An exemplary grouting program in Plant City in central
proves highly cost-effective in reducing inflow and infiltration
By Rosalie E. Leposky
Plant City, a small Florida community, has found an economical way to fix joint openings in sewer lines: grouting to reduce the escape of wastewater into the ground and prevent groundwater, sand, and other materials from getting into the pipes.
The need to prevent the escape of sewage is obvious, but keeping clear water out of the pipes is equally important. The excess water increases sewage treatment costs.
Tucked between Tampa
and Lakeland along Interstate Highway 4, Plant City covers 26 square miles
and has a population of 31,714. Although most cities its size have public
works departments with a utility-maintenance division, most don’t
operate their own inflow and infiltration (I&I) programs. Instead,
they depend on the county in which they are located, or hire a contractor.
Plant City’s I&I program is responsible for about 130 miles of sewer lines and over 200 miles of potable water lines. Between January 2003 and July 2004, I&I employees grouted 19,431 feet of sewer lines. By the end of the current budget year, they hope to finish about 30,000 feet.
“We are called to work on sewer lines that no one else knows exist,” Eric says. “The first we know there is a problem is when someone notices an odor and calls us. If no one calls, we know we’re doing our job.”
know that excess ground-water can overtax a wastewater treatment plant’s
capacity, but they may not know how to stop it. As Plant City has found,
grouting sewer lines is an effective way to curtail inflow. “In areas
where we’ve been grouting, we’ve cut several minutes of daily run time
off of our lift stations,” says Eric.
“If allowed to continue, a typical leak we repair would add 1,500 to 2,000 gallons of groundwater per year to our sewer system. In an average year, we fix about 5,000 joints. If only half of these, or 2,500, were leaky joints, they would add an extra 3.75 million to five million gallons of groundwater annually to the treatment system. In addition to stopping groundwater from entering the system, grouting reduces exfiltration, but it’s hard to measure how much escapes from the system.”
When maintaining and repairing sewer and water pipes, Plant City buys equipment with multiple features and functions. “We use Vactor trucks to do small excavations and cleaning,” says Eric. “Equipment is replaced every five to seven years. We use our equipment every day; it never sits idle for a moment unless it’s down for maintenance. Because of our active program, we very rarely have backed-up lines, spills, or odor complaints.”
Many of the city’s water and sewer lines are old. “We’re battling 90-year-old clay pipes,” says Eric. “The older clay pipes become, the more brittle they are. We can also grout cast iron and PVC pipes. If a pipe is in the ground and leaks, it can be grouted. We use grouting in pipes that carry hundreds of gallons per minute.” Grouting is just part of the city’s maintenance program: Unsound clay pipes are replaced.
Plant City replaces about 700 feet of sewer main per year. “We have an advantage over surrounding communities because we have two Vactor units to clean all our sewer pipes twice a year,” say Eric.
The first step in Plant City’s maintenance program is to
identify problem areas using Hurco smoke-testing equipment. “Throughout
the year, we use a mechanical blower to force smoke into pipelines from
manholes to look for openings that will take in water when it rains,”
Eric says. “We inject smoke and take pictures of the external
environment where the smoke is coming out of the ground. Anyplace smoke
escapes, water can get in. Photographs provide us with markers where
problems may exist.”
Before repairs are made, the crew uses CCTV to survey all laterals and identify breaks. Then Eric and Jon determine where pipes are large enough and still have enough integrity for grouting, and where excavation and replacement are called for. “Our grouting team averages about 3,500 feet per month of lateral service lines,” Eric says.
City lines have always been 4 or 6 inches or larger, but some private laterals are 3-inch pipes. “Old 3-inch pipes sometimes give customers a problem on their side of our sewer system and have to be changed out by private plumbers for 4-inch pipe,” Eric says.
To grout a sewer line’s joints, the crew uses a CCTV camera that enables a trained technician inside a truck to view pipes a thousand feet in any direction from a manhole. Where a joint needs grouting, a technician pulls a packer — a device that holds two acrylamide chemicals — through the sewer line.
The acrylamides, pumped under pressure, form a gel that swells up like a balloon on a joint’s interior and exterior and mixes with the soil outside the pipe to seal off the joint from the rest of the pipe and everything around it.
“First the technicians camera a pipe to identify cracks in joints,” says Wayne Everhart, superintendent of utilities maintenance. “Then they position a packer at a joint. The packer is connected by an air hose to a compressor on the truck. The packer has four lines — one for air, two for grouting chemicals, and one for testing.
|“First we air-test the isolated joint. A typical test runs
for about 30 seconds at a pressure of 4 to 10 psi. If the joint fails the
test, we seal it.” The technician inflates the packer and pumps the two
acrylamide chemicals through it. As pressure builds, the two chemicals
combine, expand, and seal the pipe on either side of the joint. Outside
the pipe, the grout mixes with soil media.
Many equipment options are available for grouting, “You have to select what is best for your budget and applications,” says Eric. “We had to undergo a learning curve to learn how to grout, and we gave our employees the tools to succeed.”
Plant City uses a packer from CUES, Inc. and a nonflammable acrylamide chemical grout with extremely low viscosity from Avanti International. CUES also supplies the city’s cameras. One is an ultra-short pan-and-tilt camera on a track. It is 4 inches in diameter and 15 inches long, with attachments for pipes from 6 to 48 inches in diameter. In 4-inch pipe, the city uses a CUES Pro Scout Mini Mainline Camera, 2 inches in diameter and 3 inches long.
|“The size camera we use is determined by pipe size,”
says Eric. “The smallest pipe we can televise is about 4 inches. We can
see in smaller pipes, but we can’t grout them. Equipment is available
through CUES for grouting 4-inch pipe, but we don’t have it. We grout
pipe with a diameter of 6 inches and larger.”
“Distances vary between joints. You used to be able
to order clay pipes in a variety of lengths between 3 and 5 feet. Most
were sold in 3-foot sections. Newer PVC pipes typically are sold in
13-foot sections. The resulting joints may be 3 feet to 13 feet apart.
Most manholes are 500 feet or less apart, so we generally can do the areas
served by two manholes before we have to move and set up our equipment
© Cleaner October 2004