HomeMy WebLinkAboutBLD2020-00582-05- STORMWATERstormwater calc worksheet – REV. 10/20/2014 1
DEPARTMENT OF COMMUNITY DEVELOPMENT
621 Sheridan Street, Port Townsend, WA 98368
Tel: 360.379.4450 | Fax: 360.379.4451
Web: www.co.jefferson.wa.us/communitydevelopment
E-mail: dcd@co.jefferson.wa.us
STORMWATER CALCULATION WORKSHEET
MLA # PROJECT/APPLICANT NAME:
DETERMINING STORMWATER MANAGEMENT REQUIREMENTS: This stormwater calculation worksheet should be completed first to
classify the proposal as “small,” “medium,” or “large.” The size determines whether a Stormwater Site Plan is required in
conjunction with a stand-alone stormwater management permit application, building permit application, or other land use approval
application that involves stormwater review. The basic information will also be helpful for completing a Stormwater Site Plan, if
required.
Land-disturbing activity is any activity that results in movement of earth, or 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,
excavation, and compaction associated with stabilization of structures and road construction.
Native vegetation is vegetation comprised on plant species, other than noxious weeds, that are indigenous to the coastal region of
the Pacific Northwest and which reasonably could have been expected to naturally occur on the site. Examples include species such
as Douglas fir, western hemlock, western red cedar, alder, big-leaf maple, and vine maple; shrubs such as willow, elderberry,
salmonberry, and salal; herbaceous plants such as sword fern, foam flower, and fireweed.
Impervious surface is a hard surface that either prevents or retards the entry of water into the soil mantle as under natura l
conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at a n
increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces inclu de,
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.
LAND DISTURBING ACTIVITY, CONVERSION OF NATIVE VEGETATION, AND VOLUME OF CUT/FILL
Calculate the total area to be cleared, graded, filled, Answer the following two questions related to
excavated, and/or compacted for proposed development conversion of native vegetation:
project. Include in this calculation the area to be cleared for:
Does the project convert ¾ acres or more of
Construction site for structures _________________ sq/ft native vegetation to lawn or landscaped areas?
Drainfield, septic tank, etc. ____________________ sq/ft Circle: Yes No
Well, utilities, etc. ___________________________ sq/ft Does the project convert 2 ½ acres or more of
native vegetation to pasture?
Driveway, parking, roads, etc. ___________________sq/ft
Circle: Yes No
Lawn, landscaping, etc. ______________________ sq/ft
Other compacted surface, etc. _________________ sq/ft Indicate Total Volumes of Proposed:
Total Land Disturbance ____________________ sq/ft Cut __________ Fill __________ (cu/yd)
PARCEL SIZE (I.E., SITE)
Size of parcel _________ acres An acre contains 43,560 square feet. Multiply the acreage by this figure.
Size of parcel in square feet _________________ sq/ft
O
O6,300
0
0
600
2,260
0
Olympic Terrace 2 Lot 20/Port Ludlow Associates
21,600
1,640
0
.50
10,800
stormwater calc worksheet – REV. 10/20/2014 2
The following questions will help determine whether the proposed project is considered development or redevelopment.
FURTHER INSTRUCTIONS: If the answer is yes, the proposal is considered redevelopment and the attached Figure 2 should be used
to determine the applicable Minimum Requirements. If the answer is no, the proposal is considered new development and the
attached Figure 1 should be used. At this juncture, the applicant should refer to the applicable Flow Chart to determine the
Minimum Requirements for stormwater management. DCD staff will help verify the classification of the project and the application
requirements.
For proponents of “small” projects who must comply only with Minimum Requirement #2—Construction Stormwater Pollution
Prevention—an additional submittal is not required. The proponent is responsible for employing the 12 Elements to control erosion
and prevent sediment and other pollutants from leaving the site during the construction phase of the project. Pick up the
Construction Stormwater Pollution Prevention (SWPP) Best Management Practices (BMPs) Packet . Proponents of “medium”
projects—those that must meet only Minimum Requirements #1 through #5—and for “large” projects—those that must meet all 10
Minimum Requirements—are required to submit a Stormwater Site Plan. DCD has prepared a submittal template of a Stormwater
Site Plan, principally for rural residential projects. Complete the template in the Stormwater Site Plan Instructions and Submittal
Template or prepare a Stormwater Site Plan using the step-by-step guidance in the Stormwater Management Manual.
APPLICANT SIGNATURE
By signing the Stormwater Calculation Worksheet, I as the applicant/owner attest that the information provided herein is true and correct to the
best of my knowledge. I also certify that this application is being made with the full knowledge and consent of all owners o f the affected
property.
________________________________________ ________________________
(LANDOWNER OR AUTHORIZED REPRESENTATIVE SIGNATURE) (DATE)
FOR OFFICE USE ONLY
SMALL_____ MEDIUM_____ LARGE______ REDEVELOPMENT_____ Stormwater Site Plan: Yes_____ No______
STORMWATER CALULATIONS – IMPERVIOUS SURFACE
NEW EXISTING
Structures (all roof area) _________________sq/ft Structures (all roof area) _________________sq/ft
Sidewalks _________________sq/ft Sidewalks _________________sq/ft
Patios _________________sq/ft Patios _________________sq/ft
Solid Decks _________________sq/ft Solid Decks _________________sq/ft
(without infiltration below) (without infiltration below)
Driveway, parking, roads, etc _______________sq/ft Driveway, parking, roads, etc _______________sq/ft
Other _________________sq/ft Other _________________sq/ft
Total New _________________sq/ft Total Existing _________________sq/ft
TOTAL NEW + TOTAL EXISTING* _________________sq/ft *This amount will be used to check total lot coverage.
DEVELOPMENT v. REDEVELOPMENT
Divide the total existing impervious surface above by the size of the parcel and convert to a percentage: _______%
Does the site have 35% or more of existing impervious surface? Circle: Yes No
0
2,837
0
0
0
144
0
0
Cliff OBrien Digitally signed by Cliff OBrien
DN: cn=Cliff OBrien, o, ou=Westharbor Homes,
email=cobrien@westharborhomes.com, c=US
Date: 2020.12.28 10:53:33 -08'00'
0
0
10/29/2020
0
0
4
2,260
1,496
0
3,900
Worksheet A1
Medium & Large Project Report
Submit a site plan demonstrating the project. Refer to REFERENCE A1A for examples of Best Management
Practices (BMP’s) that you can use. Remember that all site plans submitted for the project must be consistent
and accurate.
page 1 of 6
Minimum Requirement # 1 : Preparation of Stormwater Site Plan
Describe both existing and proposed site conditions for the following items as applicable in the space below each
bullet point. Attach additional pages if needed.
•structures
•
•roads
•
•utility locations
•
•wellhead locations
•
•septic drainfield locations and type
•
•stormwater run-on from neighboring properties
•
•expected excavation depths and volumes
•
•expected work to be done in Right-of-Way (ROW)
Complete the following:
Minimum Requirement # 2 : Construction Stormwater Pollution Prevention Plan (SWPPP)
A SWPPP is designed to be a stand-alone document that addresses construction stormwater management concerns. This
document is required to be kept by the contractor performing the work at the jobsite for reference and update during
the life of the project. Construction BMP’s must be indicated on the stormwater site plan. REFERENCE B1A includes
diagrams of common BMP’s that may be used on the site plan.
My completed SWPPP (WORKSHEET B1 or equivalent) is included in this application packet!
Minimum Requirement # 3 : Source Control of Pollution (not construction related)
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. A roof over a material storage area is an example of a structural source
control BMP. Washing your vehicle on the lawn rather than in the street is an operational BMP. This requirement
is generally not applicable to Single Family Residences (SFRs); however, ways to minimize pollution from moving
downstream should be considered during the design phase of every project. Specifications on standard source control
BMPs that are applicable to various commercial and industrial-type facilities can be found in Volume IV of the 2014
Stormwater Management Manual for Western Washington (SWMMWW) (continued on page 2).
X
Propesed single family residence located at parcel 978802020
N/A
Utilities stub outs are already installed and withing the 20' front setback
N/A
N/A
None
Excavation to be approximately 2 feet deep with an approximate volume of 220 cubic yards
None
X
Worksheet A1
Medium & Large Project Report
page 2 of 6
Check one of the following boxes that best represents your project with regards to MR #3.
Minimum Requirement # 3 : Source Control of Pollution (continued from page 1)
My project is a Single Family Residence (SFR) and after considering operational and structural measures to prevent
stormwater from coming in contact with pollutants, I have:
determined this MR to not be applicable. made appropriate adjustments to my project.
My project is not a SFR and after reviewing Vol. IV of the SWMMWW, I have determined that this MR is not
applicable because of the following reason:
My project is not a SFR and after reviewing Vol. IV of the SWMMWW, I have determined that the following source
control BMPs are applicable to my project and shall be incorporated into the project design and operation.
X
X
Worksheet A1
Medium & Large Project Report
Minimum Requirement # 4 : Preservation of Natural Drainage Systems
Creating new drainage patterns results in more site disturbance and more potential for erosion and sedimentation during
and after construction. to the maximum extent possible, proponents must 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 location.
NOTE: All outfalls require energy dissipation. See Table 4.5.1 in Vol. V of the SWMMWW for minimum design standards
for rock protection at outfalls.
Choose the option below that best describes your project:
page 3 of 6
The project site does not currently have any intermittent, seasonal, or continuous concentrated water
moving across any part of the property and the proposed improvements to the site will not create new
concentrated flow paths or not discharging to existing drainage systems.
The project site has existing concentrated flow drainage systems and outfalls. (NOTE: These items must
be graphically shown on the Site Plan or equivalent, to include: type, slope, dimensions, channel lining,
direction of flow, buffer, etc.) Select below how it will be addressed.
This project will not alter the existing drainage system in any way. If the existing outfall(s) show
signs of erosion and scour, energy dissipation 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.
The existing concentrated drainage system traversing the property will be impacted as part
of this project, as described in the space below and shown on the site plans. Engineering
calculations are required that show the altered drainage design can accommodate the existing
flows and the added runoff contributed by the project.
X
Worksheet A1
Medium & Large Project Report
page 4 of 6
My project is a large project. Refer to Worksheet L. If full dispersion isn’t feasible, use LIST #1
(List #2 and List #1 are the same except raingardens are not permitted in List #2).
Minimum Requirement # 5 : On-site Stormwater Management
On-site stormwater management techniques shall be implemented where possible to accommodate the permanently
added stormwater runoff being generated by development. Some on-site stormwater management techniques provide
better stormwater detention and treatment than others; however, they are not always appropriate for use due to varying
individual site characteristics. Therefore, techniques are presented to applicants on the next pages in a hierarchical order
and shall be considered for use in the order listed. The first technique on the list that is determined to be possible shall
be implemented. See WORKSHEET C to determine which techniques are feasible.
Runoff from developments occurring in drainage basins that drain directly or indirectly to a creek require a higher level
of stormwater management, thus, the techniques are presented in three lists below:
All properties will be in one of these three categories:
My project is located in a drainage subbasin that
drains to directly or indirectly to freshwater.
PROCEED to Page 5 to use LIST #1.
My Project will discharge to a subasin draining to
salt water, Dosewallips River, or Hoh River.
PROCEED to Page 6 to use LIST #3.
X
Worksheet A1
Medium & Large Project Report
My project does not have disturbed soils not covered by impervious
surfaces.
1.Post-Construction Soil Quality and Depth
Disturbed soils shall be amended (BMP T5.13: ).
My project does not have Roof areas.
1.Full Dispersion (BMP T5.30)
OR Downspout Full Infiltration (BMP T5.10A)
2.Rain Garden (LARGE PROJECTS CANNOT USE)
(BMP T5.14A)
3.Downspout Dispersion System (BMP T5.10B)
4.Perforated Stub-Out Connection (BMP T5.10)
5.Each BMP above is infeasible, see WORKSHEET C. STOP.
COMPLETE AND SUBMIT WORKSHEET B1. NO OTHER
INFORMATION REQUIRED AT THIS TIME.
My project does not have Other Hard Surface areas
1.Full dispersion (BMP T5.30)
2.Permeable Pavement (BMP T5.15)
OR Rain Garden (LARGE PROJECTS CANNOT USE) (BMP T5.14A)
Minimum Requirement # 5 : On-site Stormwater Management (continued)
LIST # 1 : Applicable to projects that directly or indirectly drain to freshwater.
INSTRUCTIONS: Check the first option that will work for Each Category Below:
For each category below, proceed through the LIST from top down. Use WORKSHEET C to determine if the BMP
can be used. If number 1 on the list is not possible, document why on WORKSHEET C and move down to number
2, and so on.
Category A: Lawn and Landscape Areas
Category B: Roofs
Category C: Other Hard Surfaces, e.g. gravel and paved
driveways, solid decks and patios without infiltration below
3.Sheet Flow Dispersion (BMP T5.12)
OR Concentrated Flow Dispersion (BMP T5.11)
4.Each item above is infeasible, see WORKSHEET C. STOP.
COMPLETE AND SUBMIT WORKSHEET B1. NO OTHER
INFORMATION REQUIRED AT THIS TIME.
X
X
X
Worksheet B1
Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan)
Submit a site plan demonstrating the construction protective measures or best management practices that will
be used for the project during the construction phase.
Refer to REFERENCE B1A for examples of Construction Best Management Practices (BMP’s) that you can use. The
activities that take place during construction are the highest risk for stormwater problems such as erosion and
sediment control (you may need to provide an additional site plan with greater detail for stormwater features. If so,
make sure it is consistent with the primary site plan. Remember that all site plans submitted for the project must
be consistent and accurate).
page 1 of 6
Element 1: Preserve Vegetation / Mark Clearing Limits
The goal of this element is to preserve native vegetation and to clearly show the limits of disturbance.
Choose any of the following that apply:
The site was cleared as part of clearing activity that is subject to an enforcement action and will be re-vegetated.
Restoration may be necessary to comply with Critical Area Regulations or stormwater requirements. Buffer Zones-
BMP C102 may apply if Critical Areas exist on-site and buffer zones shall be protected.
The perimeter of the area to be cleared shall be marked prior to clearing operation with visible flagging, orange
plastic barrier fencing and/or orange silt fencing as shown on the SWPPP site plan. Vehicles will only be allowed
in the areas to be graded, so no compaction of the undeveloped areas will occur. If this option is selected check
the BMPS you will use below:
C101 Preserving Natural
Vegetation
C102 Buffer
Zones
C103 High Visibility
Fence
It is necessary to disturb the entire property during this project due to existing site conditions, property
constraints, and proposed design. I understand that all disturbed land not covered by hard surface at the end of
the project is subject to soil amendment requirements per BMP T5.13 Post-Construction Soil Quality and Depth.
Element 2: Construction Access
The goal of this element is to provide a stabilized construction entrance/exit to prevent or reduce or sediment
track out.
Choose one of the following:
The driveway to the construction area already exists and will be used for construction access. All equipment and
vehicles will be restricted to staying on that existing impervious surface. If sediment is tracked off site, the road-
way will be cleaned thoroughly at the end of each day.
A stabilized construction entrance will be installed prior to any vehicles entering the site, at the location
shown on the SWPPP site plan. If sediment is tracked off site, the roadway will be cleaned thoroughly at the end
of each day. If this option is selected check the BMPS you will use below:
C105 Stabilized
Construction Entrance /
Exit
C106 Wheel
Wash
C107 Construction
Road / Parking Area
Stabilization
X
X
X
X
Worksheet B1
Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan)
Element 3: Control Flow Rates
The goal of this element is to construct retention or detention facilities when necessary to protect properties
and waterways downstream of development sites from erosion and turbid discharges.
This element does not apply to my project because (check any that apply):
page 2 of 6
Site is mildly sloped (<5%),
There are no individually sloped sections greater than 10%,
The bulk of the project is scheduled to occur during dry season (May 1-Sept 30)
Sediment control BMPs shall be placed at the locations shown on the SWPPP Site Plan. If this option is selected
check the BMPS you will use below:
C233 Silt FenceC231 Brush Barrier
C234 Vegetated
Strip
C232 Gravel Filter
Berm
C235 Wattles
Element 4: Sediment Control
The goal of this element is to construct sediment control BMPs that minimize sediment discharges from the site.
Select one of the two statements applicable to the project.
The site has already been stabilized and re-vegetated.
Element 5: Stabilize Soils
•Soil stockpiles will be located within the disturbed area shown on the SWPPP Site Plan.
•Soil excavated for the foundation will be backfilled against the foundation and graded to drain away from the
building.
•No soils shall remain exposed and unworked for more than 7 days from May 1 to September 30 or more than
2 days from October 1 to April 30.
•Once the disturbed landscape areas are graded, the grass areas will be amended.
•All stockpiles will be covered with plastic or burlap if left unworked.
The goal of this element is to stabilize exposed and unworked soils by implementing erosion control BMPs.
Select one of the three statements applicable to the project.
My project will ensure the following:
This element does not apply to my project because:
My project must implement specific BMP’s to ensure compliance. (Check BMP’s you will use on the next page).
X
X
X
X
X
Worksheet B1
Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan)
page 3 of 6
C120 Temporary &
Permanent Seeding
C123 Plastic CoveringC121 Mulching
C124 SoddingC122 Nets & Blankets
C125 Topsoil /
Composting
C131 Gradient
Terraces
C140 Dust Control
C235 Wattles
Element 6: Protect Slopes
The goal of this element is to design and construct cut-and-fill slopes in a manner to minimize erosion.
Select one of the two statements applicable to the project.
No cut slopes over 4 feet high or slopes steeper than 2 feet horizontal to 1 foot vertical, and no fill slopes over
4 feet high will exceed 3 feet horizontal to 1 foot vertical. Therefore, there is no requirement for additional
engineered slope protection.
The above checkbox is not checked. My submittal is designed by a licensed geologist to protect slopes. Based on
the licensed professionals recommendation (please attach their evaluation), the following BMP’s will be used:
C120 Temporary & Permanent
Seeding
C204 Pipe Slope Drains
C205 Subsurface
Drains
C206 Level Spreader
C207 Check Dams
C208 Triangular Silt Dike
(Geotextile-Encased Check Dam)
Catch basins on the site or immediately off site in the right-of-way are shown on the SWPPP Site Plan. Storm drain
inlet protection shall be installed. If this option is selected check the BMPS you will use below:
C220 Storm Drain Inlet Protection
The site has open ditches in the right-of-way or private road right-of-way.
There are no catch basins on or near the site.
Element 7: Protect Permanent Drain Inlets
The goal of this element is to protect storm drain inlets during construction to prevent stormwater runoff from
entering the conveyance system without being filtered or treated.
Select one of the three statements applicable to the project.
X
X
X
X
Worksheet B1
Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan)
A wattle shall be placed at the end of the swale to prevent erosion at the outlet of the swale. If this option is
selected check the BMPS you will use below:
C202 Channel Lining C207 Check Dams C235 WattlesC209 Outlet Protection
page 4 of 6
Element 8: Stabilize Channels and Outlets
The goal of this element is to design, construct, and stabilize on-site conveyance channels to prevent erosion
from entering existing stormwater outfalls and conveyance systems.
Select one of the three statements applicable to the project.
Construction will occur during the dry weather. No storm drainage channels or ditches shall be constructed either
temporary or permanent.
There are no existing or proposed stormwater conveyance channels on the project site.
C151 Concrete Handling C152 Sawcutting and Surfacing
Pollution Prevention
C153 Material Delivery, Storage, and Containment C154 Concrete Washout Area
If one or more of the checkboxes above are unchecked. Any and all pollutants, chemicals, liquid products and other
materials that have the potential to pose a threat to human health or the environment will be covered, contained, and
protected from vandalism. All such products shall be kept under cover in a secure location on-site. Concrete handling
shall follow BMP C151 C154. If this option is selected check the BMPS you will use below:
Element 9: Control Pollutants
This element does not apply to my project because (circle any that apply - If any box is unchecked this element applies.
The goal of this element is to design, install, implement and maintain BMPs to minimize the discharge of
pollutants from material storage areas, fuel handling, equipment cleaning, management of waste materials, etc.
There will be no concrete work,
There will be no sawcutting work,
There will be no hazardous materials on-site,
There will be no fertilizer or pesticide application,
There will be no heavy equipment associated with this project,
There will be no pressure washing, equipment maintenance or dewatering
X
X
X
X
XX
X
Worksheet B1
Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan)
C203 Water Bars C236 Vegetated Filtration C206 Level Spreader
Element 10: Control De-watering
No dewatering of the site is anticipated.
Dewatering of the site is anticipated. If this option is selected check the BMPS you
will use below:
page 5 of 6
Select one of the two statements applicable to the project.
The goal of this element is to handle turbid or contaminated water from dewatering (removal of water)
separately from stormwater.
Describe the steps you will take:
Element 12: Manage the Project
The SWPPP will be implemented at all times. If applicable to the project, erosion control BMPs will be
implemented in the following sequence:
1.Mark clearing limits
2.Install stabilized construction entrance
3.Install protection for existing drainage systems and permanent drain inlets
4.Establish staging areas for storage and handling polluted material and BMPs
5.Install sediment control BMPs
6.Grade and install stabilization measures for disturbed areas
7.Maintain BMPs until site stabilization, at which time they may be removed
Element 11: Maintain Best Management Practices
Best Management Practices or BMPs shall be inspected and maintained during construction and removed within
30 days after the County Inspector or determines that the site is stabilized, provided that they may be removed
when they are no longer needed.
The goal of this element is to maintain and repair all temporary and permanent erosion and sediment control
BMPs to assure continued performance.
The goal of this element is to ensure that the owner and those performing the site work comply with the
SWPPP and properly coordinate to ensure that all BMPs are deployed at the proper time to achieve full
compliance with county regulations throughout the project.
X
X
Worksheet B1
Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan)
C102 Buffer Zone C103 High Visibility Fence
C233 Silt Fence
C231 Brush Barrier
C234 Vegetated Strip
Applicant or Representative Signature
Element 13: Protect Low Impact Development BMPs
page 6 of 6
The goal of this element is to protect permanent stormwater management BMPs from siltation and compaction
during construction. The permanent 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.
Methods that will be used to protect permanent stormwater management BMPs include:
Sequencing the construction in a fashion to install these permanent BMPs at the latter part of the
construction grading operations,
Excluding equipment from the BMPs and the associated areas,
Using the erosion and sedimentation control BMPs listed below to protect facilities such as drywells,
raingardens, permeable pavement, or bioretention from accumulating sediment during construction and
before site restoration. If this option is selected check the BMPS you will use below:
Other
X
X
X
X
Cliff OBrien Digitally signed by Cliff OBrien
DN: cn=Cliff OBrien, o, ou=Westharbor Homes,
email=cobrien@westharborhomes.com, c=US
Date: 2021.01.04 12:46:56 -08'00'