Road work affects Silver Beach

Underground, below the sidewalk and bike lanes, crews will install perforated pipes in a bed of crushed rock, topped by 18 inches of sand. On the surface, the sidewalk and bike lanes will be made with porous concrete.

That way, rain will flow down through the sidewalk and bike lanes, then filter through the sand before reaching the pipes to be carried off to Lake Whatcom.

In effect, the road itself is designed to cleanse the runoff, rather than treat it elsewhere.

“This is a pilot model that could be used across the country,” said Joy Monjure, communications coordinator for the Bellingham Public Works Department. Why bother? Phosphorus.

Phosphorus is a mineral in soil that encourages the growth of algae in water, and Lake Whatcom has way too much of it. So much that the state Department of Ecology recently told local governments they must reduce phosphorus-laden runoff into the lake by nearly 70 percent.

Filtering runoff through 18 inches of sand, it turns out, is a state-approved way to remove phosphorus.

Northshore Drive hasn’t been repaved since the mid-’80s. City engineers decided two years ago that it was time to lay new asphalt, then they began brainstorming new ways to handle the runoff, because of concern about the lake and because soils in the area don’t drain well.

Freeman Anthony, lead engineer on the project, studied a boulevard in Olympia that used porous concrete for its sidewalks and bike lanes, then pushed the concept further with the sand and pipes underneath.

The new 5-foot-wide sidewalk will run along the north side of the road from Alabama to Silver Beach Grocery. There’s already a sidewalk from the grocery store to Britton Road.

The 5-foot-wide bike lanes from Alabama to the grocery store are a new addition. There’s not enough room for bike lanes from the store to Britton, but that stretch will gain a wider paved shoulder, Anthony said.

To slow traffic and make room for the bike lanes, the traffic lanes will be reduced in width from 12.5 feet to 11 feet. However, the lanes will keep their current width at several sharp bends, to help people driving large vehicles or hauling boats.

The project costs nearly $1.5 million, with nearly a third of the expense dealing with runoff.

Engineers didn’t calculate the cost of redoing the road with a standard runoff system, but that approach likely would have required the purchase of lakeside property for a treatment site.

Given the cost of land on the lake, it’s clear that using the sand and gravel is not pouring money down the drain.