Stormwater | Stormwater Design and Sustainable Development

Stormwater Design and Sustainable Development

By Lynn Merrill

The 2001 National Resource Inventory by the Natural Resources Conservation Service estimates that 106.3 million ac. of total land area in the continental United States is developed. Between 1997 and 2001, the rate of development has averaged 2.2 million ac./yr. with about 9 million ac. being developed. The bulk of this development came from forestland (46%), followed by cropland (20%) and pastureland (16%). In addition, it's been estimated by the Federal Highway Administration that there are 24,500 mi.² of paved public roadway, while Environmental Building News estimates that there are 10,900 mi.² of paved parking and driveways.

Nokomis wetlands in Minneapolis, MN

With these rates of growth, the impact of present and future development creates challenges for stormwater managers in both the public and private sectors. In light of the current budget crisis facing state and local governments nationwide, dollars for hard infrastructure improvements to expand stormwater facilities and fund maintenance activities are in direct competition with homeland security demands. Cash-strapped cities faced with a Solomon's choice regarding the allocation of fiscal resources in many instances turn to even more intense development to generate local jobs and tax revenues. Developers, facing shrinking profit margins and looking to cut the amount of onsite and offsite improvements as a method of improving the bottom line, challenge environmental regulation on every front.

Yet in every crisis, there is opportunity. In this particular case, it's an opportunity that is nearly 20 years in the making. The opportunity is sustainable development, and implementing its concepts will have a major impact on stormwater management in the future.

Sustainable development became the hot topic during the mid-1990s, with a focus from the Clinton administration. And it has a "warm and fuzzy" feeling, because it appears to allow both environmental stewardship and development to coexist simultaneously. But sustainability can mean many things to many people, especially when it applies to managing environmental programs, including stormwater management.

Sustainable development generally is understood to mean development that occurs with sensitivity to environmental concerns. It incorporates environmentally benign materials that have not placed a critical demand on limited resources or caused environmental damage through their harvest or manufacturing processes. Projects that use sustainable development standards also minimize the project's impacts on the natural environment through siting design, incorporating landforms and natural drainage pathways into the final building placement. Finally, buildings and structures built to sustainable standards make a minimum demand on future operational resources, such as energy and toxic materials. They might even incorporate deconstruction and recyclability into the plan so that when the building's use becomes obsolete, it easily can be taken apart and the basic materials reused or recycled.

Setting Environmental Standards

Cedar Meadows wetlands, Minneapolis

It would be easy for a developer to make a claim that a particular project is sustainable and environmentally friendly. Like mom and apple pie, being environmentally sensitive is a great marketing claim. However, the United States Green Building Council (USGBC) has taken the lead in establishing standards that allow objective measurement of environmental sensitivity.

The USGBC is a national coalition of leaders with representatives from the entire industry on environmental building issues, whose mission is to "promote buildings that are environmentally responsible, profitable, and healthy places to live and work." Comprising a 10-person executive committee and 13-member board with members of local governments, environmental policy advocates, builders, and suppliers, the USGBC is "leading a consensus for producing a new generation of buildings that deliver high performance inside and out." Supporting these efforts are 15 regional chapters located around the country.

One of the most important endeavors of the USGBC is the development of the LEED (Leadership in Energy and Environmental Design) Green Building Rating System, which establishes a national standard for developing sustainable buildings. According to USGBC, LEED was created to

define "green building" by establishing a common standard of measurement;
promote integrated, whole-building design practices;
recognize environmental leadership in the building industry;
stimulate green competition;
raise consumer awareness of green building benefits;
transform the building market.

The LEED standards provide a framework in which to assess buildings' performance, including the areas of sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality. LEED offers project certification, professional accreditation, and training.

Under the LEED certification program, a project is reviewed by using a scoring sheet and various submissions by either a civil engineer or other party to the project. The project receives points for meeting various technical requirements; a total of 69 points is possible. Four categories of certification are awarded, based on the number of points received: Certification (26-32 points), Silver (33-38 points), Gold (39-51 points), and Platinum (52-69 points). Once a project is submitted, the certification is assessed and additional documentation necessary for the audit phase may be requested.

Stormwater management practices are contained under the Sustainable Sites section, with a total of 14 points. This section also covers such technical requirements as Urban Redevelopment, Alternative Transportation, Reduced Site Disturbance, and Heat Island Effect.

To obtain the points allocated for Stormwater Management, a project must achieve the intent of limiting the amount of pollutants and disruption of natural water flows by managing the rate and quantity of runoff. A project also must address onsite treatment through increased onsite infiltration and through the elimination of contaminants. Some of the technologies and strategies that can be utilized include using garden roofs and pervious pavements, constructing wetlands and bioswales to treat stormwater, and reusing stormwater for nonpotable water uses, such as landscape irrigation and toilet and urinal flushing.

Sustainable Stormwater Management

Lake Harriet Delta, Minneapolis

Sustainable stormwater management practices have been evolving over the last 20 years, but it has been in only the last decade that the movement has gained momentum. "I've been in the water resources business as an engineer for 40 years," states Thomas H. Cahill, president of Cahill and Associates in West Chester, PA. "A significant part of that time has focused on stormwater issues, beginning from the perspective of nonpoint-source pollution. I come at it from a water-quality perspective, and much of my earlier work was related to evaluating how pollutants move across land surface and through systems."

Cahill began exploring some of the concepts that now form the basis of sustainable stormwater management in the mid-1970s. "A number of folks I was working with said, 'You've got a lot of great ideas, theoretical concepts about stormwater. Why don't you come up with some practical solutions so that we can do a better job of designing things?' We found work that had been done by the Franklin Institute on the development and application of porous asphalt concrete pavements, a mix that would let the water drain through the pavement into an underlying bed that held the water and let it infiltrate into the soil."

The concept that Cahill's firm advanced was that infiltration was a better way to manage stormwater rather than detention. "Detention basins did nothing to mitigate the volume and the quality impacts of runoffs," says Cahill. "The detention basin basically fills up, drains out, and while it mitigates the peak of runoff, it does not in any way, shape, or form reduce the increased volume that we generate from a new impervious surface. If we could manage volume by changing the kinds of impervious surfaces we build and soak the water into the ground by infiltration, that was a better technology. Twenty years ago when we promoted that idea, people said, 'You're crazy.' It was difficult to wean ourselves from that detention technology and move toward infiltration, but after a lot of lobbying and a lot of apostolic work, we'd finally managed to convince a reasonable number of people that the future of stormwater management should be centered or will center on infiltration and reuse."

Cahill became involved in the LEED program when the guidance document was undergoing a revision. "As a consulting firm, we have been preaching this gospel of what we think of sustainable site design for 20-plus years. About three years ago, the USGBC, through the LEED program, was rewriting their guidance and they wanted to improve on the site and stormwater ideas. They asked me to join them for a couple of extended weekends. The Green Building Program has become very much in vogue in the building construction business, and it's beginning to grow in the design side, mainly through architectural firms. Architects, just because they are a bit more creative than dumb engineers like me, have been ready to embrace changes in materials, in ventilation, in lighting, in all kinds of aspects of making buildings greener."

For the Chicago, IL, architectural firm of Skidmore, Owings and Merrill, whose work includes the Sears Tower, embracing the changes that come through the USGBC made sense as both an operating philosophy and a marketing strategy. "We like to feel that we integrate the concepts of sustainability into all of our projects," maintains Michael Fink, associate partner and discipline head of civil engineering. "We are an original member of the US Green Building Council, from the firm's level. We are working on projects that are going for different degrees of LEED certification that are either in construction or in design currently in Chicago, Boston, and New York. We have one person at a relatively high level here in the Chicago office who is a technical architect exclusively and totally dedicated to the green building sustainability concept. It's not a new thing for us. Being an integrated, multidisciplinary firm with all of the engineering components in-house, we have always worked for a level of sustainability that might have been above the current state of the practice. We realize it's not just a fad."

Fink feels that the firm's client base is somewhat mature as it relates to stormwater management and that site designs that incorporate detention systems are acceptable technologies. But the real challenge comes in explaining to clients that some of the new concepts, such as wetlands creation and stormwater reuse, actually are cost-effective. "Stormwater management is generally not a problem," he remarks. "The clients we work with in the Midwest are used to that requirement. Dealing with it from a cost-effective standpoint is what we are challenged with time and again. I think the sustainability aspects of the whole green building element generally have to prove themselves on a benefit/cost analysis or on a life cycle costing basis. Part of it is to investigate just how far you can push up the level of technology. I don't think that you will see clients object to appropriate stormwater management, but again, the challenge is always to provide it in a cost-effective and integrated manner so they don't feel they are paying for something that doesn't function or functions poorly."

Environmentally Gentle Management

When it comes to using environmentally gentle stormwater management programs, costs aren't the only obstacle that sustainable development practitioners must overcome. For many project developers, there is more security in the hard-number calculations and known solutions than in what, for many, is a soft approach to stormwater management. "I think that an absolute is something you can take to a client and say, 'This will work,'" says L. Peter MacDonagh, vice president of The Kestrel Design Group Inc. in Minneapolis, MN, and an adjunct faculty in the Landscape Architecture Department at the University of Minnesota. "It may be overengineered, it may be overdesigned, but we know that it will work. And that, sometimes, is the level of assurance the client is looking for. But I think there are a lot of soft solutions that can work. As much as possible, we try to keep water out of pipes in terms of the stormwater component. So we're looking at ways to intercept or infiltrate as much as possible, and we like to start as close as we can to where the water drop hits the ground - or maybe before it hits the ground."

This holistic approach that addresses the issue of stormwater at the point that the rain makes contact begins, for many structures, with an area where stormwater management opportunities are frequently overlooked in the context of site design. "Some of the strategies that we like to look at are starting on the roof," states MacDonagh. "As we move down through the development envelope through trees and shrubs, during a rain event when that material is wet, then at least a certain percentage of that rain is pulled off-line right away. As it gets down to the ground, we use pervious pavement or have infiltration beds. Or if we have impervious surfaces, we at least pitch them toward pervious surfaces so that we can get some infiltration there. We try to select water-loving plants that tend to have large root systems and pull water out of the ground and then basically pump or evaporate it out through evapotranspiration. That's the big picture of how we're looking at the envelope of development from the top of the roof down to the ground and down below the ground."

One technique that provides for stormwater management and also addresses the heat island effect is green roofs. "An extensive green roof system has a very shallow soil medium or cross-section loading," describes MacDonagh. "Typically it would be somewhere between 3 and 5 inches deep. It would sit on a membrane, something fairly thick that coats the roof up onto the parapet walls. It can't be on a very steep pitched roof - typically 20% or less, although they can go up to 30%."

The weight of the system generally is 10-15% heavier than a gravel ballast roof, MacDonagh notes, and the roof includes layers to hold water that the plants' roots can access. Plants usually are succulents no taller than 3-8 in. "If you are in a very urban area, then you reduce heat impacts," he points out. "It is not a very heavy system, and it's really a skin of green on the top of the roof to reduce temperature. It extends the life of the membrane. Typically these roofs last two to three times longer than something that is under a gravel ballast roof." Although green roofs do require some maintenance, including weeding and, on occasion, removing trees whose roots try to break through the membrane, "It's not a very maintenance intensive system," MacDonagh says.

Permeable pavements also are becoming more widely used. Asphalt pavement mix is modified to reduce the number of fines. Water then percolates through this mix into an aggregate base material that is designed to hold the water, allowing it to infiltrate into the soils. (See "Porous Asphalt Pavement With Recharge Beds: 20 Years and Still Working," May/June 2003 Stormwater). One of the biggest questions relating to permeable pavements is the issue of pollutants in the runoff potentially contaminating groundwater. "That is a concern, and it certainly warrants more investigation," notes Cahill. "But the work that's been done so far indicates that as long as the infiltrating rainwater percolates through a couple of feet - and we usually use 2 to 3 feet of soil - virtually all the pollutants that are contained in that stormwater are removed, broken down, or transformed in that infiltration/percolation process. The soil mantle has always been our best treatment mechanism for pollutants. Keep in mind that if we didn't have that soil on the face of the planet, we'd be walking on the bones of dinosaurs. There's an amazing process that goes on there. We're trying to use the natural materials that have done a fairly good job for 4 billion years of cleaning up the mess that evolution has produced of the organic critters."

Leading the Charge

The conversion to sustainable development is a process that gains converts a few at a time. For example, the construction management firm of W.S. Cumby and Son Inc. in Springfield, PA, was introduced to the concept by one of its clients. "Our involvement with sustainability really began about three years ago when we got dragged into looking at green building and sustainable design and construction by a client," comments Sandy Wiggins, corporate vice president. "They said they wanted to build a green building, and we said, 'We don't know anything about that, but we'll sure try to figure it out.' So we began educating ourselves. The more we learned about it, the more we realized that it made good sense. It fits with our corporate culture and also seems like a great marketing opportunity for us. Over a very short period of time, as more and more people in our organization got engaged in it, we realized it's not only as good from a marketing perspective, it actually led the way that we have to start doing business. Not just our company but everybody."

Wiggins and his staff began introducing the concept of sustainability and green buildings into projects and to their various clients. "Because we provide so much preconstruction service, we're often in at the very early stages of project development, so it enables us to get it on the table with them," states Wiggins. "We also started networking with other people in the Philadelphia community who had an interest. As a result, we were instrumental in pulling together a group of people who began the Delaware County Green Building Council, which is now the regional chapter for the United States Green Building Council."

Training became critical to the success of introducing the concept of sustainable development throughout the company. "We started internal training of all of our operational people - anybody who touches a project, beginning with our estimators, the project managers, even the superintendents who we have out in the field - so that all of them would eventually become LEED-accredited professionals," says Wiggins. "We've actually pushed about half of the company through that curriculum now, and by the end of this year, we'll probably have 25 LEED-accredited professionals on staff. We also recently built a new office building for our company where we're hoping to get a LEED silver certification on it."

Peck Farm Park parking lot, swale, and wetland in Geneva, IL: water-quantity and -quality improvements

The education process includes explaining these approaches to municipal officials who initially might not be comfortable with some of the concepts. "On our own office building, we used a strategy of porous paving and groundwater infiltration in beds under the parking lots," recalls Wiggins. "That allowed us to capture 100% of the stormwater in a 100-year event and put it back into the aquifer rather than clear a beautiful site and put in detention basins and stormwater piping. When we took that initial plan to the township, the township engineer basically rolled it up and sent it back to us and asked what we were trying to do. So we spent some time educating the engineer about what we were doing and backing it up with all the calculations to prove that it was going to work. We were eventually successful in convincing him that this was a good thing, and he actually got quite engaged and excited about it." Once the engineer was onboard and enthusiastic about the design, the local planning board approved the plan in a single session - "a real accomplishment in this part of the country; it usually takes several rounds," notes Wiggins. "So there we had great success. Other places, we were just running into brick walls sometimes. In the engineering community, there are sometimes individuals who don't like change and don't want to struggle with the issue."

"Unfortunately this is missionary work," states Leo Pierre Roy, vice president of The Bio-Engineering Group Inc. in Salem, MA, and a former undersecretary of environmental affairs for the State of Massachusetts. "It is education, and you have to do it on a project-by-project basis. Many regulatory schemes do have some flexibility built into them if you can demonstrate environmental benefit. That's really what we try to do: to show that, on a life cycle basis, the costs are lower and there are definitely water-quality improvements that come from this. That is the challenge that is facing us right now. In many communities this is a new idea. It doesn't fit the typical regulatory regime. As there is turnover in the engineering population and younger engineers come into the field and into these positions that have been exposed to a broader range of experience, I think there will be increasing openness to this. Every time we go to a new community and talk about a project, we have to take people back to the water cycle and say, 'Here's what happens when rain falls on a forest and when rain falls on a building.' People are receptive, but there is a knee-jerk reaction to new ideas, and we just have to be very patient and demonstrate benefits."

Lynn Merrill is director of public services for the City of San Bernardino, CA.

SW November/December 2003

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