Q: How does a dewatering bag (Dirt Bag, sediment container, Siltsack, etc.) work on a construction site to help you with your erosion and sediment control plan?
A: Temporary construction erosion and sediment control is the practice of preventing or reducing the movement of sediment from a site during construction. Soil erosion and sediment runoff to waterways are significant problems and regulated in most states. In general, you need:
- carefully crafted sediment and erosion control plans designed to reduce polluted runoff
- implementation and updating of the plan
- operation and maintenance of runoff reduction measures until the site is stabilized
- significant penalties for negligence and willful violations
The progression of activities at a construction site is as follows.
- Evaluate and assess the construction site:
Collect site information (size, slopes, soils, drainage patterns).
- Identify sensitive areas—waters, vegetation, slopes, etc.
• Produce map or drawing of the existing site.
• Create the final project design map or drawing.
• Characterize the sequence of major construction activities.
• Calculate area, infiltration, runoff and drainage system sizing.
- Select site-specific erosion, sediment and housekeeping controls:
• Review local and state permit requirements.
• Identify erosion prevention field practices and site locations.
• Select sediment control practices and field locations.
• Determine housekeeping and pollution prevention practices.
• Indicate location of best management practices (BMPs).
• Prepare a plan for inspecting and maintaining BMPs.
- Complete permitting and notification tasks:
• Identify all contractors and subcontractors.
• Develop stormwater pollution prevention plan (SWPPP).
• Submit notice of intent to agency.
• Apply for and obtain other local/state/federal permits.
• Familiarize contractors and others with SWPPP requirements.
- Construction and SWPPP implementation:
• Install stabilized exit and initial downgradient perimeter controls.
• Install and stabilize initial drainage system, traps and basins.
• Proceed with phased clearing and grading work.
• Implement phased erosion/sediment BMPs as needed.
• Stabilize disturbed areas within 14 days or as required.
• Inspect and maintain BMPs; document activities.
- Final stabilization and permit termination:
• Stabilize all disturbed areas, slopes and drainage systems.
• Remove waste and unused materials.
• Remove all temporary BMPs; stabilize BMP locations.
• File notice of termination and other required notices.
I know this is a lot so, to answer your question directly, dewatering bags offer a means to jump on the source of the problem early. For example, if you are pumping water (sediment) from an evacuation with a mud pump, direct it into a dewatering bag before discharging. They are small temporary sediment traps to treat runoff water by allowing sediment particles to settle out of the water. Typically lying in a drainageway or other point of discharge from a construction site, dewatering bags capture runoff water laden with sediment before it flows into the watershed. It is best to manage sediment at the source ASAP.