Louisiana Temporary Construction Entrance BMP
Bordering the Mississippi River to the east and the Gulf of Mexico on the south, the state of Louisiana has developed a major seafood industry supplying 25% of the nation’s total annual volume.
Louisiana Department of Environmental Quality
In 1972, the EPA revised Clean Water Act and established a permit program for all discharges into surface waters. The Louisiana Department of Environmental Quality (LDEQ) administers the Clean Water Act through the Louisiana Pollutant Discharge Elimination System (LPDES) permit program which enables oversight of all construction, industrial and municipal activities which may impact the aquatic ecosystems.
All construction operators which disturb an area of one acre or greater are required to obtain a LPDES Stormwater Permit. Construction sites which are less than five acres may be able to use the Small Construction Activities permit (LAR200000), while sites larger must use the general Storm Water permit (LAR100000). The construction operators will apply
As part of the permit application process involves the creation of a Storm Water Management Plan (SMP). The Storm Water Management Plan includes various components which are reviewed by the permit authority including blueprints of the proposed work, potential sources of pollution and sedimentation from runoff, and a list of techniques which will be used to mitigate and reduce the impact of the pollution sources. The techniques used are referred to as Best Management Practices or BMPs.
One BMP that is needed on nearly all job sites is the Temporary Construction Entrance.
Temporary Stone Construction Entrances
A temporary construction entrance is a technique that is used to reduce the amount of sediment and debris that is dragged out from job site exit points onto the paved roadways. Sediment that is deposited on paved roadways can easily wash down storm drains into the rivers and lakes causing harmful sedimentation. To minimize the impact on water sources, construction operators will install a temporary construction entrance to clean sediment and debris from vehicle tires as they exit the site.
Described in the Louisiana Coastal Zone BMP: Urban Storm Water Runoff Manual, a temporary stone construction entrance is built by placing a filter cloth underneath a gravel pad to stabilize the ground and to trap sediment in the rocks as vehicles leave the site. Bull rock or similiar coarse aggregate should be used to ensure a rough surface is created as it is more effective at dislodging debris. The filter cloth mentioned in the manual is used to keep the aggregate from sinking into the substrate and to prevent rutting. Dimensions for the entrance as described in the manual are a minimum of 6” in depth, 50’ in length, 20’ in width, but should allow vehicles to enter and exit the site while maintaining contact with the pad.
The gravel pad should be wide enough to provide an exiting lane for the largest vehicles that will be accessing the site. This technique is used at any and all construction site exits where there is a risk of mud, dust, sediment or debris to be deposit fed onto impermeable roadways. The temporary stone construction entrance pad should include a turning radius when installed perpendicular to an active roadway to allow vehicles to turn in both directions as they leave the site.
Additional BMPs may be needed to ensure stabilization when the entrance crosses a ditch.
After establishing the construction entrance, contractors should continue to monitor for effectiveness as the job progresses. As vehicles drive over the gravel pad, the rocks will become saturated with sediment and debris as well as compacted which reduces the effectiveness of the entrance. When sediment is being tracked onto the roadways, the contractors are required to perform maintenance on the entrance which includes adding aggregate to the entrance or replacing the bull rock. In addition, any debris that is deposited onto the roadway must be swept regularly before it can be washed into the storm drains.
In cases where the temporary stone construction entrance is not adequately containing sediment and debris, a wash rack may be installed. A wash rack uses pressurized water to clean mud and debris from vehicle tires. The wash rack must have proper drainage into a sediment basin to prevent sediment laden runoff from leaving the job site. Wash racks are more effective than traditional stone construction entrances, but require a source of water and power to operate.
FODS Reusable Stabilized Construction Entrance BMP
The FODS Trackout Control Mat System is a reusable and effective type of construction entrance which can increase compliance with stormwater permit regulations. The system is composed of a single layer HDPE matting material with is formed into pyramid shaped structures on the surface. As vehicles drive over the mats, the pyramids flex and deform tires allowing debris trapped in treads to break loose. The mats will hold mud, sediment and debris at the base of the pyramids away from tires. Each mat is 12’ wide and 7’ long and are typically arranged in series to create a single lane for exiting traffic, however, the system is modular and can be installed in various configurations to fit the needs of each project.
The system is highly effective at removing sediment from vehicle tires and has been shown to reduce the need for street sweeping by 59% compared to traditional rock entrances. The system is designed to be relocated and reused over and over allowing contractors to save significant costs throughout the 10+ year lifespan of the product. FODS can be installed on grade, or over concrete and asphalt enabling more flexibility when working on urban projects. The system does not require a water source or power allowing contractors to effectively mitigate sedimentation and trackout in many locations and conditions.
Maintenance of the FODS system is completed when 2.5” of sediment builds between the pyramids. The maintenance process involves sweeping the mats to remove sediment and is usually completed using a skid steer with a broom attachment or manually using a FODS shovel.
This BMP is designed to be used as a stand-alone solution for construction site trackout.
Additional Resources:
LDEQ Storm Water Permit Resources
LA DOTD Standard Specifications (Part II - Earthwork)