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20141002164325188.pdfCeJEMMEERM, M. t -425.307.3020 Jennifer Lambert Engineering Technician City of Edmonds Public Work Department RE: Third Engineering Plan Review Comments for Coleman —9Q2—9th Ave S, Permit Application #:BLD20140189 Dear Jennifer, This letter is intended to summarize the changes made bothe engineering package reviewed during the find permit review for this project. This letter addresses comments from you along with other staff members which were provided in an email dated September 24m, 2014. | have tried boformat this letter to match your comment email for easier understanding. GENERAL NOTES OK ME New Comment —9/24/14 1) It appears that the plans donot scale sd1"=2D.Please check the plans and revise oaneeded. - 9/25/14 Response: The plans are at 1."=20'sc'ale'. Thiserror could have been due to using pdf copies of the plans. We have provided original hard copies to eliminate this error. 12M, NIMUNA GENERAL NOTES UPT r 1) 9/24/14 — Comment was partially addressed. It appears that when scaling the plans the impervious surface amount is closer to 6300 not 5900. Please check the impervious surface amounts/scaling and revise the impervious surface calculations and plans as needed. - 9/25/14 Response: The total area of impervious surfaces is revised to 6,100 sf, per Randy Munson. 2) 9/24/14 — Comment was not addressed. The plans do not show what areas of the shared driveway/access road will discharge to the onsite stormwater management. a. Please clearly show what areas will discharge to the onsite stormwater management system for 902 9th Ave S. - 9/25/14 Response: The runoff from the proposed roof surfaces for the new SFR and garage will discharge to the onsite stormwater management. system. The replaced driveway located on-site (902 9th Ave S) will also discharge to the onsite stormwater management system via yard drains proposed to be located on the driveway on-site. No offsite runoff from the existing shared driveway/access road will discharge to the onsite stormwater management system. Please see the drainage plans and report for more details on the stormwater management system. b. Include the amount of impervious area from the shared driveway/access road in the stormwater calculations and revise accordingly. - 9/25/14 Response: No offsite runoff from the shared driveway/access road will discharge to the stormwater management systems. The runoff from the existing offsite shared driveway/access sheet flows northwest and drains to its existing drainage course. c. If no areas will discharge to the onsite system, please clearly show how no surface water runoff from the shared driveway/access road will discharge into the stormwater management system for 902 — 9th Ave S. - 9/25/14 Response: The runoff from the existing offsite shared driveway/access sheet flows to the northwest, according to aerial topography and grade of the land. This was also verified during the site visit. The runoff then drains west along the northern side of the shared driveway/access. No offsite flows will be affected by this project. Please see the drainage plans for flow arrows showing the direction of the runoff from the existing off-site shared driveway/access. • - _ . nlk; f 9SE9 IE'W4Mr424t, WAlk 0OZ01 ENGINEERING, INC. t 42S.:307.393.20 8/29/14 Comment: If there are portions of surface water runoff not located on the subject site that will discharge to the onsite stormwater management system, the system will need to be sized to account for the additional surface water runoff. Please show what areas of the driveway/shared access road will discharge to the onsite stormwater management system. - 9/10/14 Response: All new plus replaced impervious surfaces, including NPGIS and PGIS will discharge to the onsite detention tank. No offsite areas are proposed to discharge to the onsite stormwater management system. The existing offsite shared access road drains west. 3) 9/24/14 — Comment was addressed; however, footing drains should not discharge to the onsite stormwater system unless approved otherwise. Please see stormwater #3 comment below. - 9/25/14 Response: The footing drains will connect to a proposed dry well which shall be located on the western side of the proposed SFR. OMEOA .i. - - -- ENMNEERM, INC. tAZS.Z137-:3020 - - • •- 1) 9/24/14 Comment: Swale and yard drain that were in previous version need to be restored. 9/25/14 Response: The swale and yard drain previously proposed on the western side of the project property has been restored in the drainage plans and report. 9/24/14 Comment: Addressed OK 9/24/14 Comment: Partially addressed. Please state in the drainage report that site is required to meet the flowing peak flow control standards since it is in a creek drainage basin: 2 -yr =0.07 cfs/acre impervious; 10 -yr =0.14 cfs/acre impervious; 100 -yr =0.33 cfs/acre impervious. Also, that based on these standards the allowable discharge rates for the site based on 0.14 acres impervious are: 2 -yr =0.01 cfs; 10 -yr =0.02 cfs; 100 -yr =0.05 cfs. A detail of the detention system control structure with the proper elevations of the riser pipe orifice(s) and all pope sizes must be included in the plans so it can be constructed properly per the modeling. See detail E5.4 (http://www.edmondswa.gov/services/permits- development/handouts-forms/services-perm its -std -details -main -page -men u/services-std-details- storm-drain age -section -5 -men u. html) - 9/25/14 Response: The peak flow control standards for a creek drainage basin have been added to the"Flow Control" section of the drainage report, along with the allowable discharge rates for the proposed impervious areas. - A detention system control structure detail has also been added to the plans (Drainage and Utility Sheet) with the appropriate elevations and sizes. 2) 9/24/14 — Comment was partially addressed. It appears that the "Developed Flow Conditions Used for Pump Sizing" provided in the Appendix to the Drainage Plan used the entire 0.14 acres instead of what will flow to the proposed pump well. Also, drawing 3 has a note specified the maximum flow rate at a maximum dynamic head for a 2.5 in diameter discharge line with fittings. The drainage report does not show the calculations that lead to these values for the pump system or an overlay of the pump and system curve as required in item 4 of the pumping policy. Item 6 (dual pump and backup power) of the pumping policy can be waived since the amount of flow handled by the pump is small compared to the overall site. Item 7 (overflow path) however, needs to be discussed in the drainage report and shown on drawing 3. - 9/25/14 Response: A new analysis was run using only the roof surfaces of 0.1 acres. Since the driveway surfaces will be discharged to the detention via yard drains the impervious area was not used. Please see Appendix A in the drainage report for a revised analysis. - Dynamic head calculations have been added to the plans (Drainage and Utility Sheet). - Items 4, 6 and 7 of the pumping policy have been addressed and added to the report. ne ENMEERM., INC. t,42S.:307-:34320' - - - 3) 9/24/14 — Additional Comment: Footing drains should not be plumbed to the detention system. Use a properly sized drywell per recommendation of a geotechnical engineer (groundwater should remain groundwater). - 9/25/14 Response: The footing drains will connect to a proposed dry well which shall be located on the western side of the proposed SFR. SOIL MANAGEMENT PLAN (pg. 4 of 4) W1• Thank you for taking the time to review the revised plans for this project. Please feel free to contact me with any questions you may have. Sincerely, Rachel A. Jacobs Omega Engineering, Inc.