The Proper Order of Operations to Achieve the Maximum Sealing Benefit from the Trenchless Rehabilitation of a Collection System

Over the last 50 years, cured-in-place pipe (CIPP) has become the method of choice to rehabilitate old, crumbling, and leaking wastewater collection systems. Lower cost, speed of execution, reduced disruption, and long-term effectiveness of trenchless rehabilitation eroded support for the old 'dig and replace' approach. Today, CIPP is the most widely used trenchless method for pipe renovation. It is frequently specified by Utility Owners throughout North America, with Industry standards requiring minimum levels of quality, primarily flexural properties and chemical resistance. However, the question remains, 'is CIPP as good as new', and what steps are taken to protect residents from potentially harmful VOC emissions? Normally, sewer pipes and other pipes are manufactured in a factory under strict quality-control measures ensuring repeatability and consistent quality. CIPP, however, is manufactured in the field under less-than-ideal quality conditions producing less than ideal results. One CIPP might be tight fitting without blemishes or defects, while another has wrinkles, blisters, and delamination. CIPP can be installed and meet all requirements for physical and chemical resistance but might leak for the next 50 years. Significant opportunity remains to improve performance and overall quality of CIPP by simply changing the order of operations. The current trenchless model generally contemplates realizing comprehensive collection system rehabilitation meaning 'if you're going to control inflow and infiltration in a sewer collection system, you need to seal the entire system.' A number of issues can arise from sequencing events pursuant to current installation practices, whereby mainline rehabilitation occurs first and service pipes are lined thereafter. Clean outs are typically installed by the lateral lining contractor and are generally not in place when the mainline CIPP liner is installed. Some resulting issues involve public health and safety concerns, ranging from toilets blowing up during high velocity water jetting to homeowner complaints of headaches and paint smells during main liner curing operations. This can cause significant problems for the utility, the homeowner, and the contractor. Other issues arise when the main liner is cured but some or all service lines connected to it have not been temporarily plugged, which the author contends is a primary requirement if CIPP is produced with 'good as new' quality. In reality, under current CIPP practices, there are no substantive measures taken to ensure residents and businesses do not continue to discharge waste into the system while a resin-saturated liner is inserted and cured in the sewer pipe. Since the system is not taken out of service, not only is sewage allowed to flow and mix with the resin saturated liner, but VOC emissions amigrate up the service pipe, often contaminating air quality in a home or business. The adverse consequences of current municipal CIPP sewer rehabilitation projects include the following shortcomings where opportunities exist to improve quality, performance, and overall service life: - Sewage mixed with the resin-saturated liner may cause reduced physical properties and reduced chemical resistance. - Flow from service pipes can cause CIPP not to fully cure at service connections, leaving gooey resin that makes it difficult to reinstate the service properly. - Service pipes under head pressure can cause a 'lift' or bulge in the liner. - Main pipe sags collect condensation from steam curing, insulating the invert of the liner and preventing curing, resulting in a 'lift' The paper will argue that the solution is simple: change the order whereby segments of a collection system are rehabilitated by adhering to a specific Order of Operations with seven sequential steps: 1.Conduct a pipe survey including CCTV inspection, measuring pipe diameter, locating service pipes near private property lines, and marking exact locations for service cleanout installations; 2.Install a two-way clean out in each service line near the property line; 3.Divert system flow and take all service pipes out of service during CIPP; 4.Control groundwater influence on CIPP; 5.Install mainline CIPP after plugging service pipes and filtering emissions; 6.Install Lateral Lining after plugging service pipe and filtering emissions; and 7.Install Manhole Lining. The expanded role of the clean out drives the success of this new approach, providing the ability to plug the service pipe effectively taking the system out of service during CIPP rehabilitation. A two-way clean out allows for the inflatable plug to be positioned on the upstream side of the clean out. It also provides access to inspect, prepare, and rehabilitate the service pipe in the public right of way. An added benefit of the two-way cleanout is homeowners can have a contractor renew their private sewer from it. This more versatile clean out, adhering to ASTM F3097 and utilizing a minimally invasive installation method, is often used in conjunction with CIPP sewer system rehabilitation. A minimally invasive vacuum-excavated cleanout also answers sensitive homeowner concerns by eliminating conventional excavation, which often requires trench boxes and piles of dirt in the yard. Moreover, the minimally invasive cleanout provides for Same Day Restoration (SDR). SDR means the cleanout is installed by vacuum excavation, and landscaped areas, sidewalks and driveways are completely restored that same day, providing great benefit for all involved in the project. The first step of the Order of Operations is to conduct a comprehensive survey that measures, locates, and marks, ensuring solid knowledge of the system and its issues and the use of ASTM compliant components to tightly seal it 'good as new'. Installation of two-way clean outs on each lateral is next. They are thereafter used to improve main rehabilitation – using the cleanout to plug service pipes during main lining, together with bypass pumping of upstream basin flows, yields two improvements: 1.Removing all flows that might impair proper curing of the liner and its overall quality and performance; and 2.Bottling up VOC emissions so they do not enter structures which connect to the main through the adjoining service pipes. Moreover, it provides the capacity to filter emissions from curing operations, protecting workers and the public from potentially harmful fumes. Mainline lining then proceeds with the entire system taken out of service during insertion, inflation and curing of the new CIPP. Lateral lining then proceeds, with each service pipe plugged upstream of the cleanout during the CIPP lining process; the benefits described above are realized, ensuring CIPP is safe for residents and the public by filtering and monitoring all emissions. Finally, trenchless rehabilitation of manholes occurs. Though these changes are few and somewhat subtle, their impact is huge, yielding improved system rehabilitation, capturing and putting to good use advancements in trenchless technology, and improving the experience of those who live and work in a project area and of the utility as well.