Washington Stabilized Construction Entrance / Exit (C105)

The state of Washington occupies a distinctive geographic position in the Pacific Northwest, bounded by the Pacific Ocean on the west and the Salish Sea on the north. Its dramatic geography ranging from rocky and rugged coastlines to fertile in-land river valleys and high mountain ranges creates a climate dominated by legendary frequent rainfall, particularly on the west side of the Cascade Mountains. The abundance of precipitation sustains a dense network of interconnected rivers, lakes, and wetlands that form the foundation of Washington’s natural ecosystems.

Among the most iconic features of this beautiful ecosystem is the salmon population. Every year, salmon must migrate upstream from the ocean to their native spawning grounds, relying on clean, cold, unobstructed natural waterways. The presence of salmon is more than ecological it has long been a cultural and economic, underpinning Native American traditions, local fisheries, and regional identity. Protecting water quality in Washington is therefore not only an environmental responsibility but also a legal and social imperative.

To safeguard this delicate natural balance, the federal National Pollutant Discharge Elimination System (NPDES), established under the Federal Clean Water Act, plays a central role. Washington’s Department of Ecology is responsible for administering NPDES permits across the Washington state, ensuring that construction, industrial, and municipal activities maintain compliance with strict water quality standards.

Washington NPDES Stormwater Permits

Under the Clean Water Act signed into law in 1968, any discharge of pollutants into waters of the United States must be regulated. In Washington, this mandate is carried out by the Department of Ecology (DOE) through its NPDES Stormwater Permitting program. Construction operators, industrial facilities, and municipal governments must apply for permits if their activities risk introducing pollutants into state waters.

Permit Application and Planning

Operators seeking coverage under the NPDES Construction Stormwater General Permit or Stormwater Pollution Prevention Plan (SWPPP) and must submit detailed plans that outline how they will use Best Management Practices “BMP’s” to control pollutants on their sites. These plans typically include:

Temporary Erosion and Sediment Control Plans (TESCPs) for short-term, site-specific activities.
Stormwater Pollution Prevention Plans (SWPPPs) for larger or more complex projects requiring long-term mitigation strategies.

Both plans require operating contractors to identify pollution sources such as exposed soils, vehicle traffic, or chemical storage—and detail the Best Management Practices (BMPs) that will be used to minimize risks.

Regional Manuals

Recognizing Washington’s diverse geography, the Department of Ecology issues stormwater manuals tailored to both western and eastern Washington. Western Washington, with its heavy rainfall and dense urban areas like Seattle, Olympia, and Tacoma, has stricter design criteria than the drier eastern side of the state. Contractors must carefully consult the appropriate manual, as BMP requirements vary based on hydrology, soils, and seasonal weather conditions.

Applicability

Any construction activity disturbing one acre or more of land, whether vertical, residential, or heavy civil, must obtain coverage under the Construction Stormwater General Permit. Even smaller projects may require permits if they fall under certain criteria and are part of a larger common plan of development. For most contractors, the general permit provides a streamlined process, but individual permits may still be required for sensitive or high-risk sites.

The department creates Stormwater manuals to assist operators as they develop SWPPPs and advises about Best Management Practices (BMPs) that can be used to minimize pollution. Manuals are created for both the western and eastern parts of the state and requirements will vary depending on where the site is located.

C105 Stabilized Construction Entrance / Exit

One of the first BMPs that is established on a site is the Stabilized Construction Access or Stabilized Construction Entrance/Exit. As the original and most fundamental BMPs outlined in Washington’s stormwater manuals is the Stabilized Construction Entrance/Exit (SCE), designated as C105.

Purpose

The C105 entrance/exit serves as the first line of defense against construction sediment trackout, the process by which soil, mud, and contaminants are carried off construction sites on vehicle tires. Trackout is one of the most visible forms of stormwater pollution, as sediment deposited on public roads can quickly enter storm drains and waterways. Beyond regulatory compliance, preventing trackout also improves community relations by reducing or eliminating dust, mud, and road hazards of rocks be drug out on to the road near construction sites.

Traditional Design Standards

Washington’s manual specifies a rock-based design for C105 entrances:

Foundation: A layer of geotextile fabric placed to separate rock from soil and prevent intermixing.
Aggregate Layer: A 12-inch-thick layer of quarry spalls (large angular rock). The use of crushed concrete, cement, or calcium chloride is prohibited due to potential pH impacts on stormwater.
Dimensions: Minimum 15 feet in width and 100 feet in length, though additional entrances may be required for larger sites.

Because it is often difficult to predict access points during project planning, the manual recommends contractors prepare for the installation of additional entrances as site conditions evolve.

This BMP is designed to contain sediment and contaminants that would be tracked out on vehicle tires. The manual describes a traditional approach to establishing a Stabilized Construction Access which includes a geotextile fabric underneath a 12” thick layer of quarry spalls; crushed concrete, cement, or calcium chloride are not permitted because they will affect the stormwater pH level. The rock entrances are constructed 15’ wide and 100’ in length and must be established at each entrance/exit location. As larger sites progress through each phase, additional entrances may need to be established. The manual recommends that contractors prepare for additional entrances than were originally included in the TESCP (or SWPPP) because “it is difficult to determine exactly where access to these project will take place.”

Maintenance Requirements

Rock entrances require constant maintenance:

As soil compacts into the rock, new spalls must be added to refresh the entrance.
Entrances often need to be lengthened to maintain proper effectiveness.
Any sediment deposited on adjacent roadways and highways must be immediately removed using mechanical sweepers or hand tools.
If rock entrances are no longer sufficient, wheel wash stations must be added.

At project completion, temporary entrances must be removed, geotextiles pulled up, and disturbed soils stabilized with new topsoil and revegetation.

For more Washington State Approved C-105 entrances check out the Washington Storm Water: Construction BMP Guide.

C106 Wheel Wash

When rock construction entrances are not adequately preventing tracking, wheel wash stations can be installed. Wheel wash stations with pressure washers can effectively clean tires of vehicles when they are placed adjacent to paved roadways. The sediment laden water must be contained or diverted to a sediment basin within the site.

Wheel wash stations are either prefabricated or constructed on-site from concrete, often equipped with high-pressure sprays to dislodge soil from tires. These systems can be highly effective but require careful management:

Water handling: Wash water must be collected, controlled, and directed to a sediment basin, preventing untreated discharges.
Space and flexibility: Permanent or semi-permanent structures reduce contractor flexibility when access points change.
Cost: Installation and operation are expensive compared to simpler BMPs.

While wheel wash systems provide a valuable backup, they are often no a practical solution for dynamic construction sites.

FODS Reusable Construction Entrances

FODS Mats are made from high-density polyethylene (HDPE), which is a non-toxic, extremely durable plastic. Each mat is molded with a unique pyramid pattern across its surface. As vehicles drive across, the pyramids are engineered to flex tires and scrape away sediment lodged in the tread. Unlike rock entrances, which rely on aggregate displacement, FODS mats apply a researched and tested predictable mechanical process that is highly effective at dislodging mud.

Independent studies have shown that FODS mats can achieve up to a 60% - 80% reduction in street sweeping costs compared to traditional rock entrances.

Advantages Over Traditional Methods

Mobility: Mats can be installed, removed, and relocated within minutes—ideal for sites where access points change.
Durability: Each mat has a service life exceeding 10 years, allowing reuse across multiple projects.
Maintenance: Cleaning requires only sweeping, broom attachments, or manual shoveling—no trucking and disposal of quarried rock.
Environmental Benefits:
- No quarrying, hauling, or disposal of rock, reducing carbon emissions.
- Mats are fully recyclable at the end of their service life.
- Reduced dust and PM-10 emissions compared to rock.
Cost Efficiency: Initial investment is offset by long-term reuse and reduced maintenance costs.

FODS Mats can be relocated throughout the project allowing contractors to have more flexibility when planning their construction operations. In addition the system is designed be used on multiple projects throughout their 10+ year lifespan making them very cost effective for both contractors or industrial operators.

When sediment becomes compacted on the mats, they must be maintained to continue preventing trackout. The mats can be cleaned using a street sweeper with an adjustable head, a skid steer with broom attachment, or manually with a shovel. Because there is no rocks used in the system, remediation is often significantly reduced compared to traditional construction access techniques.

FODS Approved For Use By Washington Department of Ecology

The FODS Trackout Control System has been reviewed by the Washington Department of Ecology and has been approved for use throughout the state. Contractors in the state may benefit from the use of the FODS Construction Entrance without seeking any additional approval by the department.

Compliance, Sustainability, and Long-Term Value

Washington’s emphasis on stormwater quality reflects both regulatory mandates and the state’s cultural commitment to protecting its waterways. BMPs like the C105 entrance have long served as the default solution, but modern construction practices demand improvement in the form of better alternatives that balance product compliance, cost, and environmental responsibility.

FODS mats align with all three priorities:

Compliance: Approved for use under Washington’s manuals and fully NPDES-compliant.
Cost Savings: Lower lifecycle costs due to reuse and reduced need for street sweeping and aggregate replacement.
Sustainability: Less waste, lower emissions, and produced using recycled material while also being recyclable at the end of the product lifecycle.

For contractors working in Washington, particularly in sensitive watersheds near salmon-bearing streams or urban areas with active stormwater enforcement, FODS provides a best-in-class solution.

Conclusion

The Washington Stabilized Construction Entrance/Exit (C105) BMP plays a critical role in stormwater management, serving as the frontline barrier against sediment leaving construction sites. While rock entrances and wheel wash systems remain part of the state’s regulatory framework, innovations like the FODS Trackout Control System are rapidly reshaping how contractors approach compliance.

By combining durability, mobility, labor savings and environmental responsibility, FODS mats reduce the operational burdens that have long been associated with traditional methods while delivering measurable, third-party verified performance improvements. With Department of Ecology approval, Washington contractors now have the flexibility to adopt this modern BMP with confidence. Projects such as the recent Sound Transit Light rail expansion, Seattle’s Waterfront Park Reconstruction used FODS to protecting water quality, maintaining regulatory compliance, and advancing sustainable construction practices across the state.