Posted on

EXH AR026404: Memo — Reasonable Potential Analysis Results, STIA Third Runway

Document Library
Sea-Tac Airport
Third Runway
PCHB
Box 10

A 1998 internal memo from Parametrix, Inc. summarizes the results of a Reasonable Potential Analysis (RPA) conducted for the Seattle-Tacoma International Airport (STIA) Third Runway project, assessing whether stormwater runoff from the new runway could exceed water quality criteria in Miller Creek and Des Moines Creek. The analysis found that most pollutant concentrations after treatment with best management practices (BMPs) such as bioswales, sand filters, and wet ponds would meet criteria, with the exception of copper, which remained above acceptable levels. The memo also notes that existing pollutant concentrations in the receiving waterways during storms already exceeded criteria, even before accounting for Third Runway runoff.

Open full document

Notes

Memorandum dated July 1, 1998 from Ken Ludwa (Parametrix, Inc.) to Paul Fendt summarizing results of a Reasonable Potential Analysis (RPA) performed for the STIA Third Runway area. The RPA used outfall 005 (SDS-3) stormwater runoff data (1994–98) with two 1996 deicing sampling events removed, calculated geometric 95th percentile concentrations, and compared predicted pollutant concentrations against water quality criteria for Miller Creek (hardness 23 ppm) and Des Moines Creek (hardness 35.6 ppm). Parameters analyzed include fecals (CFU/100mL), turbidity (NTU), copper, lead, and zinc (ppb). Copper concentrations after BMP treatment remained higher than criteria. BMPs evaluated include bioswales, sand filters, and wet ponds/vaults. NPDES permit context referenced via STIA 1998 NPDES Permit Fact Sheet/Response to Comments. Meeting attendees included Lisa Zinner (Ecology), Lori Terry (Preston, Gates, and Ellis), Tom Hubbard (POS), John Rogers (CH2M Hill), Bill Taylor (Taylor and Assoc.), and Jim Good. AR 026404–026406.

Sidebar On/Off
V V