Sherwood, Ark., Tackles Manhole I/I Issues Using Trenchless Methods

Like most communities across the United States, the City of Sherwood, Ark., at 65-years-old, has its fair share of infiltration and inflow problems due to an aging sewer system.

Sherwood, located in central Arkansas in the shadow of the state capital city of Little Rock, has a growing population of 29,523 and approximately 40 miles of sewers and about 4,500 manholes that are part of the Sherwood Wastewater Utility System.

According to Sherwood wastewater supervisor Charlie Cadie, the system was established in the early 2000s after the City began taking over private systems in its coverage area and in 2011, it began looking at aggressively tackling manhole rehabilitation as part of a larger sewer system upgrade.

According to Les Price, of Crist Engineers, Sherwood’s engineer for the sewer project, the City discovered that the manholes were suffering from several problems.

“Some of the manholes were the old brick type manholes with grout and bricks missing, which caused leaks. Some of the manholes were precast concrete and were leaking at the joints and some of the manholes had bad pipe seals and were leaking around the pipe entry into the manhole,” Price said.

He continued, “Some of the manholes were leaking around the stairs and precast lift holes, and some of the manholes were deteriorated because of high levels of hydrogen sulfide.”   

Cadie estimated that the City spends $25 to $30 to treat a gallon of fluid and because of these I/I problems, during rain events, the product being treated is about 99 percent rainwater.

“It’s one of biggest things that we have that causes sewer treatment problems and flow problems,” Cadie said.

By reducing the I/I through the manhole rehabilitation program, the City will save money on treatment equipment, a cost-savings that is passed on to the system’s users.

Researching Its Options

Once Sherwood decided to address its infiltration and corrosion problems, officials set out to research different rehabilitation products and methods that had been used or trialed in nearby Little Rock.  

Sherwood was looking for systems with a 100-year life expectancy. To qualify products, Sherwood tested many cementitious and polymer products to rehabilitate its manholes. Since Sherwood’s problems were diverse, officials  expected and found that several different products would prove optimal for different circumstances, hence the need for a manufacturer with a full and diverse product line.

Likewise, officials found that the contractor applying the products was critically important so they decided to focus on compatible products from the same manufacturer and that must be applied by manufacturer trained and certified applicators.

The City did not have to look far because local manufacturer Quadex had been supplying manhole rehab products nationally since 1991 and had a full line of cements and epoxies sold only to trained certified applicators and cities with proper cement and epoxy spray equipment.

“We used a variety of Quadex products, depending on what the particular problem was at each manhole,” Price said. “Some of the manholes received a cementitious liner only, some of the manholes received a cementitious liner followed by an epoxy liner and some of the manholes received only an epoxy liner.”

Price further explained, “The cementitious followed by an epoxy liner method was used in manholes that were deteriorated due to hydrogen sulfide and were typically located near pump stations and the wastewater treatment plant.  We used the epoxy liner only method for some precast manholes in relatively new areas that had minor leaks and the manholes were in good shape otherwise.”

In all, Sherwood called upon four Quadex products: Quadex Quad-Plug, Quadex Hyperform, Quadex Aluminaliner and Quadex Structure Guard, to solve its I/I problems. The winning bidder for the manhole work went to Lewis Concrete Restoration, a Quadex certified applicator.

Quadex’s hybrid calcium aluminant cementitious product provided superior structural rebuild capabilities and moderate corrosion protection and proved to provide the best bang for the buck for structurally rebuilding deteriorated manholes and effectively stopping infiltration and mild corrosion.  

No degree of deterioration could not be repaired with 2- to 4-in. of shotcreted calcium aluminant. For more severe corrosion situations, Quadex’s Structure Guard epoxy coating proved to have superior bonds to damp underground concrete that is required for long-term bonding to newer precast manholes or concrete lift stations.  

The City turned to Structure Guard for topcoating structurally deteriorated manholes first lined with calcium aluminant cements made by Quadex.  

Phase I Finishing Up

Cadie says the program is on pace for a 2017 completion, and the first phase is 90 percent complete, with the City already looking ahead to Phase II. The manhole project complements a citywide sewer system rehabilitation and upgrade project.

In the first phase, approximately 800 manholes, with a vertical footage of approximately 3,991 ft, were identified for rehabilitation and Cadie is pleased with the results. Given the heavy rains last year and snow and ice this year, he has not noticed any signs of deterioration or significant I/I even in areas that are prone to flooding.

“They (Quadex) do some really good work and have a real good product,” Cadie said. “I am really happy with these guys, they really do real good work.”

Mike Kezdi is an assistant editor for Trenchless Technology.