Highway Construction Stormwater Information and Guidance
The construction industry is a critical participant in our efforts to protect streams, rivers, lakes, and wetlands.
As stormwater flows over a construction site, it picks up pollutants like sediment, debris, and chemicals. Preventing soil erosion and sedimentation is an important responsibility at all construction sites. Through the use of Best Management Practices (BMPs), construction site operators are the key defense against erosion and sedimentation.
- Soil disturbance associated with a construction site can increase the potential for excess erosion if not properly addressed.
- Excess soil erosion from construction projects removes the soil surface layer, rich in nutrients, and transports the sediments into surface waters contributing to sediment loading and pollution transported with the sediments.
- The excess sediment collects in reservoirs, lakes, rivers, and streams reducing their water holding capacity and quality; and is detrimental to aquatic life.
- While erosion and sedimentation are natural processes that help shape Montana's rivers and valleys, activities such as highway construction can greatly accelerate these natural processes causing serious and costly problems.
- The implementation of BMPs to prevent soil erosion and the resulting sedimentation from entering the waterways can significantly reduce serious and costly problems in the future.
- High volumes of stormwater can also cause stream bank erosion, and destroy downstream aquatic habitat.
- In addition to the environmental impact, uncontrolled erosion can have a considerable financial impact on a construction project. It costs money and time to repair gullies, replace vegetation, clean sediment-clogged storm drains, replace poorly installed BMPs, and mitigate damage to other people's property or to natural resources.
Some Soil Erosion Control Tips...
No BMPs = Dirt In
- Design the site to infiltrate stormwater into the ground and to keep it out of storm drains. Eliminate or minimize the use of stormwater collection and conveyance systems while maximizing the use of stormwater infiltration and bio-retention techniques.
- Minimize the amount of exposed soil on site. To the extent possible, plan the project in stages to minimize the amount of area that is bare and subject to erosion. The less soil exposed, the easier and cheaper it will be to control erosion.
- Vegetate disturbed areas with permanent or temporary seeding immediately upon reaching final grade.
- Vegetate or cover stockpiles that will not be used immediately.
- Reduce the velocity of stormwater both onto and away from the project area.
Good use of BMPs
- Interceptors, diversions, vegetated buffers, and check dams are a few of the BMPs that can be used to slow down stormwater as it travels across and away from the project site.
- Diversion measures can also be used to direct flow away from exposed areas toward stable portions of the site.
- Silt fences and other types of perimeter filters should never be used to reduce the velocity of runoff.
- Protect defined channels immediately with measures adequate to handle the storm flows expected.
- Sod, geotextile, natural fiber, riprap, or other stabilization measures should be used to allow the channels to carry water without causing erosion. Use softer measures like geotextile or vegetation where possible to prevent downstream impacts.
- Place aggregate or stone at construction site vehicle exits to accommodate at least two tire revolutions of large construction vehicles. Much of the dirt on the tires will fall off before the vehicle gets to the street.
- Regular street sweeping at the construction entrance will prevent dirt from entering storm drains.
- Do not hose paved areas.
- Sediment traps and basins are temporary structures and should be used in conjunction with other measures to reduce the amount of erosion.
Erosion control mat and check dams
- Maintaining all BMPs is critical to ensure their effectiveness during the life of the project.
- Regularly remove collected sediment from silt fences, berms, traps, and other BMPs.
- Ensure that geotextiles and mulch remain in place until vegetation is well established.
- Maintain fences that protect sensitive areas, silt fences, diversion structures, and other BMPs.
- Other BMPs and Activities to Control Polluted Runoff
You'll need to select other controls to address potential pollutant sources on your site. Construction materials, debris, trash, fuel, paint, and stockpiles become pollution sources when it rains. Basic pollution prevention practices can significantly reduce the amount of pollution leaving construction sites.
The following are some simple practices that should be included in the Plan and implemented on site:
Erosion control mats, fiber rolls & silt fence
- Keep potential sources of pollution out of the rain as practicable (e.g., inside a building, covered with plastic or tarps, or sealed tightly in a leak-proof container).
- Clearly identify a protected, lined area for concrete truck washouts. This area should be located away from streams, storm drain inlets, or ditches and should be cleaned out periodically.
- Park, refuel, and maintain vehicles and equipment in one area of the site to minimize the area exposed to possible spills and fuel storage. This area should be well away from streams, storm drain inlets, or ditches. Keep spill kits close by and clean up any spills or leaks immediately, including spills on pavement or earthen surfaces.
- Practice good housekeeping. Keep the construction site free of litter, construction debris, and leaking containers. Keep all waste in one area to minimize cleaning.