2600 FEDERAL AVE 2021 PORT OF EVERETT 2025-09-29

Iq:I Consulting Engineers Page 10 of 13 and will be 100% impervious. Pavement slopes are proposed to be generally flat at roughly 1 to 3 percent slope. Basin M fully developed drainage area is roughly 39.40 acres in size and includes the main cargo laydown area, the future maritime tenant area and warehouse north yard area. The area will be completely paved with asphalt and will be 100% impervious. Pavement slopes are proposed to be generally flat at roughly 1 to 3 percent slope. Federal Avenue Basin 1a consists of about 4,145 square feet of PGIS. The area will be repaved to accommodate improvements for new gate access to the site.Grading will route drainage to new CB23. Pavement slopes will be generally flat at 1 to 3 percent slope. 5.3 Hydrological Analysis Hydrological Analysis is based upon the Western Washington Hydrology Model (WWHM2012). The results from WWHM are summarized in Table 6: Water Quality Summary below and were used for sizing water quality facilities. Refer to Appendix E for a full version of the model results. Table 6: Water Quality Summary Basin Total Pollution Water Treatment Type Basin Generating Hard Quality Flow Area (AC) Surfaces (AC) (cfs(gpm)) Basin A 4.24 0.40 0.04(18) Contech Stormfilter Basin M 39.40 39.40 3.55 (1,593) Chitosan Enhanced Sand Filtration 5.4 Contech Stormfilter System Analysis(Basin A) A Contech Stormfilter will be installed in Basin A and shall be sized for the water quality flow rate of 0.04 cfs (18 gpm) as determined by the WWHM2012 modeling software. The treatment basin area consists of about 7,860 sf(0.18 ac) of on-site PGIS, 2,825 sf(0.06 ac) of Port property PGIS to the south (Dunlap leasehold) and 4,145 sf(0.10 ac) of PGIS in Federal Avenue (Basin 1a). Based upon the manufacturer's flow-based sizing criteria, as approved by the Department of Ecology, Model#SFMH48 with a treatment capacity of 0.05 cfs(22.5 gpm)will be used for the design. Model# SFMH48 is a standard 48 inch manhole plumbed for three stormfilter filter cartridges, each capable of treating 7.5 gpm. Refer to Appendix C for treatment system cut sheets.