Nebraska Stabilized Construction Exit Detail

The triply landlocked state of Nebraska is home to many stunning natural features, ranging from the towering Chimney Rock to the historic Ashfall Fossil Beds. The state's open prairie also creates a prime landscape for agriculture and livestock production. Nebraska's farms and ranches utilize about 44 million acres of land, supporting a major agricultural and livestock economy. Agriculture is a primary economic driver in Nebraska, with cash receipts for all farm commodities exceeding $31 billion in recent reporting. Portions of this industry include biofuel, corn, and cattle exports, which account for nearly 6% of the national total income.

The success of these industries relies upon the health and quality of the stormwater and watershed system within the state. Nebraska boasts nearly 80,000 miles of rivers and streams, many of which converge into the Missouri River, which flows on the eastern border of the state, and the Platte River, which cuts through the middle of Nebraska. In addition to these rivers, the natural aquifer beneath Nebraska's land is a vital water resource that supports the state's economic success and growth. The health of these water sources depends upon the observant practices of the state's industries.

The Nebraska Department of Environment and Energy (NDEE) Stormwater Permits

The federal government initiated the Federal Water Pollution Control Act in 1948, which was amended in 1972 and subsequently became the Clean Water Act (CWA). These initiatives led to the development of laws and guidelines for industries and construction projects to mitigate pollutants introduced into the watershed system. Most notable of these requirements is the National Pollutant Discharge Elimination System (NPDES) Permit created by the EPA. This permit requires industries and construction operators to develop plans that will reduce or eliminate the negative impact of their activities.

The Nebraska Department of Environment and Energy (NDEE) administers the state's NPDES permitting program. Construction stormwater permit coverage is required for sites that disturb one acre or more of land, or that are part of a common plan of development of that size, and NDEE must receive the Construction Stormwater Notice of Intent at least seven days before land clearing and grading begin.

In Nebraska, the SWPPP serves as the primary guidance document for stormwater-related strategies on a job site. Operators carefully design their SWPPPs to describe the methods and devices that will be implemented on site for erosion and sediment control purposes. The plan provides an overview of all potential pollution sources and specifies which Best Management Practices (BMPs) will be employed to minimize or mitigate contamination. Resources and forms for designing and submitting SWPPP documents can be found on the NDEE NPDES Resource page. For DOT projects, the Construction Stormwater Best Management Practices Pocket Guidebook can be referenced during the planning phase. This guidebook outlines the temporary and permanent measures that must be implemented to create a safe and controlled environment, including the use of silt fences, mulching, inlet protection, and stabilized construction exits.

Stabilized Construction Exit BMP

A Stabilized Construction Exit is usually one of the first practices implemented by an operator before other construction activities. Soil, mud, and other pollutants can cling to the tires of equipment, which can enter storm drains if the sediment is not contained. The Stabilized Construction Exit BMP is designed to prevent excessive sediment from tracking out onto public roadways from construction vehicle traffic. Stabilized Construction Entrances should be installed at every egress point on the site, which will be used by construction vehicles.

A procedural BMP that is used in conjunction with the Construction Exit is strip sweeping. Regular sweeps should be conducted to contain any fugitive gravel, soil, or sediment that is tracked onto the public roads through the entrance. This debris must be swept or vacuumed to prevent pollutants from being washed into the storm drain system, thereby containing sediment-laden water.

Aggregate Construction Exit

The traditional method for stabilized site entrances is to install a gravel tracking pad. This BMP technique uses a layer of crushed rock underlaid by a fiber filter to create a rough surface that can remove sediment from vehicle tires. The dimensions for the construction exit are designed to accommodate the largest vehicles that will access the job site, ensuring sufficient tire rotations. The size of the rock used should be large enough to prevent rocks from becoming lodged between dual tires, which can cause hazards as the stones are expelled at high speeds.

Aggregate-based entrances should be regularly inspected and maintained to ensure optimal performance. Maintenance is required when the aggregate becomes compacted or saturated with soil and debris. Maintaining the gravel entrance may require redressing with additional rock or repairing the geotextile fabric. Construction Entrances will require more frequent maintenance during weather events.

When aggregate construction entrances are not sufficient to mitigate sediment tracking, alternative measures are available.

Shaker Plates, Rumble Plates, Steel Plates, Cattle Guards

Shaker plates are structures that use rows of steel, reinforced plastic, or other materials to create a washboard effect on exiting vehicles. This system resembles a cattle guard and works to remove sediment from vehicles by shaking the tires, which causes sediment and soil to drop from the treads. Heavy equipment is used to create a void below the structure to capture debris. Equipment may also be necessary to install, adjust, relocate, or clean the steel plates.

Wheel Wash Devices

Another method for controlling sediment and pollutants at a construction ingress/egress area is a wheel wash station. In its simplest form, a tire wash is a control method that utilizes a laborer operating a pressure washer to remove remaining sediment and pollutants from vehicles as they exit the construction zone. This method requires the site to have access to a water supply and measures to divert the wastewater to a sediment trap. The wheel stations may also be automated.

FODS Trackout Control System

The FODS Trackout Control System is an effective Construction Entrance BMP for mitigating sediment. The system consists of HDPE panels that are formed into pyramid-shaped structures throughout the surface. The pyramids flex and deform tires in multiple directions to dislodge sediment, rocks, and debris that is lodged between tire treads.

The FODS system is a durable product that can be reused on multiple projects. The system is also easily relocated, which significantly reduces costs on phased projects and over various projects over the 10+ year service life of the product. Construction entrance installation, maintenance, and removal are efficiently conducted without the use of heavy equipment. The system is versatile and can be configured as needed and quickly redeployed on dirt, concrete, or asphalt in under 30 minutes.

The system does not degrade during heavy use or after rain events. The 3" tall pyramids can hold up to 2.5" of sediment, as the tires only come into contact with the tips of the pyramids. When maintenance is required, a pass with a street sweeper or a skid steer with a broom attachment is all that is needed to restore performance. Contractors can integrate maintenance during regular street sweeping to ensure the entrance is always compliant with permit requirements.

The modular FODS system outperforms traditional stone-stabilized construction entrances and is commonly specified at 50% of the length of a stone-stabilized tracking pad to provide equal performance. Additionally, the system is both flexible and cost-effective, allowing contractors to reduce sedimentation and costs on each project where the mats are used.