Compost products control stormwater runoff
on roadways
A compost sock
The next time someone tells you to “put a sock in it,” there might be a good reason—if the request is for a compost filter sock. A compost sock is a type of contained compost filter berm that can be used in place of a traditional sediment and erosion control tool such as a silt fence or straw bale barrier.
Last December, Hennepin County offered a training seminar on the use of compost to reduce stormwater runoff and improve water quality. The presenters were Dwayne Stenlund, Mn/DOT ecologist, Office of Environmental Services; Ginny Black, organics recycling coordinator, Minnesota Pollution Control Agency; Chuck Joswiak, certified compost installer, Windscapes Inc.; and Bruce Spanier, principal engineering technician with Hennepin County’s Transportation Design Division.
Spanier described how Hennepin County is using compost for its roadway project on CSAH 1 in Eden Prairie. To learn more about the project, visit www.co.hennepin.mn.us, then click on Environment, Property, & Transportation, then on Transportation, and then on Roads & Bridges.
Stormwater control is a growing priority for local government. The National Pollutant Discharge Elimination System (NPDES) permit program, authorized by the Clean Water Act, requires local agencies to control stormwater velocity. Coming in 2008, the program will also require them to control the volume of stormwater discharged.
Following are some highlights from the seminar:
Compost blown into mesh filter socks can be placed along a slope or in a ditch line, perpendicular to water flow, to slow the velocity of water, similar to silt fence or rock checks. Compost socks retain large volumes of water and stay in place under heavy flows with minimal staking. They do not need to be cut into the soil (as silt fence does), nor do they pose a hazard to vehicles that leave the roadway (as rock checks do). Compost socks also have the ability to filter pollutants from the water, including suspended solids, oils, nutrients, and heavy metals, and can ameliorate the effects of sodium.
A two-inch compost blanket can also be blown over the surface of disturbed roadside soils. The compost blanket can help dissipate energy and add valuable nutrients to what is often a very nutrient-depleted zone. The added nutrients aid in the establishment of vegetation and help to prevent aggressive, invasive species from taking hold. The compost blanket also extends the growing season about three weeks later in the fall due to the dark color holding in heat.
“Fully cooked” compost is necessary to prevent killing seeds and seedlings. All compost should be certified under the Seal of Testing Assurance (STA) program. Under Mn/DOT Spec #3890, there are three grades of compost:
- Grade 1 is from animal feedstock.
- Grade 2 is from leaf and grass clippings.
- Grade 3 is 10% Grade 1 and 90% Grade 2.
More information on compost is available at www.compostingcouncil.org. NPDES information, including a menu of best management practices, is on the U.S. Environmental Protection Agency site: cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm.
—Kathy Schaefer, CTAP instructor