The Green Way
This sea change has affected all industries, in all sectors, and our approach to infrastructure is no exception. The discussion is everywhere. How many dams should we allow on our rivers? What are the ecological effects of this construction project? Is there a way for infrastructure to do its job without increasing runoff?
When President Eisenhower set into motion the Interstate Highway System in 1956, he had two reasons for pushing it. Primarily, a vast interconnected network of well-maintained public routes would encourage interstate commerce. However, it could also serve as an invaluable logistics tool for the military, in the event of a national emergency or invasion. As a result, our highways have been lauded for decades as a national treasure. The moral of the story is that strong infrastructure is a lasting investment for a society, and it often serves more than one purpose.
So with the rise of environmentalism, the government has emphasized the ecological component of infrastructure designs. Proponents of this change argue that the best way to meet our everexpanding infrastructure needs is not through the standard impermeable engineering solutions of concrete culverts, iron grates and lead pipes.
Instead, they argue for ‘green’ infrastructure, an approach that uses plant material to slow, filter and infiltrate stormwater where it lands, reducing the need for traditional, ‘gray’ infrastructure. Green infrastructure can take many forms. In rural areas, it might be wetlands restoration, like the project to restore pollinator habitats along I-35.
In urban as well as suburban areas, it often takes the form of the stormwater mitigation measures included in construction projects. Rain gardens, green roofs, green walls, rainwater harvesting systems, bioswales and even permeable pavers are all examples of green infrastructure found on sites in and around cities.
Gray infrastructure is made of underground pipes and hard armor, and it serves a single purpose—remove stormwater as quickly as possible, preferably at low cost and high durability. Green infrastructure does a lot more than just that. It beautifies neighborhoods, filters out trash, nitrogen, phosphorous and sediment, and combats the urban heat-island effect.
Reducing the impact of runoff on the environment is one of the main goals of the NPDES and MS4 permits. Small wonder then, that the EPA has been instrumental in advocating green infrastructure to governmental bodies nationwide.
“The EPA has been leading the charge over the last decade,” says Robert Dusenbury, principal at Lotus Water in San Francisco, California. “That was the start of green infrastructure implementation on a national level.” The agency makes changes to the national rules for NPDES permits, putting pressure on the states. Whether a state has its own Department of Environmental Protection, Department of Environmental Quality or falls directly under federal EPA control, each of them is overseen by some sort of regulatory body that enforces the new guidelines.
They pass the pressure on to municipalities, and tightening MS4 permit requirements encourages new construction projects to include more permanent BMPs into their SWPPPs, often in the form of green infrastructure. If you’re involved in designing, installing, or maintaining stormwater mitigation measures, your business can benefit in the immediate future by getting involved in this national, permanent renovation of our communities.
So what do you need to know to get involved? First, urban projects and rural projects are very different from each other. “If you’re doing a large-scale green infrastructure facility in a natural setting, like building a wetlands, it can be a lot like other earthforming,” said Dusenbury. “It’s mostly about pushing dirt to where it needs to be, and using a specific landscape palette for plants.”
Urban work, on the other hand, he describes as being more finicky, requiring greater attention to detail.
Both require precision, but when you’re working in a tight space, especially within a right-of-way, there’s no room for error, and small mistakes can render the entire installation non-functional.
Let’s say you’re installing a bioretention cell—a rain garden—along a curbside. The height of the inlet relative to the curb is very important, as well as its height, relative to the outlet. If the inlet is above the outlet, the cell might function in a light rain, but it’s considerably more likely to back up. Similarly, if you aren’t careful when installing the inlet and there is a raised lip, that can serve to divert water away from the cell entirely.
Depending on the location and facing of the cell, you may actually need to set the inlet below the grade of the gutter. After all, if the water is rushing along with a lot of momentum, it’ll take some force to divert it into the rain garden, and it’s easiest to let gravity work for you.
“The world is full of poor green infrastructure installations,” said Dusenbury. “It happens when people just think they can do it all ‘off the cuff,’ so they don’t study or train, and their projects fail.” He advises anyone looking for a green infrastructure education to get in touch with their local stormwater regulators.
Bioretention cells are just one technique, but any permanent stormwater BMP that staggers peak flows, or filters out trash, nitrogen, phosphorous or sediment can qualify as green, if it also serves to help plants grow. Most do this directly— rain gardens, bioswales, restored wetlands and urban forests all put stormwater directly at plants’ roots.
Green infrastructure also usually requires regular maintenance, and like all infrastructure, comes with a finite lifespan. Plants do a great job of absorbing and breaking down the chemicals that would otherwise contribute to a city’s Total Maximum Daily Load, but no plant in the world can biodegrade the leftover wrapper from a bag of chips, or the broken tab off a soda can. These installations periodically need trash cleanup and weed pulling. Over time, the soil in a bioswale or rain garden will get compacted, and be less effective at filtrating stormwater.
There are some green infrastructure techniques where soil com- paction isn’t nearly so much of a concern. Rainwater harvesting is considered a green practice, as it helps reduce peak flows, but it only supports plant life if the water is used for irrigation. Similarly, pervious pavers reduce runoff when in- stalled in place of impermeable surfaces.
Another option that’s a little strange when you first think about it, yet is gaining in popularity, is the green roof. A green roof is exactly what it sounds like: instead of diverting stormwater from downspouts into rain barrels or cisterns, plants are placed directly on a structure’s roof.
Especially in urban areas, where space is at a premium, green roofs are an attractive option, and make their way onto a lot of building plans as a result. “It’s a distributed stormwater management approach,” says Michael Fur- Company LLC, in Baltimore, Marybish, founder of the Furbish land. “A stormwater retention pond might have an acre of area draining into it, but a green roof is receiving rainfall one-to-one where it falls.”
Most of the time, you’ll hear green roofs categorized as being either extensive (meaning the growth media is thinner, six inches or less in media, generally more than six depth) or intensive (thicker growth allows for more water retention, and inches deep.) Thicker growth media supports a wider variety of plants, but also requires greater structural strength for the roof.
According to Furbish, his company categorizes green roofs by what they do, not how thick they are. “We tend to think of a green roof as either performing a stormwater function, or an aesthetic function,” he said. It isn’t necessarily an either/or situation, though; a green roof can serve both purposes. But a space that’s designed to be only a stormwater management tool will have very different design goals from a rooftop garden or relaxation space.
Green roofs present some unique challenges, and for a contractor willing to learn and innovate, unique opportunities as well. Most such projects are based on the traditional German method. In this approach, soil is the only growth media, but a soil that is highly engineered, with its particle size distributed for optimized water retention.
“However, even at best, that’s a relatively inefficient way to hold water,” says Furbish. Of course, as the EPA tightened restrictions, green roofs had to hold more water, and engineers responded by specifying thicker and thicker media depths. Not only did that increase material and labor costs, it also increased the weight, meaning that fewer new buildings could feasibly include them in their plans.
Furbish chose a different route, separating the task of water retention from the growth media. “We like very efficient water retention at the bottom of the profile instead,” he said. “We put a layer of mineral wool at the bottom, which is 94 percent efficient at holding water, so we’ve removed the obligation to be holding water from the growth media.”
This also frees up the soil to be better optimized for the unique environmental conditions often found on the tops of buildings. “We can then use a more liberally defined particle-size distribution at the top of the profile,” said Furbish. “That really inhibits weed seed germination, and makes the environment at the surface even harsher than what it would be otherwise.” A harsher environment makes it harder for intruders to take root. At the same time, he can make the soil particles heavier, reducing how much soil the site will lose to the wind.
The trend in green roofs has been towards lighter weights, lower costs and greater water efficiency, as more buildings incorporate them as a way of meeting environmental requirements. Most installations right now are on new construction, but retrofitting old buildings with green roofs may become more prevalent in the future. Says Furbish, “I think we will see different municipalities, counties and states creating economic incentives for retrofitting green roofs, so they can be better managers of stormwater.”
Washington, D.C., already has a rebate program for encouraging buildings to be retrofitted, modeled after carbon-trading programs. A property owner who installs a green roof when he doesn’t have to can receive a credit that he can then sell to a developer who can’t otherwise make sufficient green infrastructure fit into his plans.
Sarah Loveland, chair of the Green Infrastructure Foundation in Washington, D.C., says that a lot has changed over the course of her career. “When I started in the field, all the roofers were told, ‘Get the water off of the roof as fast as you can.’ I think there’s still a lot that could be done about educating the market on the benefits of green infrastructure.”
That starts with getting away from a one-issue approach. A flat return-on-investment comparison of green vs gray isn’t likely to reflect favorably on something like reduction of combined sewer overflows in an urban setting. However, that doesn’t take into account the host of other benefits green infrastructure projects bring.
For one thing, all of them, with the possible exception of permeable pavers, help reduce the urban heat-island effect. Sunlight bakes concrete and asphalt, but the evapotranspiration of grass and trees helps cool the air. Then there’s the reduction in carbon dioxide and overall improvement in air quality that plant material brings to an area.
A survey of green infrastructure projects by the American Society of Landscape Architects in 2012 looked at case studies submitted by members. Of the 479 projects spanning 43 states, only 25 percent increased costs, while 44 percent decreased costs.
The viability of green infrastructure projects is subject to some regional differences, depending on the volume of stormwater an area can expect, and what plants are best suited to that area. Loveland advises that in urban areas with combined sewer overflows, municipalities are a good source of contracts.
“The opportunities are greatest in the specific urban areas that have stormwater issues,” she said. “You can also find out who is under a mandate from the EPA to remedy their stormwater.”
Any number of cities have faced, or are still facing, consent decrees from the EPA, resulting from violations of the Clean Water Act. The agency has even specified green infrastructure as a solution for consent decrees it has with the District of Columbia, Chattanooga, Tennessee, and Jersey City, New Jersey, among others. Given that many municipalities are facing increased stormwater woes and stagnant budgets, arguing for a cheaper solution that’s also environmentally friendly should be a home run.
There’s also a simpler reason to get involved in green infrastructure projects: they’re beautiful. Bioswales and rain gardens are prettier than catch basins and culverts. The beauty doesn’t just raise property values. Adding greenery to neighborhoods reduces peoples’ stress—how many of your other projects can you say that about?
Our country’s population continues to concentrate in our cities, forcing them to grow, increasing the demand on water resources. Stormwater managers will face higher amounts of pollutants to remove, but green infrastructure offers a lasting solution to that problem. For contractors who know the ins and outs of bioretention, the opportunities will be abundant.