 When it rains, it PORES
Narrator Says: When it rains it pours, not as in p-o-u-r but p-o-r-e. This concrete has pores and is part of the King County Department of Transportation’s ongoing efforts to minimize human impact on the environment. This new porous concrete allows more rain and storm water directly into the ground, rather than allowing it to gather roadway pollutants on its way to the stormwater system. It also aids in replenishing water tables and aquifers. The sidewalks essentially reduce the amount of stormwater run-off, in turn reducing the size of detention ponds and other stormwater treatment facilities. King County Resident Engineer Victor Daggs Says: Conventional methods, basically what you have, is you have your water runway, running into the curb gutter, going into the basins, and depending on the volume of water you have coming through there, stormwater requirements requires you to do a certain amount of filtration. So be it ponds, bio-swells something where it can get naturally infiltrated out. But if you’re in confined areas, you may have to do retention volts underneath the ground, to hold the water and let it out slowly, and treat it slowly, so that way you just don’t have an influx of polluted water, running into our lakes, streams, and waterways. So in the cost of some of these filtration systems and the maintenance of some of these filtration systems, is going to be really, really expensive, so if we can find ways to change some of our construction practices, that will allow us two things, one is allowing us to have less of an impervious area, and two able to treat water as it is processed on our projects, so basically it’s a double plus. Narrator Says: This project, at the intersection of Military Road South and South 272nd Street, is the first in which King County’s Roads Division has used the new porous concrete. A grant from the Washington State Department of Ecology, of about $424,000 dollars helped pave the way for the 1,100 yards of porous sidewalks at the site. The grant was the 2nd largest of the ten the state D.O.E. gave out in 2006. The concrete’s appearance is similar to unfinished concrete with the obvious difference; it has many small holes to let water through. The concrete itself allows up to 500 inches of rain to penetrate every hour, but the soil allows only about three inches per hour through. All the same, it’s more water directly penetrating the soil, and less water gathering roadway pollutants. King County Resident Engineer Victor Daggs Says: What we’re doing now is kind of a test, and kind of show you kind of what the rate, it won’t give you exactly the rate but it will kind of show you an example of what happens to water as it is on the, hits the actual sidewalk, so basically this is a one-gallon jug of water, basically going through the sidewalk, and when I'm done with the bottle, it's gone, and so what that will do, basically that's less water that we have to treat. \ If this was a conventional sidewalk, that material would have flushed into the curb and gutter, ran along the curb and gutter, picked up roadway oil, gasoline and other pollutants that are on the roadway, washed into the drainage systems and have to be treated in a bio-swell or some other type of mechanical device to treat the water, before it goes out into the lakes and rivers, this way it's all in here, it goes into our median underneath which stores and percs through, percs through the natural soils, so everything’s good. Narrator Says: Project managers say the intersection of Military Road and 272nd is a good place to start with the porous concrete because of its high traffic volume, but any intersection would benefit considering how much cleaner the water entering the soil could be.
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