For the City of San Diego to clear the way for a new central library downtown, a new site had to be found for the obsolete Police Vehicle Maintenance Facility. Land was available on the site of the San Diego Police Pistol Range, but redeveloping the pistol range to accommodate a new maintenance facility required relocating the K-9/SWAT facility and rehabilitating historic buildings at the pistol range.
The redeveloped site included a 2.36 acre Vehicle Maintenance Facility anchored by a two-story, 28,000 square-foot building that houses administrative offices and vehicle maintenance. The maintenance facility also includes a fuel station, oil lubrication site, vehicle wash bay, and 113 parking spaces. A new 2-acre K-9/SWAT facility, which included a 6,500 squarefoot building, 40,000 square-foot training field, 6,000 square feet of kennel space and 66 parking spaces were also to be on-site.
The redevelopment resulted in a significant increase in impervious area. Since the stormwater runoff from the new facilities would discharge directly to the Chollas Creek, the project must comply with a Section 404 permit, as required by the Army Corps of Engineers.
The creek was identified in 1998 as a “water quality limited waterbody” due to concerns about metals, toxicity, and coliform. To satisfy the permit requirements, the city would have to comply with state water quality requirements and obtain 401 certification from the San Diego Regional Water Quality Control Board.
Obtaining 401 certification required the installation of a stormwater best management practice (BMP) that the Regional Water Quality Control Board would accept. The City of San Diego challenged BDS Engineering, Inc. to find a method of stormwater treatment that would achieve water quality certification and maximize land use.
Initially, bioretention was evaluated, but not feasible due to soil conditions on the site. Another choice was detention. “There was not enough room, horizontally, on the site for a detention basin because they take up a lot of room,” said Tom Jones, P.E., a Principal at BDS Engineering.
While one small detention pond was built on the site, Jones noted that the site did not provide enough room to accommodate detention basins or bioswales large enough to hold the amount of stormwater that required treatment. To obtain 401 certification and comply with the 404 permit, Jones knew they had to achieve a higher level of pollutant removal.
If enough land is available, detention or a bioswale can provide the required level of pollutant removal. “But on this type of site where it was so tight, there just wasn’t any room for it,” said Jones. What was needed was a BMP that removed a high level of pollutants while using minimal space.
Jones was familiar with one approved BMP that was both compact and accepted for use by the San Diego Regional Water Quality Board. He decided to propose the Stormwater Management StormFilter. A passive filtration system, the StormFilter consists of an underground concrete structure housing rechargeable, mediafilled filter cartridges. The system works by passing polluted stormwater runoff through filter cartridges that are customized to remove site-specific pollutants such as sediments, metals, nutrients, trash, debris, oil and grease. A patented integrated surface-cleaning mechanism extends cartridge life and reduces maintenance intervals.
To address site requirements, BDS Engineering specified four StormFilters. Three were CatchBasin StormFilters holding one, two and three cartridges for a total of six cartridges. The fourth StormFilter, in a manhole configuration, holds three cartridges. These compact configurations fit easily within the space constraints of the site. The CatchBasin StormFilter provided the added benefit of a three-in-one design that combines a catch basin, a high-flow bypass device, and a StormFilter into a single structure.
The cartridges were filled with a blend of perlite and zeolite filter media. Perlite is a naturally occurring puffed volcanic ash effective at removing solids and oil and grease. Zeolite is a naturally occurring mineral used to remove soluble metals, ammonium, and some organics.
Jones stated that the StormFilter was chosen because it had a higher capacity for removing pollutants from stormwater runoff, which meant they would be in compliance with the 404 permit. “We had to use a much higher rated BMP, which is the StormFilter,” he said.
The Vehicle Maintenance Facility opened on July 14th. Performance of the StormFilters at the facility will be assessed during the next routine maintenance check. While maintenance of the StormFilter is typically recommended annually, site conditions, pollutant loading, and rainfall patterns ultimately define the maintenance frequency.
Based on Stormwater Management’s records and experience with StormFilter installations in Southern California, filter cartridge replacement is recommended every two to three years, with additional maintenance recommended in years of excessive rainfall.