In accordance with this program, city officials focused on implementing an urban runoff pollution mitigation system for the Centinela Basin Watershed. They wanted the system to reduce urban runoff pollution—including dry weather flows—entering nearby Ballona Creek, which flows into the Santa Monica Bay.
Recent changes in federal, state and local regulations and standards have forced a shift in management strategy to control urban stormwater runoff. The traditional end-of-pipe approach has been replaced by a sustainable watershed approach, in which the entire storm drainage area is assessed for stormwater management possibilities.
With traditional stormwater drains deemed not effective enough, local government officials and the engineers they consult have gone to great lengths to find practical alternatives. The engineers have been working diligently to evaluate the best approaches to solve the problem, either replacing existing storm drains or retrofitting them with a device that increases their efficacy.
Caltrans helps clean up Los Angeles River
The State of California Department of Transportation (Caltrans) is responsible for the design, construction, maintenance and operation of the California State Highway System, as well as the portion of the Interstate Highway System within the state’s boundaries.
In recent years, Caltrans has devoted time, energy and resources to assist the state in greatly reducing the amount of trash in the Los Angeles River. In fact, stormwater quality management is one of Caltrans’ main environmental priorities, in order to achieve compliance with its National Pollutant Discharge Elimination System (NPDES) permit obligations.
Over the next two years, the engineering firm Metcalf & Eddy (M&E) will provide technical assistance as needed for Caltrans’ stormwater program. The firm is focusing primarily on the planning and design of stormwater quality measures within the highway system.
“To assist them in continuing to meet the TMDL, Caltrans is evaluating the use of gross solids removal devices (GSRD)—structures that use screening technology to remove litter and large solids from runoff,” explained M&E Technical Specialist Foster McMasters, in a recent company newsletter.
“M&E is developing the standard plans for several different sizes and types of GSRDs that can be applied to most of Caltrans’ sites,” McMasters added. For the past decade, transportation engineering specialists at DMJM+Harris have been working closely with Caltrans on stormwater pollution prevention programs statewide.
In 2002, M&E opened an office in Orange, Calif., and formed a joint venture with DMJM+Harris to provide a team approach to the stormwater program. M&E’s James Sullivan, project manager, expressed a positive view regarding the joint effort: “M&E’s proven wet weather treatment expertise combined with DMJM+Harris’ experience in highway design, and NPDES field compliance enables us to develop effective stormwater treatment solutions that both meet Caltrans’ compliance goals and easily integrate into its highway design process.” In addition to designing effective stormwater solutions, the team is also providing training to hundreds of Caltrans’ designers and consultants statewide, to ensure consistency of local capital improvement projects.
Recently, Caltrans began conducting pilot programs to evaluate the performance of a variety of devices designed to capture gross solids. The more effective ones likely will be retrofitted into current highway drainage systems and included in all new systems.
Pilot tests prove effective
Caltrans tested nine types of GSRDs in the Los Angeles River watershed in District 7. These pilots were designed to evaluate the effectiveness of GSRDs in removing gross solids, as well as, construction operation and maintenance costs. Included in the testing were two linear radial devices (LRD), four Inclined Screen Devices (ISD), a Baffle Box (BB) and two V-screens (VS). Linear Radial Devices (LRD):
- LRD1 Configuration 1 – louvered well casing; and
- LRD2 Configuration 2 – wire mesh screens with nylon mesh bags. Inclined Screen Devices (ISD):
- ISD1 Configuration 1 – parabolic wedge wire screen;
- ISD2 Configuration 2 – parabolic wedge wire bars;
- ISD3 Configuration 3 – parabolic wedge wire screen (front-end loader); and
- ISD4 Configuration 4 – wedge wire screen, direct flow. Baffle Box (BB):
- A two-chamber concept using a 50-mm screen and then a 5-mm screen. V-screens (VS):
- VS1 Configuration 1 – forward sloping screen (FSS); and
- VS2 Configuration 2 – reverse sloping screen (RSS).
As reported in Caltrans’ Treatment BMP Technology Report released in November 2004, the testers found two of these designs effective at removing gross solids from stormwater runoff: Linear Radial Configuration 1 and Inclined Screen Configuration 1.
LRD Configuration 1 uses modular well casings with 5-mm (0.25-in. nominal) louvers to remove litter. Flow enters the casing and passes radially through the louvers, trapping litter and solids inside. The clean water flows into a vault holding the GSRD and is directed to an outlet pipe. Access doors are provided on the well casings for ease of maintenance and cleaning using a vacuum truck.
In ISD Configuration 1, flow goes over the top of a weir and falls through an inclined wedge wire screen with 3-mm spacing. Litter caught by the screen falls or is pushed down the face of the screen into a litter storage area. The litter storage area is sloped and has a drain to prevent standing water.
Testers found the Linear Radial Configuration 2, Inclined Screen Configuration 2 and Baffle Box too maintenance intensive or ineffective. As a result, these devices were removed from further consideration.
And although the Inclined Screen Configuration 3 proved a valid design concept, testers recommended a redesign to eliminate the intensive maintenance requirements documented throughout the study. The other GSRDs required further evaluation.
Chambers installed under Sun Valley Park
Located in the northeast part of San Fernando Valley, Sun Valley is well known to Los Angeles area residents as a district frequently plagued by serious flooding problems.
Due to the hard surfaces that cover most of Sun Valley’s landscape, the ground is unable to absorb stormwater runoff, leading to chronic flooding. Not long ago, the Sun Valley Watershed Stakeholders Group was formed with the key goal of reducing local flooding while retaining all stormwater runoff from the watershed. Sun Valley officials joined forces with local residents, businesses and other interested parties to implement a watershed approach to solve the flooding problem while providing additional community benefits. These include water conservation and preserving more open spaces for recreation and wildlife habitat. The group selected sites for several pilot projects in the watershed. One of the initial “Phase 1” multipurpose projects was an infiltration project at Sun Valley Park and Recreation Center. This project served as a model for subsequent endeavors throughout the watershed.
Working closely with CH2MHill’s Santa Ana office, Sun Valley officials designed a system that collects the tributary stormwater flows upstream of the park in a system of catch basins and storm drains.
The water is then carried to underground treatment units that extract the larger sediment particles, as well as grease and oil. To further treat the even more polluted low flows, a heavy metals treatment device is utilized. The treated stormwater is conveyed to two underground infiltration chambers and then trickles into the ground, ultimately restoring the groundwater supply. Because the entire system is located underground, the surface of the park can be devoted solely to recreational use.
Santa Monica manages urban runoff
In 1994, the city of Santa Monica launched its Sustainable City Program, resolving that city actions affecting the environment must not jeopardize future generations. The city council developed this program to create the foundation for a more sustainable way of life through safeguarding resources and preventing harm to the environment.
In accordance with this program, city officials focused on implementing an urban runoff pollution mitigation system for the Centinela Basin Watershed. They wanted the system to reduce urban runoff pollution—including dry weather flows—entering nearby Ballona Creek, which flows into the Santa Monica Bay. In addition to evaluating possible sites to meet the project’s objectives in the future, Black & Veatch was hired to prepare a feasibility study for installing a pollution mitigation device at the existing Centinela Avenue storm drain system to meet the project’s goals:
- Limit total suspended solids (TSS) in the treated stormwater to 75 mg/L;
- Remove 80% of soluble pollutants including oil and grease;
- Remove 100% of solid materials larger than 1/8 in. in diameter; and
- Treat up to 3/4 in. of stormwater for the tributary area over 24 hours.
With an estimated cost well over $2 million, the installation of the Centinela Basin Dry-wet Weather Urban Runoff Treatment System, this BMP treatment system includes a primary separation/ screening chamber to remove pollutants such as trash, sand, debris and oil and grease.
The filtered water then flows into another vault structure that contains various filter cartridges to remove additional soluble pollutants such as heavy metals, organic chemicals and nutrients.
Finally, the treated water is reintroduced into the storm drain system and eventually flows into the Santa Monica Bay.
