Innovative green technology is part of the answer to help the City of Los Angeles meet stormwater pollution reduction mandates and achieve its long-range goals for restoring one of its vital waterways.

The years have not been kind to the Los Angeles River, a vital component of the city’s storm-water and flood-control system. Always proactive, the city had been searching for financially feasible ways to improve its stormwater system and enhance water quality in the river before it reaches the Pacific Ocean.

With help from an innovative non-profit organization and through cooperation across numerous agencies, the city embarked on a pilot program that is showing great potential for reducing non-point-source pollution, meeting federal and state environmental Total Maximum Daily Loading (TMDL) mandates and restoring the river from its concrete channel back to a natural waterway.

The program involves the installation of natural drainage areas and biofiltration systems on open spaces at the ends of streets along the river. The installations filter pollutants from runoff and reduce its volume and impact on the river.

A rich history

The Los Angeles River is an intermittent stream that flows through Los Angeles County from its western end in the San Fernando Valley, about 51 miles to its mouth in Long Beach Harbor. For most of its length, the river flows through a constructed concrete channel. It was once the city’s primary source of freshwater. Over the years, urban runoff and other pollution has hurt the river and the region’s water quality.

Environmental groups and state and federal regulatory agencies, in an effort to control pollution and clean up the water entering local bays and wetlands are putting strict TMDLs in place. Preferring to devise its own way to meet the regulations and improve the river, the city was open to suggestions and to trying emerging technologies.

North East Trees, a non-profit environmental development organization, approached the city with a potential answer. “The city was inter-ested in looking at how they should respond to the looming TMDL mandate,” says Larry Smith, executive director of North East Trees.

“They were looking at large-scale, capture-and-release solutions, which deep down they knew were not going to be feasible for a number of reasons. They were looking for other solutions that could be applied on very small sub-watersheds to much larger sub-watershed situations.”

Smith’s group had recently completed a private project, the Bresee Ecology Park, that entailed the opening of a street’s culvert and replacing it with an open swale about one block long. Although developed as a stormwater quality improvement primarily for reducing trash loadings, it improved water quality more than anticipated.

The success of that project spawned the idea that open space at the ends of streets along the river could be used to treat and detain the city’s stormwater. Thus was born the Street Ends Biofiltration Project, now called Green Streets.

Securing funding

North East Trees first presented the technology to the city at a stakeholders meeting that included Los Angeles County Flood Control, Los Angeles County Public Works, the U.S. Army Corps of Engineers, the Los Angeles Bureau of Engineering, Bureau of Sanitation and Bureau of Streets Services, and local elected officials.

As a non-profit, North East Trees had secured several grants to design and construct a low-impact biofiltration solution for the city. Timing was critical, as the grants included deadlines.

At the initial meeting, Smith and his team met some resistance from the Bureau of Engineering, as the project would be a non-standard plan, requiring a B-Permit from the city. The concern was that the city’s permitting process would take too long.

The Bureau of Sanitation, which was responsible for meeting the TMDL mandates, went in search of ways to make it happen. Within the Bureau of Street Services is a Special Projects Division, set up to handle non-standard projects in public rights-of-way. That division stepped up to the plate. The city and North East Trees signed a memorandum of understanding so that the grants could be dispersed, and work began.

Selecting sites

Site selection for the pilot project was critical. North East Trees and the Special Projects Division worked closely to develop selection criteria. “We needed harder data on water quality before implementation, and we wanted to demonstrate significant water quality improvement with a natural, low-impact development treatment of stormwater that could be potentially replicated on other streets,” Smith explains.

“Intuitively we knew certain streets might be more suitable than others, but we didn’t want to rely on intuition. We wanted to make sure we were creating a foundation for the future selection of streets.” The team created a matrix and used it to score sites based on specific criteria, such as street size, sub-watershed size, land use, street configuration and physical location.

For example, smaller sub-water-sheds received higher rankings. Low-density, small-lot residential land uses got higher scores than mixed-use or industrial areas. The number one criterion was street configuration and location.

Ideal streets were in sub-watersheds that emptied directly into the river and had end-of-street open space. Such sites facilitated the pre- and post-project water-quality monitoring and ongoing quality-assurance inspections that the grants required.

The team narrowed the pilot project sites down to the Elysian Valley and Atwater Village areas — two communities with the most streets that dead-end at the river and were in small sub-watersheds. The team’s final selection was at the intersection of Blake and Oros streets.

Making the site ready

The site turned out to have some complications. The team thought the area had a 2.3-acre sub-watershed, but the drainage pattern of the streets had changed, and in reality the sub-watershed covered 20 acres. Property owners in the area had been complaining about the drainage for years. Rain events led to large areas of standing water that remained for long periods, posing an increased risk of West Nile Virus.

The team decided to rebuild the intersection as part of the project. This entailed repaving the intersection and part of Oros Street, changing the elevation of Blake Street (the crown) and replacing all access ramps, curbs and gutters. Although it caused some inconvenience, the reconstruction project created a spirit of cooperation for the Green Streets biofiltration technology within the neighborhood.

At the end of Oros Street lies Steelhead Park, designed and built by North East Trees several years before. “Up until this time, we had been building street-end parks along the river, but without infiltration capacity,” says Smith. “These were habitat restoration and passive recreation areas. They weren’t originally built for stormwater treatment. But we realized that we could tie the two purposes together by adding a treatment facility to the park.”

Working with the Special Projects Division, North East Trees sought to identify the type of bio-filtration most likely to achieve the desired results. Pre-project monitoring produced a profile of the pollutants coming off the streets. The first 3/4-inch of rainfall contained most of the pollutants, after which the level dropped dramatically.

Designing the system

The design team chose a system using two catch basins equipped with filters and a pit that would act as a drywell or leachfield to contain and filter runoff. Runoff would be caught and initially filtered through two Nyloplast catch basins from Advanced Drainage Systems Inc., equipped with Storm-PURE inserts and MYCELX Permakleen media by MYCELX Technologies Corp., to remove suspended solids, hydrocarbons and other pollutants before the water was conveyed to a pit constructed in the park.

The 8-foot-deep pit was excavated and graded to create proper drainage into the park substrate. In the pit, crews laid 60 feet of 24-inch perforated HDPE pipe and tied it to the catch basins’ conveyance pipe. On top of the HDPE pipe, they laid five feet (500 tons) of 1-inch gravel containing no fines. The uniform size of the non-compacted gravel enables water to percolate effectively. This gravel was covered with soil and planted with native vegetation.

Before installation of the biofiltration treatment, Oros Street had a typical capture system, according to Dean Harding, project manager with the Special Projects Division. “It was just standard surface drainage,” he says. “Curb and gutter transported runoff to the dead end, where there was one very large catch basin, which transported the water directly into the river. Whatever came down the street ended up in the river.

“Now, the water goes through the natural soil and recharges the aquifer. That’s nature’s way of filtering things out. By the time it does get to the river, which is another 20 to 30 feet down, the water is about as clean as it is going to get. It is a natural process that works really well.”

Oros Street Gardens

The second set of treatments was built directly on Oros Street. “The Oros Street treatment was a source reduction strategy,” observes Glenn Hoke, who works in design review, purchasing and construction oversight for the Bureau of Street Services. “There is a lot of paving on these properties, such as driveways and patios. The idea was to capture runoff from those areas, retain it and treat it. The best design ended up being parkway biofilter systems.”

The parkway system consists of trench drains, perforated plastic pipe, settlement and infiltration galleries, and vegetation. Most elements of design and construction of these treatments were new to the Special Projects Division: bio-filtration and green technology presented a learning curve.

Planning and research helped the crews keep the project on budget and on schedule. “Working and coordinating our efforts with the neighborhood was important,” says Bob Garcia, supervisor II for the Special Projects crew. “Advance planning was challenging, but coming up with if/then scenarios, knowing what we could handle in one day to minimize disruption, and researching the products to be used really helped.”

A special project construction crew built five biofiltration planter gardens along the street, each about 25-feet long by 6- to 8-feet wide, situated between sidewalk and curb. Each property along the street has a 6-inch-wide trench drain grate across the driveway to convey runoff through a conduit line into the planters. The conduit is a 4-inch perforated PVC pipe connected to a 12-inch riser that is filled with gravel.

This riser becomes a vertical waterway for the collected runoff to enter two 24-inch retention/ detention pipes that run the length of the planters. The pipes are laid side by side on top of a layer of gravel about 6 1/2 feet down. The pipes are then covered with gravel, geofabric, and soil, which is planted with native vegetation.

The planter garden creates a natural infiltration gallery, holding water until the surrounding soil and plants can absorb it, keeping runoff from the lot on the lot.

More can be done

The Green Streets pilot project was so successful that it earned an award from the city. The Bureau of Sanitation would like to build more projects like Oros Street in other locations along the river to help meet the TMDLs.

To make these improvements easier, the Special Projects Division will monitor the project and document its effectiveness. Findings will support standardized design plans for Green Streets projects.

The technology has become an important element in the L.A. River Revitalization Master Plan, which aims to create an infrastructure and environment that offers flood protection, improves water quality and the environment, and allows for the eventual removal of the river’s concrete channels. A significant element in the plan’s recommendations is incorporation of river-adjacent green streets to provide safe connections to the river for bicyclists and pedestrians, water quality features, and functioning habitat where appropriate.

Collaboration among city agencies, non-profit organizations and community members was key to the pilot program’s success. After the first successful Green Streets project, the crews from North East Trees and the city are excited. “This is the future,” Garcia says. “I would recommend others to look at this solution seriously.”

Local elected officials have offered their support as well. “We need Green Streets to have a clean river,” says city council president Eric Garcetti. “We’re demonstrating that a major goal of the L.A. River Revitalization Master Plan is within our reach, thanks to the collaboration between our city and North East Trees.”