Chemical grout was one of the first trenchless pipeline rehabilitation technologies and for many engineers it is still the first line of defense against infiltration into sanitary sewer systems. Recent interviews with engineers in Florida, Ohio, and California reveal similar goals, costs and results of using chemical grout.
Ed Wydra, Associate Engineer, Placer County Facilities Services, Auburn, CA, explained that his first experience with chemical grout was a small test. Based on the results of that test, he has expanded his use each succeeding year. Over the past three years, he has spent nearly $275,000 in mainline joint testing and sealing.
With this investment, he tested about 60,000 linear feet of six and eight inch sewer mains. Over 12,000 individual joints were tested, and over 2,000 (16 percent) failed a pressure test and were sealed with chemical grout. Based on those figures, he was able to stop infiltration through leaking mainline joints at an average cost of $4.50 per linear foot.
Wydra acknowledges it is very hard to determine the volume of a pipeline leak.
"If each joint was leaking at an average rate of one gallon per minute, we decreased infiltration by 2.88 million gallons per day," he said. "On the other hand, if the average rate was only one-tenth that amount, we decreased our infiltration by 288,000 gallons per day. I believe the actual amount is somewhere between those two rates.
"At an average cost of $1.50 per thousand gallons to transport and treat wastewater, we're saving somewhere between $432 and $4,320 per day during our wet season by stopping those leaks. The higher our rate of infiltration, the sooner the project will pay for itself," Wydra said.
"We don't have any long-term data yet, so I don't know how long the grout will last," Wydra said. "But, if it just lasts a few years, it's a good investment, and it's something we can do right now to stop the leaks which increase flow and treatment costs, and erode our pipe's sidefill support. If the grout will last 10 or 20 years, the savings can be significant."
Wydra said he uses chemical grout as his first line of defense against infiltration. However, pipes which require structural support are lined.
"If we used only lining to fight infiltration, we would be limited in what we could do," he said.
Application
Most infiltration enters sanitary sewer systems through leaks in manholes, mainline joints, lateral service lines, and the connection between laterals and the main. To stop these leaks, chemical grout is forced out through the leaks into the surrounding soil where it cures, or gels, with the soil to form a rubber-like, waterproof mass which cannot be forced back into the structure. This chemical grout "collar" adheres to the structure where it will stay indefinitely. If groundwater pressure increases, the mass will be pressed even tighter against the structure.
Leaks through cracks, joints, and pipe connections in manholes usually are sealed using hand-held equipment. Leaks through mainline joints, lateral lines and lateral line connections usually are tested and sealed using equipment which is remotely controlled from specially designed vans or trailers.
Chemical grout is not a structural repair. It may be applied to stop leaks through structural faults, but it will not increase structural strength.
Long Life
Jim Troike, Assistant County Sanitary Engineer, Medina County, OH, said he has been using chemical grout for almost 10 years, but the county has been using it at least four times that long.
"We recently reviewed some mainlines that were grouted almost 10 years ago and they're holding up fine," Troike said. "It was an area that has given us a lot of problems in the past, but there were no signs of leaking."
Jeff Filarski, Partner, Chagrin Valley Engineering, Cleveland, OH, and City Engineer, Lynnhurst, OH, also has been using chemical grout for many years.
"Recently, we tested some old vitrified clay pipes in Lynnhurst which were grouted 12 years ago. Ninety-five percent of the joints passed the pressure test, so we only had a 5 percent failure rate after 12 years."
Basin-to-Basin Comparison
The city of Fort Lauderdale, FL, has spent significant sums of money on sanitary sewer rehabilitation over the last few years, yet flows at its wastewater treatment plant have continued to increase faster than population growth would justify. As a result, the city hired the firm of Williams, Hatfield & Stoner, Inc. (WHS), Fort Lauderdale, to make a quantitative evaluation of the city's rehabilitation program.
Jim Davis, P.E., Project Manager, WHS, said his firm compared flow rates in two parallel drainage basins for a year to establish a computer model of the correlation between them. As a result, the effectiveness of rehabilitation work completed in one basin could be determined by comparing the resulting flow rate with flow in the control basin. The relationship would remain constant regardless of whether Fort Lauderdale experienced a wet or dry period.
Next, the pipelines in the test basin were televised to determine their condition, and an engineering economics approach was used to determine the most economical rehabilitation process for each fault. Since the city had set a budget of $545,000 for the entire project, WHS gave priority to the most critical repairs.
Chemical grout was used to seal all leaking joints in mains which were structurally sound. Grout also was used to seal leaking lateral service lines and their connections to the main. Short cracks were repaired with short, cured-in-place patches, and deep pipes with heavy structural damage were repaired with full-length cured-in-place liners. Structurally damaged pipes which were no more than eight feet deep were repaired with fold-and-form liners.
After the rehab work was complete, WHS monitored both basins for another year, then analyzed the results. The analysis shows that average flow in the rehabilitated basin was reduced from 1385 gpm to 593, a 57 percent reduction. The 792 gpm reduction translates into 1.14 million gpd of infiltration that was eliminated from the system for $495,238, or $0.44 per gallon per day. The payback period for the project was 3.1 years.
"We were able to achieve such a low cost per gallon of infiltration eliminated because of our logical, systematic approach and extensive use of chemical grout," Davis said. "Some competitors to chemical grout want to go in and line everything, but our engineering economics approach proves that it is more cost-effective to make your decisions based on the life cycle cost of each appropriate rehabilitation technology."
