By Carol Brzozowski

North America's population is mushrooming. Its piping infrastructure is dated in many places. Older stormwater and combined storm/sanitary sewer pipes are leaking or too small to accommodate an increasing populace whose housing needs mean more paved and impervious surfaces, causing a greater volume and velocity of runoff.

In urban areas there often is limited working space in which to make repairs or access the system. When cities with combined sanitary and storm sewers experience increased runoff, sewer overflows (CSOs) can result, causing raw sewage to back up into streets or basements or overwhelming wastewater treatment plants to the extent that only partially treated effluent is discharged.

Adding Storm Sewers in East York

In the Toronto, ON, region of Canada, a system that is easily a half-century old was showing its age.

"Some residents living in the East York area had experienced some basement flooding because there is a combined sewer system in this area that carries sanitary sewage and rainwater," says Harry Persaud, a senior engineer in the design and construction group in the technical services division with the City of Toronto, which assists in designing and constructing sewers and water mains.

"Because of the number of complaints we received for basement flooding, we decided to build brand-new storm sewers to alleviate the problem. So these storm sewers will be taking the load from the stormwater and hopefully minimize or eliminate the basement flooding."

Wet weather conditions forced stormwater discharge and sanitary sewage into combined sewers that do not have enough capacity. Where open fields once absorbed the stormwater, it is now being conveyed over building roofs to paved surfaces, with the combination of stormwater and sanitary sewage flooding and overcharging the wastewater treatment plants.

"In larger storms, the system can only take so much of the stormwater," Persaud points out. "It might have been designed for a five- to 10-year storm, coupled with the sanitary flow. So anything larger than that would result in some surcharging of the existing system, which would result in the backup into the basements."

In rectifying the problem in a neighborhood in East York, he says, one of the challenges was a deep sewer that necessitated the installation of a 1,200-mm- (48-in.-) diameter reinforced concrete storm sewer.

Newly constructed trunk storm sewers would collect the flow from local storm sewers and discharge the effluent to East York's Leaside trunk storm sewer. Because construction would be taking place on an existing road in a residential area with overhead wires, it seemed to engineers that the best way to approach the job was through a jack-and-bore operation as opposed to an open cut. "Most of the projects are done by open-cut method, simply because the sewers are not as deep or as big," Persaud explains. "We probably don't do the bore-and-jack method more than 10% of the time."

He notes an additional challenge: "There was a high groundwater table, and we did cross what seemed to be an underground stream. So we had to implement some redesigns to the support system for the shaft simply because of the volume of water we had there. Other than that, it was normal construction with jacking and boring."

The soil in the area is saturated below 3-5 m to a depth of 6.5 m (21.3 ft.). "The water table is at that level; once you go below that, there's water," Persaud says. The invert of the installed trunk sewer is at 9 m (29.5 ft.). A lot of water was getting into the pipe during the jack-and-bore process. "We had to constantly pump water from the boring end of the pipe back up to the top end to keep the operation as dry as possible," he adds.

Some 440 m (1,443 ft.) of 1,200-mm- (48-in.-) diameter jacking pipe was installed. Concrete pipe was chosen for the job because it is the only pipe that can be jacked and bored, states Persaud.

"Different engineers prefer different materials," he says. "I prefer concrete pipes, mostly because of durability. They're going to be here in 100 years, easily. We use a lot of plastic pipes too - generally for the pipes smaller than 18 inches, but not as much as concrete."

Persaud anticipates very little maintenance on the pipes. "It's a large pipe, which requires less maintenance than a smaller pipe. Because it's stormwater in an area that is already well established, we don't expect much in the way of silt, so it's probably not going to be a maintenance nightmare."

In considering projects, Persaud says he often relies on provincial standards, which can be used in the absence of city standards. He indicates that Toronto has a comprehensive set of specifications for constructing sewers, such as requirements for the strength of materials for sewers and water mains. For sewers, he follows provincial standards that specify trench requirements for certain depths of sewers.

Since 1998, when the cities surrounding Toronto went through an amalgamation process to create a "megacity," the way the area handles the retrofitting of systems has changed, Persaud observes. "The practices were generally different in all these different jurisdictions. In the former city, they had a lot of combined sewers at one time, and then 20 to 25 years ago they embarked on a sewer separation program." The city installed many new storm sewers in response to environmental concerns and also in an effort to prevent flooding.

"These days, they are revisiting the system, and some of the former municipalities - from before the amalgamation with the former City of Toronto - are trying to determine if the existing combined sewer system is going to be adequate to take stormwater, as well as sanitary sewage," he states.

"They may not put in storm sewers. They probably would be doing that in pockets in the city only where they're experiencing basement flooding. We can see the extent of the construction of storm sewers going down with a possibility of a rise in the increase of replacement of combined sewers."

With much of the region's infrastructure "now meeting the end of its life," Persaud says, "you can expect the city to spend a fair bit of money for rehab for many years to come."

Battling Cave-Ins in Virginia

Meanwhile, in the south, frequent cave-ins occur in Chesapeake, VA, where Richard Broad serves as the stormwater administrator. Chesapeake, with a population of more than 200,000, is the 27^th largest metro area in the country in a region with more than 1.5 million residents. It is one of the fastest-growing cities in Virginia, with a population increase of 30.7% since 1990.

Those statistics mean that the system is going to be taxed. The 353-mi.² area experiences an annual rainfall of 48 in. - sometimes more.

"Virginia is blessed with fairly even rainfall," Broad points out. "It gets about 3.5 inches a month over many, many years. So when we get more than that, it's pretty substantial."

The region experiences 200-300 collapses around pipe per year. Those cave-ins are the main problem that Chesapeake faces from a cost standpoint and from its complexity to fix, he notes.

"We have a lot of blocked ditches. And Chesapeake is essentially a county, even though it's incorporated as a city. So we've got 353 square miles - it's a lot of agricultural land. There are a lot of wooded ditches that are very difficult to get to, so that's a challenge in itself," relates Broad.

Conversely, there are many high-growth areas, with an ongoing building boom of homes and businesses. "When you have that kind of fevered pitch of building, the city's resources get stretched really thin," he contends. "You don't have the inspection staff to stand out there on every job and watch everything. A lot of times, our inspectors are juggling 14 construction projects, so they're lucky if they drive by the sites one time a day." That can impact quality control on pipe installation.

"We couldn't look at bedding, which is a big problem," Broad says. "Up until a few years ago, we didn't even require that the pipe joints be wrapped. So the ones failing now are typically the ones that were installed incorrectly or sloppily or are inherent with a lot of water and they're shallow, so you get these cave-ins over the unwrapped pipe joints and around structures."

Depending on the nature of the cave-in, it can take up to a month to fix. "When you get a very rainy period, the rain brings these to the surface. Quite literally, that's when they appear, because the rainwater seeps down, takes the surface soil down into the pipe, and so that's when the cave-in calls just mushroom," Broad observes, noting that when there was a drought last summer, there had been a slowdown in the number of calls received.

The system dates back to 1963, when the city was incorporated. The building boom started in the 1970s. Some systems, if they weren't installed correctly, have failed in as few as five years. Cave-ins not only can create traffic and structural hazards but also can pave the way for groundwater or stream contamination.

Broad says Chesapeake's first priority is to its citizens in getting the cave-ins fixed. In the last year, Chesapeake increased the number of cave-in crews from three to five by reducing the number of people in each crew and using mini-excavators and some trailers that could be towed with standard trucks rather than using large dump trucks.

Broad also has been concentrating on improving inspections of pipes in new construction projects. "The subdivisions are where we have a lot of trouble," he reports. "The city has undergone huge budget crunches here, like in every state of the union. The state coffers are way down, they've cut our funding, we've had to cut back, and we've had a hiring freeze for about a year."

Public works inspectors are not replaced, except in an emergency situation, so those who still are working are stretched thin, Broad notes. One time-saver has been using underground televising equipment for inspections. Before its use, inspection would be done visually, covering only what could be viewed from the manhole.

"When you'd get much beyond it, it was anybody's guess," he recalls. "Plus, they would use intuitive information. If they heard water running in the system constantly - or other clues with which they were familiar - they would use that to judge the system, but it was pretty unscientific."

What the camera has found is as bad as Broad suspected, and that has changed the manner in which his department operates.

"A lot of the jobs builders were used to having [projects] rubber-stamped through. We're saying that we're not accepting them or we're giving them a long punch list of things to fix," he says. "There's an uproar in the city about it because we have raised the bar a little bit on standards. We're not changing what they're required to do. We're just looking at it harder." He points out to municipal officials that either the job is done right the first time or the local government will spend much more money down the road to fix the problems created.

Broad says another problem with the systems is silt. "Some builders are not doing a very good job on erosion and sediment control. We don't have the inspection staff to turn the heat up on them. So we're changing the rules on that and beefing up the inspections."

In an effort to address Chesapeake's ongoing stormwater problems, Broad meets every other week with Sam Sawan, the city's senior stormwater engineer. One of Chesapeake's approaches to cave-ins, which for the most part are the result of leaking joins in the pipeline or to a structure, is to use filter fabric to wrap the joints. The city now requires joints to be watertight.

For concrete pipes, that means a preformed, flexible plastic sealing compound or an approved equivalent. Corrugated metal pipe joints are linked with corrugated or hugger-type connecting bands that engage at least one annular corrugation on each side of the joint. The bands are asphalt-coated with a minimum 7-in.-wide neoprene gasket. The requirement is increased to 12-in. bands for 36- to 84-in.-diameter pipes.

No dimple bands are permitted. PVC pipe gaskets must conform to ASTMF-477 Standard Specifications for Elastomeric Seals (Gaskets) for Joining Plastic Pipe. High-density polyethylene (HDPE) pipe has to conform to AASHTO M252 Corrugated Polyethylene Drainage Turing and M294 Corrugated Polyethylene Pipe, 12- to 36-inch Diameter. All pipe drains, except PVC storm drainage pipe, are required to be wrapped with a nonwoven erosion control filter material.

Broad states that Chesapeake has used a lot of corrugated metal pipes but says he's on a campaign to get rid of them because of the fair amount of salt in the local waters. He recounts an incident the day before Thanksgiving when a large-diameter corrugated metal pipe, installed in the early 1980s, failed. Merchants in the area were panicking because the day after Thanksgiving is their prime shopping day.

"It was completely rusted through, and we're going to have to spend a lot of the city's money to go in and fix it," Broad says, adding that the city had to do an emergency patch on the evening before Thanksgiving. "I think they're going to run plastic pipe through it and concrete the annular space."

New Drainage in the Midwest

An old ditch and culvert drainage system on Forest Drive, a residential street in North Pekin, IL, serving about 30 homes, was incapable of handling even an inch and a half of rain. The system dated to the 1940s, and the homes encountered serious flooding during heavy-rain events. In 1999, the city used corrugated polyethylene pipe from ADS to rectify the problem.

"The system we installed worked perfectly. We haven't had a problem with it since," says Frank Hardy, the superintendent of public works. The flow characteristics of the pipe and its Manning 'n' value are what prompted its use, he adds.

"We were able to put it in an area that had very little fall to it," he says. "It did let the water flow to a stream down the street; that's where we terminated the tile. We put tiles up and down both sides of the street with inlets, and we were able to capture all that rain that was flooding the homes. It's worked great. We haven't had one complaint."

Previously each driveway had a culvert in it, and an old concrete system was too small to handle the flows, Hardy says, noting it was "old and dilapidated."

Nine hundred feet of 15- to 24-in. corrugated pipe was used. The pipe was laid beneath 12 in. of cover. Hardy remarks that he anticipates the system will "last longer than I do."

Elsewhere in the Midwest in Greenville, MI, a major rainstorm in the mid-1980s most likely exceeded the 100-year storm and flooded the area. There was damage to apartment buildings in an area with no positive outlet, relates city engineer Doug Hinken.

"It had a pond that was subject to percolation. A development in that drainage area allowed silt to get into the pond. It silted up the basin, and it was no longer percolating," Hinken explains, adding the drainage system had been about 20 years old.

To improve drainage, the drain commissioner identified another pond west of the trouble spot that was much larger and also subject to percolation and evaporation. "It was the only way for the water to get out," he points out. "But the pond includes a much larger surface area. There was some land that we were going to cross that was potentially commercial land, but it was farmland at the time. So we needed to convey a bunch of water from the east to the west to the pond. That essentially was the problem."

Looking to build a new stormwater drainage system to accommodate the needs of new businesses in Greenville and open the gates for further development, Hinken initially designed and specified the new stormwater drainage system with concrete but switched to HDPE.

"We do our own construction. The size of the pipes I was looking for was 54 inches, and that would max out our equipment," he says of concrete. "The site we were going to be crossing was a clay material, so we were concerned with bringing in heavy pipe. We were going to have to build some kind of a haul road and rent equipment to put in the heavy pipe."

Hinken was intrigued at the development of a 60-in. HDPE pipe by Hancor. "We thought that sounded interesting because it was light enough that our equipment could handle it and we wouldn't have to build the haul road. If it was cost-effective, we would be willing to try it. We've used HDPE for many years prior to that in the smaller sizes, so we thought it would be a good possibility."

To replace the old open ditch drain system, the city used 1,060 ft. of 60-in. corrugated annular Hi-Q pipe. Greenville had been the first in the country to use the pipe. Hinken reports that the city checked the new system last year and found some deflections, which he attributed to the city's construction methods, but otherwise it was in good shape.

"I expect this should last as long as concrete," he states.

Frequent contributor Carol Brzozowski is a journalist in Coral Springs, FL.

SW - September/October 2003

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