with 8- to 48-inch pipes made of VCP, ACP, DIP and PVC.

The DTMA maintains the collection system and treatment facilities that serve a population of 18,000, and a large tourist base. The authority’s proactive maintenance program begins with routine inspection and cleaning using a CCTV inspection and grouting vehicle made by Telespector Corp. and a Model 2001 combination sewer cleaning truck from Vactor Manufacturing.

The televising/grout unit and cleaning truck have teams of two members each who work in tandem with the goal of cleaning and inspecting the authority’s entire system every five to seven years. The inspection/grout rig is equipped with two tractor-mounted mainline cameras, a winch-style camera and a pushrod mini camera. The addition of a QuickView pole camera from Envirosight LLC has helped in manhole inspection and in documenting the existence or absence of flow through manholes when residents report blockages. The camera provides an accurate quick assessment of the infrastructure without confined-space entry or time-consuming mainline camera deployment.

Mainline survey findings are collected onboard the rig using WinCan pipe survey software by WinCan America using the NASSCO Pipeline Assessment and Certification Program (PACP) standard defect coding.

The collection department prioritizes its work based on inspection findings and typically divides defects into three categories:

• Requires attention immediately/soon

• Longer-range repair

• Monitor.

Once a group of repairs is compiled, they are given to the DTMA consulting engineer, who develops project plans and specifications and puts the work out for bid.

Another level

CCTV inspection crews do things a little differently than most agencies: They make air testing and follow-up joint grouting a standard procedure in the inspection routine. After a line is inspected, DTMA inspection crews use a simple air pressure testing apparatus by Cherne Industries Inc. to check each of the line’s joints.

Two inflatable 2-foot-long plugs (packers) are inserted to sit six inches on either side of the joint. The packers are then inflated, and air is pushed through a tube in one of the packers into the annular space until the pressure reaches 2 to 3 psi. If the pressure cannot be maintained for at least 30 seconds, the crew knows there is a potential leak.

In that event, they grout the joint immediately. Grout application is similar to air testing. The same equipment is used, and a second line in the packer is used to pump a liquid grout mixture made by Avanti International into the annual space under pressure. The applied pressure forces the grout out into the leaking joint, traversing around the pipe to form a collar on the outside of the structure.

The crew monitors the pressure, pumping grout until the pressure achieves a level that indicates leaks are filled and a collar is formed. The pressure is maintained for 30 to 60 seconds to set the grout. The packer is then deflated and removed.

Although grouting adds time to inspections, the benefits outweigh the extra expense. “As long as we’re inspecting, why not run a quick air test?” says Schutz. “We know if it fails the test, the line can conceivably leak. We can reduce I&I by taking these few extra steps, so in our opinion, it’s a very good investment.”

More than sewers

During sewer inspections, crews also visually inspect and record the health and integrity of some 3,000 manholes. A manhole failure poses a serious threat of I&I, in addition to which a crumbling manhole can lead to a sinkhole or a sewer blockage.

“A manhole is the portal to the system, making it easy to spot problems quickly,” Schutz says. “We absolutely want to address the needs of our structures before they reach either of these impact levels, and we do.” The majority of the township’s manhole issues have been in structures near force main discharges. There, hydrogen sulfide builds up, causing wall erosion.

After trying many forms of manhole rehabilitation, Schutz settled on a new technology presented by Abel Recon, a local contracting firm that had a long relationship with DTMA. Hap Witmer, general manager of Abel Recon, offered a spray-applied polyurethane product from Sprayroq Inc. “We knew Wayne had been looking for a ‘right fit’ solution for a while, so we did our homework before presenting Sprayroq as a potential answer,” Witmer says.

In the spring of 2006, DTMA contracted Abel Recon to rehabilitate 52 manholes with the spray-on material. Most were of brick construction and had hydrogen sulfide damage, minor infiltration, or typical age-related problems.

The rehab process

The manhole rehabilitation process involves cleaning and surface preparation, followed by product application. In the first phase, Abel Recon adjusted the rims on the 52 manholes to ensure that they were properly set. Crews did this by breaking the rims loose, removing them, elevating them to grade, setting the rims on the angle of the grade with grade rings or bricks as needed, and setting them with hydraulic cement.

The crew then pressure washed each manhole at 3,500 psi. Next they applied a quick-setting hydraulic cement to profile the clean surface, creating a smooth and even-textured area for treatment. By properly timing the cleaning/preparation with sealant application, Abel Recon was consistently able to complete four to five manholes per day.

During the preparation period and the spray process, the manhole and incoming lines remain in service. The flows from the incoming lines are diverted using a bypass system. Before application begins, torpedo heaters and ventilators are placed in the manhole for 15 to 20 minutes to dry and heat the structure to at least 40 degrees F.

Once the structure is ready, an application specialist suited up for confined-space entry can apply the spray from the bottom of the structure. If necessary, a harness seat can move the specialist up or down from the surface.

For the DTMA pilot project, Abel Recon applied Sprayroq SprayWall, a two-part mixture of a resin and hardener that is NSF 61 approved and VOC-free. The two parts enter a heated spray system and are blended in a mix chamber that automatically measures the proper amount to be dispersed from the spray head.

The material is applied at 150 degrees F, heated onboard a specially designed truck. The heated materials are pressure pumped into the spray applicator lines at 2,500 psi. Spray application takes less than 30 minutes. Within several minutes after application, the bypass system can be removed and the structure returned to normal service. About 250 pounds of material are needed to restore an average manhole.

Abel Recon rehabilitated the 52 manholes in two months, causing little or no disruption to the neighborhoods where the work took place.

Right methodology

By staying proactive with its maintenance program, the DTMA staff keeps Hershey’s sewer system healthy. Budget constraints often mean Schutz and his team have to do more with less, but they recognize the need to do all they can to stay on schedule in caring for the infrastructure.

Schutz says new technologies have been valuable. “Be open to new ideas,” he advises. “I’m always more than willing to look at something new. No matter how great one product is, there is no such thing as a silver bullet. You have to have a complete toolbox of options at your disposal because one size just doesn’t fit all.”