Each rehabilitation project brings to the table its own set of challenges. How contractors and project designers handle and prepare for those challenges can make or break that project. Such was the case for a multi-phase project to rehab a pre-World War II concrete box storm drain culvert in the City of Baltimore.

The client for this project needed a trenchless solution that would stop the infiltration of historic industrial contaminants, as well as water, throughout a 1,500-ft section of the storm drain. The goal of the project was to seal up the section of storm drain that was the source of the infiltration so that all the contaminants would stay out of the water system and could be collected from ground wells located around the outside of culvert and jobsite.

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This drain serves as one of several stormwater collection systems for the city, necessitating that it remained open during the work.

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The Problem

The storm drain culvert was constructed more than 80 years ago, at a time when the city was a heavily trafficked, industrial shipping hub, which only got busier in the years that followed due to World War II. The storm drain serves as the watershed drainage system for a portion of the city, with rain or water from the upstream watershed flowing through this pipe and then, eventually, into the Chesapeake Bay.

The culvert structure, located approximately 30 ft underground, is rectangular in shape, with varied wall thicknesses of 12 to 18 in. “Structurally, the culvert itself was doing well for being over 80 years old; however, it had a lot of infiltration problems,” explains Warren Environmental project manager Max Silva, noting the presence of historic industrial contaminants located in the ground from previous facilities over the years. “The contaminants, combined with water, found their way into the drain, and that was a major problem.”

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“Even with a small weather event, you would see flows pick up; before the weather event the culvert may have had an inch or two of water up along the walls but would then go up to 2 ft during the weather event,” he adds.

Of primary concern was the presence of industrial product infiltration in the storm drain, as well as water infiltration. The presence of these particular contaminants made it extremely difficult for any traditional leak stopping, coating or lining technologies to adhere to their substrate or survive in the environment. The structure also suffered from unsound, eroded concrete, exposed rebar and cracks likely caused from earth movement due to active railroad tracks paralleling the culvert and, of course, old age. Silva says the culvert continues for about a half mile downstream of the work area and eventually dumps to an outfall stream that feeds into the Bay. “All the contaminants and product waste infiltrating into the drain needed to be collected at the outfall so they don’t reach the Bay,” he says.

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Project beginnings go back more than three years, with the client investigating or pilot testing various trenchless lining products to determine which would successfully rehabilitate the structure; the investigations included interior and exterior liners and spray products. The client also contemplated boring holes around the culvert and pumping in an acrylamide grout to encase it. The storm drain presented complicated shape issues and confined space concerns, as well as being a moisture-filled environment — all of which proved detrimental to the other rehab methods researched and tested.

Warren Environmental was awarded the project in 2014 and its master applicator A&W Maintenance would be applying about 5,000 gallons of its S301 100 percent solids spray epoxy at a thickness of approximately 375 mils to coat in a single layer. The project would be completed in three phases.

It was paramount that the storm drain remained open during the rehab process. The first phase of the project — which took place during a four-month period in 2015 — involved preparing the drain for the rehabilitation work by constructing a weir support wall at the upstream side of the work area to hold back flow. Behind the wall, the general contractor installed two 8-in. bypass pumps, which each individually fed their own 12-in. diameter PVC bypass pipe. “The general contractor bracketed those pipes to the top corner of the structure’s walls, running the length of the storm drain,” Silva says.

Phase I also involved grouting the entire 1,500-ft section of drain to stop as much infiltration as possible; approximately 150 gallons of Warren 151 injection grout was used for this process. Then, A&W crews spray-applied the epoxy to the floor and up the structure’s walls to the bottom of the 12-in. bypass pipes. Prior to applying the epoxy, A&W crews prepped the structure by water blasting the surface and using a solution to remove embedded salts off the walls. Also, while the flow was off the floor, flexible epoxy joints were installed approximately every 100 ft where there were existing cold joints.

“A&W Maintenance crews sprayed approximately 375 mils — about 3/8 in. — in a single coat to the 1,500-ft long drain structure and 400-lf, 60-in. diameter connecting lateral concrete pipe,” Silva says.

What made this project particularly challenging was the shape of the drain. Being rectangular shape made using a spray epoxy the right choice of rehabilitation; however, the structure also changed shape part way through the 1,500 ft. “The drain’s dimensions were 11 ft wide and 8 ft high but it changed shape a few times,” Silva says. “There was a 100-ft section where there was a cascade floor section that stepped down in 3-ft drops. On the upstream side of those drops, the drain turned into a “cathedral ceiling” type area, going from 8 ft high to 20 ft and then narrowed from 11 ft to 7 ft wide.”

After Phase I was completed, crews removed the bypass equipment. A&W returned in 2016 for Phase II to apply the epoxy to the walls (where the bypass equipment has been installed), as well as the ceiling. This phase, which also included grouting prior to applying epoxy to stop infiltration, was completed in about eight weeks.

A&W will return later this year for Phase III to finish the project, specifically to rehabilitate a 600-ft section within the 1,500-ft drain structure that contained a previously installed vinyl repair product that needed to be tied into the floor using two layers of S-Glass and epoxy.

Since the storm drain was owned by the City, the City engaged the services of a third-party engineering firm, experienced with structure repair and rehabilitation, to provide oversight of the pilot testing of the rehabilitation products and the subsequent rehabilitation of the structure utilizing the epoxy coating.

Project Challenges

This project posed numerous challenges for the A&W crews, beyond the drain’s changing dimensions. Silva notes the limited access to the structure. Access for the entire 1,500 ft of the storm drain was limited to two manholes, one a 60-in. diameter, 25-ft deep structure and the other, much smaller, approximately 800 ft from the primary manhole access. The smaller access point was to only be used to lower equipment and tools, for emergency evacuations, as well as ventilation. Given the confined space of the project, the owner’s representative provided essential health and safety oversight and management.

The material holding trailer was staged above-ground, from which a 450-ft umbilical cord ran down the primary manhole. Warren Environmental uses a 100 percent solids epoxy that is sprayed using a patented tank system. The epoxy also doesn’t use any solvents to thin it, making it easier to spray.

“Being able to spray from a 450-ft umbilical cord is fairly unique to what we have done,” Silva says. “We’ve taken on these big tunnels and figured out a way to spray at longer distances. The furthest distance we sprayed on this job was 675 ft.”

“This was a feat the company has never been able to do before and because of its success, much time and money were saved,” he adds.

Another challenge was dealing with the grout, ensuring that it adhered to the structure to stop the infiltration through chemical and mechanical fix approaches. “To apply epoxy, you can’t have an active leak. Most grouts react with water great but because there were other industrial products mixed in with the water, the grout wouldn’t always act the way you wanted it to,” Silva says. “We figured out a way and developed some techniques in the field that we trademarked to prevent not just water infiltration but also industrial product infiltration.”

The safety contractor rigorously managed the confined space safety. Air monitoring was mandatory in the work area and needed levels to be relayed to and recorded by the hole watch every 1/2 hour. It is worth mentioning that even in an eight-hour epoxy spray session with constant air monitoring, no actionable change in VOC, LELs, oxygen, and CO was recorded.

Silva says that unexpected challenges are part of the process and the ability to adjust and solve unexpected issues onsite keeps everyone on their toes. “Almost every job that I’ve been involved with goes smooth at times and then there’s always something that comes up. Something you never expect,” he says, noting how much “you need to be able to think on your feet and make it work.”

Sharon M. Bueno is managing editor of Trenchless Technology.