Setting stormwater standards

February 2012 » Features » PROJECT CASE STUDY
Low-impact development technology helps propel Southern California city toward green goals.
Abigail Kent
The city of Chula Vista installed two MWS —€“ Linear 22-foot Underground Curb Type stormwater treatment systems in restricted space between the street and sidewalk

Chula Vista, Calif., a city of more than 230,000, is committed to sustaining a clean, healthy environment, and thus hoping to land the title "Greenest City in America." Located just seven miles from downtown San Diego, this culturally diverse city has won numerous awards for its green accomplishments and become a role for others to follow.

Project
North Broadway Basin Project, Chula Vista, Calif.

Civil engineer

Chula Vista Stormwater and Engineering Department

Product application

Modular Wetlands System's Linear Underground Curb Type multi-stage stormwater treatment system fits a restricted space for a retrofit application.

Leading the state in its stormwater program, Chula Vista has set standards for new development and redevelopment that comply with the requirements set forth by the National Pollutant Discharge Elimination System (NPDES) Municipal Permit issued by the Regional Water Quality Control Board. Consequently, as the city's growth and urbanization increases, so does its need for better infrastructure, including storm drains.

In mid 2008, Chula Vista's Stormwater and Engineering Department contacted Modular Wetlands Stormwater Engineer Zach Kent to figure out how to best configure a 22-foot Modular Wetlands System for an infrastructure project they were working on along Broadway. The North Broadway Basin Project included installation of curb gutters, sidewalks, and 2,000 linear feet of reinforced concrete pipe storm drain. Designing a configuration to capture, remove, and reduce a variety of pollutants was essential to the success of the project.

Site concerns
Stormwater runoff from public roadways is one of the leading contributors of stormwater pollution to waterways, lakes, streams, and oceans. The lack of infrastructure on Broadway caused more than one concern for the city of Chula Vista. Not only was the stormwater runoff from this area draining into a 303(d) impaired body of water —€” the Sweetwater Watershed —€” but flooding along this street caused potentially dangerous situations.

With these site concerns in mind, the city needed to address these issues while working with space constraints. Like many retrofit projects, space was limited. Because of this limited space along Broadway, large-scale capture devices could not be applied. The city needed to find an alternative, cost-effective low-impact development (LID) solution to reduce and treat the runoff.

The bid was awarded in the fall of 2008 to MJC Construction for about $1.67 million. The work to be done included full street improvements and installation of a storm drain system. The city and Modular Wetland Systems (MWS) engineers worked together to achieve an optimum design configuration to address all of the site challenges, ultimately deciding on the MWS —€“ Linear 22-foot Underground Curb Type treatment system.

The first system was installed on North Broadway and D Street; the second system was installed on North Broadway just 150 feet north of C Street. Each unit was placed in a small landscape area between the sidewalk and street, just upstream of an existing catch basin to intercept the 24-hour, 85th percent storm event low flows. The incoming water is treated through a series of stages: screening, filtering, settlement, and bioretention —€” a "treatment train" approach.

Outflow from the MWS —€“ Linear then enters the existing catch basin via pipe. High flows either pass the system and enter the existing catch basin or enter the system and travel through the internal bypass. This design alleviates seasonal flooding concerns.

The city decided to eliminate landscape maintenance; therefore, the MWS —€“ Underground Curb Type was a perfect solution. These particular units have a solid concrete lid, eliminating the plant bed used in other MWS —€“ Linear systems. A special blend of biofiltration media that works without the assistance of plants was used. The beneficial bacteria and microflora within the media removes various pollutants of concern.

Results
The city of Chula Vista has worked vigorously to increase water quality through strategic planning and collaboration. The stormwater treatment systems, installed since February 2010, allow the city to meet the permit requirements for pollutant removal. Choosing this system has minimized seasonal flooding, which is an important aspect in treating stormwater. The MWS —€“ Linear is designed to treat stormwater runoff while also protecting the surrounding property.

A recent site visit demonstrated the importance of the stormwater treatment systems. In October 2010, a Bio Clean cleaning and maintenance crew, along with the city of Chula Vista's Public Works, got a firsthand look at the systems' performance.

"In less than eight months, the systems captured a variety of pollutants that would have otherwise entered the impaired Sweetwater Watershed," said Aaron Kent, Modular Wetlands' project manager. "It was visible that the first chamber was close to two-thirds full of sediment, trash, and other oxygen-demanding substances. Upon examining the BioMediaGREEN Filter Cartridges, we found high amounts of oil and grease covering the surface of the filter media."

In less than eight months, the stormwater treatment systems captured a variety of pollutants that would have otherwise entered the impaired Sweetwater Watershed. The first chamber was almost two-thirds full of sediment and trash. A worker cleans the pretreatment chamber of the multi-stage MWS —€“ Linear Underground Curb Type system.

Each of the two filter cartridges contains 35 square feet of surface area and a loading rate of less than 1 gallon per minute per square foot. This large amount of surface area makes the cartridges highly efficient and long lasting.

Abigail Kent is director of marketing for Modular Wetland Systems Inc., Oceanside, Calif. She can be contacted at abby@biocleanenvironmental.com.


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