Construction stormwater best management practice – Vehicle Tracking
Vehicle Tracking
Vehicles leaving construction sites track sediment onto adjoining road ways. This sediment can create serious safety hazards as well as contribute significantly to sediment pollution problems in waterways. Through the use of vehicle tracking pads and street sweeping, the amount of sediment and other pollutants leaving the construction site is limited and the amount of sediment discharged to surface water is decreased. Vehicle tracking pads remove mud from tires and reduce the amount of sediment leaving a construction site.
What is required by the NPDES/SDS construction stormwater permit?
The NPDES/SDS Construction Stormwater Permit states that the tracking of sediment from a construction site onto roadways must be minimized with appropriate best management practices (BMPs) such as stone pads, concrete or steel wash racks or equivalent systems. If these BMPs are not adequate in preventing sediment tracking, street sweeping is required. The permit states that all external washing of vehicles must be limited to a defined area and runoff must be contained to prevent transport of sediment offsite.
Construction site vehicle exit locations must be inspected for sediment tracked onto paved surfaces. Sediment tracked off-site must be removed within 24 hours of discovery to prevent it from being washed away by stormwater and to avoid a safety hazard. It is important to note that the permit requires street sweeping to remove sediment tracked to the street, but it is NOT an alternative to having a vehicle tracking pad. First work to minimize mud and sediment tracked from the site and follow up with sweeping to collect material that has left the site. For full details of the permit requirements, a copy of the NPDES/SDS construction stormwater permit is available online: www.pca.state.mn.us/water/stormwater/stormwater-c
What is a vehicle tracking pad?
A vehicle tracking pad is typically a stabilized pad of aggregate over a geotextile base installed at every vehicle exit utilized by construction traffic. It is designed in a way that when vehicles drive over the pad, the tires sink into the rock slightly and mud is removed. Generally the aggregate used is 1.5 to 3 inches in size and placed in a layer approximately 6 inches thick. However, the MPCA staff has observed that vehicle tracking pads consisting of coarser aggregate materials (2 to 6 inches) are often more effective in many applications. The vehicle tracking pad should be at least 50 ft long but longer pads may be required to adequately clean tires. The amount of construction traffic and frequency of use should be considered when designing a vehicle tracking pad.