Sierra Place-1139-Interbay-BLD2008-0237_SW.pdf
CITY OF EDMONDS
OMMENTS
PLAN REVIEW C
ENGINEERING DIVISION
(425) 771-0220
City Website: www.ci.edmonds.wa.us
DATE: May 13, 2009
TO: File
FROM: Jerry Shuster, P.E., Stormwater Engineering Program Manager
RE: Application #: BLD2008-0237
Project: Interbay Properties
Project Address: 1139 Sierra Place
During review of the above noted application, it was found that the following information, corrections, or
clarifications are needed.
Items reviewed:
Drainage Design Report, SWPP and O&M Manual, date June 28, 2008
Civil sheet C4, C5, and C6.
Drainage Report & Calculations/Civil Sheets
1.Introduction, Page 1: The text references the 2005 Department of Ecology Manual and the
associated minimum requirements. The current minimum requirements for this project are in the
Edmonds Community Development Code (ECDC) Chapter 18.30. The current manual is the
1992 Ecology manual.
2.Project Overview, Page 1: The text states that the site is located in the Middle Puget Sound
drainage basin. The City of Edmonds considers this site located in the Hindley Creek drainage
basin. Hindley Creek flows into Shell Creek, which discharges into Puget Sound (See comment
4).
The text states that the site area is 0.89 acres. Snohomish County assessor records accessed on
May 10, 2009 indicate it is 0.93 acres. Make this change throughout the document.
See Comment 1 and ECDC 18.30.60.B.10 requires Financial
3.Conditions Summary, Page 1:
Liability (e.g. performance bond) for the project.
4.Off-Site Analysis and Mitigation, Section 2, Page 3 and Section 3 Page 4. These sections are
incorrect. The subject property drains into an open channel at the northwest corner of the site.
The drainage primarily remains an open channel through the two private properties to the west,
and then enters the City’s pipe system on Olympic Avenue approximately 90 feet north of the
intersection with Sierra Place. Next the drainage flow north for approximately 150 feet
underneath Olympic Avenue, where it turns west, goes through properties at 747 Olympic Ave
and 1028 and 1026 Cascade Lane. The flow daylights in the channel of Hindley Creek behind
1025 Cascade Drive, approximately 975 downstream of the subject property. Please redo this
section.
Also, under Task 2A, the word “Recognizance” should be changed to “Reconnaissance.”
5.Construction Pollution Prevention, Page 6 and Plan Sheet C3 and C7: Given that the site is on a
steep slope, drains to a large wetland and a class 2 stream, a more extensive Construction
ented. Please
Stormwater Pollution Prevention Plan (SWPPP) is required that what is pres
include:
and other
Element #1: Aside from the clearing limits, the boundary of the wetland, stream
eated and fenced
areas not to be disturbed (including any associated buffers) should be delin
off using high visibility plastic fence to prevent construction equipment, personnel, or
.
materials from entering these areas causing compaction or other damage
s should sediment
Element #2: The plan should include street cleaning at the end of every day
.
be tracked off site onto the public roads
h combination of
Element #4: The text states that sediment control will be provided thoug
on through the surrounding on-site vegetation, filter fence, and straw bails. The on-site
filtrati
wetland should not be used to for sediment control.
/sequence for constructing the driveway on the steep slope
Elements #5/#6: A detailed plan
ge from rain and construction
should be included to prevent sediment transport/slope dama
equipment.
g those in the public
Element #7: The catch basins that will receive inlet protection, includin
right-of-way, must be shown on sheet C3.
t # 8: The channel slopes to be stabilized must be shown on sheet C3.
Elemen
ere hazardous
Element #9: The plan should describe and sheet C3 should show areas wh
where construction
materials such as paints, fuel, and hydraulic fluid may be stored and
to prevent any of
equipment will be parked overnight. The plan should describe methods
these and other hazardous materials from entering the wetland, creek, City storm system or
groundwater.
ent #10: The ultimate discharge point for trench dewatering water should be described.
Elem
aces and
Also, the erosion control information on the plan sheets is presented in many pl
Construction
confusing. Sheet C3 has a “SWWP Assessment” and “The 12 Elements of a
requirements plus additional
SWPP,” while sheet C7 has the City of Edmonds ESC minimum
truction pollution
notes on the temporary gravel construction entrance, and other notes for cons
arly define the steps
prevention. All this information needs to be consolidated in one place to cle
and techniques necessary to prevent damage to the wetland, stream, and city infrastructure during
struction.
con
The text states that an oil/water separator will be used. No such a device
6.Source Control, Page 6:
is presented in the document or the plans (detention pipes and associated appurtenances are not
oil/water separators the provide minor floatable control, if properly maintained).
Runoff treatment is only required when 5,000 square feet or more of
7.Runoff Treatment, Page 7:
pollution generating impervious area (PGIS) is created. Unless the proposed roof is metal, the
driveway is the only PGIS which is currently planned to be less than 5,000 square feet. If the
water quality treatment (swale) is triggered by a wetland mitigation requirement, than it should
remain.
8.Flow Control, Page 7 through 11: Per ECDC 18.30.060 A.1.a., since the site drains to Hindley
Creek, the flow control is required to limit the peak runoff rate to the pre-developed condition for
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Sierra Place-1139-Interbay-BLD2008-0237_SW
the 2-year, 24-hour design storm and the same for the 10-year and 100-year 24-hour design
storms. Note that the City has a minimum orifice size of 5/8” (to prevent clogging).
The report should describe whether any of the runoff from the pervious surfaces flows to the
imperious surfaces (such as the driveway). If any, these pervious surfaces must be included in the
modeling for sizing the detention system and conveyance system.
The 1992 Ecology Manual requires a volume correction factor for detention facilities sized using
event-based models (this also described in the 2001 Ecology manual). The volume correction
factor is based on the percent site impervious. Resize the detention system using the appropriate
correction factor.
When calculating detention storage volume, the storage in the upstream and downstream
manholes can only be used up to the invert elevation of the lowest pipe in these structures.
The conveyance analysis assumes an 18% slope on the 8-inch diameter pipe that conveys runoff
to the detention system. Plan Sheet C4 shows this pipe in two sections, a 115 foot section at
greater than 20% slope and a 15 foot section at 79% slope. The overall slope is over 29%. Note
that pipes with slopes over 20% require anchoring.
9.Wetland Protection, Page 11: This section references the Wetland Mitigation Plan prepared by
Wetland Resources Associates, Inc. Neither the Drainage Design Report nor the Wetland
Mitigation Plan addresses how the site modification will maintain the current hydrologic regime
in the wetland. The project is converting pervious surface that current drains into the wetland to
impervious surface and routes all of the runoff away from the wetland. A water balance should
be prepared to ensure the same amount of water that currently enters the wetland will be the same
after development.
Civil Sheets Only
The driveway area down slope from proposed CB#2 is not directed to the detention system.
Sheet C4:
This area (approximately 980 sf) must be picked up and conveyed to the detention system.
Connection to the drainage system from the footing drains (if any) should be shown on the plans.
For the roof runoff, the pipes must be connected to catch basins or yard drains at all changes in direction
or connecting points for maintenance purposes. These must be shown and detailed on the plans.
The invert elevation and the material type of the vent pipe should be specified.
Sheet C5:
: Delete Edmonds standard detail E5.1. It only applies to site with less than 5,000 sf of
Sheet C6
impervious surface area.
if you have specific
Please contact me at 425-771-0220 or by e-mail at mcconnell@ci.edmonds.wa.us
questions regarding these plan corrections.
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