bld20090795-Lowenthal_2.pdf
City of Edmonds
TH
121 5 AVENUE NORTH • EDMONDS, WA 98020 • (425) 771-0220 FAX(425) 771-0221
Website: www.ci.edmonds.wa.us
PUBLIC WORKS DEPARTMENT
Engineering Division
Plan Review Corrections
Plan Check :Date:
#BLD20090720 December 11, 2009
Project Name/Address:
Lowenthal – 18720 Soundview PL
Contact Person/Address/Fax:
Marci Bryant –
vmarcibryant@msn.com
Jennifer LambertDivision:Engineering
Reviewer:
During review of the subject submittal, it was found that the following information, corrections,
or clarifications would need to be addressed. Our handouts can be found online at the City of
Edmonds web site www.ci.edmonds.wa.us under City Government/Development
Services/Engineering Division.
st
Review - 12/11/09
1
nd
2 Review – 2/3/10
CA.1 – Site Plan
1.OK
2.OK
3.OK
4.OK
5.OK
6.OK
Sheet C1 – General Notes
1.OK
2.OK
3.OK
4.OK
5.OK
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6.OK
Sheet C2 – TESC Plan and Details
1.OK
2.OK
3.OK
4.OK
Sheet C3 – Grading Paving & Utility Plan
1.OK
2.OK
3.2/3/10 Comment was partially addressed. It appears that the bottom of footing elevations for the
proposed home was provided, but were not for the existing home. Please provide the grading
calculations as well.
12/11/09 Comment: Show bottom of footing elevations on site plan for new and existing home in order
to verify grading calculations.
4.OK
5.OK
6.OK
7.OK
8.OK
9.OK
10.2/3/10 Comment was partially addressed. It appears there is a portion of the proposed deck/patio
on the northwest corner of the house that is not covered by the roof. This area shall be considered
impervious. Please add this area to the impervious surface calculations. If they are already
added, please note in the impervious surface calculations were the deck/patio was included.
12/11/09 Comment: Please show deck and state what material the deck is constructed of.
11.2/3/10 Comment was not addressed.
12/11/09 Comment: Footing drains shall be piped down to the base of the slope and not allowed to
discharge on the slope.
a.Permission from BNSF is required to release storm water onto BNSF right of way. Please
provide documentation showing approval from BNSF.
b.Footing drain connection to the rain gardens or storm system may be permitted if they are
adequately sized.
12.OK
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13.OK
14.OK
15.OK
16.OK
17.OK
18.OK
19.OK
Drainage/Detention Review comments from Storm Water Engineer, Jerry Shuster, P.E.:
Items reviewed:
Outline Drainage Report dated January 8, 2010
Letter Report from GeoTech Consultants, Inc., dated December 28, 2009
Memorandum from John W. Rundall, P.E., dated January 6, 2010
Plan sheet C1 and C3 dated January 6, 2010
Preface
The comments contained in this document are contingent on a satisfactory resolution of the issue of
stormwater runoff from this site being directed to Fruitdale Creek as describe in an e-mail sent to the
project proponents on February 5, 2010 (attached).
Comments on “Outline Drainage Report” (WR Consulting, Inc., November 16, 2009)
1. OK
2. OK
3. OK
4.Comment was partially addressed. The response states that the rain gardens are designed using the
guidance from the 2009 King County Surface Water Design Manual (KCSWDM) that assumes a design
infiltration rate of 0.5 inches/hour. The report from GeoTech Consultants, Inc., dated December 28,
2009 states that the site soils are capable of an infiltration rate of at least 1 inch per hour. Aside from a
inference from the soil boring log, no rationale for this infiltration rate is presented in the submittals.
Please convert the USCS classification for the soil boring to USDA soil textural classification found on
page 3-76, Volume III, 2005 Ecology Stormwater Manual for Western Washington. A table on this page
can be used to get defensible infiltration rates. Note the difference between the short-term infiltration
rate and the estimated long term infiltration that will be used in design. Both values should be reported.
If here is a change in the design infiltration rate, it should also be reflected in rain garden freeboard
requirements and the calculations on page 5 regarding the infiltration capacity.
11/16/2009 Comment: The rain gardens have been designed using criteria from the 2009 King County Surface
Water Design Manual that include a sizing factor of 0.25 inches of rain garden volume per square feet of
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impervious surface area served. The City will may accept use of these design criteria under the following
conditions:
The 0.25 inches/sf impervious standard in the King County manual must assume an infiltration rate for
the underlying soils. This infiltration rate should be presented in the drainage report. The actual
infiltration rate for the site in the areas where the rain gardens will be located (design infiltration rate not
a field infiltration rate) needs to be verified by a geotechnical engineer. This design infiltration rate
needs to be equal to or greater than the one used for the standard in the King County manual.
The drainage analysis needs to demonstrate that the rain gardens designed to the King County standard
have release rates from the site for the 10-yr and 100-yr, 24-hour storm events under developed
conditions less that or equal to the release rate for the pre-developed conditions for the 10-yr and 100-yr,
24-hour storm events. The pre-developed condition should be modeled as secondary growth forest.
5. OK provided that infiltration rate from comment 4 is acceptable.
6. OK. The City is still working on working a declaration of covenant for the rain gardens.
7. OK
8. OK
Additional Comments on Revised Outline Drainage Report (dated January 8, 2010).
9. Runoff from the “Grasscrete” driveway is shown draining to the rain gardens. Describe how dirt and
sediment off the driveway will be handled such that it does not unnecessarily reduce the infiltration rate
of the rain garden soil or the underlying soils.
Comments on Plan sheet C3 (dated January 6, 2010)
10. The Plan sheet calls out a “Grasscrete driveway” and detail 2 shows a the cross section for this item.
TheOutline Drainage Report discusses a “Grasspave driveway.” Grasscrete and Grasspave are two
different modular pavement grid systems with different sub-base requirements for proper function.
Also, Grasspave literature does recommend the product for slopes greater than 8%. The driveway, as
designed, has segments with a slope of 10%. Decide on the type of modular pavement grid system for the
project and include the manufacturers specification for sub-base in order to qualify for the 50%
impervious treatment of these areas.
11. The City prefers that the pump system does not discharge directly into the City’s storm system for
maintenance reasons. Gravity flow from private property is the preferred approach. Also, the release
from the detention system should be controlled by the orifice and not the pumps (especially if the orifice
system is designed to release approximately 14 gallons per minute (gpm) and the pumps are capable of 25
gpm.) To this end, it is recommended that a wet well be located at lower elevation of the site connected to
the pump system. This pump system would discharge into the upstream end of a detention system
located at the northeast part of the site. This dentition system would have a control manhole that may be
able to be discharge by gravity into the City catch basin on Soundview Place.
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12. The planned configuration of the footing drains to outlet via area drains may not be appropriate so
close to the steep slope. Documentation from the geotechnical consultant regarding the potential impact
of these footing drain discharges should be included. (Note that the City does allow the connection of
footing drain discharges to stormwater systems but only downstream of detention system discharges.)
Please resubmit 3 copies of the revised plans/documents to a Development Services Coordinator. Please
contact me at 425-771-0220 if you have specific questions regarding these plan corrections.
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-----Original Message-----
From: Lambert, Jennifer
Sent: Friday, February 05, 2010 4:43 PM
To: 'robl@lsaengineering.com'; 'mcnurlen@comcast.net'; 'RMARCIBRYANT@MSN.COM'
Cc: McConnell, Jeanie; Shuster, Jerry
Subject: FW: Stormwater Options for 18720 and 18726 Soundview Place
Hello,
The purpose of this e-mail is to provide additional guidance on stormwater issues for the aforementioned properties and
to have the parties work together to design and construct code-compliant stormwater systems in a cost-effective manner.
Under existing conditions, both sites are sloped towards the BNSF right-of-way that is adjacent to Puget Sound which is
the natural discharge point for rain water that does not infiltrate into the ground. Under Edmonds Community
Development Code Chapter 18.30.060 B.2, sites that create or add 5,000 square feet or greater of new impervious
surface are subject to Minimum Requirement #2, Preservation of Natural Drainage Systems. This section of the code
states:
2. SQC Minimum Requirement – Preservation of Natural Drainage Systems. Natural drainage patterns shall be maintained, and
discharges from the site shall occur at the natural location to the maximum extent practicable. Where significant changes are
necessary downstream, drainage facilities shall be improved to allow them to accommodate the increased drainage without damage to
the drainage facilities, nearby property, or water quality.
The current design for 18720 proposes rain gardens or infiltration for part of the impervious area and the remaining
impervious (<5,000 sf) will be mitigated by using a detention system with the released water being pumped to the City
storm system on Soundview Place. This may work (I am working on some comments on the proposed system). This
storm system on Soundview Place discharges approximately 725 feet to the southwest to Fruitdale Creek (out of the
"natural drainage pattern").Based on ECDC 18.30.060.B.2, since the impervious area discharging outside of the natural
drainage pattern is under 5,000 sf, the proposal would be allowed. The overall goals of the stormwater code,
however, include (ECDC 18.30.00):
B. To protect land and the ecological balance of the receiving water bodies near development sites from
increased surface water runoff rates that could cause flooding or erosion, scouring, and deposition of sediment
due to the development;
C. To protect private and public property and city streets and rights-of-way from flooding or erosion;
Since none of the stormwater runoff from either site is currently going to Fruitdale Creek, adding any
flow to it may cause erosion problems. Note that the detention sizing worksheet provided in City
handout #E72 can be used for sizing detention systems with less than 5000 sf of impervious area, but
only controls the 10-year peak event. Recent stormwater sciencelimits the outflow from detention
systems much form storm events smaller than the 10 yr event to control stream erosion. A 1989
basin study on Fruitdale Creek done by URS Engineers for the City of Edmonds describes a problem
involving the capacity of the channel in the lower portion of the Creek. "...Urbanization upstream has
increased the amount of runoff directed to this creek. Increased runoff has exceeded the capacity of
the stream and also increased erosion in the system." In addition, a 2002 stream survey by Pentec
Environmental noted ..."At the time of the survey, the culvert \[under the BNSF tracks\] was about 40
percent clogged with gravel." This most likely indicates a continually eroding streambed.
Given all this, here are the options I see available:
1) Discuss with BNSF the option of discharging stormwater runoff to their right-of-way from a
properly designed detention systems (if this avenue has been explored and not allowed, please
provide documentation).
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2) If both properties can limit the amount of effective impervious connecting to the storm system on
and
Soundview place to under 5,000 sf per site convince the City and the property owners at 18916
and 18914 Soundview Place (Creek runs though these private properties) the additional flow to the
Creek will not exacerbate the erosion problem, this may work. Some kind of joint rain garden or
infiltration system spanning both properties should be considered to limit the amount of flow directed
to the City system on Soundview Place.
3) The stormwater from both sites may be sent towards the City's storm system on Wharf Street (to
the northeast) via a gravity line (or pump) provided that the system on Wharf Street has the capacity
to handle the additional flows. This would need to be verified by the parties involved and submitted to
the City for review. The storm system would run through the northwest side of both properties
and then through three additional properties (you would have to get a private easement from these
property owners and the system would remain private)Since this is a direct discharge to the
.
Soundyou would not be changing the natural discharge locationand it may negate the need for
,
infiltration or detention all together depending on the capacity analysis. Both parties could go in
together on a joint storm line to Wharf Street.
There are possibly other variations of these options that you may be able to work out for further
discussion with the City .
If you would like to set up a meeting to discuss these options, please coordinate between both
private parties and send me some possible times and dates.
Thank You,
jennifer.lambert@ci.edmonds.wa.us
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