Two Worlds Together

In 2010, the Transportation and Development Institute (T&DI) of the American Society of Civil Engineers (ASCE) hosted the first national Green Streets and Highways conference. This came from a need for stormwater managers to learn more about the world of road managers and vice versa. Stormwater managers realize that roads cover about 25% of urban areas, generating significant property damage from water pollution, minor flooding and combined sewer overflows in older cities. Not surprisingly, road managers view stormwater as a lower priority compared to road user safety and efficiency. Also, road agencies generally are larger than stormwater agencies at every level of government, and that typically translates into greater financial, technical and political clout.

Most road agencies view permeable pavement as suitable for car parking lots and alleys with occasional applications in low-volume residential streets. Such projects are at the margins of road agency priorities and their budgets, and many of these applications lie in the private sector. Permeable pavements have yet to be embraced by road agencies because they are seen as new and untried under regular truck or bus traffic. This is where more structural testing and evaluation of hybrid pavements may allow for more passes from higher-weight vehicles. This can place permeable pavement more in the mainstream of the road manager’s world.

Along these lines, moving permeable pavements more into mainstream acceptance and use by road managers will require several components. As noted, first and foremost is accelerated, full-scale load testing to validate the ability to withstand truck traffic. Such testing must result in structural design methods and easy-to-use, reliable thickness charts. While there has been some full-scale load testing for pervious concrete and porous asphalt, a recent full-scale load study by UC Davis on PICP resulted in design charts. This magazine issue includes a summary of the UC Davis work, cost savings implications for designers and where the charts will be used.

The second component is specifications. Cities and county road agencies often rely on, adopt and adapt construction specifications developed by state departments of transportation (DOT). Even provisionally issued specifications by a state DOT tells local road agencies that a particular technology such as permeable pavement has been vetted by knowledgeable experts. There are currently two DOTs that have published PICP specifications; Caltrans and Washington, DC. ICPI assisted in developing these. We hope to do more of this.

The third component is training. There are two sides to the training coin: one is for contractors that results in certification of competent, experienced individuals; the other is inspection training for road agency personnel. ICPI has seen fast growth in PICP classes for contractors and in those receiving a PICP Specialist Designation. This credential is becoming a requirement in local and state agency specifications. To help address this need, an inspection presentation is now available for ICPI members to present to stormwater and road agency personnel.

The fourth component is maintenance/management procedures and costs. A critical maintenance aspect for permeable pavements is regular surface cleaning with vacuum equipment. Permeable pavement will be more readily embraced by state DOTs and especially by local road agencies when existing street cleaning equipment can be used for cleaning. Regularly maintained PICP performs for decades. However, many installations don’t see regular cleaning that results in restoration of the surface infiltration with powerful vacuum equipment and perhaps water. ICPI has funded maintenance research in the past. This includes work by North Carolina State University and the Toronto and Region Conservation Authority. ICPI and its sister organization, the ICPI Foundation for Education and Research, are reviewing more research options for the near future.

This issue’s cover story features another realm where the two worlds of stormwater and pavement are usually close together, and that’s on military bases. These mostly self-contained environments are of such a scale that one person or a small group of people down the hall from each other manage pavements and drainage. There are a growing number of them using interlocking and permeable interlocking concrete pavements. The cover story provides an example of integrating the two worlds of pavement and drainage management from a need to solve flooding problems and pavement rehabilitation.

As industry, academia and governments address the four requirements for permeable pavement that lead to it becoming mainstream road infrastructure, the two managerial worlds will work more closely together. One resource that can support this process is ASCE publishing a new book called Permeable Pavements.


Inspection of PICP Systems

With the rapid growth of permeable interlocking concrete pavements (PICP), there is a pressing need for increased awareness and improved execution of inspections during construction. The greatest needs often emerge in two areas: 1) pre-construction coordination among project owners/manager, designers, product suppliers, testing labs, the contractor and subcontractors; and 2) compaction inspection for PICP system stability and long–term performance.

To better address these and other needs, ICPI released a one-hour PowerPoint presentation on PICP inspection for project inspectors. The presentation also informs designers, job superintendents, crews and product suppliers about inspection aspects common to most PICP projects.

The program is approved for one hour of ASLA and AIA continuing education credit and is also eligible for earning one professional development hour. For ICPI certified installers, this program also earns one hour of continuing education for maintaining certification. For a presentation, contact an ICPI manufacturing member with a request. To find those nearby, visit the home page of and use the “Find a local…” search engine. ICPI members providing the presentation must be ICPI-approved continuing education program presenters.


Essential Reading

Sponsored by the Low Impact Development Committee of the Urban Water Resources Research Council of ASCE’s Environmental and Water Resources Institute, Permeable Pavements presents a comprehensive, 260-page resource on design, construction and maintenance of permeable pavement systems. This e-book and printed edition represent a significantly updated compilation since Bruce Ferguson, FASLA, wrote Porous Pavements in 2005. ASCE’s book is richly illustrated with photos, diagrams and tables.

Permeable Pavements synthesizes diverse materials and practices using this technology with the help of academics, industry, civil and environmental engineers and scientists. The book benefits from these viewpoints with 17 authors plus 13 contributors and reviewers.

The book’s three primary editors, Bethany Eisenberg, LEED AP, Kelly Collins, PE and David R. Smith provided the structure, fact-checking, graphics and a consistent narrative style. The result is a book that can be used on almost every project.

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The book presents an overview of design considerations common to all permeable pavement systems in the first chapter. Detailed design, construction, use and performance information follow in separate chapters on porous asphalt, pervious concrete, permeable interlocking concrete pavement, grid pavements and some recent proprietary products. Additional chapters summarize maintenance considerations, hydrologic design approaches, essential components for specification writing and key areas for additional research. The book’s extensive use of fact sheets and checklists can be instrumental in design, construction and maintenance by stormwater agencies, designers, contractors and project owners. Appendices also include a fact sheet clarifying information on common concerns, as well as tables summarizing water quality treatment performance and costs.

The downloadable e-book and soft cover print version each retail for $120 ($90 for ASCE members). Visit the “publications” section at to order the book.


Basic Draining

Arriving at the base operations building at Peterson Air Force Base in Colorado, civil engineer Fred Brooks, P.E., LEED AP, is still struck by the beauty of an intricate compass design. It’s created with multi-colored concrete pavers, arranged in a huge circle. But he’s equally thrilled by the pavers in the parking lot. “Everyone loves these pavers,” says Mr. Brooks, U.S. Air Force Environmental Element Chief, 21st Civil Engineering Squadron. “We may have started these projects on this base as a way to handle stormwater, but they’ve done much more than that. They’ve shown how attractive and welcoming a base can look.”

Peterson AFB first started considering pavers to help meet the stormwater runoff requirements established in the 2007 Energy Independence and Security Act. Section 438 mandates all federal facilities manage runoff from 95 percent of all storms. Meeting this requirement often requires permeable pavements.

In Colorado, storms can come up suddenly with short-term deluges, causing flooding. Mr. Brooks says airfields quickly became submerged and buildings flood as well. Even without Section 438’s mandate, Mr. Brooks knew something had to change. After attending a seminar in Spokane, WA, and hearing about permeable pavers, he experienced a light-bulb moment. “This was the answer we needed,” he says. “I just had to get everyone else to see the light, too.”

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Mr. Brooks began by dividing the base into drainage catchments, focusing on the most problematic sections first. For example, one particular street with a catchment area of 35 acres included several older buildings that drained into the street. Flooding was a frequent concern, but a detention pond was deemed unfeasible and a complete sewer replacement would have been costly.

Mr. Brooks knew getting buy-in from others on base was crucial for such a significant project. Thus, he had the road to McDonald’s replaced with pavers. “Almost everyone on our base uses that road,” he says with a laugh. “I’m not sure if that’s good or not, but it’s the way it is. By paving that road first, I was able to expose people to the value of pavers, aesthetically and functionally.”

He also addressed weight load concerns by calling a special meeting (see sidebar) and composing a presentation about short-term versus long-term costs to assure base decision-makers that pavers were worth the investment. For instance, he noted that maintenance crews repainted road stripes nearly every year. By utilizing pavers as the striping instead, repainting costs would be eliminated.

In his presentation, Mr. Brooks emphasized how easily utilities could be accessed, as well as the advantages of more efficient road repair. He also discussed the aesthetic appeal of pavers. “Ultimately, we want people who are working here to be happy, and everyone feels better when they’re at a place that looks nice,” says Mr. Brooks.


After managing and shaping perceptions about cost and concerns about weight, Mr. Brooks was able to embark on a multi-stage project that involved several roads and parking lots, as well as the compass design for the entrance to the base operations building. The pavers, produced by an ICPI member, feature a minimal chamfer and smooth surface. This made them more suitable for pedestrian areas and wheelchair access and thus the design complied with the Americans with Disabilities Act design guidelines.

Mr. Brooks designed two separate permeable pavement sections for Paine St. based on flow and infiltration conditions. The first included a drainage pipe at the subgrade level below an open-graded aggregate reservoir layer. During periods of heavy runoff from storms producing flash flooding, the aggregate storage layer provides a buffer to control the discharge rate from the drainage pipe. The other section, which doesn’t require a drainage pipe, allows Mr. Brooks to assess the system’s ability to handle direct infiltration into the sandy subgrade.

The first installation involved more than 18,000 sf (1,670 m2) of pavers in a herringbone pattern, followed by another installation of the same area. In the second project, which was also a roadway, a section of the street had a low point that often flooded after storms. Although extension of storm sewer lines would have resolved flooding, that was deemed too expensive. Permeable pavers eliminated the need for storm sewers and project to outlast asphalt by a considerable amount of time.

The next phase for the base operations building included 20,000 sf (1,860 m2) of permeable pavers for the parking bays and for the compass design. The effort was so notable that the contractor, ICPI member Rocky Mountain Hardscapes, won a Hardscape North America Award in 2011 for the project. From there, two more parking lots were installed in 2012 and 2013 with more than 56,000 sf (5,200 m2) of pavers.

The permeable pavements dramatically reduced, and in many cases eliminated, the need for detention ponds for managing stormwater and snowmelt. In fact, when Mr. Brooks leads tours of the facility, he often dumps a bottle of water on the pavers to demonstrate their infiltration efficiency. Since achieving LEED credits is also important for the base, the designers were able to qualify for stormwater credits by demonstrating better control of peak flows, erosion mitigation, and increased on-site infiltration. “It’s human nature to resist change, and to look at the cheapest option,” says Mr. Brooks. “But what these projects have shown is that you can implement change in a way that’s cost-effective and appealing on a number of levels.”


Peterson Air Force Base’s use of concrete pavers serves as an example to other military bases and federal facilities, especially with regard to meeting the requirements in the Energy Independence and Security Act. Like Peterson AFB, many will be searching for ways to handle runoff while implementing long-term solutions that are durable, cost-effective, and sustainable. This appears to be happening.

Mr. Brooks notes that since Peterson AFB installed the permeable pavement, the Air Force Academy installed pavers for a 58,000 sf (5,400 m2) parking lot attached to its medical clinic, and Fort Carson utilized pavers for a test pad for tanks.

Looking to the future, it’s likely that paver projects will continue at Peterson AFB, since Mr. Brooks has mandated it. He revised the base’s “facilities of excellence” plan that outlines requirements to contractors so that permeable pavers must be used on any parking lots and low-volume roads in the future. “I wanted to make sure that these efforts wouldn’t be lost when I move on,” he says. “The pavers have made such a difference on this base, and I want that to continue.”


Weight and See

Engineers and architects often must emphasize that concrete pavers can handle the weight of large trucks, as well as heavy traffic. But on a military base, perceptions about weight can be even more acute. For example, when it comes to a 68-ton tank that repeatedly traverses one area, some assume that pavers won’t work. They believe it is a residential-only product for patios.

When considering pavers for Peterson Air Force Base, Fred Brooks also encountered hesitation from others about weight loads, especially on well-used roads. So, he invited all the base’s operations professionals to a meeting with one of the developers of permeable pavers. “A subject matter expert stood at the front of the room and everyone just threw questions at him,” says Mr. Brooks. “They were invited to ask whatever they wanted. Voicing concerns and receiving information about weight loads went a long way toward increasing assurance about the issue,” he notes.

Because the pavers can accept high loads, other military bases began noticing the success at Peterson AFB. Recently, Fort Carson in Colorado Springs constructed a permeable paver test pad for tanks in part due to the example set by Peterson AFB. The test pad easily accommodated the weight and turning forces from one of the heaviest battle tanks in service, the 68-ton M1A1 Abrams.

Photo Caption: A paver test pad at Fort Carson withstands the load of an M1A1 Abrams tank. (Credit: Continental Hardscape Systems, LLC)



Green Alleys of St. Louis

Taking cues from the successes of projects in cities like Chicago, St. Louis has installed several green alley projects since 2007 utilizing permeable pavers and interlocking concrete pavement. The Tower Grove Heights Green Alley Paver Project was completed in two phases from 2011 to 2014. It updated 400-year-old alleys with permeable pavers through a federal Community Development Block Grant, a state Department of Natural Resources grant, and local tax-based funding. PICP was used to reduce stormwater runoff and maintain the historic appearance of the alley, originally laid in brick over clay.

In 2009, the City of St. Louis commissioned a Pilot Green Alley project using donated materials and labor. Three alleys were installed that year with pervious concrete, porous asphalt and PICP. The performance of the city-owned alleys is being evaluated over time. All of these are built over open-graded aggregate reservoirs, allowing stormwater to drain through the system per the City’s specifications.

“We helped fund a portion of them because of the experimental nature of the materials at the time,” says John Grimm, of the Metropolitan Sewer District. St. Louis also used tax funds for the $41,000 Cherokee Green Alley Concrete Project, a 150-ft long by 12-ft wide alley completed in 2009. The pilot project’s outcomes are still being tested, with MSD conducting a report on flow measurements scheduled for completion at the end of 2015.

Green alleys are not unique to St. Louis, but the city’s history and layout with centuries-old alleyways and roads lends to more paver installations in the future, Mr. Grimm says. “There are some suburbs that have alley arrangements, but they are not as prevalent,” he says. “It’s mainly particular to the city.” 

return to River City Green


Permeable Design Pro Upgrade

Permeable Design Pro, a software application for hydrologic and structural design of permeable interlocking concrete pavement, now features CAD drawing output (see example drawing). Drawings are generated by the program after calculating the subbase thickness for water storage and subgrade infiltration, as well as the required subbase thickness to support anticipated traffic. The program automatically selects the thicker of the two subbase solutions and presents the CAD drawing from a menu selection. The drawing can include an underdrain, geotextile, and an impermeable liner if no infiltration into the soil subgrade is desired. The CAD drawing also specifies the height of the underdrain outlet, if the designer indicates this in the program, as a means to detain some water for infiltration.

Also, the user can modify the CAD drawing by changing the subbase thickness and the underdrain pipe diameter, as well as the presence or absence of geotextile or an impermeable liner. The CAD drawing can be saved as a .dwg file for use in project drawings or submittals.

Permeable Design Pro can be downloaded from for a 30-day free trial. The purchase price is $190 per license with a discounted price of $95 for design professionals and ICPI members.

Permeable Design Pro

Permeable Design Pro software now features CAD output of design solutions for permeable interlocking concrete pavement.


River City Green

The Midwest is no stranger to the use of interlocking concrete and permeable pavement solutions for many private, commercial, municipal and educational projects. In particular, municipalities with rivers that overflow seasonally and those receiving polluted stormwater are increasingly deploying permeable interlocking concrete pavements (PICP) for their projects and enjoying the benefits.

In St. Louis, the challenges of an aging combined sewer system and new stormwater requirements mandated in 2006 by the City’s Metropolitan Sewer District (MSD) led to the implementation of PICP in alleys, parking lots, sidewalks, trailheads and many other applications. Multiple projects including a series of green alleys constructed since the MSD mandate demonstrated concrete pavers as a trusted solution for many City initiatives, as well as for private projects. While often used to reduce stormwater pollution, the successful performance and aesthetic appeal of concrete pavers in projects across the city has led to their popularity and continued use.

Eco-Installation: Lewis and Clark Community College – National Great Rivers Research and Education Center

At the National Great Rivers Research and Education Center at Lewis and Clark Community College in East Alton, IL, it’s all about green. Established to lead research, education and outreach related to the interconnectedness of large rivers and their communities, being “green” was non-negotiable for the center’s construction. The first of two phases of construction began in 2008 with a field center to drive research and serve as a home base for educational programs.

The project secured a total of $6.8 million in construction funding with an additional $16.3 million designated by former Illinois Governor Pat Quinn. From the project’s inception, the goal was obtaining the highest Leadership in Energy and Environmental Design (LEED) certification. LEED credit-earning components for this project include: sustainable heating and cooling systems; a detention basin for stormwater quality control; plus permeable interlocking concrete pavement, as well as other pervious pavement systems.

The paver portion of the project includes a plaza, sidewalk and main access road totaling more than 25,000 sf of manually and machine-placed pavers, installed in less than one week’s time. Speed of installation was a factor in the project’s success because it quickly opened the roadway (unlike other pavement options that require downtime while curing), thus enabling multiple construction efforts to occur simultaneously.

“The facility is a showplace for green building that incorporates multiple types of green paving systems,” says Dave Godar, P.E. for Sheppard, Morgan & Schwaab, Inc. Material reuse was accomplished by using fly ash in the cast-in-place concrete and in the modified soil road base.

Also, the project had to consider the historic flood levels from the nearby Mississippi river. “We didn’t want permeable pavement where the flood level is, because it could clog,” Mr. Godar says.

The sidewalk portion of the project covers about 875 square yards; another 2,500 square yards makes up the roadway. The system uses 3-1/8 in. thick concrete pavers, 2 in. of bedding aggregate, 4 in. of open-graded aggregate base and 12 in. of larger aggregate subbase over filter fabric or geotextile.

“There are two schools of thought about using filter fabric,” Mr. Godar says. “Some say that over time the filter fabric can become clogged and prevent the rainwater from soaking into the ground. This site had sand material as the subgrade. We opted to go with filter fabric to prevent the underlying sand material from migrating up into the voids of the subbase aggregate, which could cause settlement of the pavers.” 

To reduce labor costs, project design included machine installation for the interior pavers. “It was all kind of new,” Mr. Godar says of the plans created in 2009. “We hadn’t done anything like this before, although there were some examples out there.”

Funding for the project included some federal highway money, which meant all approvals had to go through the Illinois Department of Transportation (IDOT). Because many of the components were not standard and were not covered by IDOT specifications, some of the materials were considered experimental. The project took most of the 2010 construction season to complete. “The idea was for this to be a showplace,” Mr. Godar says. “It is open to the public, so if we had clients who wanted something similar, we could point them to the National Great Rivers Research and Education Center.”

Health Appeal: Ranken Jordan Pediatric Bridge Hospital


At Ranken Jordan Pediatric Bridge Hospital, about 15 miles northwest of St. Louis, permeable pavers satisfied the hospital’s stormwater requirements, providing an overall healthy feel to the campus. Coined a “bridge” hospital, the facility staff works to help children transition between hospital and home. With a history of expansion and growth, the hospital was built in 1941 as the Ranken-Jordan Home for Convalescent Crippled Children. In the 1960s, it expanded to accommodate more patients and staff, and in 2002, moved to a new 62,000 sf, 34-bed facility in Maryland Heights, MO. Several years later, the facility required more parking for patients and visitors.

When the organization first looked into expanding its parking capacity in 2009, stormwater requirements came into play immediately. The facility includes bio-retention basins and rain gardens. PICP met the MSD’s stormwater reduction requirements.

“At the time it was fairly cutting edge,” says Ted Spaid, co-founding principal of SWT Design, based in St. Louis, which led design for the project. “The MSD had just started enacting water quality management regulations for the region.” Rather than using underground stormwater tanks and other solutions, the design team decided on PICP to meet the requirements.

The first of Mr. Spaid’s projects with PICP took place at SWT’s office as an early test run right when the pavers first became available. Having successfully worked with them, SWT decided to use them in the hospital project. The pavers were manually installed between September and October of 2009, but required some special design attention because the parking lot presented a challenge with its radial layout. The designers addressed this by taking advantage of the paver pattern. The contractor installed the entire parking lot in a herringbone pattern, which can accommodate radial layouts, and saw cut the edge pavers to fit the non-uniform shape.

Another unique design element used pavers in contrasting colors to designate parking stalls rather than paint lines on the pavement. “The installation itself was a month-long process,” Mr. Spaid says. But the outcome was several-fold, for the 20,980-sf installation. First, it satisfied required municipal green elements by draining to rain gardens to help with bio-filtration. And while there was additional expense due to the paving materials, the aesthetic appeal was a positive payback.

“Many clients are timid about wanting to spend the extra money on permeable pavers, but then they realize it delivers more than stormwater management. If you can turn stormwater management into a positive aesthetic attribute, it’s much nicer. There are multiple layers of savings by using the pavers correctly and strategically.”

For example, the parking lot design allowed for surface runoff to sheet-flow over the asphalt and infiltrate into the permeable pavers. Eventually, that water would go to a centrally located rain garden or bio-retention area, and would flow to a larger detention basin as needed to prevent downstream flooding.

“This design replaced the need for typical drainage structures and piping system that you would find throughout a parking lot,” Mr. Spaid says. “Based on a cost-benefit analysis, a traditional stormwater infrastructure design was comparable to the cost of the permeable paving system. Furthermore, the permeable pavers provided the required stormwater management to decrease the flow of runoff and help control sediment.”

The pavers and rain garden also decreased the size of the necessary detention basin and preserved land for future expansion. The project is maintained with annual vacuuming and regular cleaning. MSD requires an annual inspection report that includes dates of inspections and cleaning methodology. Additionally, the report must confirm that all stormwater structures are functioning and that watersheds have not been disrupted by pavement clogging or erosion. The report must demonstrate that all best management practices (BMPs) and landscapes are functioning as designed.

In a care setting, particularly one focused on children, the sub-story is aligning construction materials with quality and health, Mr. Spaid says. “It’s a healthy living story,” he says. “Here we are at a pediatric care facility and we want to show quality care for children. Through stormwater management and rain gardens, there’s a story to be told about water quality and creating an environment not only contributing to a healthy planet, but to human well-being and aesthetics.”

Trailhead Series: Great Rivers Greenways


Concrete pavers may be “green,” but they’re not often found in the woods. The Great Rivers Greenway (GRG) District is an exception. The network spans more than 100 miles of trails and greenways among 1,400 acres through St. Louis City, St. Louis County and St. Charles County that support hiking, biking, walking and other outdoor activities. Established in 2000, the GRG initiative set out to improve health, reduce pollution and stabilize communities, among its many goals.

That’s where PICP comes in. In 2006, the organization extended one of its trails, which involved installing two new trailheads. Given the stormwater restrictions then recently passed by the MSD, the Great Rivers Greenway project managers and designers crafted a proposal for PICP as the surface for the new sites. A handful of other trailheads and parking areas built in the following years also realized the benefits from PICP.

“We considered leaving it asphalt,” recalls Carey Bundy, project manager for GRG. “It would be cheaper on the front end,” she says, “but PICP would count toward water quality credits. We went with pavers mainly because if something did go wrong later, they are much easier to get into and work on.”

Because it spans the city and two counties, funding for GRG projects comes from various sources, including tax dollars and federal grants. GRG resources are used to build and improve the trail network and then projects are turned over to the municipalities for maintenance. Working with pavers required a lot of testing, partnerships on design elements and determining performance requirements that would satisfy the mission of the trails.

The installations were not easy. “The most challenging part is the location and site accessibility,” says Scott Rozier, president of St. Louis-based Rosch Company. “The trails go through the middle of the woods, or across old abandoned tracks, and it’s very challenging logistically to get the subbase installed and place everything where it needs to be.”

In spite of the challenges, GRG found that the PICP systems with additional green elements such as plantable walls and reclaimed water systems have performed well. So well in fact, more projects are in the design and planning stages as a result. “Initially, people said they wanted to go with the traditional route and didn’t want to try this new but different material,” Ms. Bundy says. “But it’s on the ground now in a lot of places. Getting a pilot installed so people can see what it is, that is very helpful.”


Home Advantage

Sometimes, being popular has disadvantages. In Montgomery County, MD, the area’s good schools, low unemployment rate and proximity to Washington, D.C. and Baltimore have led to an increased population density. To construct enough housing and commercial properties to support those residents, numerous neighborhoods have been built over existing streams, leading to erosion, minor flooding and property damage.

Fortunately, new solutions are being employed, and permeable interlocking concrete pavement (PICP) is one of them. PICP emerged as a solution after a pilot project identified tactics for creating healthier local landscapes conducted about 10 years ago. In response, the County’s Department of Environmental Protection created RainScapes, a pioneering program focused exclusively on reducing stormwater runoff and improving water quality in affected neighborhoods.

Designed to incentivize and implement projects that reduce stormwater runoff, RainScapes offers technical assistance and advice with a rebate program that pays homeowners and commercial building owners to use PICP among other tools. Other RainScapes techniques include tree planting, conservation landscaping, dry well installation, green roof implementation, rain garden design and cistern installation.

One of the most popular aspects of the program has been permeable pavement because the rebate helps offset the high installation costs. For residential projects, the rebate maximum is $2,500 and commercial or multi-family projects can be eligible for a rebate of up to $10,000. To receive a rebate for permeable pavement for residential properties, a homeowner must hire a Montgomery County certified contractor and convert a minimum of 100 sf (9 m2) of hard surface to PICP.

For commercial, multi-family and institutional properties, a minimum of 300 sf (28 m2) must be converted.

The amount of the rebate is meant to cover the cost difference between traditional pavers and permeable pavers, says Dan Somers, who oversees the RainScapes Rewards Rebates. “This is a way to get homeowners to feel more comfortable with permeable pavers,” he says. “When you remove that cost difference, they’re able to compare the options based on factors other than budget.”

In addition to providing the rebate incentive, Mr. Somers visits the project site, talks with homeowners and explains the programs in detail. Sometimes, a homeowner might take on several projects, like installing a rain garden and planting canopy trees, as well as considering permeable pavers.

Although PICP doesn’t make sense for every property, they’re often chosen for residential projects, Mr. Somers says. “Permeable pavers are modular, with a predictable quality, and we have good data on them for the scale of projects that we’re doing, so they come with many advantages.”

Homeowners in the county consider PICP for a number of reasons, says Ann English, RainScapes Program Manager for Montgomery County. Some want to make the property look nicer, while others might want to reduce runoff because they’ve had runoff problems in the past. Some just want to do something for the environment, she adds.

Training Program

When the RainScapes program started, Montgomery County contacted the Interlocking Concrete Pavement Institute (ICPI) for assistance in creating a successful program that would draw interest from homeowners and contractors. The county’s design manual for the RainScapes program was developed with input from ICPI staff who provided technical review of the material.

In addition to the manual, the County developed a professional training course geared toward contractors who want to learn the nuances of a permeable paving system. The daylong class covers stormwater basics, installation processes, troubleshooting and rebate specifics, so they can be more familiar with the program.

Once they complete the course, contractors are included on the County’s “professionals list,” which can be accessed by homeowners and commercial building owners. The list also includes information on how many rebates contractors have garnered, so those perusing the options can determine level of experience with permeable paver projects and RainScapes rebates.

For homeowners and other building owners, the County offers a series of consumer-friendly manuals on the RainScapes website that give more detail about potential projects and show photos of successful installations. For example, on the permeable pavement page, the Department of Environmental Protection includes a slideshow of permeable paver projects, including “before and after” photos that give a homeowner a sense of what installation might include. The website also contains information on how a homeowner can assess a property to determine the best location for a permeable paver project, and actions that can be taken to maintain it after installation.

Strong Results

With over 40 residential projects completed, Ms. English and Mr. Somers have a sense of the program’s effectiveness, finding that the RainScapes projects show significant success in handling stormwater. Although there’s some pressure from outside sources to include porous concrete or other alternatives in the program, RainScapes remains focused on PICP because of its numerous advantages, says Ms. English.

“They’re easier to clean for homeowners, and we feel very comfortable with a system that includes pavers that must be recognized by the ICPI,” she notes. “There’s an extra level of credibility and support there.”

Local contractor Mike Walters, owner of First Impressions Hardscapes in Sandy Spring, MD, installed permeable pavers on about 30 residential properties as part of the RainScapes program. In total, he’s done close to 300 projects with permeable pavers in the county. He shares Ms. English’s opinion that permeable pavers provide several benefits that would be challenging to replicate with other pervious or porous paving materials.

“The pavers are aesthetically pleasing, but what’s genius is the system below them,” he says. “That’s driving demand, because people are looking for new ways to handle water problems on their property, and using a permeable paver system dramatically cuts down on water runoff.” Mr. Walters installed a permeable paver system on his own driveway and uses the captured rainwater to water his lawn.

As an advocate of better stormwater management, Walters believes the RainScapes program could be a boon for any community, city or county as most have too much stormwater runoff. “The program is awesome, there’s great incentive for people to invest in a greener alternative here, and you’re getting an attractive product at a better cost,” he says. “In this situation, everybody wins.”

Additional Resources

To learn more about the Montgomery County RainScapes program, visit


Great Preservation

Across Iowa, cities and towns are using permeable pavement in infrastructure rehabilitation. They are exploiting the multiplier effects (and benefits) that result from combining stormwater management with pavement rehabilitation using permeable interlocking concrete pavement (PICP). These projects not only reduce local flooding and stormwater pollution, they support road rehabilitation and historic preservation.

Three Iowa cities recently completed multimillion dollar PICP projects with local, state and federal government funding. A primary funding source comes from the diversification of Iowa’s State Revolving Fund (SRF). The low-interest loans, normally used for wastewater treatment projects, are now additionally directed toward infrastructure projects that reduce stormwater runoff, specifically flows into wastewater treatment plants and combined sewer overflows (CSOs).

PICP has been deemed an eligible project element for infiltration in projects intended to reduce CSOs. Other municipalities, including those in Washington, Oregon, Michigan, California and Washington, D.C. are conducting similar projects with more on the way.

Green Alley Project: Dubuque

Situated on the Mississippi River and chartered in 1837, Dubuque lays claim to being Iowa’s oldest city. Its location and topography make it prone to damage from stormwater runoff and flooding. In 2011, the city experienced over 13 in. (325 mm) of rainfall in 12 hours, resulting in severe flooding of over 1,300 households. The event was a major impetus for the installation of nine green alleys to reduce flooding and CSOs, which led to planning for another 80 alleys, all built from PICP.

“We’re a very sustainable city, and it’s a mantra that resonates with City staff,” says Jon Dienst, civil engineer for the City of Dubuque. “The pavers were a natural fit for clean water and city design.”

City officials took cues from Chicago, now home to more than 100 green alleys under a program targeting four initiatives:

1. Stormwater management (CSO reduction)

2. Urban heat island reduction

3. Material recycling

4. Energy conservation

Dubuque’s first two alleys were piloted in 2009 using porous asphalt and PICP; funding was through the federal Community Development Block Grant program. “The City council, without even talking about the performance, just liked the look of the concrete pavers in the alleys,” Mr. Dienst recalls of the initial decision.

After the launch, the City decided to take advantage of the state’s low-interest loan funds to borrow $64 million for a major overhaul of Dubuque’s wastewater treatment plant. The alley financing comprised $9.4 million in State Revolving Funds designated by the Iowa Department of Natural Resources for wastewater and clean water projects. The alleys qualified.

The catch: the funding had to be spent within three years. “That’s a lot of alleys,” Mr. Dienst says. Forty-eight alleys will be constructed this year with an additional 25 next summer. The 25 alleys next year will have sewer and water mains and services replaced at City cost with the SRFs used for the alley pavement and stone.

The alleys are roughly 300 ft (90 m) long and 12 and 14 ft (3.6 to 4.2 m) wide. Each costs about $100,000, depending on topography. The City uses modeling software to determine the reservoir capacity and resulting thickness for open-graded aggregate subbase in each alley. A range of rain events are modeled and the subbase thicknesses determined by extensively testing the soil subgrades for infiltration. 

Each alley uses 31/8 in. (80 mm) thick concrete pavers over 2 in. (50 mm) of ASTM No. 8 stone. That sits on a 4 in. (100 mm) base layer of No. 57 stone. Under this layer is

a No. 2 stone reservoir subbase. The project team employed geotextile on the soil subgrade of each alley to help keep the stone clean.

Some of the alleys are next to buildings with foundations over 100 years old. Those installations included new waterproofing to prevent water infiltration. From a cost standpoint, this was well worth the expense, Mr. Dienst says, to prevent water in basements or worse.

“We didn’t have experience in Dubuque,” Mr. Dienst says. “We had to talk with others and learn from their mistakes.” Suppliers and contractors were hard to come by at first, but now are abundant in the area, with pricing around $3.75 to $4/sf ($40 to $43/m2). “It’s almost cheaper to put in the pavers than concrete or asphalt,” he says.

The alleys are being monitored for water quality performance and are expected to reduce nitrates by 25 percent and phosphorous by 60 to 70 percent, achievements supporting the City’s clean water initiative. An 80 percent reduction of stormwater runoff volume is expected as well. Maintenance costs are low, and the City has invested in a vacuum cleaning truck to help in that effort.

Aesthetically, pavers are well suited for a city heavily rooted in its past. “They are historically appropriate,” Mr. Dienst says. “A lot of them are downtown. We are a historic city, recently celebrating 175 years. Historic preservationists are excited about this.”

Permeable Streets: Charles City


About 130 miles (78 km) northwest of Dubuque sits Charles City with a history of flooding and runoff problems. Federal and state funding provided resources to install 27 blocks of PICP in a residential neighborhood slated for street rehabilitation. 

Through the help of now-retired City Administrator Tom Brownlow, Charles City received $3.6 million in 2010 from the American Reinvestment and Recovery Act to install the initial phase of the project. At $2 million, phase two utilized Iowa’s State Revolving Fund and 30 percent forgiveness of the eligible costs, essentially paying for the paving portion of the project. The remaining funding paid for sanitary, sewer and water line improvements.

Both projects involved city street renovations with the second phase having learned several lessons from the first. “The first time was a hard sell,” recalls Dirk Uetz, Charles City’s superintendent of streets. “People were a lot more open-minded after they had seen the first project.”

The City commissioned the Conservation Design Forum (CDF) to design the permeable streets. The designers modeled the system to capture runoff from streets, yards and alleys and infiltrate the runoff. Peak discharges for the 10-year storm were reduced by more than 90 percent, according to CDF. This reduction prevented the necessity and expense of upsizing many existing storm sewers. The design took advantage of the sandy soil subgrade by infiltrating much of the runoff rather than directing it to inlets and into storm sewers. Also, the permeable streets were narrowed by 5 ft (1.5 m), thereby increasing the tree lawns and the graceful appearance of the old neighborhood.

Phase one spanned 16 blocks and included permeable areas at intersection corners covered with large stones surrounding raised beehive intakes. These areas ultimately proved difficult for the local homeowners and for the city’s maintenance staff to clean. They also presented some risk to children playing nearby. The phase two design of six-and-a-half additional blocks reverted to regular storm drainage intakes, which were easier to maintain and presented no risks to children. Additionally, phase one used slightly depressed retention areas with amended soils in the tree lawns behind the curbs. These proved inconvenient for pedestrians and were replaced by an improved, raised design in the second phase.

While response to the new streets has been positive, the real success lies in the runoff reduction, Mr. Uetz says. “If we have a heavy rain now, you don’t see any water going down to the river,” he says. “In phase one, we opened the hydrants onto the street and let the water run. The spectators couldn’t believe it.”

Downtown Restoration: West Union


A farming hamlet about an hour’s drive west of Dubuque, West Union had its share of stormwater flooding problems including contamination of nearby Charles Stream. Moreover, its aged and worn downtown needed an update.

West Union took the opportunity to implement its Clean Green Climate Action Plan in six downtown blocks. The U.S. National Renewable Energy Laboratory weighed in on the project, which included energy conservation, greenhouse gas reduction and pedestrian infrastructure improvements. Geothermal heating and cooling systems were also built as an incentive for businesses to fill the downtown storefront vacancies, and these systems included snowmelt capabilities.

Completed in 2013, the project totaled $10 million and used state stimulus money, funding from the Iowa Department of Transportation, the U.S. Department of Energy, the Environmental Protection Agency and others. Both the Iowa Department of Agriculture and Land Stewardship and Watershed Improvement Review Board contributed $500,000 each toward the project, with the majority going toward PICP.

“Prior to the project, there was nothing for storm drainage in the downtown area,” says Jon Biederman, branch manager for Fehr Graham, an engineering and environmental firm that worked on the project design. “We were looking for a way to clean and cool water [before it runs] into Charles Stream. An easy way to accomplish this was with permeable pavers.”

The infiltration system filters runoff through an open-graded stone base to cool it and clean it, accomplishing both goals at once. It also slowed the stormwater runoff substantially. “It can take a few days versus a few minutes,” Mr. Biederman says.

West Union’s PICP design differed from the norm. While typical PICP installations include a stone subbase storage layer no more than 1- to 2-ft (0.3- to 0.6-m) thick, West Union needed much more storage. In most areas, the subbase is 3- to 5-ft (0.9 – to 1.5-m) thick to store, infiltrate water into the clay soil subgrade, and release any excess slowly to the downstream waterway. The subbase storage layer was topped with a 6-in (150-mm) layer of clean, crushed stone as a base for the bedding layer of 1½ to 2 in. (40 to 50 mm) limestone chips.

The concrete pavers rest on this bedding layer, their joints filled with small permeable aggregate.

The clay soil subgrade demonstrated that PICP can be designed to infiltrate into low infiltration soils. The City purchased a vacuum truck for the main thoroughfare and a smaller unit for the sidewalks and to clean the joints twice a year. Ultimately, the design met the project goals for infrastructure restoration, positive environmental impacts and historic preservation.

The street previously had been paved with asphalt over brick pavers placed in 1914. The contractor retrieved the old bricks and incorporated them into decorative strips in the intersection centers. They are installed on the same stone base as the concrete pavers with permeable, stone-filled joints.

“We’ve had very positive responses,” Mr. Biederman says, noting the initial skepticism of the local residents and business owners who were not initially keen on the change. “They look good.”

As demonstrated by West Union, as well as by Charles City and Dubuque, Iowa presents some groundbreaking examples of creatively funding infrastructure renovation projects with PICP.

Additional Resources

ICPI Permeable Pavement Resources

Permeable Interlocking Concrete Pavement Design Manual

ICPI Permeable Pavement Resources: