Sure Shot: CIPP Used to Rehabilitate 48-in. Section of Gravity Sewer in Virginia
Obtaining perfection is not an easy road and often means that you are presented with the biggest challenges to overcome. It also means that you are called upon when others have a problem and need a solution when faced with few alternatives and expert execution is the only path to success.
This is what was being asked of contractors when the Fairfax County Government began requesting bids to repair 1,900 lf of deteriorating 48-in. pipe where the location presented extraordinarily challenging conditions. Many solutions were considered for the rehabilitation, but, in the end, it would take nothing short of the “perfect shot” of cured-in-place pipe (CIPP) to make it happen.
Located in historic Fairfax County Virginia, home to several of America’s founding fathers, the award-winning Norman M. Cole Jr. Pollution Control Plant sits nestled in the small community of Lorton. While Lorton is better known for its rich heritage and being the home of George Mason, the Norman Cole Sewer Treatment plant has developed an impressive reputation of its own. The award-winning wastewater treatment plant, owned and operated by the Fairfax County Government, has long provided a safe, reliable and cost-effective solution for the area and its continuous operations have resulted in quality that has consistently met or surpassed the strict national and state water quality requirements. These traits have earned the plant the prestigious Platinum Peak Performance Award for 18 consecutive years.
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THE CHALLENGE
Despite its reputation as an exceptional facility, no plant is immune to issues over time. Fairfax County identified that the host pipe along the Accotink sewer line responsible for effluent from four pump stations to the treatment plant was rapidly deteriorating at the top of the pipe. As is typical with pump stations, hydrogen sulfide concentrations usually increase after pumping the effluent and being discharged into the gravity portions of the sewer infrastructure. The effects of the H2S were identified and determined to be the issue for the host pipe materials installed in the past. This particular host pipe was reinforced concrete pipe (RCP) and was showing signs of extreme degradation.
Selecting the right product to meet engineering, operational and budgetary requirements is key to any successful project. “Back in the day,” Fairfax County had previously deployed a fold-and-form product to reline their aging pipes. While a preferred method in the past, the fold-and-form product was found, in some cases, to revert back to its pre-installation folded form and also to shift the pipes it was installed in. Wanting to avoid the hassle of having the original installer go back and reinstate services that have closed off due to the shifting of the product, the County chose to move forward and use a much more efficient and long-term proven rehabilitation product, CIPP.
CIPP is a favorable product because of its strong structural capabilities and the rapid speed of the rehabilitation process compared to the traditional dig-and-replace. However, the size of the pipe, combined with the long length, led Fairfax County to initially doubt that the project could be done. Despite its concerns and minimal experience with CIPP, the County awarded the project to low bidder, SAK Construction. Located in the St. Louis region, SAK has positioned itself as an industry leader and because of the company’s experience with similarly challenging CIPP projects, Fairfax County determined that SAK had the right solution to meet all of the project requirements.
Installing the 1,900-lf shot of 48-in. liner was the biggest project challenge for the SAK team.
THE EXECUTION
The Accotink project consisted of 2,955 lf of 36- to 60-in. gravity sewer (known as The Accotink Interceptor) entering the Norman Cole Sewer Treatment plant. All of the piping was inside the facility, making the bypass and CIPP processes extremely challenging because an agreement the plant had in place with the Virginia Department of the Environment. Due to past unrelated issues, the agreement stated that any spill of any fluid in the plant was considered a sanitary sewer overflow (SSO), regardless if it was clean water or not or if it was a single or 1,000 gallons. In addition, the bypass was specified to maintain operation up to 45 mgd, while also pumping reactivated sludge with ferric chloride from the tertiary clarifiers. Each of these ancillary items posed their own specific challenges during construction.
The primary bypass system required two suction locations with three 18-in. sound attenuated pumps at each location. For testing of this system, the County required its pump station to put as much flow as possible at once into the line to recreate a loss of power situation where the line would be at maximum flow. After passing this test, the secondary bypass at the tertiary clarifier was a much smaller system, but posed its own issue with the addition of the Ferric Chloride, which was unknown at the time of bid. This chemical composed of iron and chlorine that anaerobic bacteria like to consume, assists with the degradation of the solids in the treatment plant. Unfortunately, it also deteriorates certain metals. The bypass pumps have metal impellors that create the force to pump, so when the ferric chloride deteriorates and degrades the metal of the impellors (and all other metal parts), the impellors eventually turn to paper thin fan blades and won’t pump resulting in SSOs.
As one can imagine, this caused significant damage to the four pumps at this location. Furthermore, the CIPP lining project would terminate one manhole away from the bar screens of the plant. This raised concerns with the plant staff, as it did not want the heat or styrene from the lining process to kill all of the bacteria used for its processes responsible for the breakdown of the solids in the plant. So, before release of the water used during the curing process, the plant chemists had to verify and approve the concentrations of the styrene on the cure water.
THE PERFECT SHOT
Because of these challenges, SAK Construction would need to hit the perfect shot. A “shot” in CIPP terms, is considered a single installation of CIPP. It runs from one manhole to another manhole, but those manholes are not necessarily the next manhole downstream. There could be several manholes passed with a “shot” and that effort saves money because only a single setup is needed. However, shots involving many manholes often get tricky because of the potential for transitioning liner thicknesses, higher install pressure required, longer installation durations, and a higher risk of storm events and bypass failures, among other things.
Installing the 1,900-lf shot of 48-in. liner was the biggest project challenge, but one SAK was both comfortable and familiar with given the team’s years of CIPP knowledge. The SAK team includes industry pioneers who have conquered some of the most challenging rehabilitation situations, so Fairfax County knew that they were in good hands. The entire installation, including the aforementioned “perfect shot,” went smoothly and everyone was pleased with the outcome.
“The Accotink sewer line is one of the most critical pieces of infrastructure in Fairfax and SAK was able to work with Dewberry and the County to ensure completion of a successful CIPP rehabilitation project,” said Paul Longo, project engineer, Dewberry Water and Wastewater Services. Dewberry officials admitted they were initially concerned about the prospects of the 1,900-lf, 48-in. CIPP liner installation in a single shot. They stated that “SAK’s team of professionals was able to address all of our concerns, provide supplemental design information and coordinate closely with key stakeholders to perform a successful CIPP liner installation.”
SAK Construction project manager Bob Quackenbush added, “We are always up for a challenge and trying to bring the best solutions to customers. While we are proud that the project was a success in terms of constructability and profitability, it is much more gratifying knowing that the owner was impressed with the performance of SAK Construction and wishes to continue working with us in the future.”
