On
the western edge of Los Angeles, CA, roughly halfway between Santa Monica and
the Los Angeles International Airport, Marina del Rey is an increasingly popular
Southern California entertainment destination. Built around the West Coast’s
largest small-boat harbor, it draws tourists who come to boat, hike on the
myriad of recreational paths, shop, and eat at California-cool restaurants. One
thing marring visitors’ enjoyment is the increased bacteria levels from urban
runoff during the area’s May to October dry season.
Urban
Density Means High Pollutant Discharge
Densely
populated, Marina del Rey suffers from high levels of various pollutant
discharges originating from the area’s residential, commercial, and retail
activities. Bacteria and other pathogenic discharges in stormwater and
dry-weather runoff can significantly harm the health of the harbor and
potentially hurt the local economy.
To
control bacteria, pathogens, and other pollutants, and to meet federal and local
regulations, the Watershed Management Division of the County of Los Angeles
Department of Public Works is working on several best management practices
(BMPs) to attack the problem.
We manage the watershed holistically using a
systems-based approach,” says Angela George, a senior civil engineer and Santa
Monica Bay watershed manager for the LA Department of Public
Works.
Holistic
Watershed Management
According
to George, the Watershed Management Division is responsible for a number of
flood-protection projects within the watershed, including elements of water
quality, habitat restoration, aesthetic improvements, and recreational benefits.
Her division engaged the Department of Public Works’ Design Division to develop
a retrofit stormwater solution for the Marina del Rey
watershed.
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A Mountain Flax plant installed over a bioretention system |
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Installation of a Yedda Hawthorn |
In
June 2005, a team led by Zahid Atashzay, a senior civil engineer in the Design
Division, developed a project concept for retrofitting part of Abbot Kinney
Boulevard near Marina del Rey’s harbor to handle dry-season runoff. The team
designed the project to address total maximum daily load (TMDL) requirements
established by the federal government and enforced by the Los Angles Regional
Water Quality Control Board.
Managing
Dry-Season Runoff
Throughout
the dry-weather months, pollutants that collect on the streets of cities and
unincorporated areas within the Marina del Rey watershed are carried by runoff
through the flood-control system’s network of storm drains and into the harbor.
Due to high levels of E.
coli,
fecal coliform, enterococcus bacteria, and other pollutants found in several
basins within the harbor, communities within the watershed must minimize their
contaminated runoff in the dry season.
During
dry weather, most of the communities’ storm drain outlets use low-flow
diversions to route urban runoff into sanitary sewers for treatment. Ideally,
this reduces polluted dry-weather runoff entering the Santa Monica Bay harbor.
“As one alternative, we proposed a low-flow diversion to direct flows from the
pipeline to the sanitary sewers for treatment,” George says. “However, during
design, we found that we could not address all the flows carried through the
system to the harbor because of seawater intrusion and a high groundwater level.
So we had to come up with another plan.”
“The
existing local storm drain system is submerged and subject to tidal influence
all year,” explains Atashzay. “So it was not feasible to divert the low-flow
runoff effectively from the drain system to the sanitary sewers for treatment.
Our new plan was to capture and treat the surface low-flow runoff before it
entered the drain system.”
Using
Several BMPs
To
decrease both bacteria and pollutants within the communities’ watershed, LA
County uses a suite of social marketing and structural BMPs to improve water
quality in the harbor incrementally. Designed to change public behavior, its
social BMPs have resulted in dog owners picking up their pets’ feces and
restaurant owners handling trash and food waste in ways that reduce bacteria
contamination in the harbor.
One
of the structural BMPs addressing the county’s bacteria problem is the Filterra
Bioretention System. Because this was a retrofit project using existing catch
basins, the county needed a small-footprint solution. It also preferred natural
or bioretention processes to filter dry-weather runoff. A natural approach also
complemented other BMPs used to address high levels of fecal coliform and
enterococcus bacteria, as well as other pollutants found in several basins
within the Marina del Rey watershed.
Favoring
Natural Processes
“The
county prefers using a natural process whenever possible, because it adds
intrinsic aesthetic values to the community,” says George. “The Filterra data
showed that its units had the capacity to treat the pollutants we wanted to
target, like bacteria and heavy metals. So it appeared to be a good
fit.”
For
the retrofit, the county selected Clarke Contracting, which installed the
Filterra systems. “The urban density of Marina del Rey offers limited space for
controlling urban runoff and reducing TMDL loads for collection and treatment,
making a biologic process very attractive,” notes Bob Clarke of Clarke
Contracting. “The Filterra units we installed are also easy to maintain and
clean out. They’ve only had to be maintained once since they were
installed.”
The
county had the contractor install and blend the urban-runoff retrofit units in
at the edge of sidewalks along the roadway. By design, the retrofit needed to
preserve and connect to existing, shallow catch basins.
Clarke
Contracting installed five bioretention systems along several roadways.
Preparing the sites and installing the units took about a month, according to
Clarke. “We had to tear up the sidewalk and install the Filterra systems a
little shallower than we’d expected so we could use existing catch basins,” he
says. “This meant we ran more 4-inch PVC pipe. But we were able to tie it to the
deeper end of the catch basins to get the right depth and the correct
flow.”
Biotreatment
Fits Naturally
Each
of the Filterra Bioretention Systems includes a below-grade concrete container,
a 3-inch layer of mulch, 1.5 to 3.5 feet of filter media, an observation and
cleanout pipe, an underdrain system, and an environmentally suitable plant.
Plants selected for the five Marina del Rey installations are suitable for the
area and include Western Redbud, Mountain Flax, and Yedda
Hawthorn.
“When
we considered the Filterra device, it had a strong resemblance to biotreatment
solutions that we are already using in our wetland project, for example,” says
George. “Filterra also added trees to the streets, something we try to
incorporate as often as possible in our watershed.”
As
a natural solution for treating dry-weather runoff within the watershed,
Filterra systems use Bacterra, a bioretention medium that optimizes the removal
of bacteria and other pathogens as well as total suspended solids (TSS) and
heavy metals. Physical, chemical, and biological processes all aid in the
removal of pollutants.
Now,
dry-weather runoff drains directly from the unincorporated communities’
sidewalks, streets, and other
impervious surfaces through a curb inlet into
a concrete box and passes through the mulch, plant, and Bacterra medium. Treated
water then flows out through an internal underdrain pipe connected to the storm
drainpipe.
Improved
Aesthetics, Decreased Bacteria
“While
we had to tear up the sidewalks, the installation was easy, and we certainly
improved the aesthetics of the neighborhood,” Clarke says. “People passing by
were happy to see us planting trees.”
Removing
nutrients and organics from the dry-weather runoff by using plants and biomass
to capture, transform, and hold bacteria and pollutants, the Bacterra medium
helps to prevent bacteria from growing downstream after processing. Although
laboratory tests showed bacteria removal efficiencies between 77 and 99%,
continuous onsite testing by CRG Marine Laboratories of Torrance, CA, has shown
higher removal rates ranging from 94 to 99%. In the long term, reducing bacteria
rates to these low levels not only improves the harbor’s water quality, but also
makes the community a healthier place to visit and
live.
“For
Marina del Rey’s highly urbanized environment, and with its very limited space
for treatment, Filterra was the right choice based on the existing conditions in
the watershed,” says George.