TagACC(1534)

Memorandum dated November 1, 2001 from Elizabeth Leavitt (Port Of Seattle) to Muffy Walker (U.S. Army Corps of Engineers) regarding Army Corps Section 404 review of on-site borrow areas for Sea-Tac Airport Third Runway embankment fill. Covers Borrow Areas 1, 3, and 4 located in Des Moines and SeaTac; combined 6.1 million cubic yards of

Final Natural Resource Mitigation Plan (NRMP) prepared by Parametrix, Inc. for the Port Of Seattle, covering Master Plan Update Improvements at Seattle-Tacoma International Airport (Sea-Tac Airport). Document number 556-2912-001 (03), dated November 2001. Administrative Record document AR 029275–AR 029277.

Port of Seattle Natural Resource Mitigation Plan figure (AR017604, Exhibit 46, dated 12-20-01) showing Master Plan Update Improvement Projects at Seattle-Tacoma International Airport (STIA). Map depicts Third Runway construction area, Runway Safety Areas (RSAs), MSE retaining walls used to avoid and minimize wetland impacts, relocated section of Miller Creek, Miller Creek Detention Facility, Lora Lake,

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.

US Army Corps of Engineers Regulatory Guidance Letter No. 01-1, dated 31 October 2001, providing guidance for the establishment and maintenance of compensatory mitigation projects under Section 404(a) of the Clean Water Act and Section 10 of the Rivers and Harbors Act of 1899. Covers debit/credit assessment methodology, role of preservation, inclusion of upland areas,

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

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.

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.

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.

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