The ongoing battle between
stormwater professionals and stormwater runoff has spurred the creation of a
wide range of structural best management practices (BMPs). From HDPE pipe to
sophisticated filter systems, there’s a product for virtually every situation.
Many projects combine one BMP to
treat the runoff and another to allow it to infiltrate. The following five
projects highlight some of the best of the available methods and
technologies.
Legacy Parkway and Nature
Preserve
Buried along a new 14-mile highway
between Salt Lake City and Farmington, both in Utah, HDPE pipe is protecting
valuable wetlands.
The Legacy Parkway, an alternate
road between the two cities, opened in September 2008. It runs along the newly
created 2,200-acre Legacy Nature Preserve on the southeastern shore of the Great
Salt Lake. The preserve is part of the Pacific Flyway for migratory birds.
The preserve, established to help
mitigate the impacts of the parkway on the wetlands and its wildlife, includes
more than 700 acres of wetlands. It provides habitat for more than 100 bird
species, including bald eagles, owls, peregrine falcons, shorebirds, and ducks.
“It’s nestled between a mountain
range on the east and Great Salt Lake on the west,” says Rick Campagna, a
project manager for the Utah Department of Transportation (UDOT) Legacy Project.
“The parkway is in such close proximity to the lake, we were concerned about the
wetlands. We wanted to design the project so it didn’t create a dam.”
UDOT used more than 65,000 feet of
Advanced Drainage Systems (ADS) HDPE pipe and 400 feet of Hancor HDPE pipe, for
more than 10 miles of pipe altogether.
“We were very meticulous about our
approach,” says Campagna. “We delineated the wetlands within the project in an
effort to save as much as we could. In the end, we managed to impact only about
80 acres.”
Although the parkway was very
controversial among environmentalists and others, it ensured that the wetlands
would survive. “The parkway drew a line in the sand, separating land that can be
developed in the future, on the east side of the road, and land that has been
set aside as the nature preserve, which will never be developed, on the west
side,” he says.
And in some ways, the Legacy
Project improved the wetlands. For example, one of the features UDOT took into
account was the oxbows that had formed over the years in the Jordan River, which
flows through the preserve and empties into the Great Salt Lake. Before the area
began to be developed, floodwater from the river would fill the oxbows. But with
development, the flow of the river was controlled and the oxbows dried out. The
project has put water back into the oxbows again.
Drainage has been crucial in this
project. Multiple culverts run under the parkway, allowing runoff from the
mountains to the east and the lake to the west to drain under the road.
UDOT used multiple piping systems
to handle the runoff from the mountains and the lake and multiple sizes of pipe
to handle the different flows. Some of the natural channels in the preserve have
fairly high flows and require pipes as large as 60 inches in diameter, Campagna
says. Other areas, such as roadway drainage, have lower flows and require pipes
as small as 18 inches.
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Photo: Utah DOT
Laying pipe in the trenches |
Most of the pipe came from ADS,
the world’s largest producer of HDPE corrugated plastic pipe, and was
manufactured at a nearby plant. The 400 feet of 54-inch-diameter pipe is made by
Hancor, which was founded in Findlay, OH. It is owned by ADS and operates
manufacturing facilities and service centers across the country. Both ADS and
Hancor pipes have an integral bell and spigot system, and Hancor pipes have a
polymer composite fused to the outside of the bell with a factory-installed
gasket.
UDOT chose these pipes, which have
a corrugated exterior and a smooth interior, for a number of reasons. “From a
long-term perspective, you don’t see the same kind of deterioration with HDPE as
you do with corrugated metal piping,” says Campagna. “The soil tends to be
corrosive because the lake floods in the spring. When it dries, it leaves a salt
deposit.”
The pipes are watertight,
lightweight, and cost-competitive. They can be handled with minimal equipment by
a one- or two-person crew, even in 20-foot lengths. This length reduces the
number of joints, saving labor and installation time.
“The pipes fit perfectly into our
stormwater strategy,” he says. “It’s something we looked at very carefully.
They’re improving the quality of the wetlands.”
Evanston Township High
School
When Evanston Township High School
in Evanston, IL, wanted to redo its athletic facilities and a city ordinance
required it to install stormwater detention, the school took the idea and ran
with it. The school selected a system that not only would detain most of the
stormwater runoff from the site, but also would use the runoff to irrigate the
school grounds.
“Any time we can intercept
stormwater and recycle it through irrigation, it’s a plus,” says Kevin Camino,
P.E., principal and a senior project manager at Eriksson Engineering Associates
Ltd. in Grayslake, IL, which designed the project. “Sometimes the initial cost
[of a reuse system] is more, but it will save on irrigation costs in the long
run.”
Evanston, which is north of
Chicago and along Lake Michigan, faces flooding during even moderate rainfall.
Storm runoff, which discharges into a regional deep tunnel, can exceed the
capacity of the sewer system, and water levels can rise enough to cause basement
and street flooding. The city requires that the runoff rate after development
not exceed the predevelopment rate, which is no more than 0.15 cubic feet per
second (cfs) per acre.
An underground detention system,
StormTrap, was installed at the high school in 2008. The concrete modular
stormwater detention system, built by precasters throughout the country, was
chosen because of its expected longevity and the determination that ultimately
it was the most economically viable system available.
“Underground detention is
typically more costly than aboveground detention, but it allows the land to be
utilized more efficiently,” says Camino.
A city street divides the campus
into the north side, which now has synthetic turf in the new soccer and football
stadium, and the south side, which has natural turf in the new baseball, soccer,
and softball fields. StormTrap was installed in both locations.
The project used the DoubleTrap
system, which is watertight, to maximize the total water stored while minimizing
the footprint of the system. The StormTrap system can also be configured to
allow water to infiltrate into the soil and can include treatment options such
as sand filters and sediment basins. The rectangular units that make up the
system range in height from 2 feet 4 inches to 10 feet, allowing them to be
configured to virtually any site.
Because the units used in this
project are 10 feet high, crews excavated about 12 feet deep and placed
aggregate bedding in the hole to create the StormTrap foundations. On the north
side, they discovered soft clay subsoil.
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Photo: Utah DOT
The project used more than 65,000 feet of pipe from 18 inches to 60 inches in diameter. |
“In general, the football stadium
had really bad soils,” says Camino, “and synthetic turf requires a very firm
base. We used lime stabilization to stabilize the clay before we installed the
stone drainage layer.”
In the soccer and football
stadium, the lime stabilization increased the impermeability and load-bearing
capacity of the clay to form a “bridge” between the clay and the stone
aggregate.
On the north side, crews installed
18 StormTrap units, which can handle 11,273 cubic feet of runoff. On the south
side, 71 units can handle 55,075 cubic feet.
“The system collects the majority
of the water that hits the school district’s fields,” says Camino. Runoff from
both the north and south sides flows into catch basins, where it is routed
through underdrains to the StormTrap units.
The runoff doesn’t have to be
treated, he says. “Synthetic turf is cleaner than a parking lot, and with grass
areas, you’re just talking about fertilizer.”
The stored water is pumped through
a new, fully automated irrigation system to irrigate the grounds. The system is
connected to the city’s water supply as well, so it can draw water for
irrigation from the city when necessary. The school’s system provides 80 to 90%
of its irrigation water, depending on the amount of rainfall.
Maintenance is minimal. StormTrap
should be inspected once a year for sediment.
“It was a terrific project,” says
Camino. “A lot of municipalities haven’t updated their ordinances to provide
credit for stormwater detention or water-quality systems like these, so there’s
little incentive to install them.” The city of Evanston has provided credit for
both.
Woodcrest Project
When developers Miller & Smith
built Woodcrest, a community of 81 housing units on 47 acres in Clarksburg, MD,
they faced strict water-quality regulations.
“The site is on a special
protection area; it’s very sensitive,” says Glenn Fritz, president of Deneau
Construction in Gaithersburg, MD, which installed the development’s water
treatment and infiltration system in 2008.
The community is in densely
populated Montgomery County, MD, which requires post-development stormwater
runoff from new development to equal predevelopment stormwater runoff
conditions. The county also requires advanced filtration and groundwater
recharge. In addition, Woodcrest is located next to the 3,700-acre Little
Bennett Regional Park. Runoff drains into the Little Bennett and Seneca Creeks,
and from there, into the environmentally sensitive Chesapeake Bay.
Brian Lewandowski of Gutschick,
Little and Weber designed the system. Because the site had no room for typical
recharge ponds, the treated runoff had to be stored underground. He used
StormChambers from HydroLogic Solutions to control stormwater runoff and remove
sediment and nutrients, as well as Contech Stormwater Solutions’ StormFilter,
which removes oil and grease, dissolved heavy metals, herbicides, and
pesticides.
StormChambers are made of HDPE and
have an open bottom to allow water to recharge into the ground. When three
models of the chambers—start, middle, and end—are placed in interconnecting
rows, they capture stormwater, hold the solids, treat the water, and allow it to
seep into the ground, recharging the groundwater and maintaining base flow to
streams and wetlands.
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Photo: Eriksson Engineering
Installing the bottom units of the DoubleTrap system |
“They’re basically the same thing
as a septic system,” says Lewandowski. A biomat of microorganisms forms on the
soil and stone under the chambers, metabolizing and converting pollutants and
nutrients to noncontaminating byproducts.
StormChamber units also can be
used instead of pipe to convey stormwater by placing the middle chambers end to
end. “This is the first time we’ve put in StormChamber units,” says Fritz. “They
were light and easy to install, and they didn’t require large equipment.”
Crews dug trenches, some of them
up to 14 feet deep, and then lined the bottoms with aggregate topped with a
geotextile netting. The netting allows water to infiltrate while preventing it
from eroding the underlying stone and soil.
The crews then installed the
start, middle, and end chambers as well as StormChamber SedimenTraps, units that
catch sediment that runs into the chambers. The trenches were backfilled with
more stone to 6 inches above the chambers, topped with nonwoven filter fabric,
and backfilled with soil. Sediment that accumulates within the SedimenTraps is
removed with a vacuum truck through a 10-inch riser pipe centered above the
SedimenTrap.
About 75 units are installed in
roughly 11 different locations at Woodcrest, Fritz says, all of them under green
areas. Each unit is 34.04 inches high, 5 feet wide, and either 7.6 or 8.1 feet
long, depending on the model, and can handle 10 cubic feet of water per linear
foot. Each has a side portal that can accept up to a 12-inch inflow pipe and a
top portal for clean out.
“Some StormChamber units catch
runoff from roof drains and others from the streets after the water is treated,”
says Fritz. Water from roof downspouts is sent directly to a StormChamber
system. Water from the streets, which contains oil and heavy metals from cars,
flows into storm drains to a StormFilter, which provides direct filtration. From
there it goes to a StormChamber system.
Once inside a StormChamber system,
water fills the interconnected chambers and the stone backfill. It slowly
infiltrates through the open bottom of the chambers into stormwater trenches
and, from there, down to the creeks.
Maintenance is simple. Crews
usually just check once or twice a year to make sure the chambers aren’t holding
water or sediments.
“We’ve put in similar products
that have failed,” says Fritz. “We were very happy with these. They are huge
water-quality retention systems, and residents don’t even know they’re
there.”
Westside Water Quality Improvement
Project
Runoff from two of the country’s
best-known cities pollutes some of its best-known beaches. It flows through
approximately 2,500 densely urban acres of Santa Monica and West Los Angeles,
both in southern California, during droughts as well as rainstorms. It converges
at the Sawtelle Flood Control Channel, flows into the Ballona Creek, and empties
into Santa Monica Bay on the Pacific Ocean.
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Photo: Eriksson Engineering
Installing the top unit of the DoubleTrap system |
Both the creek and the bay have
total maximum daily loads (TMDLs), according to Neal Shapiro, urban runoff
management coordinator for the City of Santa Monica and supervisor for the
city’s Watershed Management Section of the Office of Sustainability and the
Environment. Removing pollutants before they reach the bay is crucial to the
health of Santa Monica and other Los Angeles beaches, the bay, and the waters
beyond.
In 2006, Santa Monica, with the
support of the county and the city of Los Angeles, completed the Westside Water
Quality Improvement Project, which won the California Stormwater Quality
Association’s (CASQA’s) 2007 Outstanding Stormwater BMP Implementation Project
Award in the Treatment Control/Structural BMP Category.
“The issue addressed by this
project is dry- and wet-weather runoff entering the Ballona Creek,” explains
Shapiro.
He was in charge of recommending,
organizing, documenting, and reporting the project, as well as getting it
funded. The city hired an engineering consultant, Black & Veatch, to select
the products that would best meet the city’s objectives for treatment, cost, and
long-term performance. The company came up with Bio Clean Environmental
Services’ Nutrient Separating Baffle Box and Contech Stormwater Solutions’
StormFilter.
To meet TMDL requirements for both
the bay and the creek, the project diverts dry-weather and some wet-weather
runoff from the Sawtelle Channel and treats it at Mar Vista Park, in the City of
Los Angeles, before the runoff reaches the Ballona Creek. The goal is to treat
all dry-weather flow up to 2 cfs, and in wet weather to remove up to 80% of
suspended sediments and floatable trash larger than 1/8 inch in diameter—as well
as other soluble pollutants such as heavy metals associated with sediment and
trash—up to 33 cfs. Flows exceeding 33 cfs are not diverted. All treated water
is returned to the Sawtelle Channel.
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Photo: Eriksson Engineering
Installing DoubleTrap, the modular water detention system at Evanston Township High School,
Evanston, IL |
Mar Vista Park wasn’t Santa
Monica’s first choice. A number of locations in Santa Monica didn’t pan out for
various reasons, but in many ways the park was perfect. The channel runs under
the soccer field, and the park has adequate open space and no utility or traffic
issues. However, a project to redo the soccer field was already planned.
“Once the soccer field was in,
Santa Monica could not come back and put in the pipeline,” says Shapiro. “It had
to go in with the LA project.”
The solution, which required
negotiation and cooperation between the two cities, was to divide the project
into two phases: phase 1, the installation of the diversion pipeline during the
soccer field project, and phase 2, the installation of the treatment system
after the soccer field project was completed.
Now that the project is completed,
a 36-inch pipe diverts water from the channel to an adjustable weir, which is
screened to remove trash and floatables, and a splitter box, which sends wet
weather flow to the Baffle Box and dry weather flow to the StormFilter unit.
The Baffle Box can treat all of
the wet-weather flow. It can capture and store thousands of pounds of trash,
debris, and sediments, including hydrocarbons, nutrients, metals, and organic
compounds attached to the former gross pollutants, according to Janet Kent, vice
president of Bio Clean Environmental Services Inc.
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Photo: City of Santa Monica
Laying the diversion pipeline, which runs from the Sawtelle Channel to a treatment facility at Mar
Vista Park |
Sediment and water sink to the
bottom of the box. The top is screened to capture trash and debris, which allows
them to dry out between rain events and keeps the water from degrading further
during storage, preventing nutrient leaching, bacterial growth, septic
conditions, and bad odors. The screen also reduces maintenance costs, Kent says,
because the material captured on the screen can be removed dry.
The StormFilter unit is screened
and removes suspended particulates by sedimentation as well. It also provides
direct filtration, removing oil and grease, dissolved heavy metals, herbicides,
and pesticides.
According to Shapiro, “There is a
minor issue in that often more dry-weather water is flowing into the splitter
box, and the weir has to be raised slightly to retain all the dry-weather flow.”
If the weir isn’t raised, some dry-weather flow can spill over and flow to the
Baffle Box. While the Baffle Box provides screening and sedimentation, it
doesn’t filter runoff for soluble pollutants.
Maintenance could have been a
problem because the facilities belong to Santa Monica but are in Los Angeles.
Fortunately, because of the cooperative relationship they established during the
planning stages, the two cities have agreed that Santa Monica will maintain the
facilities after providing Los Angeles with proper notification.
In 2007, the project reached its
goal, according to Shapiro: “The Baffle Box had its first cleaning on November
15, 2007, in which 1,660 pounds of plastic take-out containers, aluminum cans,
plastic bottles, plant material, and sediment were removed.” Although much less
trash was found during the second cleaning, in February 2008, he speculates that
there was less trash in the channel to begin with. Most of the rain events
occurred before the first cleaning, which flushed out the built-up trash in the
upstream pipes and channels from the previous summer and fall.
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Photo: City of Olympia
Excavation before the installation of the geogrid, two layers of aggregate, perforated pipe, and StormFilter |
He says he is pleased with the way
the Baffle Box is working. “It effectively removes trash, debris, and
sediment.”
Decatur Street LID Roadway
Project
Since the summer of 2008, two
blocks of a suburban street in Olympia, WA, have been the site of a low-impact
development (LID) demonstration project comparing different methods of cleaning
and infiltrating stormwater.
“We were looking for ways to
manage stormwater in the right of way,” says Craig Tosomeen, P.E., water
resources engineer for the city’s department of Public Works. Tosomeen took the
project from conception through construction and now does the monitoring.
The area is the headwater for
Schneider Creek, which flows into Puget Sound, home to species of endangered
salmon. The roadway was originally developed with no stormwater treatment and
experienced minor flooding during rain events. Runoff from much of the
neighborhood flows into the stormwater conveyance, which then flows into the
creek.
Because no undeveloped land is
available for aboveground detention and treatment, all three methods in the
Decatur Street LID Roadway Project use under-the-road infiltration. They begin
with Tensar Biaxial Geogrids within the drainage layers. One 200-foot section
uses porous asphalt. Another uses traditional asphalt with rain gardens. The
third uses traditional asphalt and
Contech’s StormFilters.
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Photo: City of Olympia
The finished project |
Other StormFilter systems in the
city have performed very well, Tosomeen says. They target total suspended solids
(TSS), soluble heavy metals, oil and grease, and total nutrients. The geogrids,
made of HDPE, stabilize the rock in the aggregate base and distribute the weight
from the road surface, allowing the native subsoil to be disturbed as little as
possible.
The water-quality goal of the
three methods is to treat at least 91% of the stormwater that falls on these
sections of road, according to Tosomeen. Each of the StormFilter units in this
project is designed to accommodate 7.5 gallons per minute. The flow control goal
of the project is to infiltrate all the stormwater that falls on the road
sections. The design infiltration rate of the native soils is 0.15 inch per
hour. This low infiltration rate is typical of Olympia’s fine-grained native
soils.
The StormFilter system was very
easy to install, says Rolland Ireland, engineering project inspector for
Olympia’s department of Public Works. Crews excavated, then lay perforated pipe
and 12 inches of aggregate over the subsoil. They covered the aggregate with the
geogrid, an aggregate base course, and asphalt.
The biggest challenge was figuring
out how to avoid disturbing the fiber-optic system that was already buried
there, he says. “We went to design depth on the edge of the system, and came up
and over.”
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Photo: City of Olympia
Top layer of aggregate |
During a rain event, the road
surface directs runoff into one of the StormFilters. Runoff flows through a
filter cartridge and up the center tube into the collector manifold. When the
filtered water reaches the top, it flows out of the system and into the
perforated pipe. It trickles through the holes in the pipe into the aggregate
and down into the subsoil.
StormFilter has a self-cleaning
function that helps minimize maintenance. After a storm, the water level in the
StormFilter drops, air rushes in, and sediment in the filter cartridge falls to
the floor of the system, helping restore the filter’s permeability.
“We expect to change the filters
yearly,” says Tosomeen.
In the fall of 2008, the city
began a two-and-a-half year study to monitor TSS and dissolved metals and
nutrients, as well as to look at infiltration. It’s too soon to have definite
results for either type of pollutants, he says, but the StormFilter seems to be
working well.
The area has had some very large
storm events, and although the system didn’t infiltrate all the runoff, he isn’t
worried. Success would be to replicate the hydrology of the native forest, he
says, and there would have been some runoff in that predevelopment condition
with that amount of rain.
As
far as filtration, Tosomeen says, “The jury is still out, but anecdotally the
filter seems to be the best way of cleaning the water. Visually, the clarity is
very good.”