New Mexico Construction Track-Out Controls BMPs
New Mexico Offsite Tracking Prevention BMPs
As the fifth largest state in the nation, New Mexico is home to a variety of ecosystems including the beautiful desert landscape of the White Sands National Park to the vast San Juan mountain range and the Gila National Forest. A third of the state's land is managed by the US Forest Service and Bureau of Land Management conservation to preserve the 84 national monuments including natural and historic features. The state has five major river systems including Rio Grande, the nations fourth longest river, most of which have been dammed to provide water sources for agriculture.
The National Pollution Discharge Elimination System (NPDES) Permits
The Clean Water Act of 1972 established regulations on discharges of pollutants into US waters and manages construction, industrial and municipal activities through the National Pollution Discharge Elimination System (NPDES). The NPDES program requires operators to obtain permits for any discharges into surface waters. To obtain a permit, operators must either apply for an individual permit or comply with the Construction General Permit. In order to apply for coverage under the Construction General Permit, operators are required to submit a Notice of Intent as well as a Temporary Erosion and Sediment Control Plan (TESCP), also called Stormwater Pollution Prevention Plan (SWPPP), which outlines the potential sources of pollutants on the project and the techniques which will be used to contain and minimize pollution throughout the project. The specific techniques are referred to as Best Management Practices or BMPs. One of the first BMPs to be installed on any construction project is the Stabilized construction entrances/exits. In addition, the TESCP will outline maintenance schedules which ensure that the BMPs remain effective throughout the project.
Construction Track-Out Control BMPs
The EPA defined Construction Track-Out Controls in the purpose of these Construction Track-Out Controls are to minimize sediment that is tracked onto impermeable roadways by construction vehicle traffic. If not contained, soils and other pollutants can be washed into storm drains will degrade water quality of rivers and lakes. The EPA's National Menu of Best Management Practices for Stormwater - Construction lists a number of techniques that are commonly used to stabilize construction entrances including gravel pads, washing stations, shaker racks, and manufactured devices.
With any Construction Track-Out Controls, proper maintenance is required to minimize sediment from escaping the job site. Entrances should be inspected on a regular schedule as well as after storm events to determine if maintenance is required. In addition to the stabilized entrance, street sweeping is conducted regularly to capture sediment that is not contained by the entrance.
Stone Stabilized Construction Entrance/Exit BMP
One of the most common BMPs is a pad of crushed stone, concrete or other aggregate material which is laid over a geotextile filter fabric. The aggregate creates a rough surface which helps to dislodge debris from vehicle tires. The New Mexico DOT includes a rock style construction entrance in their Standard Drawings (603-01-7/7 Offsite Tracking Prevention). The NM DOT NPDES Manual defines a minimum of 50' length of the exit when using aggregate systems. The entrances must be regularly inspected to determine if maintenance is required. Additional aggregate is brought in to re-grade and top dress the aggregate to restore effectiveness after the aggregate becomes compacted and saturated with soil.
At the end of the project the aggregate and filter fabric must be excavated and removed prior to final stabilization.
Wash Station Construction Entrance BMP
When a aggregate entrance is not sufficient to contain the majority of sediment from vehicle traffic, other BMPs can be used to replace or supplement the stone pad. A common supplemental BMP is a wash station which uses pressurized water to remove soil from vehicle tires. Some systems use a filter system to reduce the water that is required for operation, but wash stations will require a water and power source throughout the project.
Shaker Rack, Cattle Guards, and Exit Grids
Shaker racks are another technique that is used to shake loose debris from vehicle tires and are commonly used to supplement a gravel tracking pad. This technique uses a structure usually consisting of steel pipes to vibrate vehicle tires as they drive over helping to dislodge sediment from tires. Voids are commonly created below the steel structure to capture sediment as it is dislodged from tires. When the void becomes full of sediment after regular use, or after storm events, the shaker rack structure is removed and the void is excavated to restore performance.
FODS Trackout Control System
The FODS Trackout Control System is a Construction Track-Out Control BMP which is made of HDPE mats which are formed into pyramid structures on the surface. The pyramids create a rough surface which deforms and flexes vehicle tires to open tread lugs and dislodge debris. This BMP is commonly used without additional trackout control BMPs such as a stone pad. The Trackout Control Mats are 12' wide x 7' long and are most commonly installed in 28-35' lengths to replace 50-70' aggregate tracking pads. Vehicle tires contact the tips of the pyramids which allows the voids between the pyramids to capture debris. When the void fills with sediment or after storm events, the mats are cleaned to remove sediment to restore performance. The mats are cleaned using a manual cleaning shovel or swept using a street sweeper or skid steer with broom attachment. In many cases, the maintenance of the entrance can be conducted as part of the regular street sweeping schedule.
The FODS Trackout Control System provides an effective solution to construction and industrial track-out which can be effectively used in short term and long term or permanent applications. The mats can be anchored to any substrate including dirt, concrete and asphalt. Compared to traditional aggregate style entrances, FODS has been shown to reduce street sweeping by 59% on high traffic volume sites. In addition, the FODS System is a durable solution which can be reused throughout the 10+ year life of the product.
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Additional Resources
EPA National Menu of Best Management Practices (BMPs) for Stormwater-Construction
EPA Construction Track-out Controls (formerly Construction Entrances)