Underground pipes and other structures do more than free up aboveground space. When they’re carefully selected and designed, they can accomplish a wide variety of goals, often in challenging situations.
For example, at the Sacred Heart Senior Apartments in Saint Francis, WI, a pipe system meets requirements for total suspended solids (TSS) removal and reduces peak runoff. At the 3M corporate headquarters in St. Paul, MN, a different pipe system in a different configuration provides required improvements in water quality, rate control, and infiltration. At a Save-A-Lot convenience store in Carbondale, IL, yet another system meets the city’s stormwater detention regulations. At the Baha’i Temple in Wilmette, IL, a concrete system functions as a cistern and captures rainwater for irrigation.
These systems may be combined with a separate water filtration system. Once they’re covered, usually by a parking lot or landscaping, they give no indication of the often very sophisticated system operating just below the surface.
Sacred Heart Senior Apartments
When the parish of The Sacred Heart of Jesus Church in Saint Francis, WI, planned a rehab and an addition to its 1960s building, Josh Russart, a project engineer at The Sigma Group in Milwaukee, WI, faced a challenge in designing the stormwater management plan.
“We had a 50% requirement for TSS removal for the entire project site,” he says, “but between the building and the impervious surfaces, there was no room whatsoever for an aboveground stormwater pond.”
The first step was to use an underground stormwater detention system. The key, though, was to design the system in a serpentine configuration, with a permanent 3.5-foot pool of water to maximize the settling time and TSS removal. “The system functions as an underground wet pond,” says Russart. “That’s how we obtained the TSS
removal.”
He used corrugated Aluminized Steel Type 2 pipe from Contech Construction Products Inc. in West Chester, OH. The aluminum coating was chosen to meet the 75-year service life required by the church. The pipe was the most economical for what the site needed, he says.
The system was installed in the late summer and fall of 2011. It was used to meet peak rate runoff requirements per the Milwaukee Metropolitan Sewerage District (MMSD) and the city, as well as TSS removal requirements.
“Part of the site was treated as new development and part as redevelopment by the DNR [Department of Natural Resources] and the city,” says Russart. In addition to renovating the sanctuary and the rectory, the parish is using former classroom space above the church as well as building a new structure to house seniors of all denominations in the new 68-unit Sacred Heart Senior Apartments. It is also building a large common room and new
parking, driveways, and garages for the residents. Approximately 80% of the 4-acre disturbance area will be impervious.
Although the church is within the Milwaukee Metropolitan Area, the only stormwater runoff comes from onsite. It flows from the church grounds into city storm sewers and from there into nearby Lake Michigan.
The runoff carries pollutants such as silt, decaying plant and animal matter, particulates from parking lots and roofs, and nutrients from landscaping. High levels of TSS in bodies of water can prevent light from reaching submerged vegetation and affect the ability of fish to see and catch food, and it often means higher concentrations of bacteria, nutrients, pesticides, and metals in the water.
An additional challenge was that it wasn’t possible to drain all the runoff to the new system. For example, Russart says, some existing storm pipes already ran to the street and it didn’t make sense from a cost standpoint to reroute them. Untreated runoff from 1.17 acres of the 4-acre area drains offsite.
However, runoff from 2.83 acres is being treated. Russart used WinSLAMM to determine how much active detention storage the pipes had to have in order to comply with the requirements.
WinSLAMM (Windows Source Loading and Management Model) is used primarily as a planning tool. It was developed in the late 1970s to help users understand the relationship between the sources of urban pollutants and the quality of runoff. It now includes a wide variety of source area and outfall control practices such as infiltration practices, detention ponds, porous pavement, street cleaning, catch basin cleaning, and grass swales, and it can be used with GIS.
“We had to obtain 50% TSS removal for the whole site, so we had to overcompensate with the detainment in the underground system to offset the areas receiving 0% TSS removal,” says Russart. According to WinSLAMM, the underground system had to have 7,390 square feet of surface area at the water line and 48,035 cubic feet of active detention storage to achieve the required percent removal.
The contractor, A.W. Oakes & Son, constructed the system. “It seems like it went pretty smoothly from a construction standpoint,” says Russart.
The corrugated steel interior walls support the pipe, which has been hot-dipped in commercially pure aluminum to increase its design life, according to Contech. In addition, the aluminum coating provides excellent barrier protection in both hard and soft water.
A.W. Oakes & Son used 644 feet of 142- by 91-inch pipe to reach the necessary storage capacity. Crews set the invert of the outlet pipe at 3.5 feet above the system’s bottom to create the permanent pool of water. Russart calculates that this results in a TSS removal of 76.6% from the underground system and a net 56.0% removal for the project site.
“The primary maintenance is needed because it’s a permanent pond, and because it’s used for TSS removal,” says Russart. “Solids will accumulate.”
The system has to be inspected at least twice a year. When the accumulated debris reaches an average of 4 inches or a depth of 6 inches in any one location, it will be removed by a combination of jetting and vacuuming. Modeling has shown that the sediment buildup would be less than 6 inches in a 20-year time span.
3M Corporate Headquarters
Usually when a building and its grounds are updated, the amount of hardscape increases. In the case of the 3M corporate headquarters in St. Paul, though, a priority of the design architects was to eliminate as much impervious area as possible. Darren Schwankl, a civil engineer with TKDA at 3M, who worked on the site design for the project, reduced almost a third of the impervious area at the site by removing an irrigation pool and replacing it with extensive landscaping and underground stormwater chambers.
City and watershed district regulations required improvements in water quality, rate control, and volume reduction. The necessity for volume reduction, or infiltration, is relatively new, Schwankl says. Within the last three to five years a number of watershed districts across the state have begun to integrate it into their requirements.
“Infiltration has really taken off,” says Schwankl. “It goes hand in hand with LID [low-impact development].”
Although the designers of the project reduced the net impervious surface, they were required to provide infiltration (volume reduction) as well, because the design included reconstructed impervious surfaces. The design architects didn’t want an infiltration pond at grade, so Schwankl chose an underground chamber system for filtration from Triton Stormwater Solutions in Brighton, MI. This system provides more than filtration, he says.
“Underground chambers provide flexibility. The volume reduction, or partial recharge, requirement is met, and the surface area above the footprint can be utilized for other site development.”
The 400-acre 3M campus is just 4 miles from downtown St. Paul. “Stormwater runoff onto the site contains all the pollutants you’d see from any urban setting,” says Schwankl, “phosphorus, heavy metals, and suspended solids.”
He designed stormwater pretreatment features to improve the water quality and the discharge rate within the construction limit and connected them to the underground chamber system. Stormwater runoff flows from the chambers’ subdrain system into the site’s storm sewer system and eventually to the Mississippi River, just 3 or 4 miles downstream.
The total disturbed area was approximately 7.5 acres. The contractor, Minnesota Utilities & Excavating (MUE) in Forest Lake, demolished the existing roads and the irrigation pool with its fountain. Eliminating just the irrigation pool reduced the impervious surface by 2 acres.
MUE built a new parking lot and a road with a turnaround in front of the building. The chambers are under the green space and landscaping adjacent to the new building entrance. They cover an area of approximately 100 by 30 feet and can hold the first 1-inch-plus of stormwater runoff from the reconstructed impervious surfaces in a storm event, some 7,500 cubic feet.
“That’s where you’re going to get the grit, and the grease, and the oil,” says Schwankl. “The chambers also achieve some rate control, but this isn’t a rate control design.”
Crews excavated approximately 8 feet deep, placed 8-inch perforated, corrugated high-density polyethylene (HDPE) pipe from Northern Pipe Products on the bottom, and covered it with an 18-inch layer of washed sand to provide the filtration component. Water filters through the sand into the holes in the pipe and from there into the site’s storm sewer system.
They then placed a layer of 6-ounce nonwoven geofabric on the sand, to separate the sand from the 6-inch layer of 3/4-inch to 2-inch clean stone placed on top of it, and then installed the chambers on the stone. The chambers are made of soy resin and are very inert, so it’s unlikely that there will be a problem with degradation, Schwankl says.
“The chambers are very simple to install,” he says. “They snap together like puzzle pieces. MUE broke ground on a Thursday, and by Tuesday at the end of the day, it was backfilled.” From a cost perspective, it was competitive with the other products on the market, and the project qualified for a cost-share grant for sustainable landscaping from the watershed district.
Instead of a header row floor from Triton, a 6-inch concrete pad was used. This is where any influent runoff solids will deposit before they can enter the chambers and where maintenance will take place.
Crews placed additional stone between the chambers, to 6 inches above them, and around the perimeter. The void spaces between the stone provide both structural support and storage volume for runoff. The void volume was included in the volume calculations. Finally, the entire system was wrapped in geofabric on the sides and top so there would be no fouling of the Triton chamber, sand, and rock system by the native materials.
“It’s a nice system,” says Schwankl. “The landscaping includes a wide variety of locally sourced perennials and native grasses, as well as aggregate and paved walking trails. It’s functional and it blends aesthetically with what the design architects were looking for.”
Save-A-Lot Convenience Store
When the buyers of a lot in Carbondale in southern Illinois demolished four small houses and built a Save-A-Lot convenience store and a parking lot in 2004, the designer and the installers of the stormwater management system faced multiple challenges. The site was virtually impervious, the project area small and sodden, and the outflow elevation of the pipes very restricted.
Praveen Sunny, a civil engineer with Asaturian, Eaton & Associates PC, a consulting engineering and land surveying company, who designed the project, chose 18-inch-diameter corrugated, perforated Mega Green pipe from ADS (Advanced Drainage Systems Inc.) in Hilliard, OH. “It was the biggest pipe you can get and still have adequate cover for loading and traffic, and enough fall for discharge,” he says.
Carbondale lies almost 300 miles south of Chicago and just north of the Shawnee National Forest. It’s the home of the main campus of Southern Illinois University, the city’s main employer. The land is fairly flat and the soil is clay.
The Save-A-Lot sits on 1.35 acres in a commercial district with a large housing area to the south. Stormwater comes from the south and discharges into the parking lot. Runoff from the site goes into the city stormwater system and then into Piles Fork, the city’s main discharge creek, and ultimately into the Mississippi River.
“The City of Carbondale has minimum regulations to detain water from a 5-year storm event with a 60-minute duration,” says Sunny. “That boils down to approximately 2.12 inches per hour.” There was no requirement for water quality.
The footprint of the pipes is approximately 110 by 45 feet, he says, and the system can hold 2,624 cubic feet of water.
The project area was quite cramped, says Steven McGee, senior vice president of Fager-McGee Commercial Construction, Inc. of Murphysboro, IL, which installed the system. Worse, though, he says, “It was a very muddy site. It was sort of swampy. We buried a couple of track hoes in there.”
Crews excavated some 8 to 10 feet down before reaching firm ground, then filled the hole with rock to approximately 4 feet below grade. They used an aggregate material for the pipe sub-base and backfill as outlined in the ADS installation guidelines. Because it’s a closed system, they didn’t use a liner.
Mega Green pipes are made with 40% recycled material to help building projects qualify for Leadership in Energy and Environmental Design (LEED) certification, according to the manufacturer. These pipes are designed for storm sewers, retention/detention systems, waterways, and other projects requiring high performance and cost effectiveness.
The outflow elevation dictated the size of the pipe. It also posed the biggest challenge: getting the required cover on the pipes with the finished grade, Sunny says. “We were stuck on the outflow elevation. We were tying into an existing storm sewer to the south, and we had minimum grade.”
Fager-McGee installed 14 laterals and a header pipe on each end to connect them together. The control structure is connected to the city system by 8-inch pipe. It’s sized to restrict the flow and let it out at a controlled rate. On a 5-year storm event, it will fill up.
Crews backfilled between and above the pipes and compacted the backfill thoroughly.
“Without enough compaction, you can lose the seals on the joints, and everything can come loose,” says Sunny.
A parking lot was built above the system.
Baha’i Temple Rainwater Harvesting Project
The Baha’i Temple in the Village of Wilmette, IL, sits on a bluff overlooking Lake Michigan. The graceful nine-sided building is surrounded by nine gardens, each with walkways and fountains. Underneath one of these gardens, a DoubleTrap stormwater system by StormTrap of Morris, IL, now captures rainwater, which the temple will reuse to irrigate its gardens.
“The gardens have been irrigated with village water for many years,” says Bill Perry, P.E., vice president of Watermark Engineering Resources Ltd. in Aurora, IL, which designed the project. “In keeping with their desire to be an environmentally friendly neighbor, the Baha’i team decided to install infrastructure that could capture the natural stormwater on the site and reuse it for irrigation purposes.”
Perry chose the StormTrap system because it could fit in the space that was provided and still store an acceptable amount of stormwater. In addition, it could be constructed under one of the gardens without disturbing the landscaping above it.
The temple grounds are very close to Lake Michigan to the east. A stormwater channel winds around from the north to the west, and a residential area lies to the south. No stormwater runs onto the 5.5-acre property from the surrounding area, so there was minimal concern about pollutants in the irrigation water.
The lower level, the oldest part of the temple, contains the cornerstone, which was laid by the son of the founder of the Baha’i faith during the groundbreaking in 1912. The temple was completed in 1953.
Perry began by researching old drawings and records. One reason, he says, was to be able use existing infrastructure wherever possible. The other, though, was to find out why abandoned pipes had been abandoned, to ensure that he didn’t repeat any past problems.
He designed a system of storm sewers around the property. Pipes take the runoff from excess irrigation as well as from storm events to the cistern. “Some of the old pipes were already in place and some are new,” he says. “We rerouted around the entire grounds.”
One challenge was to capture as much stormwater as possible while disturbing the existing infrastructure as little as possible.
“We didn’t want to tear up all the gardens,” he says. “There’s an area just north of the cistern that’s approximately 10 feet lower than the rest of the gardens, which is used as access to the lower level of the House of Worship. There was a concern that we wouldn’t be able to pick up about half the runoff from the grounds because we wouldn’t be able to take the pipe through this area. Ultimately, we were able to bring the water around underneath the entryway to the cistern, which provided an additional source of volume in the cistern.”
The timeframe for installing the DoubleTrap units was another challenge. “They wanted the grounds completed for a ceremony to recognize the 100th anniversary of the groundbreaking, in the spring of 2012,” says Perry. “The gardens had to be constructed, and they’re very intricate. Because the cistern is underneath a garden, we had to get the unit in, backfill, and then allow enough time for things to start growing again.”
The contractor, Biaggi Plumbing, set the entire StormTrap cistern in the early summer of 2011, in just one day. “The installation went very well, very quickly after the hole was dug,” says Perry.
The unit is approximately 42 by 14 by 10 feet and holds 5,200 cubic feet, or 38,300 gallons, of water. It has a long service life, he says. Because particles will enter with the water, it will need to be kept clean of debris, and the valves will need to be checked to make sure they’re in working order.
Biaggi crews excavated some 15 feet belowground, placed aggregate to level the bottom of the pit, and added sand for leveling in places that needed to be raised slightly. They installed the DoubleTrap system, wrapped it in a HDPE liner membrane to make it impermeable, and surrounded the membrane with geofabric for strength. They placed additional stone around the perimeter of the unit and filled in the 5-foot space above the unit and the stone with a layer of excavated clay soil and then a layer of topsoil for the
garden.
A valve on the cistern controls the flow of water to a separate structure that filters any remaining particles that haven’t settled out. The filtered water flows to a pump in the temple, which distributes the water to all nine gardens. In the winter months, the valve can be opened so stormwater flows directly to the Metropolitan Water Reclamation District (MWRD) channel, which empties into Lake Michigan.
“We don’t want the water to sit there and be stagnant or go through freeze/thaw cycles,” says Perry. “In the spring, they close the valve and let water accumulate. The April rains will be able to fill the cistern.”
When the cistern is full, it will provide enough water for three to four nights of irrigation. Overflow goes directly to the MWRD channel, and if there isn’t enough water, the system includes a bypass so village water can be used.
“The members of the Baha’i faith have done things that are good for the earth,” says Perry. “This is a rewarding project that we’re proud to be a part of.”