During development, the best-laid plans of engineers, designers, and planners take into account the snapshot of the area as it then exists in that time frame.
But beyond the frame, that which cannot be anticipated sometimes becomes a reality and calls for retrofitting in order to address changing needs.
Such is the case with stormwater measures. Improvements often have to be added in response to an increase in impervious surfaces. Increased runoff may necessitate larger pipes. New infrastructure might be needed when improvements are made or existing buildings are torn down and replaced. And, frequently, space can be a challenge in retrofits.
Often, municipalities and commercial entities must work with manufacturers to come up with solutions to fit a space that cannot accommodate an off-the-shelf system.
Underground in Illinois
StormTrap’s precast modular stormwater detention systems were selected in two stormwater retrofit projects recently completed by V3 Companies of Woodbridge, IL, a firm that serves clients’ land development, natural resources, and infrastructure needs.
In one project in Niles, IL, Harris Bank was building a new branch on a 1-acre site where a building previously existed and was torn down. There had been no stormwater detention requirements from the permitting agency, the Metropolitan Water Reclamation District of Greater Chicago. However, since Niles had been prone to flooding, officials requested a form of detention, notes Laura Shafer, project manager.
For the Harris site, V3 chose a StormTrap system measuring 5 feet deep, 56 feet long, and 42 feet wide with 0.26 acre-foot of storage. In choosing a location to place the system, V3 had to consider other utilities that were onsite. Although V3 chose the bank’s drive-through area as the installation site, it had to plan carefully to avoid placing it under the canopy of the drive-through area to avoid interference with the pneumatic tubes located under the ground.
“We had a small area we had to put it in. We placed it where we had the minimum amount of utilities,” says Shafer. “We worked with StormTrap to adjust the shape so it was the most compact, most efficient fit to maximize the volume for the small footprint.”
Since the system was installed a few years ago, the area has experienced no flooding issues, Shafer notes.
In another application at a school site in Chicago, V3 was asked by the Chicago Department of Water Management to provide stormwater detention in a project focusing on stormwater quality and quantity.
The project was being carried on in two phases on 2 acres. The school was being constructed during the first phase in about one-third of the area. The other two-thirds were to accommodate future construction of a parking deck and other buildings.
“We designed the stormwater for the entire 2 acres instead of just the 1 acre we were doing so we didn’t have to go back for more permits and put in a secondary system,” says Shafer. “We had to figure out where to put the StormTrap and have the correct size for future development.”
Not knowing the particulars of the future development on the site, V3 sought to minimize the footprint size and maximize the depth of the stormwater system as much as possible. A system measuring 34.5 feet wide, 84.5 feet long, and 5 feet deep, storing about 0.3 acre-foot, was installed.
The site had been developed previously with old buildings, a paved parking lot, and asphalt roofing–in other words, there were a lot of impervious surfaces, and the stormwater used to flow down into street gutters. Additionally, the site required remediation for contaminated soils prior to the new development.
“We also ended up putting in some BMPs [best management practices], such as green roofs, for future phases,” says Shafer. V3 worked with the city’s sewer department to determine the amount of detention needed rather than using straight calculations based on the impervious areas. StormTrap was flexible in helping V3 design a system that would fit the area, she adds.
Chicago is a combined sewer district, Shafer says. “The StormTrap is nice to use because you can use it in either location,” she says. “They can make these watertight, which is one of Chicago’s requirements.”
While there are higher costs at the outset because of that–open-bottomed systems cannot be used in Chicago–the StormTrap system is “a good system that can be used in multiple locations,” Shafer says.
Enhancing 1920s Infrastructure in Kansas
Goodland, KS, is like many United States towns: Stormwater retrofits are needed, but the budget doesn’t always allow for them.
Speaking to the importance of how municipalities should be preparing for stormwater retrofits in the future in response to aging infrastructure–among other factors–Darin Neufeld, an engineer with EBH & Associates in Goodland, says, “It’s tough to get smaller communities to plan far enough ahead to do large projects, whether it’s stormwater, pavement, or wastewater.”
Recognizing that, voters passed a special city/county sales tax for the purpose of funding street and utility reconstruction projects. State grants augmented the expenses. EBH was the engineering firm chosen to handle the jobs. Materials used for many of the retrofitting projects came from ADS; the storm sewer pipe had been designed around ADS N12 Ultra IB pipe, a smooth interior/corrugated exterior high-density polyethylene (HDPE) pipe. The pipe has integral bell and spigot joints, with ASTM F 477 gaskets installed on the spigot end.
The first job–enhancements on Cherry Street in Goodland–was completed in 2005. The project was a follow-up to a 2001 project EBH did for the Kansas Department of Transportation in installing a large detention pond. But there was more work to be done for stormwater capacity.
“For many, many years, people said that area was a low spot, a hole that held water,” says Neufeld. “We took the low spot and enhanced it to where we could have a street run through it, have a hiking and biking trail, seating areas, and landscaping.”
A berm was placed around the hiking and biking trails and area inlets were added.
Materials used included Nyloplast basins, 200 feet of 24-inch N12, and 100 feet of 30-inch N12.
Two projects were completed in 2006. One was a reconstruction of brick streets. There are brick intersections in Goodland dating to 1920. EBH helped renovate five intersections in the downtown area.
“A lot of the storm sewer that was installed at that time was old clay tile,” Neufeld says. “It was not even solid-cast clay; it was the old sections. Over the years, there have been points where that failed. There were voids underneath what concrete was there.
“There also were sink spots near that old storm sewer line. Part of the grant was to upgrade the brick surface. We did go back with real brick–not concrete pavers–but as we were doing that, we upgraded all of the storm sewer system underneath the area we replaced.”
Materials used include 1,000 feet of 18-inch Hancor Sure-Lok smooth interior HDPE storm sewer pipe and 240 feet of 24-inch Hancor pipe. The pipe has similar specifications to the ADS N12 pipe.
Another project completed in 2006 was along Armory Road. At five points along an existing storm sewer system that spread out over a half-mile on Armory Road, there were spots that needed new inlets or reconfiguration of existing inlets. To address the situation, EBH used 170 feet of 30-inch N12, 60 feet of 18-inch N12, and 16 feet of 24-inch N12.
The most recent project is along 17th Street. “There is only one major storm sewer system in the city of Goodland,” says Neufeld. “There are other minor ones around town, but the major one collects all of the downtown area and transports it to the east side of town to an open ditch that runs down to a tributary several miles away.”
The original system consisted of a 48-inch sectional clay line dating back to the early 1900s. “There were points where it was failing, and the brick street was in poor condition,” Neufeld says. “When they installed the original clay line, they ran it right down the middle of the street, so anytime it needed repairs, the whole street had to be closed.”
In addition, no one in the early 1920s had an inkling about the volume of water that would be moving through the pipes and the amount development that would occur, he points out.
“As we ran our calculations to find out what size we needed, we ended up sizing the new storm system for a 25-year event,” says Neufeld. Materials used included various sizes of N12, including 20 feet of 18-inch, 440 feet of 24-inch, 60 feet of 30-inch, 460 feet of 48-inch, and 1,600 feet of 60-inch.
“We would have liked to have gone bigger, but because we’re so flat here, we didn’t have the room,” he says. “In fact, it was tough to squeeze in a 60-inch. There are several places where we only have about 8 inches of base cover over the 60-inch before pavement–we’ve got 8 inches of base and then 8 inches of pavement.”
The system also cuts across a railroad right of way, which wasn’t an issue in the early 1920s, Neufeld says.
“The system ran under existing buildings that were built on top of it,” he adds. “It leads to a point of failure we didn’t want to have happen in the future. So we rerouted the storm system completely out in the street.
“However, we moved it to one side so it’s under just one driving lane, not in the center of the street. We did that partially to help us during construction so that as we were putting in the new one, the old one was still there and in place and live. Then, once we got the new one in place, we were able to go back and collapse the old one to make sure it didn’t collapse on us in the future.”
The Goodland projects are part of continuing program of reconstruction, with another project to start later in 2007 and several more in the planning stages.
EBH chose ADS products after seeing company representatives at various trade shows. “For dollar per foot, the dual wall–or, in some cases, we’ve even used the triple wall–is the cheapest way for us to replace infrastructure,” Neufeld says. “Also, it’s easy enough to work with that if we get the basics of it put in, a lot of the city crews can actually handle it and install more of it later themselves if needed, whereas if we are dealing with reinforced concrete, there are not that many options.
“We try to stay away from corrugated metal because it does not have near the lifespan of either of the other materials. And, in most of our cases, because of how flat Kansas is, we don’t have a lot of cover over our culverts or drainage systems. We want something that’s load-rated with very minimal cover.”
Defending Against a Rising Lake
In 1997, Lake Erie and Lake Ontario were at record-high levels. “We were getting near-shoreline flooding. With the baseline of the lake so high, even a minor storm would come along and cause flooding in the near-shoreline area,” says Gary Shoffstall, chief of the Emergency Management Office for the Buffalo, NY, District of the US Army Corps of Engineers. “You didn’t need a 100-year storm event to cause problems–a 10-year storm event could cause problems.”
In Oregon, OH, east of Toledo, weather events would be a source of consternation to some residents. A stormwater drainage ditch passed underneath a shoreline road and entered Lake Erie. With Lake Erie’s high level, even the slightest storm forced the lake water back up underneath the road, into the drainage ditch, and onto some housing developments, causing residential flooding and endangering the road.
The Army Corps of Engineers uses its Advanced Measures program to do preliminary proactive work in an attempt to prevent more costly damage. The program is initiated through state governors’ requests.
“A governor provides a list of sites endangered by a storm event,” says Shoffstall. “We investigate them to see if the parameters justify an Advanced Measures project. It’s set up as most federal projects are: The benefits need to exceed the cost. We also need to be able to build the project prior to landfall of the event, so this will work if we have something like high lake levels where the condition is going to be there for awhile.”
In the Oregon, OH, case, building a temporary levee around the residential structures being flooded was too expensive an option and still left the road at risk, Shoffstall says.
An alternative project was proposed and executed, which involved extending the stormwater drainage ditch from the lake through the use of a 6-foot-diameter reinforced concrete pipe (RCP). “It’s a very heavy, thick-walled pipe and can take vehicular traffic over the top of it,” explains Shoffstall.
The corps then constructed a small revetment, or portion of raised earth, and armored it with rock to withstand ice flows and wave action coming from the lake from which the RCP would extend.
“Traditionally, with the Corps of Engineers, we put on a flap gate to allow one-way flow of the water so that interior drainage water could exit into Lake Erie, but the Lake Erie waters would be prevented from coming back,” says Shoffstall.
Given that the RCP would be 6 feet in diameter, however, a flap gate to fit it would be “huge,” Shoffstall notes. “It is usually made out of metal, bronze, or brass so that it doesn’t corrode, but it’s extremely expensive, extremely heavy, extremely prone to vandalism, and also extremely prone to being compromised by debris,” he adds.
Shoffstall explains that the flap gate closes completely, providing a 360-degree seal around the pipe circumference. But if debris enters the stormwater drain and gets caught in the gate, it can’t make a seal. Any intervention required would need to be manual, he adds.
Because of what the Army Corps views as the negatives of a flap gate, alternatives were considered. One alternative came through the Red Valve Co.’s Tideflex Technologies. The Army Corps chose Tideflex elastomer (flexible) check valves.
According to the Red Valve Co., the rubber check valves are designed for no routine maintenance or repair. They operate solely on line and back pressure and require no outside energy source for operation. The check valves seal and close tightly around debris with less than 1 pound per square inch of backpressure. They will not warp or freeze, can handle large obstructions without jamming, and are banded easily on the end of a discharge or storm sewer line, eliminating the need for headwalls.
The corps chose the TF2 slip-on. “This being a 6-foot-interior-diameter pipe, we needed a slip-on, so it goes over the outside diameter of this pipe,” says Shoffstall. “By the time you pinched it shut, it measured roughly 9 feet, 2 inches, tall. Unless someone has come up with something I’m not aware of, it is the largest elastomer check valve on the Great Lakes.”
One of the advantages of the Tideflex valve is that it allowed discharge of the flow so the corps could allow the surface-water runoff in the interior to exit out into the lake, Shoffstall says.
“When the water from the lake comes back, the valve closes. It’s difficult for floating debris to come back into the valve with the wave energy, so even if floating debris does get into it, it will wrap around it and essentially form a seal.
“Every time the wave recedes and the interior flow pushes out, there’s a chance of it clearing that debris and then it can seal completely by itself.”
Shoffstall says another advantage is that if wave action brings in sediment, sands, gravels, and other debris, the system will still work, unlike a flap gate that cannot close when debris accumulates.
“In fact, because the lake levels have receded so much, the bottom third of the Tideflex is actually buried, but it still works fine,” he says. “And it is virtually vandal proof.”
The elastomer check valve also works with temperature fluctuations. “Because it is flexible, even if you get a hard freeze and for some reason a sudden runoff, the valve will open above the ice,” says Shoffstall. “The other advantage of the carbon black in its construction is that it will absorb whatever infrared radiation is being provided by the winter sun and will essentially melt the ice in close proximity, so the ice never freezes tight against it. It always has a little bit of open water around it and that gives it more ability to work.
“Because of the efficiency of the elastomer check valve, we did not have to install a positive closure unit behind it,” he says. “From a benefit/cost ratio, the original design used a flap gate, which is relatively cheap–even though a 6-foot diameter would be very expensive, but still relatively cheap. The positive closure structure raises the cost–the two mechanisms are expensive when used in tandem.
“The elastomer check valve is not cheap. When we first mentioned it to the Town of Oregon, there was some shock. But when they considered the cost of the other two components required as a pair, the single unit of the elastomer check valve was comparable, though a bit more expensive.”
City officials were sold on the system on the basis of it being virtually maintenance free.
“I’ve had nothing but compliments from the city after its installation,” says Shoffstall. “It’s been out there about nine years and hasn’t given them a lick of trouble, and it is working remarkably well if you consider a third of it is actually buried in the beach. So we’ve recommended elastomer check valves in place of flap gates for just about every project we’ve built on the Great Lakes. I love these things; they’re fantastic.”
More Stormwater Retrofits
Safety concerns abound at at-grade crossings where vehicle intersections meet with railroad lines. As such, a number of municipalities are retrofitting these dangerous intersections with a grade separation.
In a grade separation, the rail line stays where it is, and an underpass is created for automotive traffic. This in turn creates a low gravity point. Consequently, stormwater collects in the underpass and often needs to be pumped up to the level of the stormwater infrastructure.
In Chicago, a grade crossing project was done on Grand Avenue, a four-lane artery running east and west through Chicago’s western suburbs. “There was a set of tracks that was utilized by a freight rail system that was becoming quite a nuisance because it held up traffic,” explains Frank Noonan, a senior associate with CTE Engineers. “It was decided to put a grade separation in, and as a result, you’ve got to put in a pump station to evacuate all of the stormwater that runs down through the bottom of the grade separation.”
CTE Engineers in Chicago contacted Romtec for a solution, which provided a retention tank and a stormwater pumping system to evacuate the stormwater and discharge it to the sewer system. Previously, operations were based on gravity flow.
“It’s retained in the retention tanks, and it can be discharged at a lower rate,” Noonan notes.
DSW Construction, a general contracting firm in Louisville, CO, chose ACO Polymer Products in addressing a retrofitting project earlier this year at a commercial site where capacity issues were of concern. ACO manufactures precast drainage systems.
“When we designed it with ACO, we had to design it so that particular area would work,” Len Rice, a DSW superintendent, says. “We got together and came up with solution and installed it ourselves.”
DSW put in 400 feet of storm drain, retrofitting it to existing pipe. The storm drains obtained from ACO were designed to work with the existing storm line, Rice says.
The solution also involved installing catch basins at either end of the existing pipe.ACO’s FlowDrain FG100–a general-purpose, sloped trench drain system–was used in a truck unloading area. “It worked well,” Rice says of the approach. “When they flushed the fire line, 2,000 gallons of water came through and it all held it–it went into the retention pond. It’s quite a deal, how it works.”