September 18, 2007In the early 1990s, the Miami-Dade Water and Sewer Department (MDWSD) had in all likelihood the largest chemical grouting program for its sewer collection system in the United States. With its fleet of 16 television and grouting systems and trained crews, Miami-Dade was at the forefront of addressing its infiltration-and-inflow (I/I) problems with the latest technology.
Fast-forward to 2007 and MDWSD is still on the cutting edge of departments involved in rehabilitating their infrastructure. Today, the use of cured-in-place pipe (CIPP) and lateral inspection and relining replace chemical grouting at the top of the agenda of work being done in the county.
“The collection system is in better shape today than it has been in 10 to 15 years,” says Rod Lovett, chief of the MDWSD sewage collection division. “We started with a consent agreement [with U.S. EPA] in 1992 and we’ve done in total since then about $400 million to $500 million worth of work on the system. We analyze the repair method that is the least expensive way to make the repair and a good portion of that has been through trenchless technologies.”
MDWSD’s budget for trenchless has grown over the years as opportunities for use has expanded; approximately 40 percent of its rehab budget is spent on trenchless projects.
Through the use of fold-and-form (early on), CIPP, sliplining, pipe bursting, horizontal directional drilling, TV inspection, sectional and point repairs and chemical grouting of joints, the water and sewer divisions in Miami-Dade continue to invest wisely in its infrastructure — something all utilities need to be doing these days, Lovett says.
“The state of the infrastructure in Miami-Dade is the same as the rest of the country — it is in desperate need of replacement,” says Luis Aguiar, chief of the water transmission and distribution division. “We need to continue to invest money to replace the infrastructure because it is getting to be 50 to 60 years old or older. We have water mains [in Miami-Dade] that have been in service since the early 1930s. It is a challenge being faced by not only Miami-Dade but every utility across the United States where the infrastructure is getting to the point that unless we start investing money in it, it’s going to become catastrophic in the future. And it’s not just the water and sewer systems. Look at the steam pipe that blew in New York City and the bridge that collapsed in Minnesota [this summer].”
Miami-Dade County is home to the fifth largest utility in United States, in terms of miles of service and customers. MDWSD, with 440 sq miles of service area, maintains 7,100 miles of water lines and 3,600 miles of sewer lines, which serve approximately 2.4 million customers and includes 11 wholesale municipalities.
The average age of the sewer and water lines are 40 and 60-plus years old, respectively, with some sewer lines dating back as far as 1919. A majority of the sewer lines are made of clay with new pipes being fusible PVC; the forcemains are made of ductile iron and pre-stressed concrete. MDWSD operates three water and wastewater treatment plants each, along with 14 pump stations for water service and 954 pump stations for wastewater.
Trenchless methods made their first appearance in the county in the early 1990s when fold-and-form (F/F) was used to rehab aging sewer lines, as it was considered more cost-effective at the time than CIPP, says Lovett and Aguiar.
“We did some successful fold-and-form programs,” Lovett says. “But now we are pretty much exclusive to CIPP. As we progressed, the patents on the CIPP process wore off and as competition came in, the price went down. We have a contract now that we pay $21.50 per foot for 8-in. CIPP, which is actually less money than what we were paying for fold-and-form.”
So far this year, Miami-Dade has done 40,600 ft of CIPP work. “That’s probably down from previous years,” Lovett notes. “We are going back through the system [with inspection] a second time; therefore we are not finding as much of a problem as we did the first time.”
Back in the early days when everything trenchless was new, people were coming out of the proverbial woodwork, offering Miami-Dade can’t-miss solutions and products to its infrastructure problems. “About that time, everyone was coming down here with a magic wand, saying ‘I got the process that’s going to solve all your problems,’” remembers Aguiar, who at the time was working on the sewer side. “It was then we decided to hire a consultant and form a committee so we could evaluate the different processes and materials that [were being pitched] to us… That is how we started to expand our trenchless program.”
The district’s trenchless program has included over the years a variety of methods and trenchless companies, including some large diameter and interceptor sliplining work in the mid-1980s using HOBAS pipe, a program that lasted until the late 1990s. Pipe bursting has been used on the sewer side involving TT Technologies but is being utilized to a far larger extent on the water side today. Televising and grouting the sewer lines, once the main cog in its trenchless arsenal, used such companies as CUES. Re-grouting annular space for liners added Logiball to the mix.
Today, CIPP continues to be the most used trenchless method, contracting the work out to such companies as Insituform Technologies. Laterals are taking center stage these days with companies such as LMK and Perma-Liner among others getting the call.
“Miami-Dade County Water and Sewer has always been very conservative,” Aguiar says. “It took a lot of effort to accept technologies that were really new to the U.S. market. So we had to take certain chances.”
The televising and grouting program was one such chance, using technology that wasn’t largely accepted by many utilities at the time. Through the program, high levels of I/I were vastly reduced over a five-year period between 1993-98. The program proved invaluable to MDWSD and not just in terms of the I/I results but in the knowledge gained by its staff. “We had to learn how to do things,” Lovett says, noting that Larry Decker, MDSWD assistant superintendent for the sewage collection division, even created a software program at the time to record the readings from the flow monitors; based on this data, the county was able to determine where the heaviest I/I was concentrated.
Miami-Dade also did its own television work, having in excess of 16 trucks in operation, and crews working in two shifts. “Right now we have 17 truck shifts operating and eight crews that are running every day,” Lovett says. “We’ve cut back a bit because we finished the five-year cycle [of inspection] and are now on a 10-year cycle. Those trucks not only do SSES but they also do the grouting.”
The success of that initial TV and grout program allowed MDWSD to evolve into inspecting every foot of mainline in the system, as well as the laterals. “I haven’t heard of anyone else in the country that has done this,” Lovett explains. “As we go through the mainline, we stop at each lateral connection. We pan-and-tilt [the camera] into each lateral to see if there are any leaks. If there is water running down in the lateral while we’re there, we’ll wait five minutes to see if the water stops. If it does, we move on. If it doesn’t, we identify that particular lateral as a suspect lateral and a lateral inspection team will go out at a later date and check it.”
Laterals, Laterals, Laterals
One area that MDWSD has aggressively and proactively addressed in recent years has been the condition of the laterals throughout the county. Through two pilot programs, more than 1,600 laterals have been inspected and subsequently 1,000 rehabbed to this point. The county used a sanitary sewer evaluation survey (SSES) to assess the pipes’ condition. SSES uses various equipment and techniques to detect sewer pipe defects, blockages and capacity problems. These techniques include smoke tests, dye tests, closed-circuit TV (CCTV), flow monitoring, rain monitoring, building service connection location/inspection and flow isolation.
“We did the pilot programs to try to identify the source of rain-induced I/I that comes into the system during and after heavy rains,” says Lovett. “We are looking closely now at extending the program.”
The project is designed to evaluate a variety of lining systems, including CIPP and inner seals. In addition to testing these products, Miami-Dade is fine-tuning its flow monitoring techniques to ensure accurate measurements of the reduction of infiltration.
The first and smaller pilot program goes back five years and involved three basins and 99 laterals. The second and larger program recently wrapped up and involved 52 basins and 1,600 laterals. Estimated cost for the larger program is $16.5 million, with actual costs being about $14 million. “The only thing we don’t have on the second program is the rainfall data on some of the basins yet because we haven’t had enough rainfall to compare the results,” Lovett says, explaining that a “qualified rain event” is one in which at least 4 ½ in. of rain falls in a 24-hour period. “We typically get several of those during our rainy season but it hasn’t occurred across the county as a whole; it’s been spotty in the county. We have been able to qualify some basins, not all.
The program is dependent on showing the results of what we’ve done,” he adds. “There are a lot of lateral programs across the country in which all they do is go out and replace laterals but they don’t really know what they’ve done. They have no way of measuring their success. We wanted to figure out a way to do that.”
Aguiar and Lovett have been integral parts of the Miami-Dade infrastructure turnaround over the years. Aguiar just recently marked his 30th year with MDWSD and Lovett has 19 years on the job. Longevity is the norm among the 2,700 workers at MDWSD, bringing expertise to the processes being utilized. Lovett says many things have changed over the years and appreciates the expertise that his staff brings to the job.
“I don’t know if we are old pros but we do know our system very well. I’ve never felt that what [Miami-Dade does] is what everyone should do because everyone has different circumstances. We do have a better handle on things, but most of that is because of the technology.
“When I first went to work, the way we responded to sewer problems was strictly on a reactive basis,” he says. “If something was broke, we fixed it. Today, we’re probably doing 80 percent of our work on a proactive basis. That’s what’s changed and it was a long time in coming. And it was the right thing to do.”
Sharon M. Bueno is managing editor of Trenchless Technology.