Notes
King County Department of Natural Resources draft review comments (Exhibit 458, AR022912) on the December 2001 Low Streamflow Analysis – Summer Low Flow Impact Offset Facility Proposal submitted by Port Of Seattle (Parametrix Inc.). Reviews HSPF hydrologic modeling, impact assessment, and conceptual design of low-flow mitigation facilities for Walker Creek and Miller Creek under 401 Certification conditions set by Washington State Department of Ecology. Key issues include reserve storage vault filling analysis for SDW2 and SDS3A subbasins, impervious area discrepancies (7.5 vs. 11.5 vs. 16.3 acres), fill times exceeding 60 days (up to 213 days), flow frequency analysis errors (17 annual low flow events in June/July vs. August 1 start date), HSPF parameter consistency with SMP calibration, IWS lagoon infiltration as unaccounted baseflow source, non-contiguous groundwater PERLND land cover analysis, and 100-acre pervious groundwater offset mitigation. Recommends validation report for revised 1994 condition models against SMP 1994 calibration for all three streams.