BLD20090043-White-2 - Eng-Storm.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
DEVELOPMENT SERVICES DEPARTMENT
Planning • Building • Engineering
Plan Review Corrections
Plan Check :Date:
#2009-0043 January 26, 2010
Project Name/Address:
White 17808 Talbot Rd Addition/Remodel
Contact Person/Address/Fax:
Henry Byam FAX: 425-776-1917 henryb@wescoautopaint.com
JoAnne ZulaufDivision:Engineering
Reviewer:
nd
2 REVIEW
During review of the subject submittal, it was found that the following information, corrections, or
clarifications would need to be addressed. All Handouts referred to in these comments can be accessed at
under City Government / Development Services Department /
our website: www.ci.edmonds.wa.us
Engineering Division then scroll down to Handouts:
1.1/26/10 SEE STORM WATER ENGINEER COMMENTS BELOW.
2/2/09 Comment: Infiltration proposal being reviewed by the Storm Water Engineer.Comments
to follow.
2.1/26/10 Storm Drainage is not shown for all the post 1977 impervious surface. Refer to Storm Water
Engineer comments below.
2/2/09 Comment: Please show all utilities on site/plot plan: side sewer from main to house,
water service line from meter to house, storm drainage. This information must be on the reduced
Site/Plot Plan as well.
3. 1/26/10 Done.
4.1/26/10 Not Done.
2/2/09 Comment: Show footing drains on site plan and where they will connect to storm
drainage
system. Geotech report states that they should be handled separately from the tightline.
5. 1/26/10 Done.
6.1/26/10 When adding existing driveway to impervious surface calculations, it shall be considered added
as of 1982 when asphalt was installed.Refer to Storm Water Engineer commentsregarding pervious
surface.
7. 1/26/10 Done
8.1/26/10 The property corners are now including the easement. This indicates that the White’s own the
property used by others for access. Is this correct? Property corners must only be around their private
property.
2/2/09 Comment: It is confusing that there are property corner symbols on all four corners of the
20’ access easement. Please remove the round symbols from the inner corners (south) of the
easement so it is clear that the easement is a portion of this property.
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9. 1/26/10 The submitted site plan and drainage plan are very confusing. The impervious surface
calculations do not match between plans or between existing and proposed. Please review the Handout
#E72 and the Storm Water Engineer comments below to further understand the definition of impervious
surface. All impervious surface measurements should be including the building area plus any overhang,
driveways, sidewalks and any other surface or structure that prevents rainwater from reaching the
not
ground.Lot coverage and/or total structure sq footage should be addressed here. I will add a
example of how the required information is typically arranged. You may or may not need each of the
categories that are listed in this example.
Impervious Surface Calculation Example
EXISTING IMPERVIOUS SURFACE AREA
Existing Housexxx sq ft Built XXXX
(This includes total sq footage of area of building including the roof overhang.)
Existing Garagexxx sq ft Built XXXX
Existing Addition xxx sq ft Built XXXX
(only want sq footage of increased imp surface-addition of second floor over existing impervious
surface should not be included here.)
Existing Patio xx sq ft Built XXXX
Existing Driveway xx sq ft Built XXXX
Existing Walkwayxx sq ft Built XXXX
(if there is any existing)
(Any other existing impervious surface)
Do not list decks if not impervious.
A. Total Existing Impervious xxxx sq ft
(Should add up to the total of the impervious surface on the lot today.)
PROPOSED IMPERVIOUS SURFACE AREA
Proposed Additionxxx sq ft
impervious surface
(this is only the that will be added with this project which should include roof
overhang)
Proposed Drivewayxx sq ft
(see Storm Water Engineer comments regarding the pervious material proposed)
Proposed Walkway xx sq ft
(add the area of any proposed walkway)
B. Total Proposed Impervious xxxx sq ft
REMOVAL OF EXISTING IMPERVIOUS SURFACE AREA
Remove Portion of Existing Drivewayxx sq ft
(this amount will not be subtracted for detention sizing purposes-see Storm Water Engineer
comments below and Handout E#72 for clarification)
Remove portion of Existing sidewalk xx sq ft
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C. Total Removed Impervious xxx sq ft
Total Existing and Proposed Impervious xxxx sq ft=(A + B) – C
This number will equal the total impervious surface that will exist once the project is complete.
DRAINAGE PLAN:
The exact same listing of Impervious Surface should be on your Drainage Plan.
Plus you will add two additional totals in the Existing Impervious Surface section:
Total Existing Impervious built 1977 or before:
Total Existing Impervious built after 1977:
Previous Comments
: Impervious Surface Calculations: (See Handout for Site Plan B#57)
a. Please add eves to all existing structure square footage in the “new” imper. surface
calculations.
b. Please add a “Total Proposed” for all impervious surface add with this project only.
c. Indicate the year the “Walk/Patio” was added.
10. 1/26/10 Done.
11. 1/26/10 Done.
12.1/26/10 Please add BOF to site plan and also add amount of proposed grading to site plan.
Previous Comments: Please add BOF (bottom of footing) elevation and total grading amount.
13. 1/26/10 Done.
ND
REVIEW COMMENTS:
1/26/10 DRAINAGE: STORM WATER ENGINEER 2
The submittals are confusing and do not provide the information needed to ascertain compliance with the stormwater
complete storm drainage report
code in ECDC Chapter 18.30. A needs to be written with the following sections:
1.Project Description: Provide a description of what is being added to site and what is being removed. Describe
the existing drainage system on the site (if any) what it collects, how it operates, and where it discharges. Also
discuss any run-on that enters the property from the road or neighboring properties.
2.Calculate the "new" impervious surface area from the project. Generally "new" impervious surface is roofs,
driveways, walkways or any other surface that prevents rainwater from soaking into the ground created after July
7, 1977. It appears that the original house, pool and pool house were built prior to that date and technically do
not need to be included in the calculation, unless some of it is being removed (including the foundation) and being
rebuilt, in that case the rebuilt part would be "new" impervious surface. . However, given that the house is down
gradient of the large driveway, designing the drainage system for all the impervious would be beneficial. Note
that porous concrete is viewed as 50% impervious only if the slope is less than 5%. Anything greater than 5%, it
is considered 100% impervious since the water will runoff before it has a chance to infiltrate. Also, a cross-
section of the area of the intended use of porous concrete needs to be shown to ensure that the sub grade can
handle the infiltration.
3.Determine requirements based on "new" impervious surface. There are different/additional requirements for
projects with between 2,000 and 5,000 sf of “new” impervious and projects that have greater than 5,000 square
feet of “new” impervious. Read ECDC 18.30.060 carefully for the applicable requirements.
all
4.Describe how the proposed storm drainage system will meet the requirements identified in section 3. Provide
all
calculations and modeling input and output files.
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5.Describe the operation and maintenance requirements for the designed storm drainage system.On the
drawings, identify invert elevations, slopes on all piping and show how all impervious surfaces connect to the
storm drainage system (downspouts, driveways, walkways, etc.)
Edmonds Community Development Code (ECDC) Chapter 18.30.060 A.1 states that infiltration is only allowed in the
green areas shown on the enclosed map (Everett gravelly sand loam). If the applicant wants to pursue infiltration, the
exemption under 18.30.065 should be pursued by showing equivalent environmental protection, feasibility, and showing
that it will not create an flooding or erosion problem on or off the site. Please review Chapter 18.30.065 for the process
necessary for consideration of use of infiltration on this site.
If the project has less that 5,000 sf of new impervious surface, a detention system sized per Handout #E72 may be
proposed. If 5,000 or greater, the detention system must be designed by an Engineer per ECDC 18.30.060.A1.
The City is working on a new drainage code that will likely go into effect this Spring. The draft can be found at
http://www.ci.edmonds.wa.us/strm_wtr_mgmt.stm
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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