3301 SEAWAY BLVD WHOLE SITE 2025-10-30

Ms. Sabrina Fandler City of Everett```1 Public Works Department !, Engineering/Permit Services C-4- �.� August 9, 2016 ii. The conveyance calculations do not account for the tail water conditions in pipe 1 due to the peak HGL in the MWS of 425.37'. Response: The HGL in the conveyance calculations is based on a tailwater elevation in the MWS of 425.37. N. Section 3 — Site development Plan with On -Site Stormwater Management. At a minimum, City BMP 12.20 must be implemented on this site in all areas that will remain pervious after development. Response: Section 3 now states that City BMP 12.20 will be implemented on all areas that will remain pervious after development. iv. Section 8, Part C — Developed Site Hydrology. this section needs to be updated. Response: Section 8, Part C has been updated to include both downstream drainage courses from the detention pond. v. In Section 8, Part F — Conveyance Analysis, the report states the following: "The conveyance system for the site will be conservatively sized to convey the 100-year event using the SBUH methodology and the Storm Shed3G program as adopted by the City of Everett." This is an inaccurate statement. The City does not endorse the Storm Shed software, and the City's standards would require the use of the rational method for the sizing of the stormwater conveyance system on the site. In addition, the 100yr flow calculated by Storm Shed, of 7.42 cfs, is less than the 100-year return flow of 8.57 cfs estimated by WWHM2012. Response: The conveyance analysis has been revised to use the Rational Method and KCBW programs. The stormshed mimics WWHM 2012. The reason the 100- year flow rates didn't match is because the pond and other minor surrounding areas were not included in the stormshed calculations. vi. The report includes a stage -storage calculation under the heading "Size the Detention Pond" — does this information represent the actual stage -storage of the pond based on calculated areas at each given stage? The page needs to be labeled appropriately if that is the case. Response: The information is the stage -storage of the pond based on calculated areas at each given stage and the page has been relabeled for clarity. vii. I am concerned about the proposed location of the MWS, both from an access and geotechnical standpoint. The GULD for the MWS requires review and approval of the site plan by MWS to ensure that site grading and slope are appropriate for the use of a MWS unit, this review must occur for this site in addition to specific review of the location by the geotechnical engineer. In order to aid this review, two cross - sections of the unit must be provided, along its length and width, showing its location relative to the above grade and to the rockery between the unit and the NGPE boundary.