bld20100426-Denham_ENG1.pdf
City of Edmonds BLD20100426
TH
121 5 AVENUE NORTH EDMONDS, WA 98020 • (425) 771-0220 FAX(425) 771-0221
Website: www.ci.edmonds.wa.us
PUBLIC WORK DEPARTMENT
Planning • Building • Engineering
Engineering Plan Review Comments
Permit Application :Date:
# BLD20100426 July 15, 2010
Project Name/Address:
Denham – 18106 Andover St
Contact Person/Address, Fax or E-mail:
bdflyfish@comcast.net
Reviewer: JENNIFER LAMBERT Division:
ENGINEERING
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
our website: www.ci.edmonds.wa.us under City Government / Development Services Department /
Engineering Division then scroll down to Handouts:
1)Please show the impervious surface calculations as shown below:
TypeArea (square Feet)
Line
Exempt
1.
ExemptNon-Exempt
Replaced
2.
New
3.
Total Replaced +New (Non-
Exempt) =
4.
(add numbers in blue boxes)
2)Please show the year of construction on the Site Plan as shown in the Sample Site Plan provided.
3)Please fill out the stormwater worksheet provided in handout #E72 (attached) and submit with
plans
4)Please show the existing storm detention system on the plans.
5)It appears that the concrete driveway abuts the house and extends along the north side of the
home. Please revise plans to show the existing concrete as it exists.
6)Show the appropriate temporary erosion control measures to be installed and note the
appropriate City of Edmonds Standards details.
DATE E-MAILED 7/15/10 PAGE(1)
City of Edmonds BLD20100426
TH
121 5 AVENUE NORTH EDMONDS, WA 98020 • (425) 771-0220 FAX(425) 771-0221
Website: www.ci.edmonds.wa.us
PUBLIC WORK DEPARTMENT
Planning • Building • Engineering
Engineering Plan Review Comments
7)Please show all trees within the construction area and label to be removed or remain.
a.If trees are to remain and near the construction area, please show a barrier fence around
the tree to protect during construction.
8)Show the location of the side sewer from the sewer main to the house (see attached).
9) Please provide grading calculations.
a.Please show bottom of footing elevations so that grading calculations can be verified.
The stormwater portion of the application is currently being reviewed. Comments to follow.
Please resubmit 3 copies of the revised traffic control plans and associated documents with a written
response to each item to an Engineering Technician. Please contact me at 425-771-0220 ext 1321 or by e-
mail at jennifer.lambert@ci.edmonds.wa.us if you have specific questions regarding these plan
corrections.
DATE E-MAILED 7/15/10 PAGE(1)
#E72
City of Edmonds
Development Information
STORMWATER MANAGEMENT (SWM)
DRAINAGE SYSTEM DESIGN, AND
EROSION & SEDIMENT CONTROL REQUIREMENTS
Stormwaterrunofffromdevelopment,redevelopment,andconstructionsitesisregulated
underEdmondsCommunityDevelopmentCode(ECDC)Chapter18.30,includingExhibitA:
%£¬®£²3³®±¬¶ ³¤±3´¯¯«¤¬¤³Ȩ3´¯¯«¤¬¤³ȩȁ
Overall Stormwater Management Approach
This handout contains an overall summary of the requirements and options available to assist an applicant in
designing, constructing, and maintaining stormwater Best Management Practices (BMPs) in the City of
Edmonds to meet the intent of ECDC 18.30. The Stormwater Supplement booklet is available for use in our
Development Services Department as well as on the City’s Website (www.ci.edmonds.wa.us). Please refer
to the Supplement for a more detailed explanation of each requirement. Applicants are encouraged to use the
Classification Worksheet on page 5 of this handout to determine the requirements for their project.
Step 1 – Determine Applicability Step 4 – Plan Site and Select BMPs
The first step is to determine if the Stormwater Use site planning along with BMP selection and
Management code applies to your project. Use design process described in the Supplement to
Figure-A, pg 3, in this handout to establish whether meet or exceed the minimum requirements for your
your project or site meets any of the criteria listed project.
under “applicability”.
Step 5 – Submit Reports and Plans for Review
Step 2 – Determine Your Project Site’s
Submit all required reports and plans for review.
Classification and Drainage Basin
The handout for the appropriate classification of
Use the Classification Worksheet, pg 5, to gather
your project (Large, Small or Minor) will provide
the information necessary to determine whether
information regarding the submittal requirements.
your project is considered a Large, Small, or Minor
The stormwater submittals will be reviewed
Site Project. For Small Site Projects, you will
concurrently with all other permit submittals.
further determine whether it is a Category 1 or a
Revision to reports and plans may be required per
Category 2 project. See Figure-D, pg 8.
City of Edmonds review.
Identify the drainage basin for your site using the
Step 6 – Construction
City of Edmonds Watershed Map, Figure-B, pg 4.
Erosion & Sediment Control Measures must be
Step 3 – Determine the Minimum inspected and approved by the City’s Engineering
Division prior to the start of construction. The
Requirements Needed and Where on the Site
project shall be constructed per approved plans.
They Apply
Any changes proposed to the approved plans must
The minimum requirements are based on the
be submitted to the Engineering Division for
project classification determined in Step 2. A
review and approval prior to construction.
summary of the Minimum Requirements can be
found on Pg 2 of this handout. For specific site
Step 7 – Operate and Maintain BMPs
requirements per classification see handout E72a
Operate and maintain BMPs as required by the
for Large Sites, E72b for Small Sites, or E72c
approved submittals.
for Minor Sites .
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Overview of Stormwater Management Minimum Requirements
Depending on the type, location, and size of the proposed project, different combinations of these
minimum requirements apply. The following is a brief list of the overall Minimum Requirements for
Large, Small, and Minor sites. Please refer to The Stormwater Supplement and the appropriate Large,
Small, or Minor site Handout for additional information.
LARGE SITES
– See Handout E72a
A project or overall development involving 1 acre or more of land disturbing activity would
potentially require the following Minimum Requirements:
1. Preparation of Stormwater Site Plan
2. Construction Stormwater Pollution Prevention Plan
3. Source Control of Pollution
4. Preservation of Natural Drainage Systems and Outfalls
5. Onsite Stormwater Management
6. Runoff Treatment
7. Flow Control
8. Wetland Protection
9. Operation and Maintenance
10. Offsite Analysis and Mitigation
SMALL SITES
– See Handout E72b
A project that involves 2,000 square feet (sf) or more of new or replaced non-exempt
impervious surface, 7,000 sf of land-disturbing activity, 50 cubic yards (cyds) or more of grading, fill
or excavation, conversion of ¾ acre or more of native vegetation to lawn or landscaped area, or causes
an increase of 0.1 cubic feet per second (cf/s) or more in the 100 year flow frequency from a threshold
discharge area would potentially require the following Small Site Minimum Requirements (SSMRs):
1. & 2. Site Plan including an Erosion and Sediment Control Plan
3. Source Control of Pollutants (for Multi-family or Commercial Projects)
4. Preservation of Natural Drainage Systems and Outfalls
5. Onsite Stormwater Management
6. Runoff Treatment
7. Flow Control
8. Wetland Protection
9. Operation and Maintenance
10. Off-Site Analysis
11. Financial Liability
MINOR SITES
– See Handout E72c
A project that involves 500 sf or more of new development or redevelopment including land-
disturbing activity or a utility project that causes land disturbance, and is not considered Large or Small
Site Projects must employ Minor Site Construction Stormwater Pollution Prevention Practices.
Additional Requirements may be imposed to meet the intent of the Stormwater Code based on site
specific factors.
Note: Terms in Bold are defined in Handout on page 9.
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Figure-A
Determining Applicability of Stormwater Management Code ECDC Chapter 18.30
If any of the descriptions in the Blue Boxes apply to your project or project site, the
Stormwater Management Code applies.
Does your Project Site require the issuance of a City permit
Yes
under any of the following:
ECDC Title 18 - Engineering Division
ECDC Title 19 - Building Division
2
A Stormwater Permit
No
Yes
Are you submitting a Subdivision application per
ECDC Chapter 20.75?
No
Stormwater
Does your Project site involve any of the following:
Management
requirements of ECDC
500 square feet or more of land-disturbing
Yes
are
Chapter 18.30
activity,new impervious surface, or replaced
applicable to your
impervious surface?
Project or Site.
A utility or other construction projects
consisting of 500 lineal feet or more of
trench excavation?
Is located in, adjacent to, or drains into
(currently or as a result of the project) a
Critical Area or a Critical Area Buffer?
No
Stormwater Management
requirements of ECDC Chapter
not
18.30 are applicable to your
1
Project or Site
1
This chart provides an initial screening for determining applicability of ECDC Chapter 18.30. The results from using
this chart do not substitute for a determination of applicability by the Public Works Director or Designee per ECDC
Chapter 18.30.030 and the relevant portions of the Supplement.
2
If ECDC Chapter 18.30 is applicable to the proposed project and it does not require any other City-issued permit, a
Stormwater Permit and associated fees will be required.
NOTE: Terms in bold italics are defined in ECDC Chapter 18.30.010 or the Supplement.
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Figure-B
1
City of Edmonds Watersheds
Note: A larger version of the Edmonds Watershed Map is available in the Development Services Office and on the City
of Edmonds website at ci.edmonds.wa.us.
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City of Edmonds
Site ClassificationWorksheet
The project’s Classification serves to identify the specific Stormwater Management requirements applicable
to your site. Complete the worksheet below to determine whether your project falls into the classification of
Large SiteSmall SiteMinor Site
a, (Category 1 or Category 2), or a .
Step 1Exempt Impervious Surface Area
: Determine the for your project and enter it on line 1 of the
table (yellow box).
Step 2Replaced Impervious Surface Area
: Determine the for your project and enter it on line 2 of the table
below dividing the total between Exempt and Non-Exempt (orange and blue boxes); either or both may be zero.
Step 3New Impervious Surface Area
: Determine the for your project. If a portion of the new impervious surface
area is also Non-Exempt Replaced Impervious Surface Area subtract this from the total of the new impervious
surface area. Enter the final value on line 3 of the table below (blue box).
Step 4
: Add the values in the Non-exempt column for lines 2 and 3 and enter it into line 4 (green box).
Where does the existing site
Direct Discharge
runoff discharge?
Supplement
Edmonds Way Basin
(
Check all that apply)
Chapter 2.3
See Watershed Map
Creek or Lake Basin
Figure-B, Handout pg 4
TypeArea(square Feet)
Line
Impervious surface:
Exempt
Supplement 1.
How much and what type?
Chapter 2.2
ExemptNon-Exempt
(fill in colored boxes)
&
See Definitions, Handout pg 9
Replaced
Figure-C
2.
Figure-C, Handout pg 7
Examples, Handout pg 10
New
3.
Total Replaced +New (Non-Exempt) =
4.
(add numbers in blue boxes)
Land-disturbing activity area
Supplement
sf
Chapter 8
See Definitions, Handout pg 9
Grading, Fill or Excavation
sf
Area
Will project convert ¾ acre or
more of native vegetation to YESNO
lawn or landscaped area?
Project Classification Chart
Proceed to the (Figure D, pg 8) and use the data collected above to follow
the flow chart and determine the classification of your project.
Large Site (Handout E72a)Small Site (Handout E72b)Minor Site (Handout E72c)
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Figure-C
What Qualifies as New Impervious Surface?
START
Does the site have existing
Only the
impervious surfaces
that
Is this existing
impervious
after
were created July 6,
impervious surface
Yes
surfaces
1
1977?
currently connected
proposed with
to a City-approved
No
stormwater
the project are
3
facility
located on
considered
Yes
the project site?
New
Impervious
2
Surface.
No
Was a waiver granted
stormwater
for a
Yes
facility
for this
existing impervious
area?
No
Is the site zoned as single
Yes
family residential (Zone RS)?
No
No
Existing impervious surface
Creek
Is the site within a or
since
created July 6, 1977
Yes
4
Lake
drainage basin?
plus
proposed impervious
surface is considered New
Impervious Surface.
1
mitigation
This is the effective date of the City’s first drainage control ordinance. The intent of this cumulative impacts
requirement is to adequately mitigate for impervious surfaces on project sites that are submitted under separate permits. The
separate submittals could have project areas that do not meet thresholds but would meet thresholds if the projects are combined as
one project.
For parcels that were annexed to the City after this date, the date of annexation shall substitute for the effective date of the City’s
first drainage control ordinance. For annexed parcels, a functioning Snohomish County-approved stormwater management facility
can substitute for a City-approved facility.
2
For the purpose of this flowchart, it is assumed that all existing impervious surface will remain after the proposed project is
complete. If any existing impervious surface will be demolished for this project, the project may contain a combination of new and
replaced impervious surface. See Definitions, pg 9.
3
If there is an existing stormwater management system on site, contact the City’s Engineering Division to discuss whether the
existing system has the capacity for the new impervious surface area.
4
See Figure B, pg 4, and Supplement Section 2.3.
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Figure-D
Project Classification
If you have determined that your project meets the requirements for a
Stormwater Review using Figure 1, follow the Blue boxes in chart
below to determine the Classification of your project.
Yes
Does the project involve 1-
land-
acre or more of
Large Site Project
:
1
disturbing activity
?
See Handout E72a for
No
specific requirements
.
Yes
Is the project part of a larger
common plan of development or
sale
where the total disturbed area
Does the project create or add 5,000 square feet of
for the entire plan will total 1-acre
new impervious surface, replaced non-exempt
land-disturbing activity
or more of ?
impervious surfacereplaced non-
or new plus
exemptimpervious surface
?
No
OR
native vegetation
Convert ¾ acre or more of to
Does the Project involve one or more of the
lawn or landscaped area
Yes
following:
OR
new impervious
2,000 square feet or more of
effective
Through a combination of creating
surfacereplaced non-exempt impervious
,
impervious surface converted pervious
and
surfacereplaced non-exempt
or new plus
surfaces
, causes an increase of 0.1 cubic feet per
impervious surface
?
second in the 100-year flow frequency from a
OR
threshold discharge area
as estimated using an
land-disturbing activity
7,000 square feet of ?
approved model?
OR
grading, fill,
50 cubic yards or more of either
excavation
or as defined in Chapter
No
Yes
No
Category 1 Small Site Project:Category 2 Small Site Project:
See Handout E72b for specific See Handout E72b for specific
Minor Site Project
:
requirements requirements
See Handout E72c for specific
requirements
1
Land-disturbing Activity: Any activity that results in movement of earth, or a change in the existing soil cover (both
vegetative and non-vegetative) or the existing soil topography. Land disturbing activities include, but are not limited to
grading, filling, excavation, and compaction associated with stabilization of structures and road construction.
NOTES: Additional terms in bold italics are defined on pg 9 or can be found in ECDC Chapter 18.30.010 or the Supplement
Classification chart assumes the project in question meets applicability requirements of ECDC18.30.030.
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DEFINITIONS
Impervious Surface:
Hard surface area that either prevents or retards the entry of water into the
ground as it would occur in natural, undeveloped conditions. Impervious surfaces include, but are not
limited to, rooftops, driveways, walkways, concrete, asphalt, and packed earthen materials.
Decks will be considered impervious if one or more of the following apply:
Deck is made of “solid” material that does not allow rain water to run through it
Deck has “slots” where rainwater can run through but the ground under the deck does not allow
the rainwater to infiltrate into the ground.
is divided
For the purpose of determining stormwater control requirements, impervious surface
into four categories: “exempt”, “replaced exempt”, “replaced non-exempt”, and “new”. See
definitions below:
Exempt Impervious Surface:
All impervious surface area installed prior to July 7, 1977 or prior to the date the parcel
was annexed into the City from Snohomish County..
Replaced Impervious Surface
:
Any impervious surface on the project site that exists at the time of application that is proposed
to be removed* and re-established in the same footprint. This does not include impervious
surface removed for the sole purpose of installing utilities or performing maintenance.
Replaced impervious surface is further categorized as Exempt or Non-Exempt.
th
Exempt: impervious surface on site originally installed prior to July 7, 1977 or
prior to the date the parcel was annexed by the City from Snohomish County.
Non-Exempt:impervious surface on site originally installed on or after July 7,
1977 or on or after the date the parcel was annexed into the City from
Snohomish County.
*Removed, for the purposes of this definition, refers to the removal of building down to bare soil, or the
removal of concrete (PCC) or asphalt (AC) slabs, driveways, sidewalks etc. down to bare soil or base course.
New Impervious Surface:
Any impervious surface on the project site created on or after July 7, 1077 or on or after the date
the parcel was annexed into the City from Snohomish County that is not considered Replaced
Impervious Surface.
Land-disturbing Activity:
Any activity that results in movement of earth, a change in the existing soil cover (both
vegetative and non-vegetative), or in the existing soil topography. Land-disturbing activities
include but are not limited to clearing, grading, filling, excavation, and compaction of soils
associated with structure stabilization and road construction.
Pervious Surface:
Any surface that allows the entry of water into the ground as it would occur in nature.
Note: This information should not be used as a substitute for City codes and regulations. The Edmonds Community
Development Code (ECDC) may be viewed at www.ci.edmonds.wa.us/codes.stm. The applicant is responsible for
ensuring compliance with the fees and regulations that are applicable at the time of submittal. If you have a specific
question about a certain aspect of your project, please contact the Engineering Division at 121 Fifth Avenue North,
(425) 771-0220. Please note that other local, state, and/or federal permits or approvals may be required.
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EXAMPLES
ExemptReplaced ExemptReplaced Non-
The following are examples of how to determine the “,” “”, “
ExemptNew
” and “” impervious surface totals for a specific project. If you have any questions, please
contact an Engineering Technician.
Example 1:
1972 House 1200 square feet (sf) roofline
Driveway (paved) 60 sf
1999 House Addition 400 sf
2004 Detached Garage 600 sf with no stormwater system installed
Proposal: Garage Addition 140 sf roofline
The 1972 House and Driveway were constructed before to July 7,1977 so are considered “Exempt”
impervious area.
The 1999 Addition and 2004 Detached garage and current proposal are considered “New” impervious
surface since built after July 7, 1977.
Total New + Non-Exempt Impervious Surface: 1,140 sf (400sf + 600sf + 140sf) + 0 = 1,140 sf
Example 2
:
1968 House 1,500 sf roofline
Gravel Driveway 400 sf
Sidewalks/Patios 55 sf
Proposal: Pave Driveway with asphalt, same footprint as gravel driveway (400 sf).
Paving the gravel driveway counts as “Replaced Exempt” impervious surface. The driveway is a
combination of gravel and packed earthen material, this meets the definition of impervious surface. The
proposed paving will be in same footprint of the original driveway installed before July 7, 1977.
Total New + Non-Exempt Impervious Surface: 0 sf
Example 3a
:
1976 House 2,000 sf
Concrete Driveway 200 sf
1999 Garage w/concrete slab (no stormwater system) 300 sf
Proposal: New garage (300 sf) – demolish existing garage and slab, new garage will be same size and in
same location of the concrete slab and original garage to be replaced.
Proposed garage will be considered “Replaced Non-Exempt” because the existing impervious surface
(garage & slab) to be replaced was built afterJuly 7, 1977.
Total New + Non-Exempt Impervious: 0 + 300 sf = 300 sf
Example 3b
:
Same as above except concrete slab is not removed during garage demolition.
If slab remains and new garage has same roofline then no impervious surface is added or replaced.
Total New + Non-Exempt Impervious Surface: 0 sf
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Example 4:
1979 House 1,200 sf
Gravel driveway 300 sf
Patio/Walkways 100 sf
1989 Garage 250 sf
Proposal: Garage addition 200 sf and replacing gravel driveway with asphalt (300 sf)
House, patio/walkways, garage built afterJuly 7, 1977 with no storm system and therefore are considered
“New” impervious surface: 1,750 sf (1,200+100+250 +200)
Driveway was installed after July 7, 1977 so even though changing from gravel to asphalt in same footprint
it is considered “Replaced Non-Exempt” impervious surface: 300 sf
Total New + Non-Exempt Impervious: 1,750 sf + 300 sf = 2,050 sf
Example 5:
1989 House 2,800 sf
Driveway/patio/walkways 700 sf
The 1989 construction was approved with a detention system sized for 3500 sf of impervious surface that
was adequate under the provisions of the stormwater code effective at that time.
Proposal: 300 sf addition to house
Revised “New” impervious total 3,800 sf (zero replaced impervious).
The house, patio and walkways were installed after July 7, 1977 with a storm system.
The existing system does not meet the sizing requirements of today’s stormwater code for 3500 sf of
impervious surface. In this case, there are two options available to meet the stormwater flow control
requirements.
Option 1
Install a separate stormwater system that is sized only for the new addition 300sf. Since the
existing system was approved at the time of construction for requirements of the code in effect at that time,
resizing is not required.
Option 2
Upgrade the existing system to meet to handle both the existing impervious surface of (3500 sf)
and the proposed impervious surface (300 sf). The existing system would need to be sized for 3800 sf under
the sizing requirements of the current code.
In this case:
1989 Code requirements for 3500sf of impervious surface (existing system);
49 lineal ft of 18” diameter pipe with ¾” orifice.
Current Code requirements for 3800sf of impervious surface:
81 lineal ft of 18” diameter pipe with ¾” orifice.
Therefore applicant would need to add 32 lineal feet of 18”diameter pipe to existing detention system.
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