APPROVED STM BLD2020-0440 STORMWATER REPORTDECCIO Engineering Inc.
17217 7th Avenue W.
Bothell, WA. 98012
RES U B Fax: (-8(425) 25) 74141-8214
4
BLD2020-0440 Feb 17 2021
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
Coons SFD
Edmonds App # BLD2020-0440
Drainage Design Report,
O&M Manual & SWPP Report
APPLIES WITH APPLICABLE
CITY STROMWATER CODE
Property Location:
8427 202" Street SW
Edmonds, WA
May 21, 2020
Revised: September 19, 2020
Revised: December 25, 2020
Prepared for:
Mark and Jennifer Coons
Approval Note: The project has met the minimum requirement for mitigating storm water
per ECDC 18.30. However, the proposed design may result in conditions which are less
than desirable by the property owner. It should be noted that each downspout flow -path
is part of the protected BMP. The property owner will not be able to legally alter the
grades or expand improvements within these watercourses as shown without further
written approval from the City of Edmonds, appropriate offsetting mitigation for impacts
to the changed areas. No warranty of the proposed design is expressed in this approval.
Coons SFD 8427 202"d Street SW, Edmonds
STORMWATER DRAINAGE REPORT
TABLE OF CONTENTS
Page
Introduction.......................................................................................................................................... 2
Section 1: Project Overview................................................................................................................2
Section 2: Existing Site Conditions
2
Section 3: Offsite Analysis
Off -Site Analysis and Mitigation................................................................................................... 5
Section4: Minimum Requirements..............................................................................................8
Section 5: Stormwater Control Plan...........................................................................................10
Section 6: Pollution Prevention Plan..........................................................................................14
Section 7: Special Reports and Studies.......................................................................................16
Section8: Other Permits.........................................................................................................16
Section 9: Operations and Maintenance..................................................................17
List of Figures:
Site Location and Vicinity Map
Existing Site Conditions
Developed Site Conditions
Downstream Analysis and Sub -Basin Map
APPENDIX A
Soils Management Form
Soils Option 3
Small Scale PIT Report
Introduction
This report has been prepared at the request of Mark and Jennifer Coons in support of a single family
residential building permit for a site located on the north side of 202 Street SW, Edmonds,
Washington in the NE 1/4 of the SE 1/4 Section 19, Township 27 North, Range 04 East W.M. The
site address is 8427 202nd Street SW, Edmonds WA. (Parcel #27041900207400) (Refer to Site
Location and Vicinity Map).
This report addresses the drainage report contents and organization of MR 1 to MR 9 per DOE 2014
Stormwater Management Manual as adopted by the City of Edmonds. Specifically we have designed the
drainage using a review of the LID applications as outlined in Volume 1, Chapter 2, Table 2.5.1 of the
DOE 2014 Stormwater Management Manual.
Section 1: Project Overview
The project consists of construction of a new home on a 15,266 sf site. The existing lot contains a house
and garage which will be removed to build the new home and shop. The site cover is trees and lawn.
Once developed, the site will add a new home and driveway with a total of 7,322 sf of new impervious
area in the form of 4,965 sf for the roof of the home, covered deck, etc. The walks, parking and
driveway will account for the remaining 2,357 sf. The Small Scale Pit test performed for the site showed
the site soils to be clay with infiltration rates well below 0.30 inches per hour. Therefore, the site is not
suitable for any LID measures
The existing home and garage were built in 1948 before the adoption of the City's first drainage code.
The project proposes to address the runoff through the combined use of detention and BMPs in the form
of a 24" diameter detention pipe with a control structure manhole and splash blocks with 25-ft flow
paths.
The area of disturbance is 12,000 sf.
The Small Scale PIT Mportprepared for the site showed the soils were not suitableforinfiltration or any
type of dispersion.
Coons SFD Revised: December 25, 2020 Page 2
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VICINITY MAP
Section 2:
Existing Site Conditions
The project consists o construction of ahome o a15266s site. The eis+/ltc main ahome a J
garage. The site cover Gtrees and lawn. The stIc& flat witslopes less than I%and drains mthe smh
west
Coons gD Revised: December 25, 2020 Page 3
TIL
Existing Site Conditions
Coons SFD Revised: December 25, 2020 Page 4
Section: 3
Offsite Analysis Report
Per Section 2.5, Stormwater site plans and SWPP Plans have been prepared for the site and are included
with this storm drainage report. Detention is proposed for the site since the runoff from the roof, and
driveway are not suitable for LID methods and the impervious area is over 5,000 sf.
OFF SITE ANALYSIS AND MITIGATION
An Off Site Analysis and Mitigation Study meeting requirements outlined in Section 2.5.1 was
performed on March 30, 2020. The weather was partly cloudy and cool at the time of the field
inspection. See Downstream Analysis Map.
TASK I. PROJECT OVERVIEW & STUDYAREA DEFINITION
Existing Site Conditions: The project consists of construction of a home on a 15,266 sf site. The
existing lot contains a house and garage. The site cover is trees and lawn with slopes around 1-percent.
The site itself drains towards the south-west.
TASK 2: REVIEW OF AVAILABLE INFORMATION ON STUDY AREA
Resource Review:
The following is a description of the resources that were reviewed for the preparation of this Level 1
Drainage Study:
A. Basin Recognizance Summary: Enclosed within are downstream and upstream basin area
map which clearly define the flow pass and the drainage basins related to this project.
See (Downstream Analysis Map)
Evidence of Existing and Predicted Problems
Lack of capacity or constrictions in the existing drainage system.
0 On -site: No evidence of any problem.
0 Off -site: Stream None noted
Culverts None known
(no evidence of capacity or any other problems)
Overtopping, Scouring, Bank, Sloughing of Sedimentation
0 On -site: No evidence of any problem.
0 Off -site: C 12-inch pipes: N/A
C Stream Channel: none noted
Flooding etc.
0 None Noted
Significant Destruction of Aquatic Habitat or Organisms
0 None Noted
B. Adopted Basin Plans: None Known
Coons SFD Revised: December 25, 2020 Page 5
C. Floodplain/Floodway (FEMA Maps): Does not appear to be located within the flood plain of
the stream as determined by the FEMA maps.
D. Other Off -Site Analysis Issues: None Noted
TASK 3 & 4: FIELD INSPECTION AND DESCRIPTION OF DRAINAGE SYSTEM WITH
EXISTING AND PREDICTED PROBLEMS
A Level 1 drainage analysis and "Off Site Analysis and Mitigation Study" meeting requirements
outlined in Section 3.2.0 was performed. See Downstream Analysis Map.
Level 1 Downstream Drainage Analysis:
Section 1: Upstream Drainage Analysis:
The site and surrounding areas are very flat. A small portion of upstream off -site runoff may
enter the site from the east but this is minimal with nearly all upstream off -site runoff draining
mostly north-west and is diverted around the site. Therefore, the upstream runoff entering the
site is minimal.
A review of the upstream area indicated that there were no indications of problems observed.
Section 2: On -site Drainage Considerations:
All runoff from the site drains to the west and onto the neighboring property
Section 3: Site to Maplewood Coop site, to 200" Street SW to Northstream Creek.
The runoff from the site leaves the lot along the north-west property line onto the neighboring
property then onto the Maplewood Coop site, where it is intercepted by the storm pipe and catch
basin system on the property. From here the storm pipe system runs west along 200' Street SW.
It then turns and flows north along 891 Place SW before turning west and discharging into
Northstream Creek for a total piping distance of 3,200 feet. From here the stream flows north for
a distance of over 2,000 feet.
There appeared to be no issues with the downstream drainage system. However, 50% of the
downstream course was on private property and not accessible to inspection.
TASK 5: LEVEL 1 MITIGATION OF EXISTING PROBLEMS
In order to mitigate the site improvements, the project proposes the following BMP's
• The runoff from most the driveway area will be addressed using a dispersion trench with
minimum 10-ft flow path.
• The runoff from most the roof areas will be addressed using Splash Blocks with a minimum
of 25-ft flow path.
Runoff from the remaining roof and driveway area will be intercepted and detained in a
detention pipe which will then discharge to the existing catch basin at the front of the
property. This is proposed to prevent possible issues with the neighboring property to the
west.
Water Quality Requirements:
With less than 5,000 sf of PGIS area, water quality is not proposed for the site improvements.
Coons SFD Revised: December 25, 2020 Page 6
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Coons SFD Revised: December 25, 2020 Page 7
Section 4:
Minimum Requirements
• Minimum Requirement #1: Preparation of Stormwater Plans
o The civil plans and Section 5 of this report addresses the preparation of the
stormwater plans required for this project.
• Minimum Requirement #2: Construction Stormwater Pollution Prevention Narrative.
o Section 6 of this report addresses all 13-elements of a SWPP Plan
• Minimum Requirement #3: Source Control of Pollution
o Since the project is for residential lots, the project does not fall under the "High Use
Sites" covering commercial or industrial sites. Section 6 of this report covers further
details for Source Control of Pollution.
• Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls
o All runoff currently leaves the site along the south-west side of the property and the
proposed discharge location for the site improvements is to the south-west, thereby
maintaining the natural discharge location.
• Minimum Requirement #5: On -Site Stormwater Management BMP's
o Section 5 of this report addresses the on -site bmps and the justification of why they
can or cannot be used.
• Minimum Requirement #6: Runoff Treatment
o Since the PGIS area is under 5,000 sf, runoff treatment is not required.
• Minimum Requirement #7: Flow Control
o The project will require partial flow control in the form of a 24" diameter detention
pipe with controlled release.
• Minimum Requirement #8: Wetlands Protection
o There are no wetlands or other sensitive areas on site.
• Minimum Requirement #9: Operations and Maintenance.
o Section 9 of the report covers the Operations and Maintenance of the project.
Coons SFD Revised: December 25, 2020 Page 8
EDMONDS STORMWATER ADDENDUM
JUNE 2017
Does the project result in 2,000 square feet, or greater, of new plus replaced hard surface area?
OR
Does the land disturbing activity total 7,000 square feet or greater?
elies No
Minimum Requirements No. 1 through 5 apply I Minimum Requirement No. 2 applies
Next Question
Does the project add 5,000 square feet or more of new plus replaced hard surfaces?
OR
Convert 0.75 acres or more of vegetation to lawn or landscaped areas?
OR
Convert 2.5 acres or more of native vegetation to pasture?
es
Is this a road related project?
All Minimum Requirements
apply to the new and replaced Yes
hard surfaces and converted
vegetation areas.
All Minimum Requirements
apply to the new hard surfaces
and converted vegetation areas.
No
Yes
Does the project add
5,000 square feet or No
more of new hard
surfaces?
Yes
Do new hard surfaces add 50% or
more to the existing hard surfaces
within the project limits?
No
Figure 3.1. Flow Chart for Determining Requirements for Development.
No additional I
requirements.
Coons SFD Revised: December 25, 2020 Page 9
Section: 5
Stormwater Control Plan
As discussed above, once developed the site will contain a new home, shop and driveway. The total
impervious area including the home and driveway, will be 7,240 sf in size
Under the On -Site Stormwater Management Requirements" the "Low Impact Development
Performance Standards" specifically List 2 of the DOE 2014 Stormwater Management Manual,
Volume 1, Chapter 2, Table 2.5.1, and BMP T5.13 requires that each item must be review and analyzed
for use. The BMP's listed below were reviewed using City of Edmonds "Appendix A: On -Site
Stormwater Management BMP Infeasibility Criteria" as follows:
TABLE 2.5.1 LIST #2 BMP FEASIBILITY
Lawn and landscaped areas:
1. Post -Construction Soil Quality and Depth in accordance with BMP T5.13 in Volume V, Chapter
5 of this manual (Will be used)
Roofs:
1. Full Dispersion in accordance with BMP T5.30 in Volume V, Chapter 5 of this manual, or,
for single-family residential roofs and commercial roofs determined by City to have similar
runoff pollution characteristics to single-family residential roofs, Downspout Full
Infiltration Systems in accordance with BMP T5. I OA in Volume III, Chapter 3 of this
manual. (Infeasible)
The site cannot meet the required flow paths and the site has been cleared and
contains no native vegetation to implement Full Dispersion
The Small PIT testperformed on site, found that the site soils are not suitable for
infiltration with infiltration rates well below 0.30 inches/hour to implement Full
Infiltration
2. Bioretention/Raingardens in accordance with Volume V, Chap 7 of this manual. (Infeasible)
• Small PIT test performed on site, found that the site soils are not suitable for
infiltration with infiltration rates well below 0.30 inches/hour in order to
implement Bioretention and/or raingardens.
• The 1 ft vertical separation between the impermeable layer and the bottom of the
trench cannot be met.
3. Downspout Dispersion for single-family residential roofs and commercial roofs determined
by the City to have similar runoffpollution characteristics to single-family residential roofs,
Downspout Dispersion Systems in accordance with BMP T5. IOB in Volume III, Chapter 3 of
this manual.
• The site will provide splash blocks with minimum 25-ft flow paths for the roof
4. For single-family residential roofs and commercial roofs determined by City to have similar
runoff pollution characteristics to single-family residential roofs, perforated Stub -out
Connections in accordance with BMP T5.1 OC in Volume III, Chapter 3 of this manual.
• The Small PIT test performed on site, found that the site soils are not suitable for
infiltration with rates below 0.30 inches/hour.
Coons SFD Revised: December 25, 2020 Page 10
Other Hard Surfaces:
1. Full Dispersion in accordance with BMP T5.30 in Volume V, Chapter 5 of this manual.
(Infeasible)
• The site cannot meet the required flow paths and the site has been cleared and
contains no native vegetation to implement Full Dispersion
• The Small PIT test performed on site, found that the site soils are not suitable for
infiltration with rates below 0.30 inches/hour.
2. Permeable pavement in accordance with BMP T5.15 in Volume V, Chapter 5 of this
manual. NOTE: This is not a requirement to pave these surfaces. Where pavement is
proposed, it must be permeable to the extent feasible unless full dispersion is employed.
(Infeasible)
• The Small PIT test performed on site, found that the site soils are not suitable for
infiltration, with rates well below the 0.30 inches per hour in order to
implement permeable pavement.
3. Bioretention in accordance with Volume V, Chapter 7 of this manual. (Not feasible.
• Based on the flat grades for the site, the bioretention system will back up water into
the downspout pipes causing flooding of the crawl area.
• The 1 ft vertical separation between the impermeable layer and the bottom of the
trench cannot be met
4. Sheet Flow Dispersion in accordance with BMP T5.12, or Concentrated Flow Dispersion in
accordance with BMP T5.11 in Volume V, Chapter 5 of this manual. (The project will use
sheet flow dispersion with 10 ft to 15 ft flow path)
Water quality: Since the PGHS area is under 5,000 sf water quality is not required for the Driveway.
BMP T5.13 "Post Construction Soil Quality and Depth"
The top soils will be stockpile on -site and reused per "Implementation Options #3 per BMP T5.13 "Post
Construction Soil Quality and Depth" which requires "Stockpile existing top soils during grading and
replace it prior to planting... " (See work sheets "List of Figures")
Flow Control Calculations
The project proposes to pick up the runoff for part of the roof and driveway areas, then detain it in a
24-inch pipe with a controlled release. The remaining impervious areas will use BMP's to address
the runoff from the site improvements.
Under Section 6.3.1 "Sizing" the City has created a simplified method for sizing detention tanks
Coons SFD Revised: December 25, 2020 Page 11
DETENTION PIPE CALCULATIONS
• Pavement Area:
1,100 SF
• Carport Roof Area:
534 SF
• Main Roof 1 Area:
420 SF
• Main Roof 2 Area:
682 SF
Total Area to Pipe:
2,736 SF
Pipe Length Required: 2,736 sf (0.019) = 52.0 if 24" Pipe
PROPOSED STORMWA TER BMPS
• Roof Splash Blocks Required
o Roof Area: 3,965 sf to use splash blocks/ 700 sf = 6 splash blks required
• Driveway Dispersion: Requires min 10 foot vegetated flow paths. The plans show the use of
a 2 ft wide by 6" deep rockfilled trench located along the edge of the driveway to disperse
the runoff to the soil amended grass line vegetated flow path located between the driveway
and property line.
Coons SFD Revised: December 25, 2020 Page 12
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Coons SFD Revised: December 25, 2020 Page 13
Section 6:
SWPP Plan Narrative
The topography of the site containing the proposed site improvements is flat with slopes under 1 %.
The soils have identified as a type C soil not suitable for infiltration. With minimal disturbance
and standard erosion control measures such as silt fence, straw mulching and hydro -seeding,
the risk of erosion can be minimized. The limits of clearing will be restricted to the building site
and lot. Greater source control measures would have to be taken during winter construction such as
mulching or plastic sheeting. Good construction practices will prevent any sediment from leaving
the site.
The following are BMP measures to limit adverse impact upon the off -site drainage system:
• Filter fabric fences, as required
• Limited clearing area
• Rock construction entrance pad
• Seeding/ landscaping of any bare areas
• Limited months of construction
• On -Site Fueling (N/A No re -fueling will take place on -site)
• Concrete Wash -out (per BMP C-151)
Coons SFD Revised: December 25, 2020 Page 14
THE 13 ELEMENTS OF A CONSTRUCTION SWPPP
1. Preserve Vegetation/Mark Clearing Limits: The clearing limits are indicated on the plan sheet. Furthermore,
clearing and grading will be limited to only areas that need to be disturbed for grading/construction of the road
surface to preserve as much natural vegetation as possible. Field marking the clearing limits shall be completed
prior to clearing and grubbing activities.
BMP's: Preserve Natural Vegetation (VEG)
Field Marking Clearing Limits (CL)
2. Establish Construction Access: Access to the construction site shall be limited to the rock construction
entrance. The construction entrance shall be extended to provide access to the construction vehicle/equipment
staging and employee parking areas.
BMP's: Stabilized Construction Entrance (CE)
3. Control of Flow Rates: Storm water detention: No detention is proposed for the site since the increase in
volume is less minimal
4. Installation of Sediment Controls: Sediment control will be provided through a combination of filtration
through the surround on -site vegetation, filter fence, straw bails,
BMP's: Silt Fence (FF) If required
5. Soils Stabilization: Temporary and permanent soil stabilization will be provided. Temporary stabilization will
be provided through the application of straw and/or plastic sheeting to exposed, worked earth. From October 1
until April 30, no exposed soil may remain exposed and unworked for more than two days; after May 1, no
exposed soil may remain exposed and unworked for more than seven days.
BMP's: Plastic Sheeting,
6. Slope Protection: Slopes shall be protected from erosion through cover and prevention of concentrated surface
runoff flows.
BMP's: Plastic Sheeting,
7. Protection of Permanent Drain Inlets: Inlet protection will pe provided for all catch basins.
BMP's: N/A
8. Stabilization of Channels and Outlets: All channel slopes shall be constructed and protected against erosion
in accordance with City E.D.D.S.
BMP's: None required
9. Pollutant Control: Pollutants shall be controlled as described in the Potential Pollutants section of this
SWPPP.
10. Dewatering Control: De -watering: Interception of the water table is not expected to occur, even if there is an
increase in precipitation. However, should ground water flows be encountered, the flows can be directed to on
site native vegetation for cleanup.
BMP's: Native vegetation (As Required)
11. BMP Maintenance: All BMP's and SWPPP elements shall be inspected daily and maintained as required.
12. Project Management: The project shall be managed in a cooperative effort by the project manager, contractor,
engineer, and the City inspector. During the construction process, if unforeseen issues arise that cannot be
resolved on site, construction activity (other than SWPPP maintenance) shall be halted and the City inspector
and the project engineer are to be contacted and informed of the situation.
13. Protect On -Site Stormwater Management BMPs For Runoff From Roofs And Other Hard Surface
On -site stormwater management BMPs used for runoff from roofs and other hard surfaces include: full
dispersion, roof downspout full infiltration or dispersion systems, perforated stubout connections, rain gardens,
bioretention systems, permeable pavement, sheetflow dispersion, and concentrated flow dispersion. The areas
on the site to be used for these BMPs shall be protected from siltation and compaction during construction by
sequencing the construction in a fashion to install these BMPs at the latter part of the construction grading
operations, by excluding equipment from the BMPS and the associated areas, and by using the erosion and
sedimentation control BMPs. BMP C 102: Buffer Zone
Coons SFD Revised: December 25, 2020 Page 15
Water Pollution Source Control
Since the project is for residential lots, the project does not fall under the "High Use Sites" covering commercial or
industrial sites.
BMP C-151: Concrete Handling (Design and Installation Specifications)
Concrete truck chutes, pumps, and internals shall be washed out only into formed areas awaiting installation of
concrete or asphalt. Unused concrete remaining in the truck and pump shall be returned to the originating batch
plant for recycling.
Hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels shall be washed off only
into formed areas awaiting installation of concrete or asphalt.
Equipment that cannot be easily moved, such as concrete pavers, shall only be washed in areas that do not
directly drain to natural or constructed stormwater conveyances.
Washdown from areas such as concrete aggregate driveways shall not drain directly to natural or constructed
stormwater conveyances.
When no formed areas are available, washwater and leftover product shall be contained in a lined container.
Contained concrete shall be disposed of in a manner that does not violate groundwater or surface water quality
standards
Maintenance Standards
Containers shall be checked for holes in the liner daily during concrete pours and repaired the same day
Section: 7
Special Reports and Studies
"Small Scale PIT Report" Prepared by Robert Edwards PE Dated March 9, 2020
Section: 8
Other Permits
• Residential Building Permit required.
Coons SFD Revised: December 25, 2020 Page 16
Section: 9
Operations and Maintenance
Maintenance of all proposed drainage facilities is the responsibility of the property owner.
The system consists of:
• 1- Catch Basin Type 1
• 2-Type 2 Catch Basins
• 1-Control Structure
• Splash Blocks
Coons SFD Revised: December 25, 2020 Page 17
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO.3 — DETENTION TANKS AND VAULTS
Maintenance
Defect or Problem
Conditions When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Site
Trash and debris
Any trash and debris which exceed 1 cubic foot
Trash and debris cleared from site.
per 1,000 square feet (this is about equal to the
amount of trash it would take to fill up one
standard size office garbage can). In general,
there should be no visual evidence of dumping.
Noxious weeds
Any noxious or nuisance vegetation which may
Noxious and nuisance vegetation
constitute a hazard to County personnel or the
removed according to applicable
public.
regulations. No danger of noxious
vegetation where County personnel
or the public might normally be.
Contaminants and
Any evidence of contaminants or pollution such
Materials removed and disposed of
pollution
as oil, gasoline, concrete slurries or paint.
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Grass/groundcover
Grass or groundcover exceeds 18 inches in
Grass or groundcover mowed to a
height.
height no greater than 6 inches.
Tank or Vault
Trash and debris
Any trash and debris accumulated in vault or
No trash or debris in vault.
Storage Area
tank (includes floatables and non-floatables).
Sediment
Accumulated sediment depth exceeds 10% of
All sediment removed from storage
accumulation
the diameter of the storage area for % length of
area.
storage vault or any point depth exceeds 15% of
diameter. Example: 72-inch storage tank would
require cleaning when sediment reaches depth of
7 inches for more than % length of tank.
Tank Structure
Plugged air vent
Any blockage of the vent.
Tank or vault freely vents.
Tank bent out of
Any part of tank/pipe is bent out of shape more
Tank repaired or replaced to design.
shape
than 10% of its design shape.
Gaps between
A gap wider than %-inch at the joint of any tank
No water or soil entering tank
sections, damaged
sections or any evidence of soil particles entering
through joints or walls.
joints or cracks or
the tank at a joint or through a wall.
tears in wall
Vault Structure
Damage to wall,
Cracks wider than % inch, any evidence of soil
Vault is sealed and structurally
frame, bottom, and/or
entering the structure through cracks or qualified
sound.
top slab
inspection personnel determines that the vault is
not structurally sound.
Inlet/Outlet Pipes
Sediment
Sediment filling 20% or more of the pipe.
In pipes clear of sediment.
accumulation
Trash and debris
Trash and debris accumulated in inlet/outlet
No trash or debris in pipes.
pipes (includes floatables and non-floatables).
Damaged
Cracks wider than %cinch at the joint of the
No cracks more than %-inch wide at
inlet/outlet pipes or any evidence of soil entering
the joint of the inlet/outlet pipe.
at the joints of the inlet/outlet pipes.
2016 Surface Water Design Manual — Appendix A
A-5
4/24/2016
Coons SFD Revised: December 25, 2020 Page 18
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO.3 — DETENTION TANKS AND VAULTS
Maintenance
Defect or Problem
Conditions When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Access Manhole
Cover/lid not in place
CoverRid is missing or only partially in place.
Manhole access covered.
Any open manhole requires immediate
maintenance.
Locking mechanism
Mechanism cannot be opened by one
Mechanism opens with proper tools.
not working
maintenance person with proper tools. Bolts
cannot be seated. Self-locking cover lid does not
work.
Cover/lid difficult to
One maintenance person cannot remove
Cover/lid can be removed and
remove
cover/lid after applying 80 Ibs of lift.
reinstalled by one maintenance
person.
Ladder rungs unsafe
Missing rungs, misalignment, rust, or cracks.
Ladder meets design standards.
Allows maintenance person safe
access.
Large access
Damaged or difficult
Large access doors or plates cannot be
Replace or repair access door so it
doors/plate
to open
opened/removed using normal equipment.
can opened as designed.
Gaps, doesn't cover
Large access doors not flat and/or access
Doors close flat, covers access
completely
opening not completely covered.
opening completely.
Lifting Rings missing,
Lifting rings not capable of lifting weight of door
Lifting rings sufficient to lift or
rusted
or plate.
remove door or plate.
4/24/2016
A-6
2016 Surface Water Design Manual —Appendix A
Coons SFD Revised: December 25, 2020 Page 19
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO.4 — CONTROL STRUCTURE/FLOW RESTRICTOR
Maintenance
Defect or Problem
Condition When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Structure
Trash and debris
Trash or debris of more than % cubic foot which
No Trash or debris blocking or
is located immediately in front of the structure
potentially blocking entrance to
opening or is blocking capacity of the structure
structure.
by more than 10%.
Trash or debris in the structure that exceeds 1/2
No trash or debris in the structure.
the depth from the bottom of basin to invert the
lowest pipe into or out of the basin.
Deposits of garbage exceeding 1 cubic foot in
No condition present which would
volume.
attract or support the breeding of
insects or rodents.
Sediment
Sediment exceeds 60% of the depth from the
Sump of structure contains no
bottom of the structure to the invert of the lowest
sediment.
pipe into or out of the structure or the bottom of
the FROP-T section or is within 6 inches of the
invert of the lowest pipe into or out of the
structure or the bottom of the FROP-T section.
Damage to frame
Corner of frame extends more than A inch past
Frame is even with curb.
and/or top slab
curb face into the street (If applicable).
Top slab has holes larger than 2 square inches
Top slab is free of holes and cracks.
or cracks wider than Y inch.
Frame not sitting flush on top slab, i.e.,
Frame is sitting flush on top slab.
separation of more than A inch of the frame from
the top slab.
Cracks in walls or
Cracks wider than V inch and longer than 3 feet,
Structure is sealed and structurally
bottom
any evidence of soil particles entering structure
sound.
through cracks, or maintenance person judges
that structure is unsound.
Cracks wider than % inch and longer than 1 foot
No cracks more than '/4 inch wide at
at the joint of any inlet/outlet pipe or any
the joint of inlet/outlet pipe.
evidence of soil particles entering structure
through cracks.
Settlement/
Structure has settled more than 1 inch or has
Basin replaced or repaired to design
misalignment
rotated more than 2 inches out of alignment.
standards.
Damaged pipe joints
Cracks wider than % inch at the joint of the
No cracks more than Y-inch wide at
inlet/outlet pipes or any evidence of soil entering
the joint of inlet/outlet pipes.
the structure at the joint of the inlet/outlet pipes.
Contaminants and
Any evidence of contaminants or pollution such
Materials removed and disposed of
pollution
as oil, gasoline, concrete slurries or paint.
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Ladder rungs missing
Ladder is unsafe due to missing rungs,
Ladder meets design standards and
or unsafe
misalignment, rust, cracks, or sharp edges.
allows maintenance person safe
access.
FROP-T Section
Damage
T section is not securely attached to structure
T section securely attached to wall
wall and outlet pipe structure should support at
and outlet pipe.
least 1,000 Ibs of up or down pressure.
Structure is not in upright position (allow up to
Structure in correct position.
10%from plumb).
Connections to outlet pipe are not watertight or
Connections to outlet pipe are water
show signs of deteriorated grout.
tight; structure repaired or replaced
and works as designed.
Any holes —other than designed holes —in the
Structure has no holes other than
structure.
designed holes.
2016 Surface Water Design Manual — Appendix A
A-7
4/24/2016
Coons SFD Revised: December 25, 2020 Page 20
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO.4 — CONTROL STRUCTURE/FLOW RESTRICTOR
Maintenance
Defect or Problem
Condition When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Cleanout Gate
Damaged or missing
Cleanout gate is missing.
Replace cleanout gate.
Cleanout gate is not watertight.
Gate is watertight and works as
designed.
Gate cannot be moved up and down by one
Gate moves up and down easily and
maintenance person.
is watertight.
Chain/rod leading to gate is missing or damaged.
Chain is in place and works as
designed.
Orifice Plate
Damaged or missing
Control device is not working properly due to
Plate is in place and works as
missing, out of place, or bent orifice plate.
designed.
Obstructions
Any trash, debris, sediment, or vegetation
Plate is free of all obstructions and
blocking the plate.
works as designed.
Overflow Pipe
Obstructions
Any trash or debris blocking (or having the
Pipe is free of all obstructions and
potential of blocking) the overflow pipe.
works as designed.
Deformed or
Lip of overflow pipe is bent or deformed.
Overflow pipe does not allow
damaged lip
overflow at an elevation lower than
design
Inlet/Outlet Pipe
Sediment
Sediment filling 20% or more of the pipe.
In pipes clear of sediment.
accumulation
Trash and debris
Trash and debris accumulated in inlet/outlet
No trash or debris in pipes.
pipes (includes floatables and non-floatables).
Damaged
Cracks wider than % inch at the joint of the
No cracks more than Y.-inch wide at
inlet/outlet pipes or any evidence of soil entering
the joint of the inlet/outlet pipe.
at the joints of the inlet/outlet pipes.
Metal Grates
Unsafe grate opening
Grate with opening wider than 7/8 inch.
Grate opening meets design
(If Applicable)
standards.
Trash and debris
Trash and debris that is blocking more than 20%
Grate free of trash and debris.
of grate surface.
footnote to guidelines for disposal
Damaged or missing
Grate missing or broken member(s) of the grate.
Grate is in place and meets design
standards.
Manhole Cover/Lid
CoverAid not in place
CoverAid is missing or only partially in place.
CoverAid protects opening to
Any open structure requires urgent
structure.
maintenance.
Locking mechanism
Mechanism cannot be opened by one
Mechanism opens with proper tools.
Not Working
maintenance person with proper tools. Bolts
cannot be seated. Self-locking coverAid does not
work.
CoverAid difficult to
One maintenance person cannot remove
CoverAid can be removed and
Remove
cover/lid after applying 80 lbs. of lift.
reinstalled by one maintenance
person.
4/24/2016
A-8
2016 Surface Water Design Manual —Appendix A
Coons SFD Revised: December 25, 2020 Page 21
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO.5 — CATCH BASINS AND MANHOLES
Maintenance
Defect or Problem
Condition When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Structure
Sediment
Sediment exceeds 60% of the depth from the
Sump of catch basin contains no
bottom of the catch basin to the invert of the
sediment.
lowest pipe into or out of the catch basin or is
within 6 inches of the invert of the lowest pipe
into or out of the catch basin.
Trash and debris
Trash or debris of more than % cubic foot which
No Trash or debris blocking or
is located immediately in front of the catch basin
potentially blocking entrance to
opening or is blocking capacity of the catch basin
catch basin.
by more than 10%.
Trash or debris in the catch basin that exceeds
No trash or debris in the catch
'13 the depth from the bottom of basin to invert
basin.
the lowest pipe into or out of the basin.
Dead animals or vegetation that could generate
No dead animals or vegetation
odors that could cause complaints or dangerous
present within catch basin.
gases (e.g., methane).
Deposits of garbage exceeding 1 cubic foot in
No condition present which would
volume.
attract or support the breeding of
insects or rodents.
Damage to frame
Corner of frame extends more than % inch past
Frame is even with curb.
and/or top slab
curb face into the street (If applicable).
Top slab has holes larger than 2 square inches
Top slab is free of holes and cracks.
or cracks wider than Y. inch.
Frame not sitting flush on top slab, i.e.,
Frame is sitting flush on top slab.
separation of more than % inch of the frame from
the top slab.
Cracks in walls or
Cracks wider than % inch and longer than 3 feet,
Catch basin is sealed and is
bottom
any evidence of soil particles entering catch
structurally sound.
basin through cracks, or maintenance person
judges that catch basin is unsound.
Cracks wider than % inch and longer than 1 foot
No cracks more than inch wide at
at the joint of any inlet/outlet pipe or any
the joint of inlet/outlet pipe.
evidence of soil particles entering catch basin
through cracks.
Settlement/
Catch basin has settled more than 1 inch or has
Basin replaced or repaired to design
misalignment
rotated more than 2 inches out of alignment.
standards.
Damaged pipe joints
Cracks wider than % inch at the joint of the
No cracks more than %-inch wide at
inlet/outlet pipes or any evidence of soil entering
the joint of inlet/outlet pipes.
the catch basin at the joint of the inlet/outlet
pipes.
Contaminants and
Any evidence of contaminants or pollution such
Materials removed and disposed of
pollution
as oil, gasoline, concrete slurries or paint.
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Inlet/Outlet Pipe
Sediment
Sediment filling 20% or more of the pipe.
Inlet/outlet pipes clear of sediment.
accumulation
Trash and debris
Trash and debris accumulated in inlet/outlet
No trash or debris in pipes.
pipes (includes floatables and non-floatables).
Damaged
Cracks wider than % inch at the joint of the
No cracks more than Y.-inch wide at
inlet/outlet pipes or any evidence of soil entering
the joint of the inlet/outlet pipe.
at the joints of the inlet/outlet pipes.
2016 Surface Water Design Manual —Appendix A
A-9
4/2N2016
Coons SFD Revised: December 25, 2020 Page 22
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 5 — CATCH BASINS AND MANHOLES
Maintenance
Defect or Problem
Condition When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Metal Grates
Unsafe grate opening
Grate with opening wider than '/e. inch.
Grate opening meets design
(Catch Basins)
standards.
Trash and debris
Trash and debris that is blocking more than 20 %
Grate free of trash and debris.
of grate surface.
footnote to guidelines for disposal
Damaged or missing
Grate missing or broken member(s) of the grate.
Grate is in place and meets design
Any open structure requires urgent
standards.
maintenance.
Manhole Cover/Lid
CoverAid not in place
CoverAid is missing or only partially in place.
CoverAid protects opening to
Any open structure requires urgent
structure.
maintenance.
Locking mechanism
Mechanism cannot be opened by one
Mechanism opens with proper tools.
Not Working
maintenance person with proper tools. Bolts
cannot be seated. Self-locking coverAid does not
work.
CoverAid difficult to
One maintenance person cannot remove
CoverAid can be removed and
Remove
cover/lid after applying 80lbs. of lift.
reinstalled by one maintenance
person.
4/24/2016
A-10
2016 Surface Water Design Manual — Appendix A
Coons SFD Revised: December 25, 2020 Page 23
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 6 — CONVEYANCE PIPES AND DITCHES
Maintenance
Defect or Problem
Conditions When Maintenance is Needed
Results Expected When
Component
Maintenance is Performed
Pipes
Sediment & debris
Accumulated sediment or debris that exceeds
Water flows freely through pipes.
accumulation
20 % of the diameter of the pipe.
Vegetation/roots
Vegetation/roots that reduce free movement of
Water flows freely through pipes.
water through pipes.
Contaminants and
Any evidence of contaminants or pollution such
Materials removed and disposed of
pollution
as oil, gasoline, concrete slurries or paint.
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Damage to protective
Protective coating is damaged, rust or corrosion
Pipe repaired or replaced.
coating or corrosion
is weakening the structural integrity of any part of
pipe.
Damaged
Any dent that decreases the cross section area
Pipe repaired or replaced.
of pipe by more than 20 % or is determined to
have weakened structural integrity of the pipe.
Ditches
Trash and debris
Trash and debris exceeds 1 cubic foot per 1,000
Trash and debris cleared from
square feet of ditch and slopes.
ditches.
Sediment
Accumulated sediment that exceeds 20% of the
Ditch cleaned/flushed of all
accumulation
design depth.
sediment and debris so that it
matches design.
Noxious weeds
Any noxious or nuisance vegetation which may
Noxious and nuisance vegetation
constitute a hazard to County personnel or the
removed according to applicable
public.
regulations. No danger of noxious
vegetation where County personnel
or the public might normally be.
Contaminants and
Any evidence of contaminants or pollution such
Materials removed and disposed of
pollution
as oil, gasoline, concrete slurries or paint.
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Vegetation
Vegetation that reduces free movement of water
Water flows freely through ditches.
through ditches.
Erosion damage to
Any erosion observed on a ditch slope.
Slopes are not eroding.
slopes
Rock lining out of
One layer or less of rock exists above native soil
Replace rocks to design standards.
place or missing (If
area 5 square feet or more, any exposed native
Applicable)
soil.
2016 Surface Water Design Manual —Appendix A
A-11
4/24/2016
Coons SFD Revised: December 25, 2020 Page 24
List of Figures:
Soils Management Form
Soils Option 3
Small Scale PIT Report
Coons SFD Revised: December 25, 2020 Page 25
Use Achieving the Post -construction Soil Standard booklet
Project Information Complete all information on page 1, onlysite address
and permit number on additional pages.
Site add ress/Lot
No.
Permit Type Single Family
Permit Number
Permit Holder
Phone
Mailing Address
Contact Person Richard Deccio P.E.
Phone 206-390-8374
Plan Prepared By Richard Deccio P.E.
Attachments -attach the following to this plan:
* Scale stormwater site plan drawings that include areas to be
treated with Soil Treatment Options 1, 2, 3, 4.
*Completed Compostand Topsoil Calculation Worksheet results.
* Original compost and/or topsoil test results reports demonstrating
that products contain adequate organic matter (for soil treatment
options 2) and meet topsoil soil quality standard.
Note., Retain original delivery tickets for compost and/or topsoil
products for verifi cation purposes.
Soil Treatment Options for Areas Identified on Site Plan
Soil treatment options available:
*Option 1 - Leave native soil undisturbed, and protect from
compaction during construction.
*Option 2 -Amend existing soil in place.
*Option 3 - For native soil: stockpile site duff and topsoil, and reapply
after grading and construction.
*Option 4 - Import topsoil mix with 8-13% soil organic matter content.
FOR PDS USE ONLY Plan Approval Record
)ate: - Reviewer: - Approved
evisions Required:
Print Form
instructions to carry out this Soil Management Plan.
Area: 1 (referto lettered areas mapped on site plan)
Square footage: 2,600
Selected soil treatment option: Option 1 Option 2
® Option 3 Option 4
If using option 2, select type of amendment rate:
Pre -approved (2") Custom with % Target Soil
Organic Matter
Area: (refer to lettered areas mapped on site plan)
Square foot age:
�e ecte soi treatment option. ❑ Option 1 ❑ Option 2
❑ Option ❑ Option4
f using option 2, select type of amendment rate:
Pre -approved (2") ❑ Custom with % Target Soil
Organic Matter
Area: (refer to lettered areas mapped on site plan)
Square footage:
Selected soil treatment option:
❑ Option 1 ❑ Option 2
❑ Option 3 ❑ Option 4
fusing option 2, select type of amendment rate:
❑ Pre -approved (2") ❑ Custom with % Target Soil
Organic Matter
Record the compost and/or topsoil products to be used
Compost Product #1:
Test Results
Quantity in cubic yards
organic matter:
Supplier
Compost Product #2:
Test Results
Quantity in cubic yards
organic matter:
Supplier
Topsoil Product #3:
Test Results
Quantity in cubic yards
organic matter:
Supplier
Topsoil Product #4:
Date: - Reviewer: Approved: Test Results %
Revisions Required: organic matter:
Supplier
Total cubic yards compost:
Quantity in cubicyards
Total cubic yards topsoil:
Coons SFD Revised: December 25, 2020 Page 26
Option 3
Option 4
Order
Native Soil — stockpile site duff and topsoil and reapply after grading and
construction.
• Enter lettered areas from site plan where this option will be used:
LOT A
• Enter combined square footage of lettered areas in thousands 2.5
(example: for 4,525 sq ft, enter 4.525; for 500 sq ft, enter 0.5)
• Multiply combined square footage by 25 and enter product in box B
B 65 CYDS
AMOUNT OF TOPSOIL TO BE STOCKPILED AND REAPPLIED IN THESE
AREAS
Import topsoil.
• Enter lettered areas from site plan where this option will be used:
• Enter combined square footage of lettered areas in thousands
(example: for 4,525 sq ft, enter 4.525; for 500 sq ft, enter 0.5)
• Multiply combined square footage by 25 and enter product in box C:
Cj =Cubic Yards
AMOUNT OF IMPORTED TOPSOITFIESE NEEDED FOR TFIESE AREAS
Order These Amounts:
• Enter amount in Box A: Cubic Yards of Compost
• Enter amount in Box C : Cubic Yards of Topsoil
Note: MR 5 is triggered on sites with more than 2,000 sq. ft. of new, replaced, or new plus replaced
impervious surface, or 7,000 sq. ft. or greater of land disturbing activity.
Effective September 30, 2010
S:1CSCk0ocument WorehouseVORMSjCurrent Forms`Compost and Topsoil Calculation Worksheet 9_13_10.docx
Coons SFD Revised: December 25, 2020 Page 27
Small Scale PIT
Report
Single Family Residence
8427 202nd St SW
Edmonds WA 98155
March 9, 2020
Prepared For
MEC Construction
Edmonds WA
Prepared By:
Robert C. Edwards, PE
23030 76" Ave West, Suite 12
Edmonds WA 98026
Coons SFD Revised: December 25, 2020 Page 28
TABLE OF CONTENTS
CERTIFICATION
Small Scale PIT
Coons SFD Revised: December 25, 2020 Page 29
23030 761h Ave W
Suite 12
Edmonds, WA 98026
206-226-5777
RAM Technical Services, LLC
CERTIFICATION
I hereby state that this Small Scale PIT Report for the site located at 8427 202n` St SW, Edmonds,
Washington has been prepared by me or under my supervision and meets the standard of care and
expertise which is usual and customary in this community for professional engineers.
Coons SFD Revised: December 25, 2020 Page 30
March 9, 2020 Robert C. Edwards PE
8427 202nd St SW, Edmonds WA
Small Scale PIT
This report describes the Small Scale PIT performed on 8427 202,16 St SW, Edmonds WA
The test was performed to determine a design infiltration rate for development of a single family
residence.
The site soils starting a 24" below ground level are gray, slightly moist SILTS with trace gravels. This has
an SCS/USDA soil classification of "D". These soils are classified as "Till" for WWHM.
An additional test pit was excavated. The soils are identical to the first test pit. The conclusion is the
subsurface soil strata is uniform across the subject site.
No drainage problems were noted for the previous residence. The previous residence used downspouts,
splash pads, and dispersion.
These soils are not conducive to infiltration given the small grain size and limited grain size distribution.
The Small Scale PIT was performed per the Department of Ecology's Storm Water Manual for Western
Washington.
During the test the water level did not drop at all. Hence no water was added. Therefore the design
infiltration rate is 0.
The soak time for this test was one week. This is unusual. It took one week for the water levels in the test
pit to drop to an acceptable (6"- 12") level.
Conclusions:
1. The site soils do not support conventional infiltration facilities, IE ponds, trenches, etc.
2. The site soils do not support other infiltration BMPs such as rain gardens or permeable pavement.
3. Development BMPs could include dispersion or perforated tightlines.
Coons SFD Revised: December 25, 2020 Page 31
Small Scale Pilot
Infiltration
Test (PIT) ' �—
Date
03/09/20
Address 202na St SW Edmonds WA
Test Pit Dimensions (inches)
Length
_Width
60;
36
Depth
80
Time
(24hr)
Day
Level
(Inches)
Water Added
(Gallons)
New Level, Drop'
(Inches —(Inches)
Comment(s)'
1000
03/02/20
NIA
Start Soak
830
02/09/20
11.38
11.38
Start Test
845
02/09/20
11.38
0.00
11.38
0.00
900
02/09/20
11.38
0.00
11.38
0.00
915
02/09/20
11.38
0.00
11.38
0.00
930
02/09/20
11,38
0.00
11.38
0.00
End Test
Raw Infiltration Rate
CFT= CFv X CFt X Cfm
CFv
CFt
Urn
,C—F T
I
Design Rate = Raw Rate X CFT
1
0.5
0,9
0.45'
0.00
Inches/hr
l D
0
inches/hr'
Soil:
Gray, slightly damp SILT with trace gravels
No mottling or groundwater encountered
Infiltration Test.xls Page 1 03/10/2020
Coons SFD Revised: December 25, 2020 Page 32