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Public Works Small Project Stormwater Site Plan/Report (City of Everett)

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C I T Y O F E V E R E T T
Public Works
Small Project Stormwater Site Plan/Report
This Small Project Stormwater Site Plan and Report provides a simplified template to assist small projects in
meeting the City of Everett’s stormwater requirements in accordance with the 2019 Stormwater Management
Manual for Westen Washington (SWMMWW).
If you choose to use this template, you are agreeing to construct, operate and maintain the Best Management
Practices (BMPs) selected for your project as required to meet Minimum Requirements (MR) #1-5 in
accordance with the Manual. Alternatively, you may choose to hire a professional or submit your own
Stormwater Report (report and drawings) that meets the minimum standards described in the Manual.
Project Site Information
Project name:
Project address Permit number:
Contact Information
Owner name:
Owner mailing address:
Owner phone: Owner email:
Applicant name:
Applicant mailing address:
Applicant phone: Applicant email:
Primary contact:
☐
Owner
☐
Applicant
☐
Other (architect, engineer, etc.): ________________________
Primary contact name: Primary contact phone:
Primary contact email:
Report prepared by: _________________________________________ Date: _____________________
STEP 1. DETERMINE APPLICABILITY
Use the criteria below to determine if this template may be used for your project. If any
criteria below are marked “False,” this template may not be used and a report meeting
Minimum Requirements#1-9 is required and shall be prepared by a professional Engineer
licensed in the State of Washington.
What are the minimum technical requirements (MR) for a small project?
MR #1: Preparation of a Stormwater Site Plan (Report and Plans)
MR #2: Construction Stormwater Pollution Prevention Plan (SWPPP)
MR #3: Source Control of Pollution
MR #4: Preservation of Natural Drainage Systems and Outfalls
MR #5: On-Site Stormwater Management
True
Criteria
☐ ☐
This project will create 2,000 square feet (ft
2
) or more, but less than 5,000 ft
2
,
of new plus replaced hard surface area OR will have 7,000 ft
2
or greater of land
disturbing activities.
☐ ☐
This project does not drain to the combined sewer.
☐ ☐
This project converts less than 3/4 acre of existing soil cover or vegetation to
lawn or landscape areas.
☐ ☐
This project will not adversely impact a water of the state.
☐ ☐
This project will not change a natural drainage course and will not generate any
new concentrated flows leaving the site.
☐ ☐
This project will not be constructed within a critical area or a critical area buffer
and will not adversely impact a critical area. See the City of Everett Municipal
Code, Title 19.37.
☐
☐
This project will follow the SWMMWW design criteria to satisfy Minimum
Requirement #5 rather than an engineered design.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 3
STEP 2. PROVIDE BASIC PROJECT INFORMATION
Project type: ☐ Single Family Residence (SFR) ☐ Townhome
☐ Duplex ☐ Multi-Family ☐ Commercial
☐ Industrial ☐ Accesory Dwelling Unit (ADU)
Select if your project is: ☐ New development ☐ Redevelopment
Please quantify the project scope.
See glossary for definitions (e.g. hard surface, impervious, pervious, etc.)
Item
Area (
ft
2
)
Total lot size/project area ft
2
Total proposed area to be disturbed:
(project boundaries)
ft
2
Total disturbed pervious area:
(includes existing gravel)
ft
2
Converted pervious surface area:
(native vegetation to lawn or landscape)
ft
2
Proposed
new hard
surface area
(A+B=C):
A - Proposed new roof area: ft
2
B - Proposed new other hard surface area on ground: ft
2
C - Total proposed new hard surface area: ft
2
Proposed
replaced hard
surface area
(D+E=F):
D - Proposed replaced roof area: ft
2
E - Proposed replaced other hard surface area on ground: ft
2
F - Total proposed replaced hard surface area: ft
2
Proposed
new and
replaced hard
surface area
(C+F=I):
G - Proposed new plus replaced roof area (A+D): ft
2
H - Proposed new plus replaced other hard surface area on ground (B+E): ft
2
I - Total proposed new and replaced hard surface area: ft
2
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 4
STEP 3. COMPLETE MINIMUM REQUIREMENTS #1-5
The following subsections address MR #1-5. The more information provided in these subsections typically
corresponds to faster review and permit issuance times. Submitted checklists that lack the necessary
information for review are considered incomplete and will be returned unprocessed to the applicant.
MR #1: Preparation of Stormwater Site Plan
The purpose of MR #1 is to convey all relevant information about the proposed project to the City for review
to ensure the project is in compliance with the current City and State stormwater management standards.
This is your opportunity to inform the reviewer about the project fundamentals as well as highlight the
significant and insignificant aspects of the project with regards to stormwater management.
Task 1: Describe existing site conditions
Provide description of existing site conditions:
Describe existing structures (location, type):
Describe slopes on your site (flat, rolling, steep, %):
Describe hard surfaces (roof, ground treatment):
Describe vegetative surfaces (location, quanity ft
2
):
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 5
Describe drainage flow paths (direction, location):
Are there Critical Areas? What are they and where are they located relative to your project?:
Task 2: Describe proposed project
Describe your proposed project:
How will your project change the existing condition?:
Describe roofs, patios, driveways, or structures added:
How will stormwater be managed?:
Describe how the project will affect existing drainage systems onsite or on adjacent properties
or both:
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 6
Task 3: Attach Project Specific Stormwater Site Plan (required)
See City of Everett standard drawings #100-104 for stormwater site plan requirements and
examples, including a Temporary Erosion & Sediment Control (TESC) plan example and
drainage plan example, available online at:
everettwa.gov/1531/Design-Construction-Standards
Task 4: Attach Topographic Survey (required for some projects)
A topographic survey prepared by a registered land surveyor, civil engineer or other
qualified professional is required if your project site includes steep slopes, critical areas,
flood or geologic hazards or at the discretion of the stormwater reviewer.
Task 5: Attach Declaration of Covenant and Grant of Easement
To ensure future maintenance and allow access for inspection, any On-Site Stormwater
BMP (MR #5) constructed as part of the project must have a Declaration of Covenant and
Grant of Easement. Fill out and attach the Declaration of Covenant and Grant of Easement.
For a copy, visit everettwa.gov/1985/Stormwater-Technical-Resources
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 7
MR #2 Construction Stormwater Pollution Prevention
(SWPPP)
All new development and redevelopment projects are responsible for preventing erosion and discharge of
sediment and other pollutants into receiving waters. A Construction Stormwater Pollution Prevention Plan
(Construction SWPPP) is designed to be a stand-alone document that addresses construction stormwater
management concerns. A copy of this SWPPP is required to be kept by the contractor performing the work at
the jobsite for reference and updated during the duration of construction.
Task 1: Describe the project during construction
(You may attach a narrative that answers the following questions)
Nature and purpose of the construction project:
Adjacent areas, including streams, lakes, wetlands, residential areas, and roads that might be
affected by the construction project:
How upstream drainage areas may affect the site:
Downstream drainage leading from the site to a receiving body of water:
Critical areas that receive runoff from the site up to one-quarter mile away:
Special requirements and provisions for working near or within critical areas:
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 8
Areas on the site that have potential erosion problems:
Locations where surface water leaves the site:
Task 2: Select Construction Best Management Practices (BMPs) to be used on your project
All new development and redevelopment projects are responsible for preventing erosion and sedimentation
during construction. Each of the 13 requirements below contains a list of Best Management Practices (BMPs)
that are accepted by the Washington State Department of Ecology (Ecology) for satisfying each requirement.
The BMPs below are the most common. For a complete selection of BMPs please see Volume II of Ecology’s
Stormwater Management Manual for Western Washington.
Each of the 13 Elements below must be considered in the SWPPP. Select all
BMPs that you will be using to satisfy each requirement. All requirements must
have at least one item selected.
Element 1. Preserve vegetation/mark clearing limits:
☐ BMP C101: Preserving Natural Vegetation
☐ BMP C102: Buffer Zones
☐ BMP C103: High Visibility Plastic or Metal Fence
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 2. Establish construction:
☐ BMP C105: Stabilized Construction Entrance/Exit
☐ BMP C106: Wheel Wash
☐ BMP C107: Construction Road/Parking Area Stabilization
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 9
Element 3. Control flow rates:
☐ BMP C203: Water Bars
☐ BMP C240: Sediment Trap
☐ BMP C241: Temporary Sediment Pond
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 4. Install sediment
controls
:
☐ BMP C231: Brush Barrier
☐ BMP C232: Gravel Filter Berm
☐ BMP C233: Silt Fence
☐ BMP C234: Vegetated Strip
☐ BMP C235: Wattles
☐ BMP C240: Sediment Trap
☐ BMP C241: Temporary Sediment Pond
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 5. Stabilize soils:
☐ BMP C120: Temporary and Permanent Seeding
☐ BMP C121: Mulching
☐ BMP C122: Nets and Blankets
☐ BMP C123: Plastic Covering
☐ BMP C124: Sodding
☐ BMP C125: Topsoiling/Composting
☐ BMP C126: Polyacrylamide for Soil Erosion Protection
☐ BMP C130: Surface Roughening
☐ BMP C131: Gradient Terraces
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 10
Element 6. Protect slopes:
☐ BMP C120: Temporary and Permanent Seeding
☐ BMP C130: Surface Roughening
☐ BMP C131: Gradient Terraces
☐ BMP C200: Interceptor Dike and Swale
☐ BMP C201: Grass-Lined Channels
☐ BMP C203: Water Bars
☐ BMP C204: Pipe Slope Drains
☐ BMP C205: Subsurface Drains
☐ BMP C206: Level Spreader
☐ BMP C207: Check Dams
☐ BMP C208: Triangular Silt Dike (Geotextile Encased Check Dam)
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 7. Protect drain inlets:
☐ BMP C220: Storm Drain Inlet Protection
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 8. Stabilize Channels and Outlets:
☐ BMP C202: Channel Lining
☐ BMP C 209: Outlet Protection
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 11
Element 9. Control pollutants:
☐ BMP C151: Concrete Handling
☐ BMP C152: Sawcutting and Surfacing Pollution Prevention
☐ BMP C153: Material Delivery, Storage, and Containment
☐ BMP C154: Concrete Washout Area
☐ BMP C250: Concrete Stormwater Chemical Treatment
☐ BMP C251: Construction Stormwater Filtration
☐ BMP C252: High pH Neutralization Using CO2
☐ BMP C253: pH Control for High pH Water
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 10. Control dewatering:
☐ BMP C236: Vegetative Filtration
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 11. Maintain BMPs:
☐ BMP C150: Materials On Hand
☐ BMP C160: Certified Erosion and Sediment Control Lead
(CESCL not required on-site for <1acre).
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Element 12. Manage the Project:
☐ BMP C150: Materials On Hand
☐ BMP C160: Certified Erosion and Sediment Control Lead
(CESCL not required on-site for sites <1acre)
☐ BMP C162: Scheduling
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 12
Element 13. Protect low impact development:
☐ BMP C102: Buffer Zones
☐ BMP C103: High Visibility Plastic or Metal Fence
☐ BMP C200: Interceptor Dike and Swale
☐ BMP C207: Check Dams
☐ BMP C208: Triangular Silt Dike (Geotextile Encased Check Dam)
☐ BMP C231: Brush Barrier
☐ BMP C233 Silt Fence
☐ BMP C 234: Vegetated Strip
☐ Other Per the SWMMWW: __________________
☐ Not applicable to my proposed project
Explain: ________________________________________________
Task 3: Construction SWPPP drawings
Provide a Temporary Erosion and Sediment Control (TESC) plan for your project.
Show on your TESC Plan all BMPs selected above to satisfy the 13 Elements on your
TESC Plan.
See City of Everett Public Works TESC Plan Example #103
everettwa.gov/DocumentCenter/View/7040
Note: Construction Stormwater Pollution Prevention Plans (Construction SWPPPs) that
involve engineering calculations must also be prepared by or under the direction of a
Washington State professional licensed engineer.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 13
MR #3: Source Control of Pollution
The intent of source control is to prevent stormwater from coming in contact with pollutants. Source control
BMPs can be operational or structural in nature. This section contains practices and procedures to reduce
the release of pollutants.
Provide a description of all known, available and reasonable source control BMPs that will be used on your
site to prevent stormwater from coming into contact with pollutants. Source control BMPs must be selected,
designed and maintained in accordance with the 2019 SWMMWW Volume IV.
Task 1: Describe the applicability of BMPs selected for your project
☐ My project is a Single-Family Residence (SFR) and source control BMPs are not
applicable to my project.
☐ My project is not a SFR and after reviewing Vol. IV of the Manual, I have determined
that Source Control BMPs are not applicable because of the following reason:
____________________________________________________________________________________
____________________________________________________________________________________
If you checked one of the boxes above, STOP and go to the next section, MR #4.
If you did not select a box above, complete Task 2 on the following page and select
the source control BMPS to be used on your project.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 14
Task 2: Select the following source control BMPs required for this project
☒ Source Control BMPs are required on all sites. Correcting illicit connections to storm
drains (S410), formation of a pollution prevention team (S453), preventative
maintenance/good housekeeping (S454), spill prevention and cleanup (S455), employee
training (S456), inspections (S457) and recordkeeping (S458).
☐ BMP S421 for Parking and Storage of Vehicles and Equipment
☐ BMP S411 for Landscaping and Lawn/Vegetation Management
☐ BMP S427 for Storage of Liquid, Food Waste, or Dangerous Waste Containers
☐ BMP S409 for Fueling at Dedicated Stations
☐ BMP S419 for Mobile Fueling of Vehicles and Heavy Equipment
☐ BMP S414 for Maintenance and Repair of Vehicles and Equipment
☐ BMP S433 for Pools, Spas, Hot tubs, and Fountains
☐ BMP S440 for Pet Waste
☐ BMP S443 for Fertilizer Application
☐ BMP S451 for Building, Repair, Remodeling, Painting, and Construction
☐ BMPS431 for Washing and Steam Cleaning Vehicles and Equipment
☐ BMP S417 for Maintenance of Stormwater Drainage and Treatment Systems
☐ BMP S426 for Spills of Oil and Hazardous Substances
☐ BMP S418 for Manufacturing Activities Outside
☐ Other BMPs found in Volume IV of SWMMWW applicable to project (see Worksheet 1 of
this packet for entire list of source control BMPs and list other applicable BMPs below):
------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 15
MR #4: Preservation of Natural Drainage Systems
Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural
location. This Minimum Requirement has two main components to achieve: 1) maintain the natural on-site
drainage pattern and concentrated discharge location at the downstream property boundary, and 2) prevent
erosion at and downstream of the discharge locations. This requirement includes maintaining or replacing
systems which convey runoff accross the site from upstream areas. All outfalls require energy dissipation.
Task 1: Document existing and proposed drainage patterns and discharges
Check the boxes that apply below:
☐ This site has existing drainage systems or outfalls. These items are shown on the
Stormwater Site Plan provided in MR #1 and are to include: type, slope, dimensions,
channel lining, direction of flow and buffer.
☐ This project will not alter the existing drainage system in any way. If the existing
outfall(s) show sign of erosion and scour, energy disipation measures will be installed
or improved upon. Construction activity of any kind will not occur within at least 10 ft
of the edge of the channelized flow, BMP C102: Buffer Zones will be implemented
during the life of the project to include visible flagging or other demarcation technique.
If this requirement is not met a Hydraulic Project Approval (HPA) may be required from
the Washington Department of Fish and Wildlife.
☐ The site does not have any existing drainage systems or outfalls.
Describe how stormwater will be discharged from the site without causing erosion and
flooding downstream:
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
☐ The existing concentrated drainage system traversing the property will be impacted as
part of this project and is shown on the stormwater site plan.
Describe how your project impacts or changes the existing drainage systems as a result
of your project and how you will address it:
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 16
Task 2: Select where the project will discharge its stormwater
☐ An existing piped conveyance system
☐ Outlet protection such as rip-rap pad (less than 0.3 CFS)
☐ Dispersion trench or other dispersion facility (0.3 to 0.75 CFS)
☐ Piped conveyance to appropriate discharge location with easement if required
(greater than or equal to 0.75 CFS)
☐ Other: ___________________________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 17
MR #5: On-Site Stormwater Management
All projects meeting the thresholds for this Small Project Stormwater Report shall employ on-site
stormwater management BMPs to infiltrate, disperse and retain stormwater runoff on-site to the extent
feasible without causing flooding or erosion impacts on-site or downstream.
Task 1: Determine whether infiltration has been pre-determined to be infeasible
for any portion of your project site.
Review the infiltration infeasibility mapping tool available on “Map Everett”
everettwa.gov/mapeverett.
On the mapping tool, select “Geotechnical/Infiltration Infeasibility Area” and the
applicable “Property” layers from the Layer List.
Zoom into your project site and print the resulting map to show the project site
boundaries and the infiltration infeasibility mapping results.
Areas mapped as red have been pre-determined to be infeasible for infiltration.
Areas mapped as green are potentially feasible for infiltration and must be
assessed further for infiltration feasibility, as discussed further below.
Attach a printed copy of the map clearly showing your project site boundary and the
infiltration infeasibility mapping results.
Task 2: Determine whether the project is flow control exempt.
How do I know if my project is flow control exempt?
Your project is flow control exempt if 1) your project discharges directly to the Puget Sound
or Snohomish River, or 2) your project discharges to a stormwater system entirely man-made
from the site to either of those water bodies, although subject to the following: the project
will reduce discharge rates to an existing stream or wetland, or the conveyance system has
adequate capacity to accommodate increased flows without flooding or causing erosion.
See Ecology SWMMWW Volume 1 for more information on flow control exempt criteria.
Select one of the boxes below:
☐ Project is not flow control exempt and List #1 will be used to satisfy MR #5 (Go to page 18).
☐ Project is flow control exempt and List #3 will be used to satisfy MR #5 (Go to page 19).
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 18
Task 3: List #1 approach to MR #5 compliance
You are required to use the first applicable BMP that is considered feasible in each
category (lawn, landscape, and hard surfaces) below. Mark whether the BMP is feasible or
infeasible. If you selected infeasible, cite the reasons for infeasibility (see Worksheet 2)
and or a professional, site specific reference to supporting documentation (such as a
geotechnical report).
List #1: On-Site Stormwater Management BMPs for MR #1-5 Projects
* If you selected BMP T5.10A Downspout Full Infiltration submit 1 and 3 below.
* If you selected BMPT5.15 Permeable Pavement, or T5.14A Rain Gardens in List#1, on-site soils information for sizing
or infeasibility determination is required from 1 through 4 below.
Submit the following information to Permit Services with this report:
1) A USDA Custom Soil Report from websoilsurvey.sc.egov.usda.gov
2) Small-scale Pilot Infiltration Tests (PIT) per SWMMWW specifications
3) USDA Soil Type(s)= ___________
4) Measured Infiltration Rate = ___________ in/hr (from PIT)
Category 1
-
Lawn and
L
andscaped
A
reas
Feasible Infeasible If infeasible provide justification
BMP T5.13: Post-Construction Soil Quality
and Depth
☐ ☐
Category 2
-
Roofs
Feasible Infeasible If infeasible provide justification
BMP T5.10A:
or
BMP 5.30:
Downspout Full Infiltration*
Full Dispersion
☐
☐
☐
☐
*Soils report required for this BMP
BMP T5.14A:
or
BMPT7.30:
Rain Gardens*
Bioretention Cells, Swales,
and Planter Boxes
☐
☐
☐
☐
*Soils report required for this BMP
BMP T5.10B: Downspout Dispersion
Systems
☐
☐
BMP T5.10C: Perforated Stub-out
Connections
☐ ☐
Category 3
-
Other Hard Surfaces
Feasible Infeasible If infeasible provide justification
BMP T.530: Full Dispersion
☐ ☐
BMP T5.15:
or
BMP T5.14A:
or
BMPT7.30:
Permeable Pavements*
Rain Gardens*
Bioretention Cells, Swales,
and Planter Boxes
☐
☐
☐
☐
☐
☐
*Soils report required for this BMP
BMP T5.12:
or
BMP T5.11:
Sheet Flow Dispersion
Concentrated Flow Dispersion
☐
☐
☐
☐
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 19
Task 4: List #3 approach to MR #5 compliance (flow control exempt projects only)
You are required to use the first applicable BMP that is considered feasible in each
category (lawn, landscape and hard surfaces) below.
Mark whether the BMP is feasible or infeasible. If you select infeasible, cite the reasons for
infeasibility (See Worksheet 2) and or a reference to supporting documentations (such as a
geotechnical report).
List #3: On-Site Stormwater Management BMPs for Flow Control Exempt Projects
Category 1
-
Lawn and landscaped areas
Feasible Infeasible If infeasible provide justification
BMP T5.13: Post-Construction Soil
Quality and Depth
☐ ☒
Category 2
-
Roofs
Feasible Infeasible If infeasible provide justification
*BMP T5.10A:
or
BMP 5.30:
Downspout Full Infiltration
Full Dispersion
☐
☐
☐
☐
*Soils report required for this BMP
BMP T5.10B: Downspout Dispersion
Systems
☐
☐
BMP T5.10C: Perforated Stub-out
Connections
☐ ☐
Category 3
-
Other Hard Surfaces
Feasible Infeasible If infeasible provide justification
BMP T5.12:
or
BMP T5.11:
Sheet Flow Dispersion
Concentrated Flow
Dispersion
☐
☐
☐
☐
Task 5: Attach sizing implementation for the BMP selected above in List #1 or #3.
Worksheet 3 (attached) provides tools for sizing your selected BMP. Fill out the sizing
justification sheet for your selected BMP in Worksheet 3 and submit to Permit Services
attached to this report.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 20
DONE!
You have now completed the Small Project Stormwater Report.
Please review any sections you may have skipped to ensure all areas have been completed.
Ensure the following attachments have been added:
☐ Project Specific Stormwater Site Plan
☐ Topographic Survey
☐ Declaration of Covenant and Grant of Easement
☐ Construction SWPPP Drawings
☐ Map of Project Site Boundary and the Infiltration Infeasibility Mapping Results
☐ Worksheet 3 – Sizing Justification Worksheet for your Selected BMP
☐ Underground Injection Well (UIC) Registration*
* You may need to register with the Washington State Department of Ecology at least 60
days prior to commencing UIC Construction. For more information, visit:
everettwa.gov/1985/Stormwater-Technical-Resources
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 21
Glossary
Definitions are arranged alphabetically by term. For a complete reference, please see
the Stormwater Management Manual for Western Washington (SWMMWW):
fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm
Best Management Practice
(BMP)
The schedules of activities, prohibitions of practices, maintenance procedures,
and structural and/or managerial practices, that when used singly or in
combination, prevent or reduce the release of pollutants and other adverse
impacts to waters of Washington State.
Compaction The densification, settlement, or packing of soil in such a way that permeability of
the soil is reduced.
Compost Organic material that has undergone biological degradation and transformation
under controlled conditions designed to promote aerobic decomposition at a solid
waste facility in compliance with the requirements of Chapter 173-350 WAC, or
biosolids composted in compliance with Chapter 173-308 WAC. Composting is a
form of organic material recycling.
Critical Area At a minimum, areas which include wetlands, areas with a critical recharging effect
on aquifers used for potable water, fish and wildlife habitat conservation areas,
frequently flooded areas, geologically hazardous areas, including unstable slopes,
and associated areas and ecosystems.
Dispersion Release of surface and stormwater runoff such that the flow spreads over a wide
area and is located so as not to allow flow to concentrate anywhere upstream of a
drainage channel with erodible underlying granular soils.
Hard Surface An impervious surface, a permeable pavement, or a vegetated roof.
Impervious Surface A non-vegetated surface area which either prevents or retards the entry of water into
the soil mantle as under natural conditions prior to development. A non-vegetated
surface area which causes water to run off the surface in greater quantities or at an
increased rate of flow from the flow present under natural conditions prior to
development. Common impervious surfaces include, but are not limited to, roof
tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt
paving, gravel roads, packed earthen materials, and oiled, macadam or other
surfaces which similarly impede the natural infiltration of stormwater. Open,
uncovered retention/ detention facilities shall not be considered as impervious
surfaces for the purposes of determining whether the thresholds for application of
Minimum Requirements are exceeded. Open, uncovered retention/detention
facilities shall be considered impervious surfaces for purposes of runoff modeling.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 22
Land Disturbing Activity Any activity that results in a change in the existing soil cover (both vegetative and
non-vegetative) and/or the existing soil topography. Land disturbing activities
include, but are not limited to clearing, grading, filling, and excavation. Compaction
that is associated with stabilization of structures and road construction shall also
be considered a land disturbing activity. Vegetation maintenance practices,
including landscape maintenance and gardening, are not considered land-disturbing
activity. Stormwater facility maintenance is not considered land disturbing activity
if conducted according to established standards and procedures.
New development Land disturbing activities, including Class IV-general forest practices that are
conversions from timberland to other uses; structural development, including
construction or installation of a building or other structure; creation of hard
surfaces; and subdivision, short subdivision and binding site plans, as defined and
applied in Chapter 58.17 RCW. Projects meeting the definition of redevelopment
shall not be considered new development.
New Impervious Surface A surface that is:
changed from a pervious surface to an impervious surface (e.g.
resurfacing by upgrading from dirt to gravel, asphalt, or concrete), or
upgraded from gravel to asphalt or concrete, or
upgraded from a bituminous surface treatment (“chip seal”) to asphalt or
concrete.
Pervious Surface A surface material that allows stormwater to infiltrate into the ground. Examples
include lawn, landscape, pasture, native vegetation areas, and permeable
pavements.
Rain Garden A non-engineered shallow landscaped depression, with compost-amended native
soils and adapted plants. The depression is designed to pond and temporarily store
stormwater runoff from adjacent areas, and to allow stormwater to pass through the
amended soil profile. See BMP T5.14: Rain Gardens.
Redevelopment On a site that is already substantially developed (i.e., has 35% or more of existing
hard surface coverage), the creation or addition of hard surfaces; the expansion of
a building footprint or addition or replacement of a structure; structural development
including construction, installation or expansion of a building or other structure;
replacement of hard surface that is not part of a routine maintenance activity; and
land disturbing activities.
Replaced Hard Surface For structures, the removal and replacement of hard surfaces down to the
foundation. For other hard surfaces, the removal down to bare soil or base course
and replacement.
Sheet flow Runoff that flows over the ground surface as a thin, even layer, not concentrated in
a channel.
Stormwater Management
Manual for Western
Washington (SWMMWW)
Prepared by Ecology, contains BMPs to prevent, control or treat pollution in
stormwater and reduce other stormwater-related impacts to waters of the State.
The SWMMWW is intended to provide guidance on measures necessary in western
Washington to control the quantity and quality of stormwater runoff from new
development and redevelopment.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 23
Worksheet 1
Source Control BMPs from Volume IV of SWMMWW
Activity
Code
Type of Activity
Check if this
activity will
occur on the
site
IV-1 Source Control BMPs Applicable to all Sites
S410 Correcting Illicit Connections to Storm Drains
☐
S453 Formation of a Pollution Prevention Team
☐
S454 Preventative Maintenance/Good Housekeeping
☐
S455 Spill Prevention and Cleanup
☐
S456 Employee Training
☐
S457 Inspections
☐
S458 Recordkeeping
☐
IV-2 Cleaning and Washing
S431 Washing and Steam Cleaning Vehicles/Equipment
☐
S434 Dock Washing.
☐
S441 Potable Waterline Flushing, Water Tank Maintenance, and Hydrant Testing
☐
IV-3 Roads, Ditches, and Parking Lot
S405 Deicing and Anti-Icing Operations for Airports
☐
S406 Deicing and Anti-Icing Operations for Streets/Highways
☐
S415 Maintenance of Public and Private Utility Corridors and Facilities
☐
S416
Maintenance of Roadside Ditches
☐
S417
Maintenance of Stormwater Drainage and Treatment Systems
☐
S421
Parking and Storage of Vehicles and Equipment
☐
S430
Urban Street
☐
IV-4 Soil Erosion, Sediment Control, and Landscaping
S407 Dust Control at Disturbed Land Areas and Unpaved
☐
S411
Landscaping and Lawn/Vegetation Management
☐
S425
Erosion and Sediment Control at Industrial Sites
☐
S435
Pesticides and an Integrated Pest Management Program
☐
S444
Storage of Dry Pesticides and Fertilizers
☐
S449
Nurseries and Greenhouses
☐
S450
Irrigation
☐
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 24
Activity
Code
Type of Activity
Check if this
activity will
occur on the
site
IV-5 Storage and Stockpiling
S427
Storage of Liquids, Food Waste, or Dangerous Waste Containers
☐
S428
Storage of Liquids in Permanent Above Ground Tanks
☐
S429
Storage or Transfer (Outside) of Solid Raw Materials, By Products, or
☐
S445
Temporary Fruit Storage
☐
IV-6
Transfer of Liquid or Solid Materials
S409
Fueling at Dedicated Stations
☐
S412
Loading and Unloading Areas for Liquid or Solid Materials
☐
S419
Mobile Fueling of Vehicles and Heavy Equipment
☐
S426
Spills of Oil and Hazardous Substances
☐
S439
In-Water and Over-Water Fueling
☐
IV-7
Other
S401
Building, Repair, and Maintenance of Boats and Ships
☐
S402
Commercial Animal and Handling Areas
☐
S404
Commercial Printing Operations
☐
S413
Log Sorting and Handling
☐
S414
Maintenance and Repair of Vehicle and Equipment
☐
S418
Manufacturing Activities-Outside
☐
S420
Painting/Finishing/Coating of Vehicles/Boats/Buildings/Equipment
☐
S422
Railroad Yards
☐
S423
Recyclers and Scrap Yards
☐
S424
Roof/Building Drains at Manufacturing and Commercial
☐
S432
Wood Treatment Areas
☐
S433
Pools, Spas, Hot Tubs, and Fountains
☐
S436
Color Events
☐
S438
Construction Demolition
☐
S440
Pet Waste
☐
S442
Labeling Storm Drain Inlets on Your Property
☐
S443
Fertilizer Application
☐
S446
Well, Utility, Directional and Geotechnical Drilling
☐
S447
Roof Vents
☐
S451
Building, Repair, Remodeling, Painting, and Construction
☐
S452
Goose Waste
☐
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 25
Worksheet 2 Infeasibility Criteria
MINIMUM REQUIREMENT #5 On-Site Stormwater Management
The following tables summarize infeasibility criteria that can be used to justify not using various on-site
stormwater management best management practices (BMPs) for consideration for Minimum Requirement
#5. This information is also included under the detailed descriptions of each BMP in the 2019 SWMM but is
provided here in this worksheet for additional clarity and efficiency. Where any inconsistencies or lack of
clarity exists, the requirements in the main text of the Stormwater Manual shall be applied.
Evaluate the feasibility of the BMPs in priority order based on List #1 or #3. Select the first BMP that is
considered feasible for each surface type. Document the infeasibility (narrative description and rationale) for
each BMP that was not selected. Only one infeasibility criterion needs to be selected for a BMP before
evaluating the next BMP on the list. Attach additional pages for supporting information if necessary.
Lawn and
L
andscaped
A
reas
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.13
Postconstruction
Soil Quality and
Depth
☐ Siting and design criteria provided in BMP T5.13
(Stormwater Manual Volume V, Section 5.3) cannot be achieved.
☐ Lawn and landscape area is on till slopes greater than 33 percent.
Roofs
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.30
Full Dispersion
☐ Site setbacks and design criteria provided in BMP T5.30
(Stormwater Manual Volume V, Section 5.3) cannot be achieved.
☐ A 65 to 10 ratio of forested or native vegetation area to
impervious area cannot be achieved.
☐ A minimum forested or native vegetation flowpath length of 100
feet (25 feet for sheet flow from a non-native pervious surface)
cannot be achieved.
T5.10A
Downspout
Full Infiltration
☐ Evaluation of infiltration is not required per the Infiltration
Infeasibility Map due to steep slopes, erosion hazards, or
landslide hazards.
☐ Site setbacks and design criteria provided in BMP T5.10A
(Stormwater Manual Volume III, Section 3.1.1) cannot be
achieved.
☐ The lot(s) or site does not have out-wash or loam soils.
☐ There is not at least 3 feet or more of permeable soil from the
proposed final grade to the seasonal high groundwater table,
hardpan layer, or other impermeable layer.
☐ There is not at least 1 foot or more of permeable soil from the
proposed bottom of the infiltration system to the seasonal high
groundwater table, hardpan layer, or other impermeable layer.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 26
Roofs
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.14A
Bioretention
or Rain Gardens
Note: Criteria with setback distances are as measured from the bottom
edge of the bioretention soil mix.
Citation of any of the following infeasibility criteria must be based on
an evaluation of site-specific conditions and a written
recommendation from an appropriate licensed professional
(e.g., engineer, geologist, hydrogeologist):
☐ Where professional geotechnical evaluation recommends
infiltration not be used due to reasonable concerns about erosion,
slope failure, or down-gradient flooding.
☐ Within an area whose ground water drains into an erosion hazard,
or landslide hazard area.
☐ Where the only area available for siting would threaten the safety
or reliability of pre-existing underground utilities, pre-existing
underground storage tanks, pre-existing structures, or pre-existing
road or parking lot surfaces.
☐ Where the only area available for siting does not allow for a safe
overflow pathway to stormwater drainage system or private storm
sewer system.
☐ Where there is a lack of usable space for bioretention areas at
redevelopment sites, or where there is insufficient space within the
existing public right-of-way on public road projects.
☐ Where infiltrating water would threaten existing below grade
basements.
☐ Where infiltrating water would threaten shoreline structures such
as bulkheads.
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Evaluation of infiltration is not required per the Infiltration
Infeasibility Map due to steep slopes, erosion hazards, or landslide
hazards. See City's infiltration infeasibilty map.
☐ Within setback provided for BMP T7.30 (DCSS Section 4-4.1(3))
☐ Where they are not compatible with surrounding drainage system
as determined by the city (e.g., project drains to an existing
stormwater collection system whose elevation or location
precludes connection to a properly functioning bioretention area).
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 27
Roofs
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.14A
Bioretention
or Rain Gardens
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Where land for bioretention is within an erosion hazard, or
landslide hazard area.
☐ Where the site cannot be reasonably designed to locate
bioretention areas on slopes less than 8 percent.
☐ Within 50 feet from the top of slopes that are greater than 20
percent and over 10 feet of vertical relief.
☐ For properties with known soil or groundwater contamination
(typically federal Superfund sites or state cleanup sites under the
Model Toxics Control Act [MTCA]):
Within 100 feet of an area known to have deep soil
contamination.
Where groundwater modeling indicates infiltration will
likely increase or change the direction of the migration of
pollutants in the groundwater.
Wherever surface soils have been found to be
contaminated unless those soils are removed within 10
horizontal feet from the infiltration area.
Any area where these facilities are prohibited by an
approved cleanup plan under the state MTCA or Federal
Superfund Law, or an environmental covenant under
Chapter 64.70 RCW.
☐ Within 100 feet of a closed or active landfill.
☐ Within 10 feet of an underground storage tank and connecting
underground pipes when the capacity of the tank and pipe system
is 1,100 gallons or less. As used in these criteria, an underground
storage tank means any tank used to store petroleum products,
chemicals, or liquid hazardous wastes of which 10 percent or more
of the storage volume (including volume in the connecting piping
system) is beneath the ground surface.
☐ Within 100 feet of an underground storage tank and connecting
underground pipes when the capacity of the tank and pipe system
is greater than 1,100 gallons.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 28
Roofs
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.14A
Bioretention
or Rain Gardens
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Where field testing indicates potential bioretention/rain garden
sites have a measured (a.k.a., initial) native soil saturated hydraulic
conductivity less than 0.30 inches per hour. A small-scale or
largescale PIT in accordance with SWMMWW Volume III, Section V-
5.4 shall be used to demonstrate infeasibility of bioretention areas.
If the measured native soil infiltration rate is less than 0.30 in/hour,
bioretention/rain garden BMPs are not required to be evaluated as
an option in List #1 or List #2.
☐ Where the minimum vertical separation of 3 feet to the seasonal
high groundwater elevation, hardpan layer, or other impermeable
layer would not be achieved below bioretention that would serve a
drainage area that exceeds the following thresholds (and cannot
reasonably be broken down into amounts smaller than indicated):
5,000 square feet of pollution-generating impervious
surface (PGIS)
10,000 square feet of impervious area
0.75 acres of lawn and landscape.
☐ Where the minimum vertical separation of 1 foot to the
seasonalhigh groundwater or other impermeable layer would not be
achieved below bioretention that would serve a drainage area less
than the above thresholds.
☐ Within 100 feet of a drinking water well, or a spring used for
drinking water supply.
☐ Within 10 feet of small on-site sewage disposal drainfield,
including reserve areas, and grey water reuse systems. For
setbacks from a “large on-site sewage disposal system,” see
Chapter 246-272B WAC.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 29
Roofs
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.10B
Downspout
Dispersion
Systems
☐ Site setbacks and design criteria provided in BMP T5.10B
(SWMMWW, Section V-4.1) cannot be achieved.
☐ For splash blocks, a vegetated flowpath at least 50 feet in length
from the downspout to the downstream property line, structure,
stream, wetland, slope over 15 percent, or other impervious
surface is not feasible.
☐ For trenches, a vegetated flowpath of at least 25 feet in between
the outlet of the trench and any property line, structure, stream,
wetland, or impervious surface is not feasible. A vegetated
flowpath of at least 50 feet between the outlet of the trench and
any slope steeper than 15 percent is not feasible.
T5.10C
Perforated
Stub-out
Connections
☐ Evaluation of infiltration is not required per the Infiltration
Infeasibility Map due to steep slopes, erosion hazards, or landslide
hazards
☐ For sites with septic systems, the only location available for the
perforated portion of the pipe is located up-gradient of the
drainfield primary and reserve areas. This requirement can be
waived if site topography will clearly prohibit flows from
intersecting the drainfield or where site conditions (soil
permeability, distance between systems, etc.) indicate that this is
unnecessary.
☐ Site setbacks and design criteria provided in BMP T5.10C
(SWMMWW, Section V-4.1 or DCSS Section 4-4.1(3) cannot be
achieved.
☐ There is not at least 1 foot of permeable soil from the proposed
bottom (final grade) of the perforated stub-out connection trench
to the highest estimated groundwater table, hardpan, or other
impermeable layer.
☐ The only location available for the perforated stub-out connection
is under impervious or heavily compacted soils.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 30
Other Hard Surfaces
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.30
Full Dispersion
☐ Site setbacks and design criteria provided in BMP T5.30
(SWMMWW, Section V-4.1) cannot be achieved.
☐ A 65 to 10 ratio of forested or native vegetation area to impervious
area cannot be achieved.
☐ A minimum forested or native vegetation flowpath length of 100
feet (25 feet for sheet flow from a non-native pervious surface)
cannot be achieved.
T5.15
Permeable
Pavement
Citation of any of the following infeasibility criteria must be based on
an evaluation of site-specific conditions and a written
recommendation from an appropriate licensed professional (e.g.,
engineer, geologist, hydrogeologist):
☐ Where professional geotechnical evaluation recommends
infiltration not be used due to reasonable concerns about erosion,
slope failure, or downgradient flooding.
☐ Within an area whose ground water drains into an erosion hazard,
or landslide hazard area.
☐ Where infiltrating and ponded water below the new permeable
pavement area would compromise adjacent impervious
pavements.
☐ Where infiltrating water below a new permeable pavement area
would threaten existing below grade basements.
☐ Where infiltrating water would threaten shoreline structures such
as bulkheads.
☐ Down slope of steep, erosion prone areas that are likely to deliver
sediment.
☐ Where fill soils are used that can become unstable when saturated.
☐ Excessively steep slopes where water within the aggregate base
layer or at the subgrade surface cannot be controlled by detention
structures and may cause erosion and structural failure, or where
surface runoff velocities may preclude adequate infiltration at the
pavement surface.
☐ Where permeable pavements cannot provide sufficient strength to
support heavy loads at industrial facilities such as ports.
☐ Where installation of permeable pavement would threaten the
safety or reliability of pre-existing underground utilities, pre-
existing underground storage tanks, or pre-existing road
subgrades.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 31
Other Hard Surfaces
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.15
Permeable
Pavement
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Evaluation of infiltration is not required per the Infiltration
Infeasibility Map due to steep slopes, erosion hazards, or landslide
hazards (See City infiltration and infeasibility map).
☐ Within an area designated as an erosion hazard, or landslide
hazard.
☐ Within 50 feet from the top of slopes that are greater than 20
percent where the setbacks listed in DCSS Section 4-4.1 (3) cannot
be achieved.
☐ For properties with known soil or groundwater contamination
(typically federal Superfund sites or state cleanup sites under
MTCA):
Within 100 feet of an area known to have deep soil
contamination.
Where groundwater modeling indicates infiltration will
likely increase or change the direction of the migration of
pollutants in the groundwater.
Wherever surface soils have been found to be
contaminated unless those soils are removed within 10
horizontal feet from the infiltration area.
Any area where these facilities are prohibited by an
approved cleanup plan under the state MTCA or Federal
Superfund Law, or an environmental covenant under
Chapter 64.70 RCW.
☐ Within 100 feet of a closed or active landfill.
☐ Within 100 feet of a drinking water well, or a spring used for
drinking water supply, if the pavement is a pollution-generating
surface.
☐ Within 10 feet of a small on-site sewage disposal drainfield,
including reserve areas, and grey water reuse systems. For
setbacks from a “large on-site sewage disposal system,” see
Chapter 246-272B WAC.
☐ Within 10 feet of any underground storage tank and connecting
underground pipes, regardless of tank size. As used in these
criteria, an underground storage tank means any tank used to store
petroleum products, chemicals, or liquid hazardous wastes of
which 10 percent or more of the storage volume (including volume
in the connecting piping system) is beneath the ground surface.
☐ At multi-level parking garages, and over culverts and bridges.
☐ Where the site design cannot avoid putting pavement in areas
likely to have long-term excessive sediment deposition after
construction (e.g., construction and landscaping material yards).
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 32
Other Hard Surfaces
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.15
Permeable
Pavement
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Where the site cannot reasonably be designed to have:
Porous asphalt surface < 5% slope
Pervious concrete surface < 10% slope
Permeable interlocking concrete pavement surface <12%
slope
Grid systems < 6-12% slope (check with manufacturer
and local supplier to confirm maximum slope)
☐ Where the subgrade soils below a pollution-generating permeable
pavement (e.g., road or parking lot) do not meet the soil suitability
criteria for providing treatment. See soil suitability criteria for
treatment in the SWMMWW, Section V-5. Note: In these instances,
a 6 inch sand filter layer meeting city specifications for treatment
may be used to provide treatment.
☐ Where underlying soils are unsuitable for supporting traffic loads
when saturated. Soils meeting a California Bearing Ratio of 5
percent are considered suitable for residential access roads.
☐ Where replacing existing impervious surfaces unless the existing
surface is a non-pollution generating surface over an outwash soil
with a saturated hydraulic conductivity of 4 inches per hour or
greater.
☐ Where appropriate field testing indicates soils have a measured
(a.k.a., initial) subgrade soil saturated hydraulic conductivity less
than 0.3 inches per hour. Only small-scale PIT or large-scale PIT
methods in accordance with SWMMWW Section V-5.4 shall be
used to evaluate infeasibility of permeable pavement areas. (Note:
In these instances, unless other infeasibility restrictions apply,
roads and parking lots may be built with an underdrain, preferably
elevated within the base course, if flow control benefits are
desired.)
☐ Roads that receive more than very low traffic volumes, and areas
having more than very low truck traffic. Roads with a projected
average daily traffic volume of 400 vehicles or less are very low
volume roads (AASHTO 2001) (U.S. Department of Transportation,
2013). Areas with very low truck traffic volumes are roads and
other areas not subject to through truck traffic but may receive up
to weekly use by utility trucks (e.g., garbage, recycling), daily
school bus use, and multiple daily use by pick-up trucks,
mail/parcel delivery trucks, and maintenance vehicles. (Note: This
infeasibility criterion does not extend to sidewalks and other non-
traffic bearing surfaces associated with the collector or arterial).
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 33
Other Hard Surfaces
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.15
Permeable
Pavement
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ At sites defined as “high-use sites” (refer to the Glossary in the
SWMMWW Volume I).
☐ In areas with “industrial activity” as identified in 40 CFR
122.26(b)(14).
☐ Where the risk of concentrated pollutant spills is more likely such
as gas stations, truck stops, and industrial chemical storage sites.
☐ Where routine, heavy applications of sand occur in frequent snow
zones to maintain traction during weeks of snow and ice
accumulation.
☐ Where the seasonal high groundwater or an underlying
impermeable/ low permeable layer would create saturated
conditions within 1 foot of the bottom of the lowest gravel base
course.
T5.14A
Bioretention
or Rain Gardens
Note: Criteria with setback distances are as measured from the bottom
edge of the bioretention soil mix.
Citation of any of the following infeasibility criteria must be based on
an evaluation of site-specific conditions and a written
recommendation from an appropriate licensed professional (e.g.,
engineer, geologist, hydrogeologist):
☐ Where professional geotechnical evaluation recommends
infiltration not be used due to reasonable concerns about erosion,
slope failure, or down-gradient flooding.
☐ Within an area whose ground water drains into an erosion hazard,
or landslide hazard area.
☐ Where the only area available for siting would threaten the safety
or reliability of pre-existing underground utilities, pre-existing
underground storage tanks, pre-existing structures, or pre-existing
road or parking lot surfaces.
☐ Where the only area available for siting does not allow for a safe
overflow pathway to stormwater drainage system or private storm
sewer system.
☐ Where there is a lack of usable space for bioretention areas at
redevelopment sites, or where there is insufficient space within the
existing public right-of-way on public road projects.
☐ Where infiltrating water would threaten existing below grade
basements.
☐ Where infiltrating water would threaten shoreline structures such
as bulkheads.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 34
Other Hard Surfaces
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.14A
Bioretention
or Rain Gardens
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Where evaluation of infiltration is not required per the Infiltration
Infeasibility Map due to steep slopes, erosion hazards, or landslide
hazards (See City infiltration and infeasibility map).
☐ Within setback provided for BMP T7.30 (DCSS, Section 4-4.1(3.)
☐ Where they are not compatible with surrounding drainage system
as determined by the city (e.g., project drains to an existing
stormwater collection system whose elevation or location
precludes connection to a properly functioning bioretention area).
☐ Where land for bioretention is within an erosion hazard, or
landslide hazard area.
☐ Where the site cannot be reasonably designed to locate
bioretention areas on slopes less than 8 percent.
☐ Within 50 feet from the top of slopes that are greater than 20
percent and over 10 feet of vertical relief.
☐ For properties with known soil or groundwater contamination
(typically federal Superfund sites or state cleanup sites under the
Model Toxics Control Act [MTCA]):
Within 100 feet of an area known to have deep soil
contamination.
Where groundwater modeling indicates infiltration will
likely increase or change the direction of the migration of
pollutants in the groundwater.
Wherever surface soils have been found to be
contaminated unless those soils are removed within 10
horizontal feet from the infiltration area.
Any area where these facilities are prohibited by an
approved cleanup plan under the state MTCA or Federal
Superfund Law, or an environmental covenant under
Chapter 64.70 RCW.
☐ Within 100 feet of a closed or active landfill.
☐ Within 10 feet of an underground storage tank and connecting
underground pipes when the capacity of the tank and pipe system
is 1,100 gallons or less. As used in these criteria, an underground
storage tank means any tank used to store petroleum products,
chemicals, or liquid hazardous wastes of which 10 percent or more
of the storage volume (including volume in the connecting piping
system) is beneath the ground surface.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 35
Other Hard Surfaces
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.14A
Bioretention
or Rain Gardens
(continued)
The following criteria can be cited as reasons for infeasibility without
further justification (though some require professional services to
make the observation):
☐ Within 100 feet of an underground storage tank and connecting
underground pipes when the capacity of the tank and pipe system
is greater than 1,100 gallons.
☐ Where field testing indicates potential bioretention/rain garden
sites have a measured (a.k.a., initial) native soil saturated
hydraulic conductivity less than 0.30 inches per hour. A small-scale
or largescale PIT in accordance with SWMMWW, Section V-5.4
shall be used to demonstrate infeasibility of bioretention areas. If
the measured native soil infiltration rate is less than 0.30 in/hour,
bioretention/rain garden BMPs are not required to be evaluated as
an option in List #1 or List #2.
☐ Where the minimum vertical separation of 3 feet to the seasonal
high groundwater elevation or other impermeable layer would not
be achieved below bioretention that would serve a drainage area
that exceeds the following thresholds (and cannot reasonably be
broken down into amounts smaller than indicated):
5,000 square feet of pollution-generating impervious
surface (PGIS)
10,000 square feet of impervious area
0.75 acres of lawn and landscape.
☐ Where the minimum vertical separation of 1 foot to the seasonal
high groundwater, Hardpan layer, or other impermeable layer would
not be achieved below bioretention that would serve a drainage
area less than the above thresholds.
☐ Within 100 feet of a drinking water well, or a spring used for
drinking water supply.
☐ Within 10 feet of small on-site sewage disposal drainfield,
including reserve areas, and grey water reuse systems. For
setbacks from a “large on-site sewage disposal system,” see
Chapter 246-272B WAC.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 36
Other Hard Surfaces
(continued)
BMP and
applicable lists
Infeasibility criteria
Infeasibility description
and rationale for each
BMP not selected
T5.12
Sheet Flow
☐ Site setbacks and design criteria provided in BMP T5.12
(SWMMWW V4.1) cannot be achieved.
☐ Positive drainage for sheet flow runoff cannot be achieved.
☐ At Area to be dispersed (e.g., driveway, patio) cannot be graded to
have less than a 15 percent slope.
☐ At For flat to moderately sloped areas, at least a 10 foot-wide
vegetation buffer for dispersion of the adjacent 20 feet of
contributing surface cannot be achieved. For variably sloped areas,
at least a 25 foot vegetated flowpath between berms cannot be
achieved.
T5.11
Concentrated
Flow Dispersion
☐ Site setbacks and design criteria provided in BMP T5.11
(SWMMWWV4.1) cannot be achieved.
☐ A minimum 3 foot length of rock pad and 50 foot flowpath OR a
dispersion trench and 25 foot flowpath for every 700 square feet of
drainage area followed with applicable setbacks cannot be
achieved.
☐ More than 700 square feet drainage area drains to any dispersion
device.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 37
Worksheet 3 BMP Sizing Worksheets
DISPERSON BMPS
BMP T5.11 Concentrated Flow Dispersion
Concentrated flow dispersion BMPs shall be designed in accordance with the SWMMWW. Clearly show the
vegetated flowpath on the site plan. A maximum of 700 ft
2
of roof area can drain to each dispersion BMP.
Hard surface area requiring mitigation: _________________
Hard surface draining to dispersion BMP: _______________
# of dispersion BMPs: Total Hard Surface = _______________
700 ft
2
Dispersion trench required? ☐ Yes ☐ No
(must be included if flow path is 25 to 50 ft)
BMP T5.12 Sheet Flow Dispersion
Sheet flow dispersion BMPs shall be designed in accordance with the SWMMWW.
Hard surface area requiring mitigation: ___________________
Width of paved surface discharging into sheet flow dispersion BMP: _______________
Minimum required width of vegetated buffer: __________________
(10 ft for every 20 ft of paved/hard surface, or fraction there of)
BMP T5.30 Full Dispersion
Full dispersion BMPs shall be designed in accordance with the SWMMWW.
Residential (impervious surfaces). All calculations are for areas with a single Threshold Discharge
Area (TDA). If multiple TDAs exist, provide a calculation for each.
Total Impervious (ft
2
)*100% = ___________% (must be less than 10% to use BMP)
Total Area (ft
2
)
Required Dispersion Area (ft
2
) = Total Impervious Area (ft
2
)* 6.5
Required Dispersion Area (ft
2
)* 6.5 = __________________ ft
2
Dispersion area provided: __________________
(Note: Dispersion area must be preserved as forest or native vegetation.)
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 38
ROOF DOWNSPOUT BMPS
Roof downspout BMPs include infiltration trenches, dry wells, and partial dispersion systems
BMP T5.10A Roof Downspout Full Infiltration
Downspout full infiltration systems are trench or drywell designs intended for use in infiltrating runoff from
roof downspout drains.
Infiltration Trench
The minimum trench length is based upon the soil type in the location of the infiltration trench.
The soils report will provide the USDA Soil Type. The table below provides the minimum trench
length per 1,000 ft
2
of contributing roof area. Roof downspout infiltration trenches shall be
designed in accordance with the SWMMWW.
USDA Soil Type
Minimum
trench length
(ft) per 1,000 ft
2
of roof area
“Coarse sand” (more than 50% of sand fraction remains on #4 sieve) 20
“Medium sand” (more than 50% of sand fraction remains on #40 sieve) 30
Loamy sand 75
Sandy loam 125
Loam 190
Silt loam 275
Fill (only per SWMMWW requirements) 60
Trench length required (ft) = Roof area (ft
2
) *((minimum trench length) (ft))
1000 (ft
2
)
Roof area requiring mitigation (ft
2
): ________________
USDA Soil Type per soils report: ________________
Trench length required: ________________
(Trench length cannot exceed 100 ft. If length exceeds 100 ft, multiple trenches will be required.)
Number of trenches: ________________
Length of each trench: ________________
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 39
Infiltration Dry Wells
The minimum rock volume and dry well rock layer height are based upon the soil type in the location
of the drywell. The soils report will provide the USDA Soil Type. The table below provides the volume
of washed rock and height of washed rock required. Roof downspout dry wells shall be designed in
accordance with the SWMMWW.
Roof area requiring mitigation (ft
2
): ________________
USDA Soil Type per soils report: ________________
Rock layer height required: ________________
Volume of washed rock required: ________________
Volume of Washed Rock Required = Tributary Impervious Area (ft
2
)*Standard Volume
1000 (ft
2
)
BMP T5.10B Roof Downspout Dispersion Systems
Downspout dispersion systems are splash blocks or trenches, which serve to spread roof runoff over
vegetated pervious areas.
Downspout Dispersion Trench
Roof downspout dispersion trenches shall be designed in accordance with the SWMMWW.
Trenches serving up to 700 ft
2
roof area may use a Simple Dispersion Trench (2 ft wide X 10 ft
length). Multiple simple dispersion trenches maybe used as long as none exceeds 700 ft
2
of
tributary area and the flow paths from the trenches do not overlap.
Roof area requiring mitigation: ________________
Number of simple dispersion trenches proposed: ________________
☐ See attached sketch which identifies the roof area, including square footage draining to
each dispersion trench.
USDA Soil Type
Volume of
washed rock (ft
3
)
per 1000 ft
2
of
impervious area
Drywell
r
ock
l
ayer
height at 48in
diameter per 1000 ft
2
of impervious area
“Coarse sand” (more than 50% of
sand fraction remains on #4 sieve)
60 4’9”
“Medium sand” (more than 50% of
sand fraction remains on #40 sieve)
90 7’2”
Note: Stormwater facilities that infiltrate stormwater by means of an underground facility such as
an infiltration trench or dry well may need to be register as an underground injection well (UIC).
For more information, visit everettwa.gov/1985/Stormwater-Technical-Resources
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 40
Notched Grade Board Trench
For roof areas larger than 700 ft
2
, dispersion trenches with notched grade boards may be used with
a total length not to exceed 50 ft.
Notched Grade Board Trench Length (ft) = (10 ft)* (Roof Area to Trench (ft
2
))
700 (ft
2
)
Notched grade board trench length required: ________________
If greater than 50 feet needed more than one trench will be required
Number of notched grade board trenches required: ________________
Length of each notched grade board trenches: ________________
☐ See attached sketch.
Splashblocks
Splashblocks shall be designed in accordance with the SWMMWW. A maximum of 700 ft
2
of roof
area can drain to a single splashblock.
Roof area requiring mitigation: ________________
Roof area discharging to splashblock: ________________
☐ See attached sketch.
BMP T5.10C Perforated Stub-out Connections
Perforated stub-out connections shall be designed in accordance with the SWMMWW.
Roof area requiring mitigation (ft
2
): ________________
Roof area discharging to perforated stub-out connection: ________________
Perforated pipe length (ft): ________________
Perforated Pipe Length (ft) = (10 ft)*(Roof Area to Facility (ft
2
))
5000 (ft
2
)
The minimum perforated pipe length shall be 10 ft.
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 41
INFILTRATION BMPS
T5.15 Permeable Pavements
Project submission requirements include submitting results of infiltration (Ksat) testing, groundwater
elevation testing (or other documentation and justification for the rates and hydraulic restriction layer
clearance) with the justification for the feasibility decision regarding permeable pavement, and as
justification for assumptions made in the runoff modeling.
BMP T5.14A - Rain Garden
The top of the ponded surface area below the overflow shall be at least 5% of the total hard surface area
draining to the rain garden. If lawn/landscaped areas will also be draining to the rain garden, it is
recommended that the top of the ponded surface area below the overflow be increased by 2% of the
lawn/landscaped area. The table below provides rain garden geometry based upon contributing area. Refer
to the Rain Garden Handbook for Western Washington: A Guide for Design, Installation, and Maintenance
(Hinman et.al. 2013) for construction guidance. Rain gardens shall be designed in accordance with the
SWMMWW.
Side
Slope
Contributing
Area
(ft
2
)
Minimum Top of
Ponding Area
(ft
2
)
Minimum Bottom
of Ponding Area
(ft
2
)
Minimum Top
of Berm Area
(ft
2
)
2:1 800 or less 40 0.11 50
2:1 1400 or less 70 0.13 110
3:1 3000 or less 150 0.06 235
Hard surface area requiring mitigation (ft
2
): ________________
Lawn/landscape contributing area (ft
2
): ________________
Total contributing area (ft
2
): ________________
Top of Ponded Surface Area (ft
2
) = 0.05*(total hard surface area (ft
2
)) + 0.02*(lawn/landscape area (ft
2
))
= 0.05*( ________________ ft
2
) + 0.02*( ________________ ft
2
)
= ________________ ft
2
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 42
MISC LID BMP
T5.13: Post Construction Soil Quality and Depth
This section applies to lawn and landscape areas.
On your site plan, show the edge of all ground and vegetation that will be disturbed by the project.
1. Total Disturbed Area: ......................................................................................__________ ft
2
(Should match line 1 on the Stormwater project, page 2)
2. Onsite hard surfaces: .................................................................................... __________ ft
2
(Should match line 5 on the Stormwater project information, page 2):
3. Area of lawn or turf: .......................................................................................__________ ft
2
4. Area of landscaping and planting beds: ............................................................. __________ ft
2
5. Areas exempted from soil amendment requirements: .......................................... __________ ft
2
(Due to existing tree roots, steep slopes, or wetland soils)
6. CHECK: The total of lines 2 through 5 should equal line 1. =
Calculate the Amendment Amount Needed
TURF/LAWN AREA
7. Area of lawn or turf (from line 3 above) ........................................................... ___________ ft
2
Multiply by conversion factor from 1.75 inches to cubic yards (yd
3
): x 0.0054
8. Amendment quantity needed for lawn or turf .................................................... ___________ yd
3
9. Area of landscaping and planting beds (from line 4 above) ................................. ___________ ft
2
a. Multiply by conversion factor from 3 inches to cubic yards (yd
3
): x 0.0093
10. Amendment quantity needed for landscaping/planting beds ............................... ___________ yd
3
11. TOTAL AMENDMENT QUANTITY NEEDED
(total of lines 8 and 10) + = ___________ yd
3
City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 43
SOURCES: Portion of total amendment quantity (from line 11) that is:
12. Purchased from off-site sources ..................................................................... ___________ %
13. Stockpiled soil and duff from on-site ................................................................ ___________ %
14. Chipped and stockpiled woody material from on-site ........................................... ___________ %
15. Imported topsoil .......................................................................................... ___________ %
16. CHECK: The total of lines 12 through 15 should total 100% ................................... 100%
PLANTING BEDS
17. Area of landscaping and planting beds (from line 4 above) .................................... ___________ ft
2
a. Multiply by conversion factor from 3 inches to cubic yards (yd
3
): x 0.0093
18. MULCH QUANTITY NEEDED ............................................................................. _____________ yd
3
SOURCES: Portion of total mulch quantity (from line 18) that is:
19. Purchased from off-site sources ............................................................................ ___________ %
20. Chipped and stockpiled woody material from on-site .............................................. ___________ %
21. CHECK: The total of lines 19 and 20 should total 100% ......................................... 100%
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