When changes in California industrial stormwater regulations removed the exemption for small school districts, the McKinleyville Union School District, took a proactive approach to treating washwater and stormwater runoff from its bus maintenance facility. By installing an underground filtration system, the school district achieved compliance with California Phase II industrial stormwater regulations.
Every week, the district’s maintenance facility washes each of their 82-passenger school buses. Workers use long-handled brushes and a mild, environmentally-friendly soap to remove dirt and a hose with spray nozzle to wash and rinse the buses. The average water flow rate is about 10 gpm for 20 minutes when two buses are washed. Prior to the installation of the filtration system, washwater was collected in a low spot adjacent to the outside wash area, directed to a swale and then discharged into a nearby creek.
While the district was already using source controls at the facility, the bus washing activity had the potential to introduce metals, antifreeze, tire particulates, cleaning solvents, lubricants, grease, oil, fuel and debris into the storm drain system.
In order to address these pollutants and assure compliance, the district’s engineering afirm recommended a qualified best management practice (BMP) – the CatchBasin StormFilter™ – manufactured by Contech. This system was selected to treat the facility’s stormwater and residual washwater runoff before discharge into the swale and creek.
“We had always been careful about things like oil spills and lubricant drips around the garage, with our equipment maintenance manager taking great pride in running a clean and tidy operation,” said Nancy Howatt, assistant superintendent for the McKinleyville Union School District.
“To continue setting a good example for our children, we want to also use best available practices, and we feel it’s not a bad thing to have the state checking on that.”
Based on flow rate and testing data, Contech recommended the steel CatchBasin StormFilter with one 7.5 gpm filtration cartridge containing the company’s patented CSF® leaf media.
During bus washing, polluted runoff enters the steel unit through a traffic-bearing grate and flows into a settling chamber, where heavier solids drop to a sump. Runoff then flows under an oil retaining baffle into a cartridge chamber, where lighter solids and soluble pollutants such as heavy metals are removed through media filtration. A diversion valve on the storm drain bypass line directs treated washwater into the sewer sump from where it is pumped to the district’s sanitary sewer system.
When the area is not being used for bus washing, the bypass line to the storm drain is opened and flow goes directly into the storm drain system, which empties into the swale. A cover is also placed over the storm drain inlet to minimize rainwater inflow to the sewer system.
Installation of the system took one day, using labor from the school system and a paving company. The project was supervised by the director of maintenance and operations. “It was pretty much a basic task for our people, who were already familiar with plumbing and drainage,” explained Howatt.