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Stormwater System Mapping

Stormwater Inventory Crew Member (Greg) on SR 7 near Alder Lake 
Stormwater Features Inventory Crew Member (Terran) on SR 162 in Orting 
 Field Staff Performing Stormwater
Features Inventory near
Alder Lake (top) and in Orting (bottom)

A complex system of drainage inlets, pipes, ditches, stormwater treatment and flow control facilities, and other structures direct and manage stormwater running off of WSDOT property. The stormwater management system discharges stormwater to surface water bodies, connect to municipal stormwater systems, or detains stormwater so that it will infiltrate into the ground.

WSDOT uses Geographic Information System (GIS) software to store and manage a digital inventory of its stormwater management system. Mapping and documenting the system helps WSDOT operate and maintain the system, identify illicit discharges into the system, and prioritize retrofits to improve the system.


As required by WSDOT's municipal stormwater permit, WSDOT mapped all known stormwater outfalls and structural stormwater treatment and flow control facilities (BMPs) by March 2014. Continued efforts will map and field-verify WSDOT's complete stormwater system including:

  • outfalls, discharge points, and BMPs found, modified, or newly constructed
  • connection points between WSDOT and other public entities
  • associated drainage features conveying highway runoff to WSDOT outfalls and discharge points
  • drainage areas associated with WSDOT outfalls and discharge points

The Stormwater Features Inventory Program staff identify stormwater management system features from as-built construction plans and supporting documents and enters them into a database. Staff also collect stormwater feature data in the field using global positioning system (GPS) equipment to verify and update existing data and enter new data into the database.

Underground Injection Control (UIC)

Injection wells include drywells and infiltration trenches containing perforated pipe. Washington regulates discharges of fluids into injection wells to prevent groundwater contamination. The UIC Program regulations require WSDOT to ensure injection wells meet the non-endangerment performance standard. WSDOT has registered and assessed all known existing UIC facilities and continues registering new UIC facilities with the Department of Ecology.

To register a new UIC, refer to the instructions in Chapter 2 of the Highway Runoff Manual.

Standard Operating Procedures and Manuals