HomeMy WebLinkAboutBLD2021-00300 - 05 Stormwater or Approved 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
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 natural
conditions prior to development. A hard 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.
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
May 14 2021
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.
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
projects those that must meet only Minimum Requirements #1 through #5 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
May 14 2021
May 14 2021
Worksheet A1
Medium & Large Project Report
structures
roads
Complete the following:
May 14 2021
Worksheet A1
Medium & Large Project Report
May 14 2021
Worksheet A1
Medium & Large Project Report
Engineering
May 14 2021
Worksheet A1
Medium & Large Project Report
LIST #1
LIST #1 LIST #3
May 14 2021
Worksheet A1
Medium & Large Project Report
LIST # 3
Roof
*
Other Hard Surface areas
*
May 14 2021
Worksheet B1
Choose any of the following that apply:
Choose one of the following:
May 14 2021
Worksheet B1
This element does not apply to my project because (check any that apply):
Select one of the two statements applicable to the project.
Select one of the three statements applicable to the project.
This element does not apply to my project because:
May 14 2021
Worksheet B1
Select one of the two statements applicable to the project.
Select one of the three statements applicable to the project.
May 14 2021
Worksheet B1
Select one of the three statements applicable to the project.
This element does not apply to my project because (circle any that apply -
May 14 2021
Worksheet B1
Select one of the two statements applicable to the project.
Describe the steps you will take:
May 14 2021
Worksheet B1 May 14 2021
1
Worksheet C
What’s the best option for your site?
Roofs
BMP and
Applicable
Lists
Reason why the BMP will not work on site. Additional Comments
If needed
Lawn and Landscaped Areas
BMP and
Applicable
Lists
Reason why the BMP will not work on site. Additional Comments
If needed
Minimum Requirement #5 (On-Site Stormwater Management)
The following tables summarize the criteria that can be used to justify why you cannot use various 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 Department of Ecology’s Stormwater Management Manual for
Western Washington (SWMMWW [2014]). Where any inconsistencies or lack of clarity exists, the requirements in the main
text of the SWMMWW shall be applied.
HOW TO USE:
Evaluate the feasibility of the BMPs in priority order based on Worksheet A1 page 5 (List #1) or 6 (List #3) or
Worksheet L for Large Projects (List #2). Only one criterion needs to be selected for a BMP before evaluating the
next BMP on the list.
Full Dispersion
BMP T5.30,
SWMMWW Volume V,
Section 5.3
A 65 to 10 ratio of forested or native vegetation area to
impervious area cannot be achieved.
surface) and protected by easement cannot be achieved.
Siting and design criteria cannot be achieved on site.
There is an alternatie septic system on this lot or an adjacent
treatment unit). Therefore, there is not at least 3 feet or
seasonal high groundwater table or other impermeable layer.
There is not at least 1 foot or more of permeable soil from
high groundwater table or other impermeable layer.
Downspout Full
BMP T5.10A,
SWMMWW Volume
III, Section 3.1.1
Post-construction
Soil Quality
and Depth
(BMP T5.13
SWMMWW Volume V,
Section 5.3)
Lawn and landscape area is on till slopes greater than 33
percent.
Siting and design criteria cannot be achieved on site.
List #1, #2 and #3
List #1 and #2
List #1, #2
and #3
None of the above boxes are checked. This is the BMP that must be used for lawn and landscaped areas. On
Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types
applicable to the project. If none, STOP.
None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that
this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none,
STOP.
May 14 2021
2
Worksheet C
What’s the best option for your site?
Roofs (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Where professional geotechnical evaluation recommends
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
Where the only area available for siting does not allow for
private storm sewer system.
Where there is a lack of usable space for bioretention areas
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
recommendation from an appropriate licensed professional (e.g.,
engineer, geologist, hydrogeologist):
such as bulkheads.
basements.
Bioretention or
Rain Gardens
BMP T7.30 or T5.14A
SWMMWW Volume V,
Section 7.4
List #1 (both)
and List #2
(bioretention
only)
Downspout Full
(cont.)
BMP T5.10A,
SWMMWW Volume
Slopes steeper than 25% or less than 200’ from slope
steeper than 40%.
Siting and design criteria cannot be achieved on site.
None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that
this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none,
STOP.
May 14 2021
3
Worksheet C
What’s the best option for your site?
Roofs (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Bioretention or
Rain Gardens
(cont.)
BMP T7.30 or T5.14A
SWMMWW Volume V,
Section 7.4
Where land for bioretention is within an erosion hazard, or
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.
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
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.
The following criteria can be cited as reasons for infeasibility
services to make the observation):
Within setback provided for BMP T7.30 (SWMMWW Volume
V, Section 7.4)
Where they are not compatible with surrounding drainage
system as determined by the county (e.g., project drains to
an existing stormwater collection system whose elevation
or location precludes connection to a properly functioning
bioretention area).
May 14 2021
4
Worksheet C
What’s the best option for your site?
Roofs (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
garden sites have a measured (a.k.a., initial) native soil
saturated hydraulic conductivity less than 0.30 inches per
SWMMWW Volume III, Section 3.3.6 (or an alternative
be used to demonstrate infeasibility of bioretention areas.
to be evaluated as an option in List #1 or List #2. In these
slow draining soils, a bioretention area with an underdrain
underdrain is elevated within a base course of gravel, it will
achieve Minimum Requirement #7.
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):
o 10,000 square feet of impervious area
o 0.75 acres of lawn and landscape.
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 drinking water well, or a spring used for
drinking water supply.
Bioretention or
Rain Gardens
(cont.)
Where the minimum vertical separation of 1 foot to the
seasonal high groundwater or other impermeable layer would
not be achieved below bioretention that would serve a drainage
area less than the above thresholds
May 14 2021
5
Worksheet C
What’s the best option for your site?
Roofs (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Perforated
Stub-Out
Connections
BMP T5.10C
SWMMWW Volume
III, Section 3.1.3
For sites with septic systems, the only location available for
permeability, distance between systems, etc.) indicate that
this is unnecessary.
device on this or an adjacent lot. Therefore, there is not at
highest estimated groundwater table or other impermeable
layer.
connection is under impervious or heavily compacted soils.
The only location available is on or above slopes greater than
20%
Siting and design criteria cannot be achieved on site.
length from the downspout to the downstream property line,
structure, stream, wetland, slope over 15 percent, or other
impervious surface is not feasible.
between the outlet of the trench and any property line,
structure, stream, wetland, or impervious surface is not
outlet of the trench and any slope steeper than 15 percent is
not feasible.
Siting and design criteria cannot be achieved on site.
Downspout
Dispersion
Systems
BMP T5.10B
SWMMWW Volume
III, Section 3.1.2
List #1, #2
and #3
List #1, #2
and #3
including reserve areas, and grey water reuse systems. For
None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that
this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none,
STOP.
None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that
this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none,
STOP.
None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that
this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none,
STOP.
May 14 2021
6
Worksheet C
What’s the best option for your site?
Other Hard Surfaces
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Where professional geotechnical evaluation recommends
Within an area whose ground water drains into an erosion
hazard, or landslide hazard area.
pavement area would compromise adjacent impervious
pavements.
area would threaten existing below grade basements.
such as bulkheads.
Down slope of steep, erosion prone areas that are likely to
deliver sediment to the area of pervious pavement.
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
Citation of any of the following infeasibility criteria must be
recommendation from an appropriate licensed professional (e.g.,
engineer, geologist, hydrogeologist):
Permeable
Pavement
BMP T5.15,
SWMMWW Volume
V, Section 5.3
List #1 and #2
Full Dispersion
BMP T5.30
SWMMWW Volume
V, Section 5.3
A 65 to 10 ratio of forested or native vegetation area to
impervious area cannot be achieved.
surface) cannot be achieved.
Siting and design criteria cannot be achieved on site.
List #1 and #2
None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1,
indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the
project. If none, STOP.
* Note that
Raingardens
may be used
in lieu of
permeable
pavement if
subject to
List #1.
May 14 2021
7
Worksheet C
What’s the best option for your site?
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Permeable
Pavement
(cont.)
BMP T5.15,
SWMMWW Vol
ume V, Section
5.3
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.
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.
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
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 drinking water well, or a spring used
generating surface.
The following criteria can be cited as reasons for infeasibility without
make the observation):
strength to support heavy loads at industrial facilities such
as ports.
Where installation of permeable pavement would threaten
subgrades.
* Note that
Raingardens
may be used
in lieu of
permeable
pavement if
subject to
List #1.
May 14 2021
8
Worksheet C
What’s the best option for your site?
including reserve areas, and grey water reuse systems. For
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.
bridges.
Where the site design cannot avoid putting pavement
deposition after construction (e.g., construction and
landscaping material yards).
Where the site cannot reasonably be designed to have a
porous asphalt surface at less than 5 percent slope, or a
pervious concrete surface at less than 10 percent slope, or
a permeable interlocking concrete pavement surface (where
upper slope limit can range from 6 to 12 percent; check with
manufacturer and local supplier.
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
Volume III, Section 3.3.7. Note: In these instances, the
construction.
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
an outwash soil with a saturated hydraulic conductivity of 4
inches per hour or greater.
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Permeable
Pavement
(cont.)
BMP T5.15,
SWMMWW
Volume V,
Section 5.3
* Note that
Raingardens
may be used
in lieu of
permeable
pavement if
subject to
List #1.
May 14 2021
9
Worksheet C
What’s the best option for your site?
measured (a.k.a., initial) subgrade soil saturated hydraulic
SWMMWW Volume III, Section 3.3.6 (or an alternative small
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,
or less are very low volume roads (AASHTO 2001) (U.S.
Department of Transportation, 2013). Areas with very low
utility trucks (e.g., garbage, recycling), daily school bus use,
trucks, and maintenance vehicles. Note: This infeasibility
bearing surfaces associated with the collector or arterial.
the SWMMWW Volume I).
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
conditions within 1 foot of the bottom of the lowest gravel
base course.
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Permeable
Pavement
(cont.)
BMP T5.15,
SWMMWW
Volume V,
Section 5.3
None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1,
indicate that this will be the BMP used. (List #1 may use Raingardens in lieu of Permeable Pavement). CONTINUE to
complete the form for other surface types applicable to the project. If none, STOP.
* Note that
Raingardens
may be used
in lieu of
permeable
pavement if
subject to
List #1.
May 14 2021
10
Worksheet C
What’s the best option for your site?
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Where professional geotechnical evaluation recommends
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
Where the only area available for siting does not allow for
private storm sewer system.
Where there is a lack of usable space for bioretention areas
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
recommendation from an appropriate licensed professional (e.g.,
engineer, geologist, hydrogeologist):
such as bulkheads.
basements.
The following criteria can be cited as reasons for infeasibility
services to make the observation):
Within setback provided for BMP T7.30 (SWMMWW Volume
V, Section 7.4)
Where they are not compatible with surrounding drainage
system as determined by the county (e.g., project drains to
an existing stormwater collection system whose elevation
or location precludes connection to a properly functioning
bioretention area).
Bioretention or
Rain Gardens
BMP T7.30,
SWMMWW Volume V,
Section 7.4
List #1 (both)
and List #2
(bioretention
only)
May 14 2021
11
Worksheet C
What’s the best option for your site?
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Bioretention or
Rain Gardens
(cont.)
BMP T7.30,
SWMMWW Volume V,
Section 7.4
Where land for bioretention is within an erosion hazard, or
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.
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
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.
Where the minimum vertical separation of 1 foot to the
seasonal high groundwater or other impermeable layer
would not be achieved below bioretention that would serve a
drainage area less than the above thresholds
May 14 2021
12
Worksheet C
What’s the best option for your site?
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
garden sites have a measured (a.k.a., initial) native soil
saturated hydraulic conductivity less than 0.30 inches per
SWMMWW Volume III, Section 3.3.6 (or an alternative
be used to demonstrate infeasibility of bioretention areas.
to be evaluated as an option in List #1 or List #2. In these
slow draining soils, a bioretention area with an underdrain
underdrain is elevated within a base course of gravel, it will
achieve Minimum Requirement #7.
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):
o 10,000 square feet of impervious area
o 0.75 acres of lawn and landscape.
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 drinking water well, or a spring used for
drinking water supply.
including reserve areas, and grey water reuse systems. For
Bioretention or
Rain Gardens
(cont.)
BMP T7.30,
SWMMWW Volume V,
Section 7.4
None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1,
indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the
project. If none, STOP.
May 14 2021
13
Worksheet C
What’s the best option for your site?
Other Hard Surfaces (cont.)
BMP and
Applicable
Lists
Reason why the BMP will not work on site.Additional Comments
If needed
Sheet Flow
Dispersion
BMP T5.12,
SWMMWW Volume
V, Section 5.3
Area to be dispersed (e.g., driveway, patio) cannot be graded
to have less than a 15 percent slope.
contributing surface cannot be achieved. For variably sloped
cannot be achieved.
Siting and design criteria cannot be achieved on site.
Concentrated
Flow
Dispersion
BMP T5.11,
SWMMWW Volume
V, Section 5.3
sq. ft. of drainage area followed with applicable setbacks
cannot be achieved.
More than 700 sq. ft. drainage area drains to any dispersion
device.
Siting and design criteria cannot be achieved on site.
List #1, #2
and #3
List #1, #2
and #3
None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1,
indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the
project. If none, STOP.
None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1,
indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the
project. If none, STOP.
May 14 2021