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. Repairs were needed for 1,900 lf of deteriorating 48-in. pipe where the location presented extraordinarily challenging conditions.
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.
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.”