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Introduction
Like air quality legislation, everyone has to be concerned with water quality. Professionals involved with constructing a highway, developing a new commercial building site
or maintaining an industrial operation are searching for the least expensive way to comply with these new laws. National Pollutant Discharge Elimination System (NPDES) Phase II requires all small municipal separate
storm sewer systems (MS4s) within urbanized areas, any MS4 that serves a population of at least 10,000 people with a population density of 1,000 people/square mile or any MS4 that contributes substantially to storm
water pollutant loading submit a General Permit application. Phase II also requires that Storm Water Pollution Prevention Plans (SWPPP) be completed for every construction site of greater than one (1) acre.
Since Phase II requires both General Permits and SWPPPs include specific details of the storm water best management practices (BMPs) intended for use, SI Geosolutions offers a wide variety of solutions that are the
foundation for success. Whether it's GEOTEX geotextiles for stabilized construction entrances or our LANDLOK turf reinforcement mats for grasses swales, our structural BMPs offer a variety of proven pollutant
removal efficiencies to enhance your storm water "treatment train". These can be either temporary construction measures employed during construction or permanent BMPs to improve storm water quality after
construction.
BMP Descriptions
Seeding
This practice reduces soil erosion by quickly revegetating disturbed site areas. By unrolling on a properly prepared seedbed, our LANDLOK degradable erosion control
blankets (ECBs) protect the soil from raindrop impact and accelerate the development of vegetation. Once established, the ECB biodegrades and the root system holds down the soils so that they are less apt to be
carried offsite by storm water runoff or wind. Temporary seeding also reduces the problems associated with mud and dust from exposed soil during construction.
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Mulching
This is a temporary soil stabilization or erosion control practice where materials such as LANDLOK ECBs are placed on the soil surface. In addition to stabilizing soils,
mulching with ECBs can reduce the speed of storm water runoff over an area. When used together with seeding or planting, they can aid in plant growth by holding the seeds, fertilizer and topsoil in place and helping
to retain moisture-regulating temperatures.
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Silt Fence
Also called a "filter fence", this BMP is a temporary measure for
sediment control. It usually consists of GEOTEX woven geotextiles stretched across posts and sometimes supported with a wire or plastic mesh. The lower edge of the fence is vertically trenched and covered by
backfill. A sift fence is used in small drainage areas to detain sediment. These fences are most effective for sediment removal from overland, sheet flow. Aside from the traditional wooden post and filter fabric
method, there are several variations of silt fence including varieties with draw cords for easy maintenance and pre-sewn pockets to accept the use of field-driven steel posts. SI Geosolutions provides master rolls
of our high quality geotextiles to fabricators and marketers of these valuable BMPs in addition to offering smaller rolls for rapid installation.
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Stone Filter Berm
This BMP is a temporary ridge of loose gravel, stone, or crushed rock. It slows and filters storm water flow, diverting it from exposed traffic areas. Diversions constructed of
compacted soil may be used where there will be little or no construction traffic within the right-of way. They are also used for directing runoff from the right-of-way to a stabilized outlet. For maximum
performance, GEOTEX woven monofilament geotextiles should be used as a porous foundation filter beneath the berm to prevent undermining and improve stability.
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Sediment Basin
This BMP is a type of settling pond used to collect and store sediment produced by construction activities. A sediment basin can be constructed by excavation and/or
building an earthen dike across a low area or drainage swale. The slopes of the basin should be seeded and covered with LANDLOK degradable erosion control blankets. It functions to detain storm water from larger
drainage areas long enough to allow sediment to settle. These basins typically have controlled release system consisting of a riser pipe and a grassed spillway reinforced with a LANDLOK turf reinforcement mat (TRM),
which allows for the slow release and filtration of storm water runoff. By removing sediment, the basin prevents clogging of offsite conveyance systems and reduces sediment loading of receiving waterways.
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Construction Road Stabilization
During construction, temporary access roads must be constructed so vehicles can operate without
causing erosion. Stabilized construction roads are designed so that water does not puddle or flood the road during wet weather. It typically will have a reinforced vegetated drainage swale along the road to collect
and carry away runoff. Stabilized construction roads should have a layer of crushed stone or gravel which will cover the GEOTEX geotextile, which stabilize and protects the soil below from erosion or contamination
of the imported gravel.
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Stabilized Construction Entrance
The area designated by the contractor where all
vehicles enter should be constructed with GEOTEX geotextiles and large stone. The primary purpose of a stabilized construction entrance is to reduce the amount of soil tracked off of the construction site by
vehicles leaving. The rough surface of the stone will dislodge soil from tires and provide a stable operating surface for traffic. The geotextile separates the stone from the soil below, preventing the large stone
from being ground into the soil. It also reduces the amount of rutting by spreading the weight of the vehicles over a larger soil area than just the tire width.
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Dust Control
These measures reduce the surface and air transport of fine soil particles that may be picked up by wind from a construction site. Although ideally treated as a
permanent measure, vegetation can be established using a LANDLOK S2 erosion control blankets and properly selected seed. The immediate coverage from the blanket and eventual vegetated cover reduces soil exposure and
eliminates air quality concerns. For more information, obtain a copy of the EPA Storm Water Fact Sheet.
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Seeding and Planting
Site specific seeding and plantings provides stabilization of the soil by holding soil particles in place. Vegetation reduces sediment by slowing runoff velocity and permitting greater infiltration. Vegetation also
filters sediment, helps soil absorb water, improves wildlife habitat, and enhances the aesthetics of a site. When vegetation alone will resist the anticipated erosion stresses, LANDLOK erosion control blankets
function as a mulch to enhance the development of vegetation. For channeled flows and steeper slopes, LANDLOK turf reinforcement mats are required to reinforce the grass and expand its performance under more
demanding conditions.
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Buffer Strip
These BMPs are vegetated areas of the site designed to remove sediment from sheet flow. Buffer
(or grass filter) strips are used to decrease the storm water velocity, which helps to prevent soil erosion. This can also be an area of vegetation left undisturbed during construction or it can be a newly planted
area of the site. When establishing a buffer strip on a construction site, LANDLOK erosion control blankets aid to quickly establish vegetation.
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Sod Stabilization
Sodding stabilizes an area by immediately covering the surface with vegetation and providing areas where storm water can infiltrate. Our LANDLOK 407GT is an open weave geotextile
ideally suited as a soil underlayment. Laid on the soil and properly anchored, this product provides continuous reinforcement and support for sod stabilization.
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Stream Bank Stabilization
When a continuous flow channel or stream erodes its banks, basic land conservation practices require the face to be protected from further exposure.
Techniques used for stream bank stabilization are vast and may include combinations of live, natural and synthetic components. Placed horizontally for internal reinforcement within the backfill during
reconstruction, GEOTEX woven geotextiles and GEOFIBERS fiber reinforced soil are very economical solutions. These are typically combined with surface stabilization methods that involve LANDLOK erosion control
blankets and toe protection using BonTerra BIOLOGS and live willow stakes. Once constructed, stabilized stream banks can resist flows twice as strong as before.
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Soil Retaining Measure
These structural BMPs typically involve systems used to hold the soil firmly in its original place or to confine as much as possible within the site boundary.
There are many different methods for retaining soil. Examples of soil retaining measures include steepened slopes, vegetated wrapped face walls and segmental retaining walls. These systems also include GEOTEX woven
geotextiles and GEOFIBERS fiber reinforced soil as primary reinforcement and LANDLOK turf reinforcement mats for surficial protection and revegetation.
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Earth Dike
This structural BMP is used to protect work areas during construction from upslope runoff and divert sediment-laden storm water to appropriate traps or stable
outlets. Ideally, the dike consists of compacted and seeded soil protected with LANDLOK turf reinforcement mats to extend the hydraulic performance of the vegetation used to stabilize the channel. This lining system
is much more cost-effective and features higher pollutant removal efficiency than rock riprap.
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Drainage Swale
Moderate storm
water flows during and after construction is typically handled through a lined earthen channel called a drainage swale. While traditional lining systems include rock riprap, asphalt or concrete, these systems are
best constructed by incorporating a LANDLOK turf reinforcement mat to reinforce the vegetation. This helps filter sediment and promotes groundwater recharge at up to half the cost of rigid lining systems.
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Interceptor Dike
Vegetated ridges of compacted soil and excavated depressions are used to keep upslope runoff from crossing areas where
there is a high risk of erosion. These interceptor dikes can be constructed to direct storm water toward a stabilized outfall or sediment trap, or simply away from areas having a high risk of erosion. Since they
collect runoff and convert it to concentrated flow, establishing should stabilize the surface of interceptor dikes vegetation reinforced with LANDLOK turf reinforcement mats instead of other hard armor lining
systems.
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Subsurface Drain
This BMP differs from others as it addresses challenges associated with ground water, not surface
water. A subsurface drain is a perforated pipe or prefabricated drainage composite placed at a designed depth and grade. It is used to drain an area by lowering the water table. Regardless of the drainage media, the
perimeter should be covered with GEOTEX nonwoven geotextiles to filter fine soils from entering the drainage system.
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Storm Drain Inlet Protection
This structural BMP is a filtering mechanism placed in or around inlets to trap sediment before it has a chance to enter the drainage system. If properly installed and maintained these
devices virtually eliminate the potential of clogging the inlet, storm drainage systems, or receiving channels. Inlet protection may be constructed with natural or man-made components or a combination thereof.
Combined systems includes gravel, concrete blocks, or sod typically underlain with a GEOTEX nonwoven geotextile to help stabilize and filter unwanted soil from contaminating the system. Manufactured BMPs are
fabricated using GEOTEX geotextiles and a durable support frame. Examples include Silt Sack from Atlantic Construction Fabrics.
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Sediment Trap
Simply excavating a small pond or placing an earthen embankment across a low area on the site or within the drainage swale creates traditional sediment traps. A spillway is then built using
LANDLOK turf reinforcement mats in lieu of aggregate to slow and filter the release of runoff. The trap retains runoff long enough to allow silt to settle. Any time rock riprap is required, a GEOTEX woven
monofilament geotextiles should be placed on the subgrade to improve the stability of the trap.
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Detention/Retention Pond
This
BMP is used to collect and store storm water runoff after construction activities have ceased. A detention or retention pond can be constructed by excavation and/or building an earthen dike around the perimeter. The
slopes of the basin should be seeded and covered with LANDLOK turf reinforcement mats. It functions to hold storm water from long enough to allow sediment to settle and ground water to recharge. These ponds may also
have a controlled release system for 100-year storm events consisting of a riser pipe or a grassed spillway, which would also be reinforced with LANDLOK turf reinforcement mat (TRM). This allows for the slow release
and filtration of storm water runoff. By removing sediment, the pond reduces sediment loading of receiving waterways.
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Outlet Protection
Anytime piped or channeled flow empties into a wider drainage area, a structural BMP should be constructed to reduce the speed of concentrated storm water flows, scour potential, and downstream erosion.
Although typically achieved with rock riprap or paved aprons, PYRAMAT high performance turf reinforcement mats (HPTRMs) can be used instead as long as proper vegetative selection and installation procedures are
maintained.
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Check Dam
In order to reduce the speed of concentrated flows in storm water conveyance channels, a check dam is
commonly constructed using stone underlain with a GEOTEX woven monofilament geotextile for improved stability. The slower runoff significantly reduces erosion and gullying and allows sediment to settle out of the
flow. Geosynthetic check dams can also be constructed by installing a silt fence system using GEOTEX woven geotextiles and a metal or polymeric grid backing.
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Gradient Terrace
Small embankments constructed along the face of a soil slope at regular intervals are referred to as gradient terraces. They enhance storm water quality by
capturing surface runoff and directing it to a stable outlet at a speed that minimizes erosion. Gradient terraces are typically seeded and lined with LANDLOK turf reinforcement mats.
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Dewatering
One method to remove excess sediment from storm water at a construction site is by dewatering. The most common procedure is pumping water out of areas where
it does not otherwise drain off, such as excavated areas, sediment basins, and sediment traps. Dewatering may also include methods used to lower the ground water table to provide a stabilized area for construction.
These discharges can be pumped into a GEOTEX tube for rapid dewatering of the sediment-laden runoff.
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Porous Pavement
Promoting
ground water recharge in most areas of the country is very important to minimize runoff and the erosion potential of soils. Pavements can be designed and constructed to promote infiltration using modular concrete
blocks or porous concrete or asphalt. Precast blocks are typically laid on a sand-bedding layer, which is underlain by a GEOTEX geotextile and filled with soil or loose stone. Poured-in-place concrete or asphalt
employs a similar design, but usually has a greater pavement thickness for heavier anticipated loads.
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Bioretention
This is a
technique that utilizes soils and both woody and herbaceous plants to remove pollutants from storm water. Runoff is conveyed as sheet flow to the treatment area, which consists of a buffer strip, sand bed, ponding
area, plants and a mulch layer. Plant establishment in these areas is enhanced with a variety of products from SI Geosolutions such as BioLogs for herbaceous plants, LANDLOK erosion control blankets for vegetated
buffer strips. Lastly, the sand bed should be wrapped with a GEOTEX nonwoven geotextile long-lasting filtration performance. For more information, obtain a copy of the EPA Storm Water Fact Sheet.
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Infiltration Drainfields
These are large structures designed to promote the percolation of collected storm water into subsoils. The
system is usually constructed of a pretreatment structure, a manifold system, and a drainfield. The storm water is distributed evenly over the drainfield through the use of perforated pipe. The runoff then
percolates through underlying aggregate and a filter, such as a GEOTEX nonwoven geotextile, and then into the water table. The flow path removes all contaminants from the storm water. For more information, obtain a
copy of the EPA Storm Water Fact Sheet.
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Infiltration Trenches
This is a 3 to 12-foot deep, excavated trench constructed in
urban areas (or places with limited land availability), filled with free-draining stone and lined with a geotextile. The purpose of this trench is to remove contaminants from storm water and promote groundwater
recharge. Typically, a style such as our GEOTEX 111F woven monofilament geotextile is used as the critical filtration element in the system. For more information, obtain a copy of the EPA Storm Water Fact Sheet.
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Sand Filters
A standard sand filter system consists of several chambers or basins that treat storm water runoff by removing a vast
amount of the pollutants. The final chamber of basin usually contains a rigid grate, which is wrapped in a geotextile, such as GEOTEX 117F woven monofilament geotextile. These systems are very effective in retrofit
or new urban construction projects. For more information, obtain a copy of the EPA Storm Water Fact Sheet.
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Wetlands
Wetlands are
those areas of land typically inundated with water that supports vegetation. They can be incidental, natural or constructed. Designs can vary from a shallow marsh, extended detention, pond system, and pocket
wetlands. In any case, our LANDLOK and BONTERRA degradable erosion control products are natural solutions to support vegetative growth and plant establishment. For more information, obtain a copy of the EPA Storm
Water Fact Sheet.
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