Raindrops and runoff

Protecting the ground and water during construction

Straw wattles help protect cut slopes from erosion.

Straw wattles help protect cut slopes from erosion.

PHOTO Courtesy of butte County public works

Sustainable Space columnists Lori Brown and Greg Kallio are professors in the College of Engineering, Computer Science and Construction Management at Chico State University.

Rain rappin’
On average, North Staters can expect about 5 inches of rain during January—one of the wettest months of the year in Chico. The rainy season usually lasts from about Oct. 15 through April 15. These months are by far the least desirable for most builders to start construction, especially if preparing the site involves “clearing and grubbing.”

Grubbing removes most—if not all—of the vegetation from a site, either mechanically or manually, leaving soil completely exposed to the elements, such as wind and rain. During rainfall—or a “storm event,” as civil engineers refer to them—is when negative environmental impacts, such as soil erosion and sedimentation, can enter our storm drains, due mainly to surface runoff. Of course, this happens when control measures are not implemented.

Ground rules
Stormwater runoff occurs naturally, in small amounts, from almost any type of land, especially during large storms. In urban areas, it typically flows into storm drains, and in some cases into nearby streams. As the runoff flows, depending on its rate, it picks up sediments, trash, debris, and pollutants such as oil, grease, pesticides, animal feces and other toxins. Yuck.

Keeping this stuff out of our drains and waterways is pretty important considering our needs for clean water and the costs to transform it to potable standards. Some experts say water will become the next oil. In other words, clean water could become a more scarce and valuable resource.

Protections for watersheds have evolved over the decades. In 1948, Congress passed the first version of the Federal Water Pollution Control Act (Clean Water Act). In 1972, a significant amendment established the National Pollutant Discharge Elimination System, and the first phase focused on point sources of pollution like sewage-treatment plants and wastewater from industrial processes.

Further Environmental Protection Agency studies revealed that non-point sources, such as stormwater runoff from construction sites, were significant contributors to polluting streams—primarily with sediments. Beginning with raindrops breaking down the soil structure and dislodging particles, the runoff carrying the soil particles becomes sheet erosion. This eventually forms rills and larger gullies.

Simply the best
To reduce erosion and sedimentation, federally mandated control measures called Best Management Practices have been established for construction sites. Wattles are probably the most commonly recognized BMP for keeping sediments out of our waterways and preventing increasing turbidity levels in streams. You’ve likely recognized them as the “snakes” of straw bound together with mesh and placed around the perimeter of the entire construction site near graded areas. Wattles collect the sediment to keep it from entering the storm drains and streams.

Bottom to top
In California, construction projects disturbing more than an acre of soil are required to implement a Storm Water Pollution Prevention Plan (SWPPP, pronounced “swip-pe”). New buildings attempting to achieve LEED certification must implement a Construction Activity Pollution Prevention Plan that conforms to the 2003 EPA Construction General Permit, or local code; whichever is more stringent.

Without question, environmental responsibility on construction sites begins from the ground up.