A Sewer System Dragnet

This is the city: Los Angeles, California. The second largest in the United States. Beneath the feet of the almost 4 million people who live in the metropolis is a vast network of more than 6,500 miles of sewer pipeline, operated and maintained by the city. The majority of these sewers are secondary sewers — 15 in. and smaller in diameter — which are the most susceptible to blockages and overflows. More than 50 percent of the secondary sewers are older than 50 years. When all of these sewer lines are working as designed, everybody’s happy. Once in a while, one of these pipes makes trouble. That’s when the city’s sewer experts go to work.

With such an expansive and aging sewer system, the Los Angeles Department of Public Works needs a dragnet to round up those troublesome pipelines. Thankfully, the department has one, in its aggressive program to revitalize the city’s suspect sewers by replacement or rehabilitation.

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While the majority of the sewer replacement projects in Los Angeles are done by traditional open-cut methods, the city uses a variety of trenchless methods for rehabilitation and new installation. Such trenchless means to a healthy sewer system end include sliplining, cured-in-place pipe, fold-and-form, cast-in-place, microtunneling and traditional tunneling. Horizontal directional drilling (HDD) is used on some installation projects, but that is typically limited to canyon regions.  

The city does not perform much pipe bursting, says Keith Hanks, senior environmental engineer in Los Angeles’ Bureau of Engineering, but he adds that they would like to do more of it.  

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Three bureaus within Public Works make up the city’s experienced and efficient trenchless team: the Bureau of Engineering, the Bureau of Sanitation and the Bureau of Contract Administration. These three units work together to design and implement the projects to upgrade Los Angeles’ sewers.  

The city has sewer pipes with diameters that range from 6 to 150 in. Pipe materials include vitrified clay, brick and cement (unprotected, plastic lined and clay tiled), all in varying shapes from circular (the majority) to semi-elliptical and elliptical.  

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Parts of the city’s sewer system date back to the 1870s, when the first known sewer was installed. The Central Outfall Sewer was built around 1906. The system then experienced large growth periods in the 1920s and again in the 1950s. And currently, Los Angeles is further expanding its sewers with such projects as the 11-mile East Central Intercept Sewer, which went in service September 2004, and the Northeast Intercept Sewer, which is in Phase 2 pre-design and is scheduled for completion in 2019.
However, some of the older sewer lines are causing trouble for the city, especially those sewers built in the 1920s, Hanks says. Those lines are primarily large diameter, tile-lined pipes. The tiles resist corrosion, but don’t stop acids from working through to the cement pipe walls.

“Many of our sewers have tiles that have fallen to the bottom, causing corrosion and blockages,” he says. “The city is rehabbing or replacing these lines to reduce odor and corrosion problems.” The city’s ongoing program to rehab these large, unprotected sewers mostly involves sliplining.

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Blockage and overflows became a major concern in some of the city’s smaller diameter pipes, such as the 15-in. diameter and smaller secondary lines, which led to a lawsuit in 2004. As a result, the U.S. Environmental Protection Agency and the California Regional Water Quality Control Board agreed that Los Angeles would replace or rehabilitate 60 miles of sewer pipeline each year.  

Los Angeles’ aging sewer system and the 2004 EPA mandate have led to the city’s aggressive renewal program, which uses innovative technology and methodology to increase efficiency in the effort to preserve and protect important infrastructure.

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60 Miles at a Time

In 2004, Los Angeles launched its Secondary Sewer Renewal Program — commonly referred to as the 60-Mile Program — to combat sanitary sewer overflows (SSOs), leaks, root intrusion, grease infiltration and other capacity-related issues in the city’s smaller diameter pipelines. Los Angeles has approximately 6,000 miles of secondary sewers in its system.

The 60-Mile Program was the result of the city’s 10-year settlement with the EPA and included a three-year ramp-up to address 420 miles of problem sewers, which were indicated in a study of the system.

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According to the settlement, Los Angeles must replace or rehab these sewers over the course of 10 years. However, the city is committed to extending the program beyond the settlement period, says Richard Pedrozo, the city’s civil engineer who oversees the 60-Mile Program.  

“The city has at least 15 projects ongoing now with more being prepared to bid,” Pedrozo says.
The secondary sewers are ranked by priority, based on condition and recorded history of failure as determined by a study that pinpointed 220 drainage basins in the city that required attention. The city then assembled a list of the top 100 basins to address — a most wanted list for its aggressive pursuit of a healthy sewer system.  

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“The city performed exhaustive CCTV evaluations and generated the list from manhole to manhole — or what we call maintenance hole to maintenance hole,” Hanks says. “Our goal is to break up the projects into $3 to $5 million chunks and average 60 miles of work each year.”

In the early years of the 60-Mile Program, the bulk of projects were remove-and-replace by traditional open-cut methods, Pedrozo says. Now, the projects are trending toward trenchless rehabilitation. That trend quickens the timeframe for project completion, allowing the city to do more in less time.
“With remove-and-replace, we average about 50 ft per day,” Pedrozo says. “With rehab, it takes a day and a half to two days for the whole process.”

If the 60-Mile Program continues as planned, the city’s entire secondary sewer system will be replaced every 100 years, says Wayne Lawson, principal engineer for the Wastewater Conveyance Engineering Division, which is responsible for designing sewer improvements in the city’s Bureau of Engineering.
“The program has been very successful,” Lawson says. “It has helped reduce secondary sewer overflows and helped improve overall maintenance.”

Los Angeles’ current budget for overall wastewater treatment and collection-related construction is $140 million per year, down from $250 million in the past year because of the recession. Of that $140 million, Lawson says, the city sets aside $40 million specifically for its Secondary Sewer Renewal Program. Since 2004, the city has replaced or renewed approximately 200 miles of sewer as a result of the 60-Mile Program.

Showing Their Smarts

An aggressive sewer renewal plan — especially one that includes the likes of Los Angeles’ 60-Mile Program — requires an efficient approach. Otherwise, those 6,500 miles of pipeline could become a labyrinth so tricky to navigate that the city’s Public Works Department might just rather face the Minotaur. Instead, sewer projects are approached with a straightforward method that streamlines the design and bid process.

The Los Angeles Bureau of Engineering plans its smaller scale projects with “drawings free” designs, using a propriety, GIS-based system, called SMARTS, which stands for Sewer Maintenance and Record Tracking System. The city’s Public Works Department developed SMARTS to address the needs of its sewer renewal program based on the experiences gained from the Northridge earthquake in 1994, which caused approximately $20 billion in damage throughout the city.

After the devastating earthquake, the department knew that it would have to work efficiently to address the sewer damage, Hanks says. That same efficient approach has carried over to address the 60-Mile Program and other sewer projects in the department.

SMARTS allows the engineers to compile all information on a sewer line — combining substructure, utilities and aerial maps — in one 8 ½- by 11-in. format, therefore speeding up the design phase so that the project can get to bid in a timelier manner.

“The system puts all the needed information at the designers’ fingertips,” Pedrozo says. “Maps are overlaid all on the same computer screen. It’s much faster than creating a plan sketch because there is no drafting involved. It’s a self-contained program.”

In addition, SMARTS saves the city time and resources in design because it reduces paper waste and time spent drawing plans, says project engineer Mina Azarnia.

“The engineers are still required to walk the line of each project to make sure nothing is missed in the design stages that would prevent the project from moving forward,” Hanks says. “It’s a matter of self preservation.”

When the bureau first started using SMARTS, it took about one year to design a project, an improvement over traditional drawn plans, which took one to two years to get to the street, Lawson says. Now, designing a project takes about six months to complete, and some engineers can design three projects in a year.  

SMARTS is not used for larger projects, where drawn plans are still the norm, but it has been adapted to other smaller size programs. For instance, Los Angeles is in the midst of a three-year program to upgrade the city’s sewer traps and maintenance holes, Lawson says. These sewer traps are meant to deter odor from leaking out of the sewer line.

Many of the traps in Los Angeles’ sewer system were built with clay pipe, which has broken in some cases. The program, which stemmed from the same settlement as the Secondary Sewer Renewal Program, is an effort to replace those deteriorated sewer traps with stainless steel.  

In the case of both renewal programs, SMARTS makes the design process more efficient, which Lawson says was a necessity in order for the city to increase productivity and meet its settlement agreements with the EPA.

The bid process is another area where the Public Works Department maximizes its efficiency, by selecting from a list of pre-qualified contractors. These contractors are not used for the 60-Mile Program, but for emergency and specialty sewer projects, such as large scale tunnels.

The city currently has a list of 24 pre-qualified contractors, says Rajni Patel, senior civil engineer in the construction division of the Bureau of Engineering.  Pre-qualification requires contractors to register with the city, divulging a track record of experience for sewer projects, insurance and bond information., which the city keeps on record and renews every five years.  

Pre-qualifying contractors is a prudent measure for emergency projects, Patel says. The normal bid process for a construction project takes about four to six months. Sometimes the city can’t wait that long if a pipeline failure occurs. Instead, the city turns to the contractor at the top of its list and offers the project. The contractor is paid for time on the job plus materials.

“The benefit of the pre-qualified contractors list is that our sewer system is pretty old and the infrastructure is aging,” Patel says. “We have a good maintenance program to keep up with it, but emergencies do arise. In the winter, the rainy season, more emergencies tend to crop up. The list helps us address those in a timely manner.”

The list also benefits the contractors because they can expect regular work. The pre-qualified contractors are queued on a revolving basis, moving to the bottom of the list once they accept a job. If a contractor cannot take on a specific job, the city moves to the next one down on the list.

Large scale specialty projects still go through the bid process, but only the pre-qualified contractors — therefore, the most experienced — can apply. Since the city has already checked the contractors’ track history, the project can move onto the build phase in a more efficient manner.

Such efficiency in designing, building and rehabilitating the aging sewer system in Los Angeles helps the city’s Department of Public Works revitalize its aging infrastructure and protect its citizens from suspect sewer pipelines.

Bradley Kramer is a contributing editor to Trenchless Technology.

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