Iowa Stabilized Construction Entrance Detail
Adjacent to the Missouri, Mississippi, and the Big Sioux rivers, Iowa is the only state whose East and West borders are almost entirely formed by rivers. Before western settlements in the region, Iowa historically contained millions of acres of wetlands, many of which were drained and converted to agricultural land. A vast majority of these wetlands have been emptied and replaced by prairie and agriculture; combined, these make up 90% of the geological landscape of modern Iowa. The drainage system created to drain the wetlands continues to direct runoff water throughout the state. Stormwater is collected in several natural and artificial lakes; the most notable of these is the chain of lakes known as the Iowa Great Lakes.
The surface waters in Iowa are used for agricultural irrigation and public drinking water, and therefore are critical to the state's economy and public health. Another vital source of water in Iowa is its groundwater aquifer systems, including shallow alluvial aquifers and deeper bedrock aquifers that support municipal and agricultural water supplies. Both of these resources have been overused and contaminated, limiting their ability to supply the state with high-quality water. The ecosystem also suffers from declining water quality as the list of endangered species lengthens.
The mitigation and reversal of these concerns is the responsibility of the residents, visitors, businesses, and government agencies within the state. Recognizing the main points of pollution introduction into the stormwater drainage system is the first step in protecting the purity of the surface waters. Acting on this knowledge and working together to create and implement plans that mitigate these pollutants is vital to improving and protecting Iowa's safety.
IOWA Department of Natural Resources (DNR) NPDES Stormwater Construction Permits
Iowa's Department of Natural Resources (DNR) administers the National Pollution Discharge Elimination System (NPDES) permit program, which regulates all surface water discharges. The NPDES stormwater permit program requires construction, industrial, and municipal operators to obtain an NPDES permit before commencing activity. NPDES permits are required before any construction activity that disturbs an area equal to or larger than one acre.
The most common permit for construction activity is the Iowa NPDES Construction Stormwater General Permit, which authorizes stormwater discharges associated with construction activities. (Storm Water Discharge Associated with Construction Activities). To obtain an NPDES permit, the construction site operator must submit a Notice of Intent (NOI) that describes the scope of the construction plan and the timeline for the project. Another necessary step in receiving a NPDES permit is to create a SWPPP (Stormwater Pollution Prevention Plan). The SWPPP identifies probable sources of pollution discharge from the construction area and the techniques to mitigate their introduction into the stormwater system. Guidance for choosing techniques, also called Best Management Practices (BMPs), is listed in the Iowa Construction Site Erosion Control Manual.
Stabilized Construction Entrance Detail
One of the first BMPs implemented on any construction site is a stabilized construction entrance, designed to prevent erosion and sediment from tracking off the site on vehicle tires. The stabilized construction entrance works in conjunction with other BMPs, including street sweeping, sediment traps, silt curtains, erosion fences, and vehicle egress sediment trapping. Temporary construction entrances are placed at all egress points from the construction site where traffic will exit directly onto a paved roadway or public right-of-way. This Stabilized Entrance works by removing soil and other pollutants from construction vehicles' tires.
All construction entrance BMPs require regular maintenance to ensure proper function. In addition, street sweeping is necessary to remove any debris that escapes the entrance and is deposited on the active roadway. Inspections must be conducted at least weekly and after storm events, with maintenance performed as needed to ensure the entrance remains effective.
Gravel Construction Entrance
The Manual includes an example stabilized construction entrance design that uses a traditional aggregate-based system to clean vehicle tires before they exit the job site. A stone-stabilized construction entrance is created by installing a pad of 2-inch crushed rock or gravel. The area is filled to a minimum depth of 6" over a 50' length. The rough surface created by crushed stone captures sediment and debris on vehicle tires. Rocks should be sized to the largest vehicles on site to prevent traffic hazards. Small stones may be tracked onto the active roadways or become lodged between dual-tire vehicles and expelled at high speeds.
The entrance should be monitored daily as the gravel will become compacted and saturated with sediment and debris. When the surface is no longer rough, operators must introduce additional aggregate to ensure adequate performance. If the aggregate entrance is ineffective at removing sediment from vehicles, the pad length must be extended to protect public roads and the stormwater system from sediment effectively. A wheel wash is commonly added to a gravel entrance to remove any pollutants that still cling to the vehicle.
Wheel Wash
When a stone-stabilized construction entrance is not sufficient to contain sediment tracking onto the roadway, a wheel wash is often used. Wheel washes can be used as a standalone BMP or as a supplement to an aggregate construction entrance. A wheel wash, wash rack, or tire wash station is an area where a vehicle can receive additional cleaning from pressurized water to clean vehicle tires. Wheel wash stations will require power and water to operate. The wheel wash requires a water supply and the installation of a sediment basin to collect, filter, and appropriately discharge the used water.
FODS Trackout Control System
The FODS Stabilized Construction Entrance System is a modular, reusable BMP designed to minimize construction site track out. The system is comprised of durable 12' wide by 7' long matting, which is formed into pyramids. The pyramids create a rough surface, which causes tire treads to spread open and release trapped debris.
Compared to traditional techniques, FODS offers several benefits to site operators. The FODS system does not degrade or compact over time and is up to 59% more effective than aggregate-based systems. FODS can be installed on any substrate and do not require power or water to operate. Because the system does not use rock, there is a risk of stones entering the roadways or being expelled from dual-tire vehicles.
Because the system is more effective than rock, the mats are well-suited for compact work environments. A 1x5T mat configuration (35' extended) is commonly used to replace a 70' rock entrance while providing a wide turning radius for exiting traffic. The mats offer significant savings for contractors, as they can be reused for 10+ years, eliminating the cost of construction entrance materials. FODS can be installed in as little as 30 minutes and can be anchored to dirt or on concrete and asphalt in urban settings.
The system can be deployed in as little as 30 minutes, allowing contractors to relocate and reuse it as needed on each project. The mats are designed to be reused on multiple projects throughout their 10+ year lifespan.