Low-impact development mimics natures handling of water.
Nature has its ways of dealing
with stormwater. Some percolates into the ground, some pools, and some makes its
way to larger bodies of water; often, which route water takes depends upon the
state of the soil and the plant life growing within it. A sandy soil allows
water to pass through; a clay soil absorbs only so much, then creates a muddy
mess. A site containing a water-loving tree, such as a weeping willow, will
eagerly drink up as much moisture as it can get, while other plants suffocate
from lack of soil oxygen and resign themselves to becoming peat.
Once humans have altered a site,
however, all bets are off, especially since most of our construction materials
are nonporous. Therefore, a variety of manufactured products and earth-altering
tactics are used to compensate for our changing nature’s status quo.
What Is LID?
“Low-impact development [LID] is
an approach to stormwater management and site design that uses natural
hydrologic processes to preserve or recreate that hydrology at the site level,
or to meet goals,” explains Neil Weinstein, executive director of Beltsville,
MD’s Low Impact Development Center, a nonprofit organization dedicated to the
advancement of LID technology. “LID mimics how nature handles water. It’s a
performance-based approach. Old regulations used prescriptive approaches—such as
‘achieve 80% TSS [total suspended solids] removal’—which are somewhat ambiguous.
For example, what’s the incoming load? We’ve previously used generic,
one-size-fits-all approaches, rather than looking at the land use and how the
BMP [best management practice] responds to it.”
 |
Photo: Best Management Products Inc.
A manufactured device, such as BMP Inc.’s Snout, can trap pollutants, whether oil, styrofoam peanuts, tennis shoes, or hypodermic needles. |
Is LID expensive to accomplish?
“LID is most cost-effective and best performing, environmentally,” says
Weinstein. “It brings a business-based approach, where we can use the most
cost-effective and environmentally efficient technology for the problem. We’ve
been working with Green Highways Partnership and partnering with EPA Region 3
and the Federal Highway Administration, moving stormwater into the 21st century
economy. We’re looking at a watershed-based approach toward
stormwater—recycling, environmental programs through greening, and
conservation—where highways can be the foundation for Environmental Management
Systems and watershed restoration.”
Weinstein points out that Section
438 of the Energy Independence and Security Act requires all federal facilities
to meet all preconstruction hydrology for new building construction. “But this
has to be a site-based approach—doing what makes sense at that site, like using
permeable concrete for the right land use,” he says. “Does the site have
compacted clay soil? Maybe you can’t get water to percolate back into the soil,
but you can reuse that water, which creates the same results. LID gets people
thinking about the process. What we tended to do before is build it and forget
it; now, LID moves things into management systems, one looks at the site’s whole
life cycle. Instead of just building a retention pond, you might be able to put
in retention tanks and use the land once set aside for the pond. You have
options.”
Rain is often fickle; some areas
get too much, others not enough. “People often forget this country has a water
crisis,” says Weinstein. “Stormwater is a valuable resource! It can be used for
so many things, and we haven’t yet been thinking about using it for potable
water. Watering restrictions pop up all over the nation during the summer;
people are willing to pay for water because they like lawns and gardens. We need
the freedom to use water wisely.”
Keeping more rain on each site and
out of municipal stormwater systems also has benefits. “This could lower
capacity, so we don’t have to build all this infrastructure,” says Weinstein.
“LID is not the answer to everything, but if there’s the option for everyone
taking responsibility for their own area, that’s a step in the right direction.”
Many technologies can help accomplish LID’s goals: “Who’d heard of a green roof
10 years ago? Now it’s cheaper to have one, and people will build what’s
cheaper, especially since many roofs are already structurally built for green
roofs.”
Unfortunately, money isn’t always
being put where the mouths are. “People are asking for instant answers, but the
nation’s not putting money into looking into these options,” adds Weinstein.
“People are fighting for research dollars everywhere. Who’s really putting
R&D [research and development] into retention cells? The only way something
like this gets done is if someone thinks it up in his basement.” However, ideas
can, and do, come from anywhere: “Engineers are designing rain gardens.
Landscapers suggest more useful plants or soil mix. We can recycle items one
would never think of using for stormwater. For example, the blasting sand left
over after cleaning railroad car wheels—it’s mainly iron oxides, which attract
pollutants. The trouble is, maybe some of these workable ideas don’t fit
standard BMP codes, and it can take years and money to change minds and
codes.”
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Photo: Chip Hatter Photographics
This beautiful expanse of lawn can also serve as a parking area. |
The Low Impact Development Center
positions itself as a clearinghouse for this type of information. “We’re a
nationwide group of seven people, and we have an office in California that will
grow,” says Weinstein. “Stormwater has to be looked at as an economic and
business model; the most effective type or design of permeable pavement in
Chicago may not be the right one for Oregon.”
Weinstein believes LID has
advantages. “It gives us the ability to look at things holistically, to save
infrastructure. Maybe it will help create green jobs. And, although it can be
implemented nationally, or state by state, it has benefits even at the local
level; each ‘little’ project helps. For example, some counties are subsidizing
homeowners for installing permeable driveways and rain gardens. If you explain
the concept to Joe and Jane Homeowner, they can ‘get’ it; if you tell them that
putting a rain garden in their yard will reduce their stormwater costs by, say,
$20 a month, they’ll start digging! Having neighborhoods dotted with rain
gardens is much cheaper than building new infrastructure.”
Natural State—Only “Natural”
Products?
Does nature always have the “best”
way of solving a problem—or, since people often caused the drainage problem, is
it our job to devise a solution? An increasing number of manufacturers in the
stormwater industry say “yes” to the latter: Manufactured products can do an
equal, or sometimes better, job than land-based systems. To promote this
message, the industry has created the Stormwater Equipment Manufacturers
Association (SWEMA). Formed in 2008, the groups members are producers of
stormwater devices—many of them competitors now working together to provide a
voice for the industry and to lobby for such things as standard testing
procedures and proper maintenance of stormwater BMPs.
“I’ve been trying to get SWEMA
going for five years, since someone at a StormCon conference said it was a good
idea,” says John Moll, CEO of Atlanta, GA’s CrystalStream Technologies. “I don’t
mind selling against others in my field; our products are different. But the
‘enemy’ was state codes. If an engineer brings in the specs for a certain
stormwater product, whether or not the item really works, it has to be put in.
Our point is that no one understands how natural items, such as ponds,
work—there are no maintenance records.”
Sometimes, manufactured products
“don’t get no respect.” “I was asked to talk to a meeting organized by EPA
Region 6,” recalls Moll. “The subject was ‘LID versus manufactured products.’ On
the panel, I sat near the LID speaker, which confounded the moderator. I
explained to him, ‘We are LID. How
can you get lower impact than a couple manhole covers on the ground and an
underground tank?’ The number one function manufactured items offer in LID
design is that we save footprint. The square footage saved can be left in its
natural state, such as woods.”
T.J. Mullen, president of Best
Management Products Inc., in Lyme, CT, agrees that SWEMA is an idea whose time
has come. “My company is a SWEMA member. We manufacture the Snout stormwater
quality system, which separates out pollutants—especially gross pollutants, such
as trash, floatables, and sediment—from stormwater runoff. This August, I’ll be
speaking at StormCon; I think people who’ll attend are pretty much aware that
structural devices are available for LID stormwater requirements. SWEMA promotes
the idea that manufactured devices should receive fair and equal treatment as a
method to improve the quality of stormwater runoff—just as a land-based or
public domain system. In fact, there are some things manufactured items do that
natural things can’t—such as skimming off trash and floatable debris, for
instance.”
 |
Photo: Filterra Bioretention Systems
The grating and the shrub are integral parts
of the Filterra stormwater system. |
SWEMA is actually the
reincarnation of a previous group, the Manufactured Water Quality Products
Association (MWQPA). “To prove some of our products, we went to famed Alden Labs
in Holden, MA, an independent testing lab,” says Moll. “Since we’d like to have
a stormwater fairness doctrine, if we’re going to vet manufactured products, we
want to make sure they meet best management practices.”
Testing, or the lack thereof, is
one of SWEMA’s main concerns. “We’ve learned a lot over the years of making our
products,” he adds. “We think regulators need to require testing of public
domain systems, too—does a pond work better than our products? My product is not
the best solution for every site; I know that—but a wet pond is not the best for
every Georgia site, either.”
SWEMA is also concerned with
maintenance. “When establishing the MWQPA, the first committee we organized was
‘maintenance,’” says Moll. “We sold maintenance from the first, because we
realized it was the key factor in having the systems do what we’d said they’d
do, and in securing customer satisfaction. One thing that always bothered us
about retention ponds is why do they end up as dumps? Evidently, no one thought
of maintenance, or didn’t want to pay for it. The fact that manufactured
products can be cleaned gives them an advantage over natural systems. We set up
our product out in the field; when it fills up, we service it and take all the
collected debris out of it. Some folks say, ‘Really? We never do that with
ponds.’ When I drive away after performing maintenance, the unit is like brand
new. Six months later I have to do it again, but the point is, that debris
didn’t get into the watershed. My CrystalStream system keeps trash and debris
dry so it doesn’t rot. In a pond the stuff will rot, which will flood the area
with nutrients, such as nitrogen and phosphorus. One of the most horrid things
that can get into stormwater—oil—can be caught and removed by manufactured
products. Ponds can’t do that.”
Moll points other potential
problems with retention ponds. “Some folks avoid open water at all costs because
it attracts rodents and nuisance birds, such as Canada geese, which can cause
disease problems. Gas stations know there will always be some sort of spill
sometime; cleaning my company’s unit is much faster and cheaper than cleaning
out a pond. There’s a huge benefit in manufactured products if you want to be
‘green.’”
Manufactured units can also save
water. “We’re working right now to put cisterns all over the southeastern US,”
says Moll. “We go to people who are landscape-conscious and tell them if they
have watering restrictions, they can save and use the roof runoff. No matter how
you develop a site, it will always have three times the runoff as it did when it
was just ‘nature’; if you can keep any water onsite, you catch the pollution,
and, eventually, the water you save will recharge the groundwater, which
supports streams in time of drought.”
Are testing protocols biased
against manufactured units, or inaccurate? “When cleaning my units, I’m finding
more pollutants than the regulators said would be collected, because they used
automated samplers and only test the first flush,” explains Moll. “Some of EPAs
protocols, such as TSS 160.2, don’t test effectively. The Federal Interagency
Sediment Project (FISP) has questions about EPA’s TSS testing process; we’ve
been sitting here with a bunch of assumptions on bad tests and data for so long,
yet others are afraid to move forward. Who’s going to inspect things, to make
sure they work?
 |
Photo: Filterra Bioretention Systems
An Inkberry shrub was planted in this unit. |
“I can think of only one example,”
he continues. “Montgomery County, MD, has monitored its maintenance costs for 15
years; otherwise, you can find very little information. The manufacturers of
stormwater products have more testing results and more influent/effluent
data.”
Moll hopes SWEMA’s member
companies can answer questions and offer solutions. “We can police ourselves
while we compete; we joined together to say ‘Ignorance is no excuse; it’s not us
or green, its us and green.’ Measure us by what pollutants our products have
caught, which we’ve carted off to landfills and kept out of lakes and
streams.”
Mullen of Best Management Products
emphasizes that SWEMA itself is not a testing organization. “We will be
advocates—a clearinghouse of information for manufactured systems. Our goal is
to offer performance data or results in a consistent and uniform manner, and ask
that performance on land-based systems be presented in the same way and be
subject to the same level of scrutiny as manufactured devices. What we’ve seen
in the past is that a stormwater pond is given tacit approval as a BMP, but the
data from a pond’s performance have not been given the same level of scrutiny as
that directed toward manufactured systems. Some regulatory agencies don’t put us
on equal footing as a stormwater pond; manufactured systems might be as good in
some situations, especially on a site where space is tight and a pond is not
feasible. We’re just trying to level the playing field through education and
good science.”
 |
Photo: Hanson Engineering Division of Dresdner Robin
Burying a StormTrap system, instead of digging a retention pond, saved valuable lot space. |
In many jurisdictions, Mullen
explains, post-development runoff must exceed the predevelopment runoff rate.
“Of course, other stipulations may apply regarding the quality of the runoff,
and this is where manufactured systems can play such an important role in
safeguarding the environment.”
He notes that sometimes
manufactured detention systems are used on a site. “There must be some reason
why the developer decided on collecting the runoff, storing it, and letting it
go at a controlled rate, instead of collecting it and letting the runoff perk or
infiltrate back into the soils onsite. Maybe you’re in an area where the water
table is too high, and retention or infiltration may not be a viable option.
“You might store some of this
stormwater in chambers or pipes to detain the water—under a parking lot, for
example. Or, you could send it 100 yards or a half-mile away, where it can
percolate into the soil. You have to pick and choose your methods, which are
determined by the site. Sites have varying hydrology. Let’s say we know that the
preconstruction discharge rate is
0.5 cubic feet per second. Based on site hydrology, the design engineer
will create a stormwater detention or retention facility—either manufactured,
land-based, or a combination of both—that will control the runoff, clean it up,
and discharge it at the rate allowed by the jurisdiction, or have it percolate
back into the soil. In any case, it’s a fairly straightforward design process,
and having manufactured systems as an allowable option drastically increases the
variety of ways stormwater runoff can be managed, while its quality is
improved,” concludes Mullen.
Permeable Products
Asphalt or turf? For LID, the
question’s a no-brainer; installing a permeable surface when one can is usually
a good idea. When the area’s Mount Sinai Hospital needed a fire lane—but not
more concrete—Rosenberg Gardner Landscape Architecture of Miami, FL, installed
Invisible Structures’ Grasspave2. The porous paving surface allows parking,
driving, and walking on a beautiful grass surface. Performing the functions of
asphalt or concrete pavement, Grasspave2 does the job while providing the
appearance of a lawn.
Enhancing the environment was the
main objective when Kevin Neal, ASLA, project manager at Jeffrey Carbo Landscape
Architects in Alexandria, LA, installed Grasspave2 at a residential estate. “A
new 23,000-square-foot home was being built in DeRidder, LA. The former house
had burned, and the owners knew what changes they wanted to make. They wanted to
push the drive away from the house so visitors would get a nice view, whether
they were coming to the house or looking out toward the grounds from inside the
home. The owners didn’t want to see paving in front of the house; they chose
Grasspave2 for aesthetic reasons, rather than for stormwater management. The
grassy drive, which takes guests past a decorative pond and fountain, leads to
the home’s front door and a grass auto court; however, for everyday traffic, the
homeowners utilize a somewhat-hidden paved drive that leads to their
garage.”
Invisible Structures also
manufactures the Rainstore3, a plastic structure used to store stormwater
underground. Made from injection-molded plastic, a single panel contains 36
vertical columns and exceeds H-20 loading (a maximum front-axle load of 8,000
pounds), allowing the construction of driving areas, parking lots, or other
small structures above the system. Built-in compression fittings allow units to
be easily stacked to a variety of depths up to 8 feet, 4 inches.
 |
Photo: Hanson Engineering Division of Dresdner Robin
The underground system extends from the manhole cover, in the center of the photo, to
approximately the point from which the photo was taken. |
When the Harvard Westlake Middle
School in Beverly Hills, CA underwent a substantial upgrade, its increased
footprint not only caused more runoff, but also less places to contain it.
Psomas of Santa Clarita, CA, used Rainstore3 to solve the problem. “We put in
under the mall area, between two buildings, where school children gather,” says
senior project manager Dave Martin. “We really needed to save land, as the
school is located on a hillside, and there was not much area in which to install
conventional drainage storage.”
Let Trees Do Some of the
Work
Because LID is designed to leave a
site functioning much as it did its natural state, perhaps “nature” should be
incorporated into the solution. In addition to grassy swales and the like, some
manufactured devices also incorporate natural elements. When in the spring of
2007, Quincy, MA’s Kimley-Horn & Associates were called in on a project,
they kept that option in mind.
 |
Photo: Hanson Engineering Division of Dresdner Robin
Site prepared for placement of StormTrap units |
 |
Photo: Hanson Engineering Division of Dresdner Robin
The open bottom allows water to infiltrate. |
“We were working on the
redevelopment of a former naval air station that had been built in the 1940s,”
says Kimley-Horn associate Brian Brewer. “The master redeveloper, LNR Property
Corp., turned the 1,400-acre site into a mixed-use project, which included more
than 2,800 residential units and 2 million square feet of retail and commercial
space. Our first step was to spruce up the main entrance, which included
widening of the road, as well as increased landscaping. We incorporated
stormwater treatment features that were not there before, such as bioswales and
Filterra units.”
Filterra Bioretention Systems of
Ashland, VA, sells treatment systems that involve placing engineered soils in a
precast concrete vault, which is installed underground. Trees or shrubs are then
planted in that soil. The unit treats runoff and allows it to infiltrate, and it
provides landscaping at the same time. The combination of landscape vegetation
and a specially designed filter media allows bacteria, metals, nutrients, and
TSS to be removed naturally. With a small footprint and a high removal
efficiency for many stormwater pollutants, Filterra units can be used in highly
developed sites such as landscaped areas, green space, parking lots, and
streetscapes.
“Using Filterra units made sense,”
says Brewer. “The site already had a curbed roadway; we didn’t want to break up
curbs and put in bioswales. We installed six along the entrance section of the
roadway and another six during the next phase of work. The units we installed
contained Inkberry shrubs; Filterra provides plant recommendations, based upon
your site and climate. Filterra also has a sizing chart, noting how much runoff
each unit can take, and you can install overflow structures on either side in
case you have a really large storm event.”
Brewer says the purpose of this
retrofit project was mainly to improve stormwater quality. “It’s wasn’t really
to achieve LID, as the stormwater eventually does reach the city’s stormwater
system. But, with this entry road into the former base, we created some pleasing
open space. The right thing to do was try to treat stormwater, even if it hadn’t
been treated before, especially as this site is located next to wetlands—and we
needed to do so in a small footprint.”
Don’t Let the Stormwater Escape—Use
It!
Some LID devices offer the
advantage of stockpiling rainwater, a boon for landscapes in water-rationing
areas. When the Orland Park, IL police station was rebuilt in 2007, plenty of
green space was included in the plans; canny designers found a way to contain
runoff while also conserving rainwater for irrigation.
“The main idea was water reuse,”
says Frank Childers, president of G&C Consulting Engineers in Des Plaines,
IL. “We were working with SRBL Architects, which had specified lots of green
space and landscaping around the station, which was a reconstruction of an old
carpet warehouse. The landscape architect determined that 7,500 gallons of water
would be needed yearly for irrigation on the 10-acre site. Also, Orland Park
wanted the site to be LEED [Leadership in Energy and Environmental Design]
certified, and it did earn a LEED Gold rating.”
The LEED Green Building Rating
System, devised by the US Green Building Council, encourages sustainable
building and development practices. Newly constructed or redeveloped buildings
can earn points in several areas, including energy performance, materials used,
and water efficiency. Depending on the number of points achieved, a building can
achieve a LEED Platinum, Gold, or Silver rating.
 |
Photo: Hanson Engineering Division of Dresdner Robin
Installation of the units on a two-acre industrial site |
Childers’ solution was to install
a modular, precast StormTrap system beneath a landscaped area to collect runoff.
“To make sure the water collected is clear of debris, StormTrap is fed only by
the building’s roof drain,” he notes. “Because we’re taking only rainwater and
snowmelt from the roof, the water doesn’t contain oils or salt, as opposed to
runoff you’d collect from parking lots. The flat roof feeds interior downspouts,
which converge into a single storm sewer, which we intercepted and diverted to
the StormTrap. If the StormTrap gets filled, water then discharges into a
detention pond.”
During summer dry spells, the
stored water keeps the police station’s landscape green and healthy. “We
installed a pressurized system connected to the StormTrap,” explains Childers.
“There’s a suction pump outside on the ground so the yard workers can take the
water out. The StormTrap was put in during a dry spell, and 2008 was a pretty
wet year here, so, thus far, this system has taken care of all the landscape
water needs.”
StormTrap, based in Morris, IL,
offers the SingleTrap, fashioned from reinforced, high-strength concrete, in
customized sizes ranging from 1 foot, 2 inches to 5 feet. This configuration
provides a large infiltrative surface area, which allows water to filter into
the soil. The DoubleTrap ranges in size from 2 feet, 4 inches to 10 feet; it can
be designed to allow infiltration or can be configured as a completely contained
system.
“The whole system was installed in
a couple days,” recalls Childers. “In this unique application, we created a
cistern for that water in an environmentally friendly way. However, this system
may not be unique for long; the whole six-county area around Chicago is changing
building codes and developing more cistern facilities, requiring stormwater
detention.”
G&C Consulting Engineers has
used StormTrap before, mostly in new facilities. “We use it where the site owner
can afford it for detention. As land becomes more and more valuable, a StormTrap
versus a retention pond becomes more appealing. Instead of setting aside land
for a pond, they can bury the StormTrap and put a parking lot over it.”
Manufactured Items Can Leave More
Natural Areas
Matt Hainzl, senior engineer with
the Hanson Engineering Division of Dresdner Robin in Wayne, NJ, uses StormTrap
to retain valuable square footage as well as to reduce runoff. “In spring 2008,
we refurbished a rundown, two-acre industrial site for Donnelly Industries, a
total rehab and building expansion,” he says. “We used StormTrap to expand the
amount of useful area for stormwater management. The site also has a
grass-bottomed retention basin on the property. Putting in a StormTrap
accomplished the client’s goals, as there wasn’t enough usable space on the
surface. Of course, as this was an old site, before we did the redevelopment
there was nothing channeling stormwater. Everything used to flow offsite with no
treatment at all; however, we were required to bring the site up to current
standards, which had been revised
in 2004.”
The StormTrap catches only roof
runoff. “The StormTrap, which has 4,500 cubic feet of storage, has an open
bottom; water infiltrates into the sandy-loamy soil. The unit should be able to
handle all roof runoff, unless there’s a 100-year storm,” says Hainzl. “Of
course, the water can run off to the retention basin, if needed. But whereas the
basin doesn’t do anything with sediment, the StormTrap settles out anything that
might get in the water.”
Hainzl’s firm uses StormTrap in
many area projects. “It was our first choice for this project; it’s easy to
install, and we always get great support from StormTrap’s staff. Plus, because
the various pieces are individually sized, you can make a smaller unit. We used
18 precast sections and shaped them to fit the site.”
Does Hainzl envision more
LID-friendly projects in the future? “Yes—municipalities are all for it, and
developers want to get everything they can on their sites. A unit such as
StormTrap accomplishes both tasks.”
Prevent Roof Runoff Before It
Starts
Roofs are a major source of
runoff. What if a roof could be created that actually absorbed runoff? Green
roofs do just that. Grand Valley State University (GVSU) in Allendale, MI, chose
that option on a recent building addition.
“As an institution of higher
learning and leadership, as well as a public university supported by tax
dollars, Grand Valley State University believes it has a responsibility to
practice sustainable development,” says Brad Newman, GVSU’s project manager for
facilities planning. “One way we accomplish this is by building for LEED
certification when undertaking new construction or major renovation projects. By
doing so, we help ensure the balance of the ‘triple bottom line’ factors—people,
places, and prosperity—that characterize sustainable development, while modeling
behavior needed from all businesses, institutions, and individuals.
“Sustainability is also an
important part of Grand Valley’s curriculum and campus culture,” he continues.
“Because we believe they contribute to the practice of achieving sustainability,
we’re very interested in green roofs at GVSU for several reasons: they’re an aid
to stormwater management; they provide a pleasing aesthetic solution to the
viewer, as opposed to a white roof that will soon discolor; and, to some degree,
their added materials help improve energy performance.”
During the summer of 2008, GVSU
installed modular green roof systems from LiveRoof of Spring Lake, MI, on its
new MAK Unit B addition, which totals 6,600 square feet at two locations. “We
selected the LiveRoof to install a green roof that was already green, as opposed
to waiting for other green roof products to take time to develop green
growth.”
Each LiveRoof module contains
full-grown plants when it arrives at the job site. The prevegetated modules
discourage weeds; other systems may require three or more years of intensive
care for plants to become established. Well-established LiveRoof plants and
roots create an instantly functional green roof, which can be maintained for as
little as $0.15 to $0.30 per square foot. GVSU’s LiveRoof modules contain sedum
plants, which flower in various colors, so the roof changes color with the
seasons.
Plants,
soil, and the water they absorb are weighty; any problems? “Installation went
very smooth and on time,” reports Newman. “The weight of the modules was
calculated by our structural engineers during design development so that the
right steel was ordered for the project. Some structural analysis was performed
to look at various additional locations for additional installs. For the most
part, the roof modules have indicated they will be somewhat maintenance free.
The fast install was a great plus during project-completion crunch time. For
maintenance, we’re performing various inspections, soil testing, and irrigating
when hot, dry weather persists, and mowing is recommended in the
fall.”