TagThird Runway(1067)

This 2001 email chain discusses how fill materials used in the construction of Seattle-Tacoma Airport's Third Runway Embankment should meet environmental criteria under a 401 water quality permit. State regulators and Port of Seattle staff debated which materials — including topsoil, utility backfill, base course, and general embankment fill — required testing, supplier certification, or quality assurance plans to demonstrate compliance. Officials agreed that highly processed materials like topsoil could be covered by supplier certification, while bulk embankment fill would require a statistical sampling and QA/QC program.

A November 2001 email chain discusses a meeting held on October 30, 2001, regarding errors discovered in a low flow analysis related to environmental modeling near Seattle. Raymond Hellwig of NWRO confirms that revisions to the low flow analysis may be considered to correct previous modeling errors, but stresses that any revised submissions must include thorough documentation and clear rationale. The correspondence involves multiple agencies and contractors, including Floyd Snider McCarthy, Inc., the U.S. Army Corps of Engineers, and Port of Seattle representatives.

These draft meeting notes from October 30, 2001 document a technical review session in which Port of Seattle consultants disclosed and explained several errors found in the low streamflow modeling for the Sea-Tac Airport Third Runway project. The key errors included a 1/24th magnitude conversion factor mistake in embankment fill data input, incorrect input files used for embankment modeling, and an overlap in which approximately 8 acres of the Walker Creek embankment appeared to be counted in both the Hydrus embankment model and the HSPF stream model. The meeting outlined corrective steps to be taken by the Port's consulting team to fix these errors before finalizing the revised Low Streamflow Analysis required under 401 Permit conditions.

Memorandum dated October 30, 2001 from Michael Kenrick of Hart Crowser, Inc. to Jim Thomson of HNTB, CC Elizabeth Leavitt of Port Of Seattle, project number 4978-06. Addresses wetland hydrology impacts of Third Runway Embankment Fill construction at Sea-Tac Airport, covering depression wetlands, slope wetlands, and riparian wetlands. References Miller Creek and Walker Creek baseflow,

Meeting notes from an October 30, 2001 technical session addressing errors discovered in the low streamflow modeling for Sea-Tac International Airport's Third Runway project. Consultants identified six modeling errors, including a conversion factor mistake that caused embankment flow contributions to be understated by a factor of 24, along with incorrect input files and improper groundwater routing. Representatives from the Port of Seattle, King County, the Department of Ecology, and the Army Corps of Engineers agreed on corrective revisions to be incorporated into a revised Low Streamflow Analysis and Summer Low Flow Impact Offset Facility Proposal required under the 401 Permit.

Final meeting notes from October 30, 2001 Low Flow Analysis meeting regarding Port Of Seattle’s revisions to the Low Streamflow Analysis and Summer Low Flow Impact Offset Facility Proposal per 401 Permit conditions for Sea-Tac Airport Third Runway. Attendees included Ann Kenny (Dept. of Ecology), Kelly Whiting and David Masters (King County), Lisa Scott (Corps

Memorandum dated October 30, 2001 from Michael Kenrick of Hart Crowser, Inc. to Jim Thomson of HNTB (project number 4978-06), CC Elizabeth Leavitt of Port Of Seattle, regarding wetland hydrology impacts of the Third Runway Embankment Fill at Sea-Tac Airport. Covers depression wetlands, slope wetlands, and riparian wetlands; references FEIS for the Master Plan Update

This technical memo from Hydrocomp, Inc. (authored by Norm Crawford) outlines recommendations for improving hydrological computer modeling of Miller, Walker, and Des Moines Creeks near Seattle-Tacoma International Airport's new runway construction. It describes how rainfall and runoff from the new impervious runway and taxiway surfaces and surrounding pervious grasslands are tracked through a linked series of models (HSPF, Hydrus, and Slice) to estimate groundwater movement and seepage through underlying soil layers. The document identifies several discrepancies in the existing model setup and recommends corrections to better account for water flow paths, drainage areas, and groundwater recharge in the fill areas created by airport expansion.

A October 26, 2001 transmittal from Parametrix, Inc. to the U.S. Army Corps of Engineers (ACOE) provides responses to the ACOE's request for additional information regarding the Seattle-Tacoma International Airport (STIA) Master Plan Update (MPU) Natural Resource Mitigation project. The package includes maps and aerial photographs identifying wetland areas and acreages within Borrow Area 1, submitted on behalf of the Port of Seattle.

In this October 24, 2001 letter, the Port of Seattle notified the Washington Department of Ecology of a mathematical error discovered in hydrological modeling software used to assess the Seattle-Tacoma International Airport Master Plan's impacts on Miller and Walker Creeks. The error caused stream flow impacts to be overestimated at 1/24th of their actual value, meaning required mitigation facilities could be smaller than originally planned. As a result, the Port requested an extension of the Low Streamflow Analysis submittal deadline from November 5 to November 21, 2001.