4620_001.pdfIEC
INSIGHT ENGINEERING CO.
September 26, 2018
Zack Richardson
121 5 1h Ave NE
Edmonds, WA 98020
(425) 771-0220
Re: Zimmerman Edmonds SFR — BLD20180576
IECO No. 17-0858
Dear Zack,
The project referenced above is revised in response to the review comments dated August 2 1,
2018 (Amended 9/10/18). The review comments are numbered on the letter and have been
addressed in italics as follows:
Review Comments:
1. Update the drainage report, to reflect the critical areas as determined through
CRA20170078, as needed to address additional comment below, and identify any and all
pipes or systems on -site which discharge to the creek.
The pipes to the system have been identified and shown on the revisedplan.
2. Staff have been made aware of the presence of a storm drain system underneath and
within the footprint of the existing garage which is believed to be the creek. Update plans
and report to show the system, identify the system as private, and address as needed.
The pipes have been shown on the revisedplan. The pipe layout is based on information
the homeowner provided and uncovered.
3. Update drainage report to reflect the observed conditions noted in the geotechnical report
include seeping walls, discharging sub -surface pipes, creeks, and groundwater expressed
on surface; identify where these flows travel for conveyance and address concerns as
needed.
a. If no improvements to address the groundwater of the site are proposed, engineer
shall explain why this condition is proposed to remain as -is.
PO Box 1478 # Everett, WA 98206 * Phone: (425) 303-9363
Fax: (425) 303-9362 # Email:info@insightengineering.net
The plans have been updated to show the numerous pipes onsite. The homeowner
is working with his geotechnical engineer tofix the seeping walls. No other
subsurface mitigation is beingperformed
4. City records for the private 4" drainage system within the Dayton St ROW and driveway
do not match that shown on the plans and the information provided is not sufficient to
connect to this existing private system.
a. It is believed that the 4" private system conveys runoff across the property
frontage without bringing the runoff onto private property as shown in the topo
and that the driveway system is not actually connected to the ROW system.
Uponfurther investigation, we believe this to be true as well. Please see the new
design to the existing system in Dayton Road
b. It is also believed that portions of this line may be perforate pipe and therefore not
eligible to carry additional conveyance flows; this pipe appears infeasible for
connection of the project drainage and will not be permitted without significant
additional information to verify pipe condition/make-up/ownership/etc.
Understood. Please see answer to 4a.
c. Runoff will not be permitted to be discharged across the public walkway either
(ic. bubble -up with surface overflow not an option).
We areproposing a tightline to the existingpipe system within thepublic right-of-
way of Dayton Road.
d. The 6" public line further into Dayton (see map.edmondswa.gov) may be used for
connection (at a new CB), but conveyance calculations still need to be provided to
verify adequate capacity of the 6" system.
The outletfrom the detention pipe has been connected to the 6 "public line in
Dayton St. Refer to the conveyance analysis in appendix E of the drainage report.
5. Update drainage report to include a sizing calculation for how the impervious surfaces
proposed were converted into the detention pipe size proposed.
Refer to appendix Bfor the detention pipe sizing calculations.
6. Update plans and report to address the retrofit requirement per ECDC 18.30.060; MR #5
must be applied to 25% of the existing impervious surfaces to remain.
a. Please verify the existing impervious surfaces to remain value on the plans; staff
scaled -off a different value for just the existing roofs than is shown.
Table on sheet C1 has been updated.
PO Box 1478 * Everett, WA 98206 # Phone: (425) 303-9363
Fax: (425) 303-9362 # Email:info@insightengineering.net
7. By interpolation, detention sizing appears to have been done for the new plus replaced
surfaces only, however it is unclear how the engineer intends to separate and collect only
the runoff from those impervious surfaces. Either,
a. Update plans and report to be size the BMP for all impervious surfaces actually
draining to the facility, OR
The new and 25% of the existing roof of the home will be directed to the detention
system per the City ofEdmonds code. Refer to the revisedplans and drainage
reportfor more information. The existing roof drains on the north and northwest
corner of the house will continue to drain to the existing downspouts.
b. Provide enough roof sloping, downspout location, and/or grading information to
show how the only areas requiring mitigation will be collected and routed into the
system.
Refer the downspout locations shown on sheet C1. Grading information has been
shown on sheet C2. The existing roof drains on the north and northwest corner of
the house will continue to drain to the existing downspouts.
8. Cl: Update hatchings in impervious section exhibit for consistency/elarity; shed, house,
and garage all appear to be different hatch types or line thicknesses but only I of them
matches the legend.
The hatch for the shed, house, and garage match the legend and are all considered
existing impervious to remain.
9. Cl: Update the table of treatment areas to:
a. Include a retro-fit value equal to 25% of the existing to remain and a proposed
BMP for the retrofit requirement, and
b. Include a lawn and landscaping value equal to all disturbed pervious areas and list
BMP T5.13 as the stormwater facility.
The table has been updated accordingly.
10. C 1: C13 #2 and the detention system all have invert values which are below the discharge
point of CB #1; correct elevation as needed for positive flow.
Invert elevations have been revised accordingly.
11. C 1: Include the missing invert elevation (NE) at CB # 1.
Invert elevations have been shown.
12. C I: Add callouts for all 4" drain -line systems (ie. frontage system and alley system):
"Private drainage system; not maintained by City "
PO Box 1478 # Everett, WA 98206 * Phone: (425) 303-9363
Fax: (425) 303-9362 # Email:info@insightengineering.net
Callout has been added.
13. C I: Identify the start and end invert of the detention pipe (or provide dimensions from
12" invert in detail)
Inverts have been shown.
14. C 1: Correct inconstant rim elevation between CB #2 callout and control structure details.
Rim elevation has been revised
15. C 1: Update detention detail to include vent pipe. ..
Vent pipe has been added to the detail.
16. Cl: Update detention detail to include an underdrain and identify the discharge point.
An underdrain has been added to the detention detail.
17. C2: Identify "VEG" in the legend.
The legend has been updated accordingly.
18. C2: Add notes to reflect the need to apply BMP T5.13 to all disturbed pervious areas and
provide detail or specifications sufficient enough for the contractor to install soils
meeting requirements.
Note has been added to sheet C2.
19. C2: Identify the limits of storm drain line proposed for removal (or update plans to reflect
4 connections at C13 #1 and potential conflict with C13 #2).
The storm system has been updated. Refer to the revisedplan.
20. C2: Provide perimeter protection on the downhill sides of clearing limits; insufficient
vegetation length appears to exist before the property line to the west or critical area
buffer to the south to be a suitable standalone BMP.
Siltfence has been added.
21. C2: Provide enough grading information (spot elevations at comers, grade breaks, and
low points) to verify that runoff from the driveway surface will be directed to the CBs as
intended.
Spot elevations have been added to the driveway.
PO Box 1478 * Everett, WA 98206 * Phone: (425) 303-9363
Fax: (425) 303-9362 4 Email:info@insightengineering.net
Please feel free to contact me with any questions or comments you may have.
Sincerely,
B alab, P.E.
PO Box 1478 # Everett, WA 98206 # Phone: (425) 303-9363
Fax: (425) 303-9362 4 Email:info@insightengineering.net