Though it's a cost-effective sanitary and storm sewer rehabilitation method, cured-in-place pipe (CIPP) is an in-ground manufacturing process that must be monitored for quality.
Unfortunately, not everyone knows what's necessary to ensure an installation provides a full 50 years of service life. The consulting engineer doesn't check the contractor's design calculations. The owner doesn't test material samples collected from the jobsite. The inspector doesn't know what to look for or understand the implications when reviewing wet-out, installation, and material testing results.
The most important parameters for bending strength and long-term performance are flexural strength, flexural modulus, and long-term creep, all of which can be measured in a materials testing lab. Conversely, a liner may meet strength parameters, but pinholes may develop because material was mishandled during installation.
When the contractor submits post-construction closed-circuit television (CCTV) tapes that show a pristine liner, everyone thinks they've solved all their problems.
Not necessarily. In 2004 we launched a $16 million bond-funded capital improvement program to renovate our wastewater treatment plant, setting aside about half for sanitary collection and conveyance system upgrades. Since then we've installed 65,000 lineal feet. We prefer curing-in-place because it's less expensive than full replacement and eliminates the disruption and inconvenience caused by excavation.
We also know that all installations will have some leakage. Cured-in-place pipe consists of felt impregnated with a resin. The felt tube is sown together from flat sheets, so the tube has a seam where failures can occur. Root intrusion from private laterals becomes noticeable after one to two years, as do areas where the resin has washed out.
But that's to be expected. Here are my recommendations for the best return on investment:
Develop performance-based specifications. A prescriptive specification works well only when the finished product has a limited number of defects.
For example, in one instance a colleague's installation displayed blistering, peeling, and cut liners; leaks; numerous pinholes; bulges; discoloration; overcut laterals; and over-grouted lateral connections. He questioned the quality and compatibility of the resins and felt, as well as the wet-out procedures.
The contractor was confident he could demonstrate that the specification had been met because he'd installed the pipe according to prescription. He couldn't show the quality of the materials and manufacturing processes because he hadn't been required to test samples during installation.
After 2½ years of testing and additional consulting, the department had to excavate portions of the lined pipe to run materials samples. The 90- to 120-day project schedule was blown out of the water, and the associated costs weren't recovered.
A solid performance-based specification:
We tailored a free template from the National Association of Sewer Service Companies (NASSCO) to develop our performance specifications.
Of course, enforcing these requirements is not without costs.
Thoroughly reviewing contractor submittals requires consultant time. A battery of thickness, bending strength, and flex modulus tests runs about $200/ sample. Long-term performance and chemical resistivity tests are $5,000 to $6,000 each.
Follow strict inspection procedures. Without adequate field documentation of the installation, the cause of defects becomes harder to determine. Inspectors must know what to look for and what to document and, ideally, be certified.
In addition, require CCTV inspections during the post-construction bonding period. My colleagues think this is a waste of money, but every one I've done has shown defects. The dollar value of having the contractor address them has always exceeded the cost of the inspection.
Lean on the experts. NASSCO's inspector-certification program should be required for government employees as well as consultants.
In addition to cured-in-place pipe, the two-day course addresses other rehabilitation methods, field monitoring, documentation, performance specification development, and testing methods. For more information, visit www.nassco.org.
I went through it, and it was the genesis of our changes. We're not where we want to be yet with respect to quality, but we'll get there. Without accountability the pursuit of quality is a fool's errand.
— Michael Smith (email@example.com) is an environmental engineer for the Bethel Park Municipal Authority in Pennsylvania, which serves a population of 34,000.