bld20080847-SWM compliance review-Herrera Review.pdf
March 2,2016
City of Edmonds Public Works Department
Engineering Division
121 5thAvenue North
Edmonds, WA 98020
Attn: Jeanie McConnell
Subject:Stormwater Plan Review of WillowdaleTownhomes (BLD2008-0847)
Dear Ms. McConnell:
The revised Stormwater Analysis (2/3/16)forthe Willowdale Townhomeshas addressed the
City’s previous comments and concerns. Weonly had twoadditional comments(that will not
require resubmittal):
1.Recommendadding the date that the resurveying of vault elevations occurred either
in the main text or in Appendix C (refer to response to previous comment #1 below).
2.Appendix H -maintenance standards for Wetvaults(No. 12) from the Stormwater
Management Manual for Western Washington are not required to be included in the
Operations and Maintenance Manual. The maintenance standards for Closed Detention
Systems (Tanks/Vaults) (No. 3) are sufficient to address the vault system.
We also reviewed the status of the previous comments fromJeanie McConnell and Jerry
Shuster dated 11/2/15. Responses are shown belowin blue text and are dated 3/2/16.
1)3/2/16 –The vault elevations were resurveyed and the elevations included in Appendix
C of the Stormwater Analysis (2/3/16) have been updated.
11/2/15 –For the westernmost vault, the survey says the following: “Bottom vault =
431.60, Top of vault = 438.82, Water Level = 7.75.” If the water level is at 7.75 ft, it
would be over the top of the vault. Please reconcile.
2)3/2/16 –The invert elevation (432.48’) was added to the survey information included
in Appendix C of the Stormwater Analysis (2/3/16).
11/2/15 –There is no survey information for the invert of the outlet pipe from the
westernmost vault, therefore, it is not possible to verify that the live storage depth is
4.9 feet as use in the modeling.
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Stormwater Plan Review of Willowdale Townhomes
March 2, 2016
Page 2
3)3/2/16 –Effective storage has been calculated as 3.81 ft based on the revised
elevations provided in the survey information included in Appendix C of the
Stormwater Analysis (2/3/16).
11/2/15 –Provide evidence for assuming the easternmost vault has a live storage
volume of 4.9 ft.
4)3/2/16 –The survey information in Appendix C of the Stormwater Analysis (2/3/16)
has been revised.
11/2/15 –For the 54” dia. control structure manhole, the survey says: “8 gate valve
(out) 433.80±.” Is this the shear gate? Shouldn’t it be 12”? Why doesn’t the 18” dia.
inlet pipe from the north show up on the survey? It is difficult to understand which
pipes are inlets to the control structure and which are outlets. Please reconcile.
5)3/2/16 –A small area of the drive aisle (approximately 750 sf) bypasses the detention
system.
11/2/15 –Provide the amount of impervious area, if any, that bypasses the detention
system.
6)3/2/16 –A copy of the detail has been added to Appendix G of the Stormwater
Analysis (2/3/16).
11/2/15 –Since the control structure will need to be modified to meet current flow
control standards, use current Engineering StandardDetail E5.4 for the new control
structure.
7)3/2/16 –Maintenance standardshave been added to Appendix H of the Stormwater
Analysis (2/3/16).The Operation and Maintenance (O&M) Manual should also include
the name of the party (or parties) who are responsible for maintenance and operation.
A copy of the O&M Manual shall be retained on-site or within reasonable access to the
site, and shall be transferred with the property to the new owner.
11/2/15 –Prior to final approval, all stormwater facilities (filters, CBs, vaults, control
structure, etc.) shall be brought up to current maintenance standards (2005 Ecology
Stormwater Management Manual for Western Washington, Volume V, Section 4.6).
Sincerely,
Herrera Environmental Consultants, Inc.
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Rebecca Dugopolski, PE
swm compliance review
Senior Engineer
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