Geosynthetics April/May 2023 - 10

Q & A GMA Techline
DEWATERING BAGS FOR EROSION
AND SEDIMENT CONTROL
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
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* 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. G
10
Geosynthetics | April May 2023
http://www.GeosyntheticsMagazine.com
Geosynthetics April/May 2023

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