Retrofitting an Existing Stormwater System to Meet Numerical Effluent Limits – Stormwater Management at Seattle-Tacoma International Airport

Owned and operated by the Port of Seattle, Seattle-Tacoma International Airport (STIA) is the 28th busiest airport in the world. A Section 401 Water Quality Certification was issued to the Port to allow its expansion projects to proceed. This certification required existing portions of the airport be retrofitted to meet current stormwater standards. In addition, the Port's renewed NPDES permit contained new effluent limits for stormwater discharges that will be effective starting in 2008. Port management initiated a new capital program focused exclusively on improving the existing stormwater systems and designing new systems to ensure compliance with these conditions.A key programmatic consideration was cost – the airline industry has been suffering through its worst recession in history. Since the Port passes a significant portion of the cost of building and operating new projects onto the airlines in the form of landing fees and passenger emplanement charges, scrutiny on any spending was intense and cost justification was paramount.Another key driver was schedule. A timeline of only 5 years was available from the creation of the program to the successful implementation of all the facilities. Because of the high development density of the existing airport, any stormwater improvements would be difficult to implement. Potentially innovative technologies or combinations thereof would be necessary for implementing the suite of Best Management Practices (BMPs) necessary to meet effluent limits. Finally, all stormwater improvements needed to be consistent with the airport's wildlife hazard management plan. An FAA Advisory Circular specifically discourages open water within 10,000 foot of an active runway. Working cooperatively with the Airport Biologist, techniques were developed to mitigate any wildlife attraction posed by the new stormwater infrastructure.