Permeable pavement is taking center stage now as erosion control and stormwater green infrastructure projects aim to reduce runoff and improve water quality.
Stopping Nonpoint-Source Pollution
In Columbia, MO, the Public Works Department received a Clean Water Act 319 grant for stormwater improvements to reduce nonpoint-source pollution into the creeks and streams. Several projects were part of the grant that Boone County had received from the Missouri Department of Natural Resources through the EPA funding.
Erin Keys, an engineer with the Columbia Public Works Department, says the city acted as a consultant on the grant.
“Our portion was to retrofit an industrial site with some stormwater BMPs [best management practices],” she says. “We chose to retrofit our public works operations facility here in town. Our phase 1 projects included a bioretention basin, a bioswale, and a rain garden. The phase 2 projects were to retrofit an existing detention basin.”
The Columbia Public Works Department needed to expand the parking area for its employees and construct a detention basin to address the additional water coming off of the new parking lot.
In the 1980s, stormwater design focused on major detention for significant storm events, so the detention basin that was constructed at that time was large enough to hold back significant amounts of water from large rain events, says Keys. However, water from less significant events would flow right through the large pipe. The detention basin needed to be smaller to address water quality.
“We wanted that detention basin work a little bit harder and decided to convert that detention basin into an underground detention facility and porous pavement,” Keys says.
The area was excavated and a layer of rock was laid down, followed by filter fabric.
Next, 1,000 Atlantis D-Raintank Modular Rainwater Storage System units were installed. Keys likens the tanks to a “fancy milk crate. It’s mostly void space, but it’s got structural stability so that when you cover it with the fabric and the rock, we’re able to drive cars over the top of the pavement,” she says.
For porous pavement, PaveDrain-a permeable articulating concrete mat that integrates the reservoir to maximize onsite stormwater capacity during extreme storm events-was chosen.
“I wanted to do some kind of porous pavement,” Keys says of the project’s elements. “I like the idea of PaveDrain, that you could lay it in mats. Most paver systems have individual blocks you can lay. This you can lay down in a complete mat and so the installation seems easier.”
The product is designed to improve the typical storm hydrograph, increase environmental performance, and reduce stormwater infrastructure costs. PaveDrain mats can be preassembled in a variety of configurations.
The PaveDrain system enables a vertical infiltration path, recharging local groundwater and reducing first-flush pollutants by filtering out suspended sediments.
(To view how the construction took place, see www.youtube.com/watch?v=qOGeP3zJAKM.)
“What’s interesting about the PaveDrain blocks is we were able to place them in mats,” says Keys. The mats were delivered off semitrucks and placed on the appropriate place on the lot. The pieces were interlocked like a puzzle.” The pavement will stay in place despite turns and other movements by vehicular traffic, she adds.
“The Atlantis D-Raintanks are used for the detention part with the PaveDrain on top, with the idea that the water would infiltrate through the PaveDrain into the Atlantis tanks and be filtered, then stored for 48 hours and released slowly over that 48-hour period,” Keys says.
The water infiltrates through the spaces along the edge into the rock below, she says. Each block has an arch to provide strength and stormwater runoff storage capacity. The system features a monitoring port for visual indication of how much stormwater is being stored.
The second phase of the project was completed in June 2014. The project’s first phase, a bioretention basin, has been monitored by the county, with positive results. For many of the pollutants being studied, there has been between 90 and 99% removal. Some pollutants have yielded removal rates of 40-70%, which Keys notes is “still significant. It’s good to know we’re removing those pollutants from the runoff before they get to our creeks and streams.”
Keys says she anticipates the PaveDrain system will handle the winter well.
“During the last couple of years, we’ve had some pretty good snowy winters,” she notes. “One of the selling points is that the spaces between the blocks in the PaveDrain are such that you don’t have to fill those spaces, so it can take a lot more water between the spaces. That helps with rain but it also helps with snow. So we’re hoping we won’t need to plow it as much because that’s going to filter through those pavement blocks.
“I don’t think plowing is going to be an issue,” she adds. “They usually hold their blade up above the pavement anyway, so I think because of the margin above the pavement, it shouldn’t hurt any of the blocks. We’ll have to take a wait-and-see approach if we’re going to need any salt.”
Keys also believes that the block spaces will stay open and the blocks will hold the heat longer to allow the water to infiltrate between them.
One challenge that occurred during the construction phase involved the equipment used to do the installation.
“When we were planning to lay the mats down, we were looking at the equipment we had available,” she says. “The ideal equipment would be a crane to set the mats, but we didn’t have that available. So we were using a piece of equipment where we had to roll out back to set the mats.”
She says if her department had to do it all over again, there would be more attention given to how the mats were staged.
“We would have staged them in a different way, because one of the things you have to do before you lay the mat down is use a plate compactor to compact the rock,” Keys says. “We would have staged it in such a way that we could have plate-compacted a whole row or column so we could set all of those mats and come back and plate-compact the next row.
“As it was, we had to do some plate compaction, set a mat, do some plate compaction, set a mat. That was an error on our part as far as planning.”
Post-installation, Keys notes that the system is working well as expected, with the underground detention system filling up when it rains.
Kimberling City Center
Elsewhere in Missouri, another EPA 319 grant from the Missouri State Department of Natural Resources helped the Kimberling City Center finance a retrofit of existing infrastructure with newer BMPs for stormwater management.
Runoff from the Kimberling City Center’s aging commercial mixed-use parking lot in scenic Kimberling, MO, posed a threat to the health of the Ozark’s Table Rock Lake. Missouri native Layne Morrill co-owns a retail shopping center adjacent to Table Rock Lake in the Ozarks near the Arkansas border. The lake’s 856 miles of shoreline-upon which Morrill himself spent time canoeing, fishing, and swimming-attracts residents and tourists for recreational activities.
When Morrill learned that installing a permeable interlocking concrete paver (PICP) parking lot could help protect the lake’s water quality while improving his real estate investment, he endorsed the idea. He and his retail center co-owners considered alternate surfaces for the 3-acre, 30-year-old parking lot of Kimberling City Center, which encompasses a post office, hotel, church, condominiums, stores, and restaurants.
The group met with Gopala Borchelt, executive director for the nonprofit water-quality organization Table Rock Lake Water Quality Inc., who had researched various options and served as construction manager for the project. She brought representatives from Belgard Hardscapes to discuss PICP solutions and benefits.
The pavers are placed over layers of aggregate that filter stormwater runoff from the parking lot down between the pavers and through varying-sized stones. As it moves through the aggregate, the water is cleaned and can be temporarily stored in a basin before its release to natural aquifers or, as in the case with Table Rock Lake, directly back into the lake.
In her research, Borchelt learned that a PICP system at Kimberling City Center was estimated to capture approximately 8 pounds of nitrogen, 1.5 pounds of phosphorus, 4 pounds of metal (iron, copper, and lead), and 125 pounds of soil and minerals per year, which otherwise would compromise the lake’s water quality.
“Water quality is a very important issue,” Borchelt says. “People live here, visit here, and move here for the White River Valley. We wanted to do something that would protect the lake better than it had been in the past.”
She considered alternate surfaces.
“We didn’t want to use porous asphalt or pervious pavement because of the labor and equipment needed for installation, and both are high maintenance,” Borchelt says, adding that other surfaces would have required repair or replacement approximately every four years, whereas Belgard Hardscapes PICP promotes a 50-year pavement design.
Keeping the parking lot accessible during installation was also a consideration, because tenants needed to keep their business open, and the pavers enabled that.
Permeable interlocking concrete pavers can be installed by a machine. Aqua-Paving Construction of Yorkville, IL, installed more than 1,000 square feet of pavers per hour at Kimberling City Center. The company compacted the paver surface with a 7,000-pound plate compactor and swept chips into the openings between the pavers that will allow the water into the system.
The aggregate system includes 3-inch stone under 4 inches of three-quarter stone that has been washed and cleaned.
The washed rock helps water pass through the aggregate and removes contaminants before the runoff reaches the groundwater. Aqua-Paving Construction placed a 2-inch setting bed of 3/8-inch paved chips and then laid the pavers.
Some 133,000 square feet of product was used, with a total of $300,000 spent on the hardscape.
Stormwater runoff from asphalt enters streams and lakes at elevated temperatures, which can be harmful to aquatic life, notes Chuck Taylor, PIPC technical consultant for Belgard Hardscapes.
In the late 1990s Table Rock Lake suffered an algae bloom in the James River arm of the lake. In addition to the elevated temperatures, “it’s quite possible [runoff from the asphalt] is a source,” Taylor says. “Algae bloom occurs in summer, typically because there’s an excessive amount of nutrients in the water.
“Those nutrients will consist of excess phosphorous and nitrates. In addition to pavement runoff, you have farmers’ fields and peoples’ yards where fertilizers in the grass often contribute to and excessive amount of nutrients in the stormwater that enter the pipes and lakes.”
“A permeable paver system ensures less contaminants enter the water than when water washes off an asphalt parking lot, and the water enters the lake at a cooler temperature,” says Dave Farrero, Aqua-Paving field superintendent.
A recent public survey by Ozarks Water Watch of residents in the Upper White River Basin indicates the public’s largest concern in the Table Rock Lake area is stormwater runoff from development.
The potential temperature reduction of water entering the lake was another factor driving Kimberling City Center’s owners to use a PICP system.
“We plan to use this highly visible location to not only help protect water quality and improve the overall appearance of the community center, but also as a demonstration site for other local businesses and municipalities to learn from,” says Borchelt. “Developers have the option of replacing old, worn-out pavement areas or creating new areas in a way that reduces the negative impacts on surrounding hydrology and water quality.”
“Our goal should be to capture the water, put it back in the soils, and let it move through the ground to the riverways,” says Taylor. “That’s the natural way of treating stormwater.”
The paver design included Belgard Hardscapes’ Aqualine L in both Gascony tan and red complemented by Belgard’s Holland in the same shades in the crosswalks and soldier course around curbs, islands, and bioswales.
The Miller-Blevins Construction Company of Reeds Spring, MO, served as the general contractor. The project also involved the work of Stalzer Engineering of Branson, MO.
The decision to go with Belgard PICP not only acted to protect the lake, but also provide an aesthetic solution, Morrill notes. “It’s just gorgeous,” says Morrill. “One of the best things about the new parking lot is the mental attitude-how proud we are to have done something that no one else around here has done.”
Taylor says the Belgard PICP can provide 12-14 LEED credits based on such factors as the use of recycled material, non-roof impervious surface, heat island reduction, and stormwater quality rate and flow.
Its use reduces winter maintenance costs. The rounded edges of the pavers mean that snow plow blades cannot rip them out of position, he adds.
Expanding a Parking Lot
Christ Chapel in Fort Worth, TX, is a growing church with expanding space needs: in particular, the need for more parking spaces to accommodate more congregants. During the summer of 2014, Concrete Paver Systems wrapped up a seven-month project that included providing erosion control for a temporary parking lot.
Concrete Paver Systems in Duncanville, TX, installs paver systems using concrete, clay, sand-set, mortar-set, and flagstone pavers as well as segmental retaining walls.
The company has used Grasspave² from Invisible Structures (ISI) in previous installations; the engineering specifications called for Grasspave² in this project. Grasspave² porous pavement is designed to function similarly to asphalt or concrete pavement with the aesthetics of a lawn.
It provides a pervious load-bearing surface, filters and treats stormwater, reduces airborne dust, and reflects heat.
“The church had three parking lots and wanted to put in Grasspave² so they could actually have grass in the parking lot,” notes Roger Henjum, partner with Concrete Paver Systems.
The engineer’s plans had called for a 20-mil liner on the bottom.
“Then we put in a drain core system, which is actually Grasspave² turned upside down,” says Henjum. “We put a six-ounce filter fabric on top of that. We put in 12 inches of a sandy gravel mix for a base, then we came in with the Grasspave² on top and filled the cores with sand. After that, a landscaper came in and put grass on top.”
Runoff that doesn’t flow across the surface into the curb and gutter goes down through the rock to the drain core system at the bottom, hits the liner, and flows to the lowest end of the lot, where Concrete Paver Systems has set up a sump pump.
Some 70,000 square feet of Grasspave² was used on the surface area and another 70,000 square feet of the product was used in the lower layer.
The project provides temporary parking for the church.
“They don’t open it up full-time,” says Henjum. “They don’t want people driving in there for the heck of it, so they put bollards up at the entries, and on the weekends when they need the additional parking they take the bollards out and let the people in there.”
ISI specializes in site-development products that help with stormwater management such as porous pavements, underground stormwater storage, erosion control, and drainage and conveyance, says Dustin Glist, ISI’s media and information director. Six of the company’s seven products are manufactured from 100% recycled content.
“Since Grasspave² has real grass as the surface course, we treat maintenance like any turfgrass system with the exception of aeration,” Glist notes. Grasspave² does not need to be aerated because of its sand-based root zone and because the roots are protected from compaction by the structure.
Maintenance includes irrigation-if needed for climate and grass type-mowing, and fertilization with NPK fertilizers.
Permeability holds up in cold climates, says Glist.
“Tests have shown that porous pavements melt ice and snow faster, freeze water slower, and allow for better traction,” he adds. “Grasspave² comes in rolls that flex with freeze-thaw cycles and normal undulations in the terrain.”
Salt, magnesium chloride, and other snow and ice melting agents cannot be used on the system, Glist says. “Grasspave² has real grass, and chemicals will kill the grass. Snow removal should be done with skids or rollers attached to the bottom of the blade to ensure the blade does not make contact with the structure itself. Or a snow removal operator can raise the blade three-quarters of an inch above the surface.”
Grasspave² is often used when LEED points are desired as it is manufactured with recycled content and offers urban heat island mitigation. For site development, it is designed to protect and restore habitat and maximize open space.
A Grid of Protection
WM. J. Keller and Sons Construction Co. in Castleton, NY, was tasked with providing erosion control at various locations around the Sterling and Francine Clark Art Institute in Williamstown, MA, during summer 2014.
As per design, the company installed 20,000 square feet of Purus North America’s EcoRaster in a parking lot, a fire truck access area, and a delivery entrance area. Following the installation, the landscaper covered the areas with topsoil and seed.
Manufactured from recycled plastics, EcoRaster is an interlocking grid system designed to provide turf protection, ground reinforcement, and erosion control. The product offers choices with its various designs of curve wedges, slope angles, and car park markings, and it can be cut to size. It is designed to withstand frost and UV radiation.
“Fine-grading the subbase is a key element to installing the product correctly and having a uniform finish overall,” notes Jameson Phillips, an estimator and project manager for Keller and Sons.
To achieve that, the company used Trimble GPS equipment for grade control.
Hyundai Goes for Gold
In completing its new US headquarters in Fountain Valley, CA, Hyundai Motor America is going for the gold-LEED gold, that is.
Designed by Gensler, an integrated architecture, design, planning, and consulting firm, the building is sleek and modern, yet classic. Constructed on a structural pedestal foundation with floating translucent glass floors above, the two-story-high entrance leads to an open-to-the-sky public courtyard in the building’s center, with a showroom of vehicles visible from the freeway side.
Gold is the second-highest LEED rating, and the building achieved it through efficient use of light and energy, recycled water use from the site’s landscaping-including the rooftop garden above the testing garage-recycled materials used in the construction, and future recycling of some construction waste materials.
Sustainable Paving Systems’ Grasscrete-a pervious concrete void structured system designed to provide structural load capacity, recycled content, and water management attributes-was chosen for the emergency fire lane access. Some 29,000 square feet of the product was used in the November 2013 installation. Ahbe Landscape Architects was part of the construction team, as was Valleycrest Landscape Development.
Installed with biodegradable molded pulp formers, the Grasscrete system was placed in an area for emergency vehicle access to provide management of stormwater runoff and reduce the heat island effect.
The Concealed Grasscrete System incorporated drought-tolerant UC Verde Buffalograss, which, when established, can thrive on as little as one-quarter inch of water per week in some locations, resulting in a 75% water consumption reduction.
Design for a Dealership
Meanwhile, a new Maserati and Ferrari dealership in Wilsonville, OR, installed Xeripave’s Dupont XeriBrix in its entryway and sales building drive-through. XeriBrix was chosen for its sustainability, durability, and aesthetic value. Xeripave LLC is an affiliate of Ultrablock, StoneTerra, and Verti-Crete NW.
The construction of Ron Tonkin’s Gran Turismo’s new dealership location called for pervious bricks to be used in several areas. Some 3,000 square feet were installed in the 2014 project, designed by LRS Architects.
Xeripave’s Super Pervious (SP) pavers are segmented pavers designed for immediate installation and to offer an infiltration rate of up to 1 gallon per second per square foot. Water drains through the body of the paver, which filters out gross contaminants and helps recharge groundwater supplies.
The pavers are available in a variety of colors, designs, and sizes. They are designed to be unaffected by salt and ultraviolet rays and will not fade or deteriorate with severe weather changes. They also provide an ADA slip- and skid-resistant surface.
Xeribrix pavers are smaller than some other types, with dimensions of 4.5 by 9 by 2.38 inches. They are typically used for parking lots, curbsides, and other low-impact vehicular applications.
Wake Forest University
Students, faculty, and staff at Wake Forest University in Winston-Salem, NC, may give little thought to the school’s brick-lined pathways, but those paths are more than an attractive surface upon which to walk. They also help to better manage stormwater as part of an extensive project that the university undertook over two summers to install Pine Hall Brick’s StormPave permeable pavers.
The permeable pavers match the university’s red brick architectural design while managing stormwater in the available space.
Rainwater filters through bricks and is then absorbed by 18 inches of aggregate beneath them. The aggregate acts to keep the pavers stable and serves as a reservoir to hold the rainwater, releasing it slowly to the ground underneath.
The new pavers were also placed a 24-foot-wide plaza on the east side of Farrell Hall, which houses the university’s business school. The plaza encircles most of the building and extends out to the Polo Road entrance. Sidewalks have been extended to the North Dining Hall and the Dogwood and Magnolia residence halls. Additionally, a new 150-yard walking path leads from a parking area to Wait Chapel.
The permeable pavement is the university’s solution to meeting Winston-Salem’s stormwater mitigation requirements, which address the challenge of excess water and downstream surges that cause erosion, flooding, and property damage. Stormwater management mechanisms such as permeable pavers keep more rainwater onsite and lower the volume of downstream flows.
In addition to the StormPave pavers, other campus stormwater control measures include the installation of two large concrete cisterns under the parking lot at the Porter B. Byrum Welcome Center. The cisterns hold 110,000 gallons and dissipate the stormwater at a slower rate. The cisterns are used in conjunction with three bioswales to slow water flow into Lake Katherine and Silas Creek.
At the new South Residence Hall, two bioswales were created to collect rainwater in a 5-foot-deep crushed rock bed. There are also several inground mini-cisterns with a rock filtering system connected to the stormwater system under Jasper Memory Lane.
Although the bioswales serve as effective stormwater management choices, the StormPave installation was desired as a cost-effective approach that didn’t require much space.
As for maintenance, a clay paver installation must be swept or vacuumed regularly to keep debris from clogging up the areas in between the pavers, notes Walt Steele, paver sales manager for the Pine Hall Brick Company.
“A small amount of aggregate-similar to tiny pieces of gravel-will need to be kept on hand to sweep into the spaces in between the pavers to replace that which has been removed by sweeping or vacuuming,” Steele adds.
The product retains its permeability in cold climates, Steele says. “We’ve had reports of rainfall going directly into the aggregate field and disappearing before overnight freezing temperatures set in,” he adds. “The result is that there is no ice on the surface of the pavers.”
Road salt does affect its appearance, says Steele, adding that the company recommends the use of magnesium chloride.
“Using ordinary road salt can cause efflorescence-a white, powdery substance on the surface,” Steele says. “It does not affect the paver’s strength, but it does affect its appearance. Efflorescence can be removed by rinsing with water.”
Snow plows and shovels equipped with rubber-tipped blades reduce chipping on the paver edges, Steele says.
