How do you increase in-place stormwater infiltration in a parking lot without ripping up 39 acres of asphalt pavement? Ventura County’s Watershed Protection District in California figured out how: replace existing traditional concrete gutters with pervious concrete gutters to allow stormwater runoff to flow through it, infiltrating into the soil below.
That’s how the "first flush" — the 70% of pollutants that are carried during the first 20 minutes of a rainfall — from the County’s Government Center are treated. Instead of waste, the runoff is now a resource.
“We installed 4,805 linear feet of pervious concrete gutters,” says Ewelina Mutkowska, stormwater program manager at Ventura County. “This new system allows stormwater to be drained and then filtered through an aggregate-filled infiltration trench that flows into dry wells, reaching soil that can accept groundwater recharge.”
These pervious gutters are placed throughout the multiple parking lots at the Government Center, each marked with a blue Clean Drain sticker. When they fill up, the rest of the water flows into existing storm drains.
No trees had to be removed, nor any additional right of way acquired.
“The project is part of a multijurisdictional initiative to reduce urban runoff pollution and protect our watersheds,” says Mutkowska. Ten cities and unincorporated areas share responsibility for complying with a countywide National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) permit adopted most recently in 2010.
Most of the project’s $1.5 million funding came from California’s Proposition 84 Stormwater Grant Program, which voters approved in 2006. CalRecycle, the state Department of Resources Recycling and Recovery, also contributed.