Grass Valley looks ahead with groundwater recharge projects | TheUnion.com

Grass Valley looks ahead with groundwater recharge projects

A new program in Grass Valley could help store water that would otherwise be whisked away into storm drains.

The first phase of the city's groundwater recharge efforts was implemented this summer on North School Street. A portion of the road was resurfaced with pervious concrete, which allows water to seep through and into the groundwater basin.

A grant awarded to American Rivers helped pay for the materials, which included 4,500 square feet worth of pervious pavement, according to Bjorn Jones, Grass Valley's senior civil engineer.

Jones said the trial run has been a success.

"Installation went well and the product appears to be functioning as desired," he said in an email. "You can observe this by dumping a glass of water on the surface and watching it disappear. I have observed it in storm events by the minimal flow in the gutter pan that might normally be inundated with runoff."

The section of road on North School Street between West Main and Richardson Streets was in dire need of repair, according to Jones, which made it the perfect place to try out the pervious pavement.

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The city recently received another grant which is set to pay for 10,000 square feet of permeable concrete.

"We're looking at places where we could use that," Jones said.

The permeable concrete Grass Valley used is made up of "carefully controlled amounts of water and cementitious materials … used to create a paste that forms a thick coating around aggregate particles," according to PerviousPavement.org.

"A pervious concrete mixture contains little or no sand, creating a substantial void content," the site states. "Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly. Typically, between 15 and 25 percent voids are achieved in the hardened concrete, and flow rates for water through pervious concrete are typically around 480 inches per hour, although they can be much higher."

Though the city doesn't use groundwater for its supply, Jones said the project has other benefits for Grass Valley, besides recharging the basin.

Runoff from streets often contains contaminants that are carried into streams and other waterways, he said. The pervious pavement prevents pollution in the local watershed.

"By infiltrating that into the ground, rather than into a creek, you're able to help the environment and reduce runoff contaminants," Jones said.

To contact Staff Writer Matthew Pera, email mpera@theunion.com or call 530-477-4231.

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