Screen Reader Users: Make sure settings include reading (1) strikethrough and underline font attributes, and (2) superscripts and subscripts.
The City of Seattle
title
An ordinance relating to the 2026 Stormwater Code Update; updating stormwater control requirements for development, roadways, utilities, and maintenance activities; strengthening stormwater treatment and infiltration standards; clarifying vesting and review thresholds; ensuring the City’s compliance with requirements of the City’s 2024-2029 Phase 1 Municipal Stormwater Permit issued by the State Department of Ecology; and amending Chapters 22.800, 22.801, 22.802, 22.803, 22.805, and 22.807 of the Seattle Municipal Code.
body
Recitals:
Recital 1. The City of Seattle is committed to protecting local creeks and lakes, the Duwamish River, and Puget Sound.
Recital 2. The City fosters a healthy people, environment, and economy by partnering with the community to equitably manage water and waste resources for today and for future generations, including but not limited to the reduction of pollutants and contaminants of emerging concern from stormwater runoff that can harm local water bodies.
Recital 3. The City is aware that emerging contaminants from stormwater runoff, such as 6PPD-q, a chemical in tire dust, adversely affect local salmon populations, and supports greater water quality treatment where possible.
Recital 4. The City is working to address urgent housing needs and must balance protecting people, property, and the environment with increased development.
Recital 5. The City uses stormwater regulations to protect people, property, and the environment from damage related to stormwater runoff, for the purposes stated in Section 22.800.020 of the Seattle Municipal Code.
Recital 6. The City has committed to achieve thirty percent tree canopy coverage by 2037, and the amendments to the Stormwater Code adopted by this ordinance reflect that commitment by expanding opportunities for tree planting.
Recital 7. The City is subject to the 2024-2029 Phase I Municipal Stormwater Permit (National Pollutant Discharge Elimination System and State Waste Discharge General Permit for Discharges from Large and Medium Municipal Separate Storm Sewer Systems) issued July 1, 2024 (the “MS4 Permit”), by the State of Washington Department of Ecology (“Ecology”) in compliance with the federal Clean Water Act and state law, as effective August 1, 2024.
Recital 8. The MS4 Permit requires the City’s Stormwater Code and associated technical manual include minimum requirements, thresholds, definitions, and other specified requirements, limitations and criteria that are equivalent to Appendix 1 (Minimum Technical Requirements for New Development and Redevelopment) of the MS4 Permit and Ecology’s Stormwater Management Manual for Western Washington, 2024 edition.
Recital 9. This ordinance, to be known as the 2026 Stormwater Code Update, contains amendments to comply with the MS4 Permit and other amendments not required to comply with the MS4 Permit, to further the purposes of the Stormwater Code.
Recital 10. Ecology has reviewed the proposed revisions to the Stormwater Code contained in this ordinance and found them, together with concurrently proposed Seattle Stormwater Manual revisions, to comply with the requirements of the MS4 Permit.
Recital 11. In developing this ordinance and other stormwater regulations that protect the functions and values of critical areas, including those in the Shoreline District, the City has included the best available science. Therefore,
Be it ordained by The City Of Seattle as follows:
Section 1. Chapter 22.800 of the Seattle Municipal Code, last amended by Ordinance 126336, is amended as follows:
Chapter 22.800 Title, Purpose, Scope, And Authority
* * *
22.800.040 Exemptions, adjustments, and exceptions
A. Exemptions
1. The following land uses are exempt from the provisions of this subtitle:
a. Commercial agriculture, including only those activities conducted on lands defined in RCW 84.34.020(2), and production of crops or livestock for wholesale trade; and
b. Forest practices regulated under Title 222 Washington Administrative Code, except for Class IV general forest practices, as defined in WAC 222-16-050, that are conversions from timber land to other uses.
2. The following land disturbing activities are ((not required to comply with)) exempt from the following specific minimum requirements ((listed below.)) :
a. Maintenance, repair, upgrade, or installation of underground or overhead utility facilities, such as, but not limited to, pipes, conduits and vaults, ((and)) that ((includes replacing)) replaces the ground surface with in-kind material or materials with similar runoff characteristics ((are not required to comply with)) is exempt from Section 22.805.070 (Minimum requirements for on-site stormwater management), Section 22.805.080 (Minimum requirements for flow control), ((or)) and Section 22.805.090 (Minimum requirements for treatment), except ((as modified as follows: 1) Installation)) installation of underground or overhead utility facilities that are integral with and contiguous to a trail or sidewalk project, parcel-based project, or a road-related project ((shall)) must comply with Section 22.805.040 (Minimum requirements for trail and sidewalk projects), Section 22.805.050 (Minimum requirements for parcel-based projects), or Section 22.805.060 (Minimum requirements for roadway projects), respectively.
b. Pavement maintenance practices, as defined in Section 22.801.170, ((limited to the following activities)) are ((not required to comply with Section 22.805.060 (Minimum requirements for roadway projects),)) exempt from Section 22.805.070 (Minimum requirements for on-site stormwater management), Section 22.805.080 (Minimum requirements for flow control), ((or)) and Section 22.805.090 (Minimum requirements for treatment), except ((:)) pavement maintenance practices that are integral with and contiguous to a parcel-based project or a road-related project must comply with Section 22.805.050 (Minimum requirements for parcel-based projects) or Section 22.805.060 (Minimum requirements for roadway projects), respectively.
((1) Pothole and square cut patching;
2) Overlaying existing asphalt or concrete or brick pavement with asphalt or concrete without expanding the area of coverage;
3) Shoulder grading;
4) Reshaping or regrading drainage ditches;
5) Crack sealing; and
6) Vegetation maintenance.))
c. Land disturbing activity that includes replacing the ground surface with in-kind material or with materials having equivalent runoff characteristics and is associated solely with soil remediation or tank removal for the purpose of removing contaminants and pollutants and not associated with other development is not required to comply with subsections 22.805.050.A and 22.805.060.A (Soil amendment), Section 22.805.070 (Minimum requirements for on-site stormwater management), or Section 22.805.080 (Minimum requirements for flow control). Projects that include any development in addition to soil remediation or tank removal ((replaced with in-kind material or with materials having equivalent runoff characteristics)) are not exempt.
d. Drainage control facilities that are part of a public retrofit project installed to meet Appendix 12 to the City's municipal stormwater NPDES permit or for combined sewer control, or other voluntary retrofit project, are not required to comply with Section 22.805.070 (Minimum requirements for on-site stormwater management), Section 22.805.080 (Minimum requirements for flow control), or Section 22.805.090 (Minimum requirements for treatment). This exemption does not include land disturbing activities or hard surfaces that are not integral ((to)) with or are in addition to the drainage control facilities described above, or installation of drainage control facilities that are otherwise required to meet this subtitle.
e. Additional work associated with an activity exempted by this subsection 22.800.040.A.2 that is necessary to comply with the federal Americans with Disabilities Act is included in the exemption granted.
3. Sites that produce no runoff as determined by a licensed civil engineer using a continuous runoff model approved by the Director are not required to comply with Section 22.805.080 (Minimum requirements for flow control).
4. When a portion of the site being developed discharges only to the public combined sewer, and that portion is not required to implement source controls pursuant to Section 22.803.040 for specified activities, the Director has the authority, to the extent allowed by law, to issue an order under Chapter 22.808 requiring the responsible party to undertake source controls, if the Director determines that these activities pose a hazard to public health, safety or welfare; endanger any property; adversely affect the safety and operation of City right-of-way, utilities, or other property owned or maintained by the City; or adversely affect the functions and values of an environmentally critical area or buffer.
5. Residential activities are not required to comply with the provision of subsection 22.805.020.I (Install source control BMPs) unless the Director determines that these activities pose a hazard to public health, safety or welfare; endanger any property; adversely affect the safety and operation of City right-of-way, utilities, or other property owned or maintained by the City; or adversely affect the functions and values of an environmentally critical area or buffer.
6. With respect to all state highway right-of-way under Washington State Department of Transportation (WSDOT) control within the jurisdiction of The City of Seattle, WSDOT shall use the current, approved Highway Runoff Manual (HRM) for its existing and new facilities and rights-of-way, as addressed in WAC 173-270-030(1) and (2). Exceptions to this exemption, where more stringent stormwater management requirements apply, are addressed in WAC 173-270-030(3)(b) and (c).
a. When a state highway is located in the jurisdiction of a local government that is required by Ecology to use more stringent standards to protect the quality of receiving waters, WSDOT shall comply with the same standards to promote uniform stormwater management.
b. WSDOT shall comply with standards identified in watershed action plans for WSDOT rights-of-way, to the extent required by state law.
c. Other instances where more stringent local stormwater standards apply are projects subject to tribal government standards or to the stormwater management-related permit conditions imposed under Chapter 25.09 to protect environmentally critical areas and their buffers (under the Growth Management Act), an NPDES permit, or shoreline master programs (under the Shoreline Management Act). In addition, WSDOT shall comply with local jurisdiction stormwater standards when WSDOT elects, and is granted permission, to discharge stormwater runoff into a municipality's drainage system or combined sewer system.
* * *
22.800.070 Minimum requirements for City agency projects
A. Compliance. A City ((agencies)) agency shall comply with all the requirements of this subtitle except as specified below:
1. City agencies are not required to obtain permits and approvals under this subtitle for work performed within a public right-of-way or for the operation and maintenance of city park lands, ((other than)) except for inspections as set out in subsection 22.800.070.B and review and approval when applying roadway project infeasibility as provided in subsection 22.805.060.E((, for work performed within a public right-of-way or for work performed for the operation and maintenance of park lands under the control or jurisdiction of the Department of Parks and Recreation. Where the work occurs in a public right-of-way, it shall also comply with Title 15, Street and Sidewalk Use, including the applicable requirements to obtain permits or approvals)).
2. A City agency project((, as defined in Section 22.801.170,)) that is not required to obtain permit(s) and approval(s) pursuant to subsection 22.800.070.A.1 and meets all of the conditions set forth below, is not required to comply with amendments to ((Sections 22.800.020 through 22.808.110)) this subtitle that take effect on ((July 1, 2021)) July 1, 2026, except the amendments to this subsection 22.800.070.A.2 ((.)) , provided that:
a. The project begins land disturbing activities ((within five years of the effective date of this subtitle)) before July 1, 2031; and
b. The project complies with the Stormwater Code that was made effective ((January 1, 2016)) July 1, 2021, by Ordinance ((124872)) 126336, ((which requires compliance)) and with Directors' Rules SDCI ((17-2017)) 10-2021/SPU DWW 200 effective ((January 1, 2016)) July 1, 2021; and
c. The project ((meets one or more of the following criteria)) is financed in whole or in part by funds:
1) ((Project funding was appropriated as identified in Ordinance 126237 titled, "An ordinance adopting a budget, including a capital improvement program and position modifications, for The City of Seattle for 2021")) Appropriated by ordinance as part of the City’s 2026 budget; or
2) ((Project received or will receive voter approval of financing)) Approved by voters before ((January 1, 2021)) July 1, 2026; or
3) ((Project received or will receive funds based on)) Received as a result of a state or federal grant ((application(s))) application submitted before ((January 1, 2021)) July 1, 2026.
* * *
22.800.100 ((Transition to revised)) Stormwater Code vesting
A. ((Any building or grading permit issued prior to June 30, 2020, (1) which was not considered, either in the initial application process or in a renewal process, under the version of the Stormwater Code in effect on or after January 1, 2016, and (2) pursuant to which construction has not started by June 30, 2020, shall expire on June 30, 2020.
B. Any building or grading permit (1) which was considered under a version of the Stormwater Code in effect on or after January 1, 2016, but before July 1, 2021, and (2) pursuant to which construction has not started by July 1, 2026, shall expire on July 1, 2026.
C. Any master use permit issued prior to June 30, 2020, for a project not requiring a building permit (1) which was not considered, either in the initial application process or in a renewal process, under the version of the Stormwater Code in effect on or after January 1, 2016, and (2) pursuant to which construction has not started by June 30, 2020, shall expire on June 30, 2020.
D. Any master use permit for a project not requiring a building permit (1) which was considered under a version of the Stormwater Code in effect on or after January 1, 2016, but before July 1, 2021, and (2) pursuant to which construction has not started by July 1, 2026, shall expire on July 1, 2026.
E. Neither Section 23.22.028, Section 23.22.064, Section 23.24.050, RCW 58.17.033, nor RCW 58.17.170 shall require any permit application submitted on or after January 1, 2016, to be considered under a version of the Stormwater Code in effect prior to January 1, 2016, or require any permit application submitted on or after July 1, 2021 to be considered under a version of the Stormwater Code in effect prior to July 1, 2021. For purposes of this subsection 22.800.100.E, "permit application" means an application for any permit required for construction within a plat or short plat or for construction of facilities and improvements for a plat or short plat, including, but not limited to, master use, building and grading permits.
F. Neither Section 23.22.028 nor Section 23.22.064 shall authorize starting construction, after June 30, 2020, of facilities or improvements for any plat without compliance with the version of the Stormwater Code in effect on or after January 1, 2016, or authorize starting construction, after July 1, 2026, of facilities or improvements for any plat without compliance with the version of the Stormwater Code in effect on or after July 1, 2021.
G. For purposes of this section, "starting construction" or "started construction" means the site work associated with and directly related to the approved project has begun. For example: grading the project site to final grade or utility installation such as water, sewer, drainage, gas, or electrical infrastructure installed to serve the project and associated with the application. Simply clearing the project site or installing conduit does not constitute the start of construction.)) Applicability. Except as provided in Section 22.800.070, all project applications must comply with the Stormwater Code in effect as follows:
1. Applications submitted on or after July 1, 2026, must comply with the Stormwater Code in effect on or after July 1, 2026.
2. Applications submitted before July 1, 2016, must be revised to comply with the Stormwater Code in effect on or after July 1, 2026, if construction has not started by July 1, 2021.
3. Applications submitted on or after July 1, 2016, but before July 1, 2021, must be revised to comply with the Stormwater Code in effect on or after July 1, 2026, if construction has not started by July 1, 2026.
4. Applications submitted on or after July 1, 2021, but before July 1, 2026, must be revised to comply with the Stormwater Code in effect on or after July 1, 2026, if construction has not started by July 1, 2031.
B. Expiration of permits or approvals when construction has not started. For any project that has not met the applicable deadline to start construction set forth in subsection 22.800.100.A, the associated permit or approval shall expire on that applicable deadline unless the project application is revised to comply with the Stormwater Code in effect on or after July 1, 2026, and approved by the Director.
C. Definition of “project application,” “start,” and “started.” For purposes of this Section 22.800.100:
1. "Project application" means a complete application, as determined by the Director, for a permit or approval required for development, including construction within a plat or short plat or for construction of facilities and improvements for a plat or short plat, including, but not limited to, master use, building, street use, and grading permits.
2. “Start” or "started" with respect to construction means, at a minimum, that site work associated with and directly related to the approved project has begun. For example: grading the project site to final grade or utility installation such as water, sewer, drainage, or electrical infrastructure installed to serve the entire project and associated with the application. Simply clearing the project site or installing conduit does not constitute the start of construction. Additional requirements for determining the start of construction may be established by rules promulgated by the Director.
D. Permit vesting and construction authorization relative to Stormwater Code. Section 23.22.028, Section 23.22.074, Section 23.24.050, Section 23.76.029, RCW 58.17.033, and RCW 58.17.170 shall not be construed to:
1. Determine the Stormwater Code applicable to a project; or
2. Authorize starting construction after the deadlines identified in subsection 22.800.100.A without compliance with the version of the Stormwater Code in effect under subsection 22.800.100.A.
Section 2. Chapter 22.801 of the Seattle Municipal Code, last amended by Ordinance 127376, is amended as follows:
Chapter 22.801 Definitions
* * *
22.801.020 "A"
* * *
"Aquatic life use, fresh water" means "aquatic life uses" as defined in WAC 173-201A-200 (Fresh Water Designated Uses and Criteria). For the purposes of this subtitle, at minimum the following water bodies are designated for fresh water aquatic life use: small lakes, ((creeks,)) streams, wetlands, and fresh water designated receiving waters.
"Aquatic life use, marine water" means "aquatic life uses" as defined in WAC 173-201A-210 (Marine Water Designated Uses and Criteria) and includes marine surface waters of the state of Washington.
* * *
22.801.040 "C"
* * *
"City agency" means "City agency" as defined in Section 25.09.520.
“Closely related projects” means two or more projects that are concurrently under review, under issued permits not yet approved for final construction, or both, and share any of the following physical or functional interdependencies:
1. A feature physically spans the property lines between lots or the project sites, such as shared structures, shared driveways, shared pedestrian access (including easements to rights-of-way), shared drainage and utility designs, foundation footings, or retaining walls. For purposes of this subsection, abutting driveways or pedestrian accesses are not considered to span the property lines if the required driveway or pedestrian access width for each project independently meets development standards;
2. A shared driveway is proposed to access a parking area for more than one project, regardless of whether the parking is required;
3. Parking, including maneuvering, aisle requirements, or other parking related easements, regardless of whether the parking is required, is proposed to be provided (or partially provided) on the site of another project, even if the project sites do not abut each other;
4. Proposed structures are joined or share a common wall;
5. Proposed projects share required open space, amenity area, or both;
6. The design of two or more project sites are dependent on grading, construction of retaining walls or foundations, or both across the lot lines or project sites;
7. One site is required to permanently access, construct, and maintain the structures or development features on an abutting or adjacent site; or
8. Other features that create physical or functional interdependence between the projects.
"Combined sewer." See "public combined sewer."
"Combined sewer basin" or "public combined sewer basin" means the area tributary to a public combined sewer feature, including, but not limited to, a combined sewer overflow outfall, trunk line connection, pump station, or regulator.
“Common plan of development or sale” means a site where multiple separate and distinct construction activities may be taking place at different times on different schedules and/or by different contractors, but still under a single plan. Examples of “common plan of development or sale” include:
1. Phased projects and projects with multiple filings/lots, even if the separate phases or filings/lots will be constructed under separate contract or by separate owners (e.g., a development where lots are sold to separate builders);
2. A development plan that may be phased over multiple years, but is still under a consistent plan for long-term development;
3. Projects in a contiguous area that may be unrelated but still under the same contract, such as construction of a building extension and a new parking lot at the same facility; and
4. Linear projects such as roads, pipelines, or utilities.
* * *
"Construction ((Stormwater Control Plan)) stormwater control plan" means a document that explains and illustrates the measures to be taken on the construction site to prevent erosion and discharge of sediment and other pollutants on a construction project.
* * *
"Creek" means ((a Type S, F, Np or Ns water as defined in WAC 222-16-031, or as defined in WAC 222-16-030 after state water type maps are adopted, and is used synonymously with "stream.")) “stream” as defined by Section 22.801.200 and is used synonymously.
22.801.050 "D"
* * *
"Development" means the following activities:
1. Class IV-general forest practices that are conversions from timberland to other uses;
2. Land disturbing activity;
3. The addition or replacement of hard surfaces;
4. Expansion of a building footprint or addition or replacement of a structure;
5. Structural development, including construction, installation, or expansion of a building or other structure;
6. Seeking approval of a building permit, other construction permit, grading permit, street improvement permit, or master use permit that involves any of the foregoing activities; and
7. Seeking approval of subdivision, short plat, unit lot subdivision, or binding site plans, as defined and applied in chapter 58.17 RCW, or other master use permit.
Development is a type of project.
* * *
"Drainage water" means stormwater and all other discharges that are permissible pursuant to ((subsection)) subsections 22.802.030.A and 22.802.030.B.
22.801.060 "E"
* * *
(("Enhanced treatment facility" means a drainage control facility designed to reduce concentrations of dissolved metals in drainage water.))
* * *
22.801.080 "G"
* * *
"Groundwater" means “groundwater” as defined in chapter 173-200 WAC (Water Quality Standards for Groundwaters of the State of Washington) and includes water, perched or otherwise, in a saturated zone or stratum beneath the surface of land or below a surface water body. ((Refer to Ground Water Quality Standards, Chapter 173-200 WAC.))
22.801.090 "H"
"Hard surface" means an impervious surface, a permeable pavement, or a vegetated roof.
"High-use sites" means sites that typically generate high concentrations of oil due to high traffic turnover or the frequent transfer of oil or other petroleum products. High-use sites include:
1. An area of a commercial or industrial site subject to: an expected average daily traffic (ADT) count equal to or greater than 100 vehicles per 1,000 square feet of gross building area; 300 or more total trip ends per day; or both;
2. An area of a commercial or industrial site subject to petroleum storage and transfer in excess of 1,500 gallons per year, not including routinely delivered heating oil;
3. An area of a commercial or industrial site subject to parking, storage or maintenance of 25 or more vehicles that are over 10 tons gross weight (trucks, buses, trains, heavy equipment, etc.);
4. A road intersection with a measured ADT count of 25,000 vehicles or more on the main roadway and 15,000 vehicles or more on any intersecting roadway, excluding projects proposing primarily pedestrian or bicycle use improvements.
22.801.100 "I"
* * *
"Impervious surface" means any surface exposed to rainwater from which most water runs off. Impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, formal planters, parking lots or storage areas, concrete or asphalt paving, areas with underdrains designed to remove stormwater from subgrade (e.g. playfields, athletic fields, rail yards), gravel surfaces ((subjected)) subject to vehicular ((traffic)) use, compact gravel, 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 stormwater modeling.
* * *
"Infiltration facility" or “infiltration BMP” means a drainage control facility that temporarily stores, and then percolates, drainage water into the underlying soil.
* * *
22.801.130 "L"
* * *
"Large project" means a project including:
1. ((Five thousand)) 5,000 square feet or more of new plus replaced hard surface; or
2. ((One acre)) 10,000 square feet or more of land disturbing activity. ((;
3. Conversion of 3/4 acres or more of vegetation to lawn or landscaped area; or
4. Conversion of 2.5 acres or more of native vegetation to pasture.))
* * *
22.801.140 "M"
"Master use permit" means a "master use permit" as defined in ((subsection)) Section 23.84A.025.
"Maximum extent feasible" means the requirement is to be fully implemented, constrained only by the physical limitations of the site, practical considerations of engineering design, and reasonable considerations of financial costs.
"Metals treatment facility" means a drainage control facility designed to reduce concentrations of dissolved metals in drainage water.
“Municipal separate storm sewer system” (MS4) means “municipal separate storm sewer system” as defined in the municipal stormwater NPDES permit.
"Municipal stormwater NPDES permit" means the permit issued to the City under the federal Clean Water Act for public drainage systems ((within the City limits)).
22.801.150 "N"
"Native vegetation" means "native vegetation" as defined in Section 25.09.520.
"New hard surface" means ((a)) the creation of a hard surface ((that is: changed from a pervious surface to a hard surface)) or the conversion, modification, or upgrade of an existing hard surface to another hard surface. Examples of a new hard surface include, but are not limited to, (((e.g.,)) converting, modifying, or upgrading:
1. Vegetation, lawn, dirt, or other earthen material to a hard surface (e.g., compact gravel, packed earthen material, permeable pavement, ((resurfacing by upgrading from dirt to gravel,)) a bituminous surface treatment ("chip seal"), asphalt, concrete, or a ((hard surface)) structure); ((or upgraded from gravel))
2. Gravel to permeable pavement, chip seal, asphalt, concrete, or a ((hard surface)) structure; ((or from a))
3. A hard surface to a modified hard surface (e.g., grading an existing parking area and repaving);
4. A hard surface to a ((hard surface)) structure; or
5. A structure to another hard surface or another structure not otherwise meeting the definition of replaced hard surface).
((Note that if)) If asphalt or concrete has been overlaid by a chip seal, the existing condition ((should be)) is considered ((as)) asphalt or concrete.
If, for a structure, the existing foundation is removed or, for any other hard surface, the subgrade or base course grade elevation is modified beyond what is required to repair the existing hard surface or base course, then the structure or other hard surface is a new hard surface.
(("New impervious surface" means a surface that is: changed from a pervious surface to an impervious surface (e.g., resurfacing by upgrading from dirt to gravel, a bituminous surface treatment ("chip seal"), asphalt, concrete or an impervious structure); or upgraded from gravel to chip seal, asphalt, concrete, or an impervious structure; or from a impervious surface to an impervious structure. Note that if asphalt or concrete has been overlaid by a chip seal, the existing condition should be considered as asphalt or concrete.))
* * *
22.801.170 "P"
"Parcel-based project" means any project that is not a roadway project, ((single-family residential project,)) sidewalk project, or trail project. The boundary of the public right-of-way shall form the boundary between the parcel and roadway portions of a project.
“Pavement maintenance practices” means repair and maintenance of an existing surface including sidewalks, limited to:
1. Targeted pothole and square cut patching;
2. Overlaying existing asphalt, concrete, or brick pavement with asphalt or concrete, so long as the base course is not exposed;
3. Shoulder grading;
4. Reshaping or regrading drainage systems, including adding curb, gutter, or wedge curbs;
5. Crack sealing; and
6. Vegetation maintenance.
“Pavement maintenance practices” does not include work that: increases the vehicle capacity of a roadway or parking area; adds new hard surface or results in replaced hard surface (except for pothole or square cut patching); or materially alters a roadway’s characteristics.
* * *
"Pollution-generating hard surface" means those hard surfaces considered to be a significant source of pollutants in drainage water. ((See definition of pollution-generating impervious surface in this Section 22.801.170 for surfaces that are considered significant sources of pollutants in drainage water. In addition, permeable pavement subject to vehicular use or other pollutants as described in the definition for pollution-generating impervious surfaces is a pollution-generating hard surface.)) Such surfaces include those that are subject to any of the following: vehicular use; industrial activities; and storage of erodible or leachable materials, wastes, or chemicals, that receive direct rainfall or the run-on or blow-in of rainfall. Such surfaces also include roofs subject to venting of significant sources of pollutants and metal roofs unless coated with an inert, non-leachable material (e.g., baked-on enamel coating).
(("Pollution-generating impervious surface" means those impervious surfaces considered to be a significant source of pollutants in drainage water. Such surfaces include those that are subject to any of the following: vehicular use; industrial activities; storage of erodible or leachable materials, wastes, or chemicals, and that receive direct rainfall or the run-on or blow-in of rainfall. Such surfaces also include roofs subject to venting of significant sources of pollutants and metal roofs unless coated with an inert, non-leachable material (e.g., baked-on enamel coating).
A surface, whether paved or not, shall be considered subject to vehicular use if it is regularly used by motor vehicles. The following are considered regularly used surfaces: roads; unvegetated road shoulders; bike lanes within the traveled lane of a roadway; driveways; parking lots; unfenced fire lanes; vehicular equipment storage yards; rail lines and railways; and airport runways.
The following are not considered regularly used by motor vehicles: sidewalks and trails not subject to drainage from roads for motor vehicles; paved bicycle pathways separated from and not subject to drainage from roads for motor vehicles; fenced fire lanes; and infrequently used maintenance access roads with recurring routine vehicle use of no more than once per day.))
"Pollution-generating pervious surface" means any pervious surface subject to any of the following: vehicular use; industrial activities; storage of erodible or leachable materials, wastes, or chemicals, and that receive direct rainfall or run-on or blow-in of rainfall; use of pesticides and fertilizers; or loss of soil. Typical pollution-generating pervious surfaces include lawns((,)) and landscaped areas, such as golf courses, parks, cemeteries, and sports fields (natural and artificial turf).
"Pre-developed condition" means the vegetation and soil conditions that are used to determine the allowable post-development discharge peak flow rates and flow durations, such as pasture or forest.
"Private drainage system" means a drainage system that is not a public drainage system.
"Project" means any proposed action to alter or develop a site, including development. ((Development is a type of project.))
* * *
22.801.190 "R"
* * *
"Replaced hard surface" or "replacement of hard surface" means((, for)) :
1. For structures, the removal of the structure down to (i.e., exposing the top of) the foundation without removing the foundation and replacement of the structure; and((, for))
2. For other hard surfaces, the removal of the surface down to the existing base course or exposing the top of the subgrade ((or base course)) and replacement, including repair of the base course layer.
If, for a structure, the existing foundation is removed or, for any other hard surface, the subgrade or base course grade elevation is modified beyond what is required to repair the existing hard surface or base course, then the structure or other hard surface is a new hard surface.
(("Replaced impervious surface" or "replacement of impervious surface" means, for structures, the removal down to the foundation and replacement and, for other impervious surfaces, the removal down to existing subgrade or base course and replacement.))
* * *
22.801.200 "S"
* * *
(("Single-family residential project" means a project that constructs one Single-family Dwelling Unit as defined in subsection 23.84A.032 and any associated accessory dwelling unit located in land classified as being Neighborhood Residential 1 (NR1), Neighborhood Residential 2 (NR2), or Neighborhood Residential 3 (NR3) pursuant to Section 23.30.010, and the total new plus replaced hard surface is less than 5,000 square feet.))
"Site" means the area defined by the legal boundaries of a parcel or parcels of land subject to development. For roadway projects, the length of the project site and the right-of-way boundaries define the site. A site may include multiple parcels and/or sections of right of-way, if multiple parcels and/or sections of right-of-way are subject to development.
"Slope" means an inclined ground surface.
"Small lakes" means Bitter Lake, Green Lake and Haller Lake.
"Small project" means a project with:
1. Less than 5,000 square feet of new and replaced hard surface; and
2. Less than ((one acre)) 10,000 square feet of land disturbing activities.
* * *
"Stream" means a ((Type S, F, Np or Ns water as defined in WAC 222-16-031, or as defined in WAC 222-16-030 after state water type maps are adopted, and is used synonymously with "creek.")) watercourse through which naturally occurring surface waters flow sufficiently, whether on a perennial or intermittent basis, to carve a defined channel or bed evidencing the passage of water, including but not limited to bedrock channels, gravel beds, alluvial mineral beds, defined-channel swales, and beds containing hydraulically sorted sediments. “Stream” does not include watercourses created entirely by artificial means, such as irrigation or roadside ditches, stormwater runoff devices, or canals, unless the watercourse conveys a stream that flowed naturally prior to the creation of the watercourse. “Stream” is used synonymously with “creek”.
"Surface waters" means “surface waters of the state” as defined in chapter 173-201A WAC (Water Quality Standards for Surface Waters of the State of Washington) and includes lakes, rivers, ponds, streams, inland waters, saltwaters, wetlands and all other surface waters and watercourses within the jurisdiction of the state of Washington.
* * *
22.801.220 "U"
"Uncontaminated" means ((surface water or groundwater)) not containing sediment or other pollutants or contaminants above natural background levels and not containing pollutants or contaminants in levels greater than City-supplied drinking water when referring to potable water.
22.801.230 "V"
"Vegetation" means "vegetation" as defined in Section 25.09.520.
“Vehicular use” means regular use of a hard or pervious surface by motor vehicles. The following surfaces, whether paved or not, are considered subject to regular vehicular use: roads; unvegetated road shoulders; bike lanes within the traveled lane of a roadway; driveways; parking lots; unfenced fire lanes; vehicular equipment storage yards; rail lines and railways, including light rail elevated and non-elevated guideways and tracks; and airport runways and other surfaces intended for movement or storage of aircraft.
The following are not considered regularly used by motor vehicles: sidewalks and trails not subject to drainage from roads for motor vehicles; paved bicycle pathways separated from and not subject to drainage from roads for motor vehicles; fenced fire lanes; and infrequently used maintenance access roads with recurring routine vehicle use of no more than once per day.
22.801.240 "W"
"Wastewater" means "wastewater" as defined in Section 21.16.030.
"Water Quality Standards" means Surface Water Quality Standards, ((Chapter)) chapter 173-201A WAC, ((Ground Water)) Groundwater Quality Standards, ((Chapter)) chapter 173-200 WAC, and Sediment Management Standards, ((Chapter)) chapter 173-204 WAC.
* * *
Section 3. Chapter 22.802 of the Seattle Municipal Code, last amended by Ordinance 124872, is amended as follows:
Chapter 22.802 Prohibited And Permissible Discharges
* * *
22.802.020 Prohibited discharges
A. Prohibited ((Discharges)) discharges. The following common substances are prohibited to enter, either directly or indirectly, a public drainage system, a private drainage system, or a receiving water within or contiguous to Seattle city limits, including but not limited to when entering via a service drain, overland flow, or as a result of a spill or deliberate dumping:
1. ((acids;)) Acids;
2. ((alkalis)) Alkalis including cement wash water;
3. ((ammonia;)) Ammonia;
4. ((animal)) Animal carcasses;
5. ((antifreeze)) Antifreeze, oil, gasoline, grease, and all other automotive and petroleum products;
6. ((chemicals)) Chemicals not normally found in uncontaminated water;
7. ((chlorinated)) Chlorinated/brominated swimming pool or hot tub water;
8. ((chlorine)) Chlorine/bromine;
9. ((commercial)) Commercial and household cleaning materials;
10. ((detergent;)) Detergent;
11. ((dirt;)) Dirt;
12. ((domestic)) Domestic or sanitary sewage;
13. ((drain)) Drain cleaners;
14. ((fertilizers;)) Fertilizers;
15. ((filter)) Filter backwash wastewater;
16. ((flammable)) Flammable or explosive materials;
17. ((food)) Food and food waste;
18. ((gravel;)) Gravel;
19. ((herbicides;)) Herbicides;
20. ((human)) Human and animal waste;
21. ((ink;)) Ink;
22. ((laundry)) Laundry waste;
23. ((metals)) Metals in excess of naturally occurring amounts, whether in liquid or solid form;
24. ((painting)) Painting products;
25. ((pesticides;)) Pesticides;
26. ((process)) Process wastewater;
27. ((sand;)) Sand;
28. ((soap;)) Soap;
29. ((solid)) Solid waste;
30. ((solvents)) Solvents and degreasers;
31. ((steam-cleaning)) Steam-cleaning waste; and
32. ((yard)) Yard waste.
* * *
22.802.030 Permissible discharges
A. Conditionally ((Permissible Discharges to Drainage Systems and Receiving Waters)) permissible discharges to drainage systems and receiving waters. Discharges from the sources listed below are permissible discharges only if the stated conditions are met and unless the Director of SPU determines that the type of discharge, directly or indirectly to a public drainage system, private drainage system, or a receiving water within or contiguous to Seattle city limits, whether singly or in combination with others, is causing or contributing to a violation of the City's NPDES stormwater permit or is causing or contributing to a water quality problem:
1. Discharges from potable water sources, including, but not limited to, flushing of potable water lines, hyperchlorinated water line flushing, fire hydrant system flushing, pipeline hydrostatic test water, and washing of potable water storage reservoirs. Planned discharges shall be de-chlorinated to a total residual chlorine concentration of 0.1 ppm or less, pH-adjusted if necessary, and volumetrically and velocity controlled to prevent resuspension of sediments in the drainage system. No chemicals may be added, and settleable solids must be removed prior to discharge;
2. Discharges from swimming pools, spas, hot tubs, fountains, or similar aquatic recreation facilities and constructed water features, provided the discharges have been de-chlorinated/de-brominated to a total residual ((chlorine)) concentration of 0.1 ppm or less, free from sodium chloride, pH-adjusted and reoxygenated if necessary, volumetrically and velocity controlled to prevent resuspension of sediments in the drainage system, and thermally controlled to prevent an increase of temperature in the receiving water. Swimming pool cleaning wastewater and filter backwash shall not be discharged;
3. Discharges of street and sidewalk washwater when the surfaces are swept prior to washing, detergents are not used, and water use is minimized;
4. Discharges ((of water)) from routine external building washdown when detergents are not used and water use is minimized at (i) buildings built or renovated before 1950 and after 1980, (ii) single detached dwelling units and associated accessory structures (e.g., garage), and (iii) structures built or renovated between 1950 and 1980 (inclusive) and determined to be without PCB containing materials on their exterior;
5. Discharges of water used to control dust when water use is minimized; ((and))
6. Discharges from lawn watering and other irrigation runoff, including from reclaimed water sources, when water use is minimized; and
7. Other non-stormwater discharges, provided that these discharges are in compliance with the requirements of a pollution prevention plan that addresses control of such discharges and is approved by the Director.
B. Permissible ((Discharges)) discharges. Discharges from the sources listed below are permissible discharges unless the Director of SPU determines that the type of discharge, directly or indirectly to a public drainage system, private drainage system, or a receiving water within or contiguous to Seattle city limits, whether singly or in combination with others, is causing or contributing to a violation of the City's NPDES stormwater permit or is causing or contributing to a water quality problem:
1. Discharges from surface waters, including diverted stream flows;
2. Discharges of uncontaminated groundwater, including uncontaminated groundwater infiltration (as defined at 40 CFR 35.2005(b)(20)), uncontaminated pumped groundwater, and rising groundwaters;
3. Discharges of air conditioning condensation;
4. Discharges from springs;
5. Discharges of uncontaminated water from crawl space pumps;
6. ((Discharges from lawn watering; 7.)) Discharges from ((irrigation runoff, including)) irrigation water from agricultural sources that is commingled with stormwater and that does not contain prohibited substances;
((8.)) 7. Discharges from riparian habitats and wetlands;
((9.)) 8. Discharges from approved footing drains and other subsurface drains or, where approval is not required, installed in compliance with this subtitle and rules promulgated pursuant to this subtitle;
((10.)) 9. Discharges from foundation drains;
((11.)) 10. Non-stormwater discharges authorized by another NPDES permit or State Waste Discharge permit;
((12.)) 11. Discharges that are from emergency fire fighting activities; and
((13.)) 12. Discharges of non-toxic tracing dye used to establish or verify a drainage or sewer connection.
* * *
Section 4. Chapter 22.803 of the Seattle Municipal Code, last amended by Ordinance 126336, is amended as follows:
Chapter 22.803 Minimum Requirements For All Discharges And All Real Property
* * *
22.803.020 Minimum requirements for all discharges and real property
* * *
C. Requirements to maintain facilities. All treatment facilities, flow control facilities, drainage control facilities, and drainage systems shall be maintained as specified in rules promulgated by the Director in order for these facilities and systems to be kept in continuous working order. Facility components must be kept accessible for inspection and maintenance purposes, including for inspections conducted by the City.
* * *
22.803.030 Minimum requirements for source controls for all real property
For all discharges, responsible parties shall implement and maintain source controls to prevent or minimize pollutants from leaving a site or property, as specified in the joint SPU/SDCI Directors' Rule titled "Seattle Stormwater Manual" at "Volume 4-Source Control.” Source controls that are required for all real property include, but are not limited to, the following, as further described in rules promulgated by the Director:
* * *
H. ((Rooftop)) Constructed dog runs. Dog runs located on private property, whether located at or above grade (e.g., on rooftops, podiums, or ((above-grade)) plazas), must prevent stormwater from the dog run from discharging directly or indirectly to a public drainage system, private drainage system, or receiving water body.
22.803.040 Minimum ((requirements for)) source controls for ((businesses and public entities for)) specific activities
A. In addition to the source controls required by Section 22.803.030 for all real properties, businesses and public entities must implement source controls, to the extent allowed by law, for specific pollution-generating activities as specified in the joint SPU/SDCI Directors' Rule titled "Seattle Stormwater Manual" at "Volume 4-Source Control," as necessary to prevent discharges prohibited by Section 22.802.020 or Chapter 21.16, as applicable. Source controls include, but are not limited to: segregating or isolating wastes to prevent contact with drainage water; enclosing, covering, or containing the activity to prevent contact with drainage water; developing and implementing inspection and maintenance programs; sweeping; and taking management actions such as training employees on pollution prevention.
B. For all discharges, source controls shall be implemented, to the extent allowed by law, by businesses and public entities for the following specific pollution-generating activities as specified in the joint SPU/SDCI Directors' Rule titled "Seattle Stormwater Manual" at "Volume 4-Source Control," ((to the extent)) as necessary to prevent prohibited discharges as described in ((subsection 22.802.020.A through subsection 22.802.020.D)) Section 22.802.020, and to prevent contaminants from coming in contact with drainage water or being discharged to the drainage system, public combined sewer, or directly into receiving waters:
1. Fueling at dedicated stations, for new or substantially altered fueling stations.
2. Mobile fueling of vehicles and heavy equipment.
3. In-water and over-water fueling.
4. Maintenance and repair of vehicles and equipment.
5. Concrete and asphalt mixing and production.
6. Concrete pouring, concrete/asphalt cutting, and asphalt application.
7. Recycling, wrecking yard, and scrap yard operations.
8. Storage of liquids in aboveground tanks.
Source controls include, but are not limited to, segregating or isolating wastes to prevent contact with drainage water; enclosing, covering, or containing the activity to prevent contact with drainage water; developing and implementing inspection and maintenance programs; sweeping; and taking management actions such as training employees on pollution prevention.
((B. For all discharges except those that drain only to the public combined sewer, source controls shall be implemented, to the extent allowed by law, by businesses and public entities for specific pollution-generating activities as specified in the joint SPU/SDCI Directors' Rule titled "Seattle Stormwater Manual" at "Volume 4-Source Control," to the extent necessary to prevent prohibited discharges as described in subsection 22.802.020.A through subsection 22.802.020.C, and to prevent contaminants from coming in contact with drainage water or being discharged to the drainage system or directly into receiving waters. Source controls include, but are not limited to, segregating or isolating wastes to prevent contact with drainage water; enclosing, covering, or containing the activity to prevent contact with drainage water; developing and implementing inspection and maintenance programs; sweeping; and taking management actions such as training employees on pollution prevention.))
Section 5. Chapter 22.805 of the Seattle Municipal Code, last amended by Ordinance 127375, is amended as follows:
Chapter 22.805 Minimum Requirements For All Projects
22.805.010 General
* * *
B. Closely related projects, projects under a common plan of development or sale, subdivisions, and short plats ((shall be)) are considered as one project for purposes of applying the Stormwater Code, including but not limited to determining whether the thresholds for applicability of particular Stormwater Code minimum requirements are met. ((The Director shall determine whether two or more projects are closely related as specified in the joint SPU/SDCI Directors' Rule titled "Seattle Stormwater Manual" at "Volume 1-Project Minimum Requirements."))
* * *
D. In the case of a subdivision under Chapter 23.22 and short plat under Chapter 23.24, unless an adjustment pursuant to subsection 22.800.040.B is approved by the Director, for the purposes of applying the thresholds in this Chapter 22.805((,)) :
1. A subdivision of property does not affect or reduce the requirements of this subtitle, Chapter 21.16, and associated rules promulgated by the Director. The proposed parcels within a subdivision or short plat shall meet the standards required by the higher area threshold of the entire property being subdivided, rather than the standards required for each of the proposed parcels individually.
2. In neighborhood residential (NR) zones, the hard surface coverage is the maximum lot coverage allowed per Subtitle III of Title 23, ((Land Use Code,)) plus required and proposed pedestrian and vehicular access and amenities, including roadways, driveways, walkways, plazas, and patios identified on the preliminary drainage control plan and associated preliminary site plan, unless otherwise approved by the Director. In all other zones, the hard surface coverage shall be based on an approved site plan showing the maximum allowed build-out including all phases of the subdivision or short plat.
E. Construction of drainage control facilities and drainage systems for plats
1. In the case of a subdivision under Chapter 23.22, drainage control facilities or drainage systems that are identified on the associated preliminary drainage control plan or the approved preliminary plat and will serve multiple proposed lots, parcels, tracts, or rights-of-way shall be constructed prior to approval of the final plat unless a bond is provided according to subsection 23.22.070.C. If a bond is provided in lieu of construction prior to approval of the final plat, the construction permit for the facilities or systems must be issued prior to issuance of any building permit for any other construction within the subdivision and construction of the facilities or systems shall be completed and final inspection approved prior to final inspection approval of any building permit for any other construction within the subdivision and prior to occupancy of any buildings, but in no event later than two years after final plat approval.
2. In the case of a short plat under Chapter 23.24 with shared drainage control facilities or drainage systems that are identified on the preliminary drainage control plan and will serve multiple proposed lots, parcels, tracts, or rights-of-way((, the following shall occur)) :
a. The construction permit ((for)) that includes the shared facilities or systems shall be issued prior to issuance of any other building permit for any other construction within the lots, parcels, tracts, or rights-of-way served by the shared facilities or systems; and
b. Construction of the shared facilities or systems shall be completed and final inspection approved prior to final inspection approval of any building permit for any other construction within the lots, parcels, tracts, or rights-of-way served by the shared facilities, and prior to occupancy of any buildings on these lots, parcels, or tracts.
* * *
22.805.020 Minimum requirements for all projects
* * *
C. Minimum requirements for flood-prone areas. On sites within flood-prone areas, responsible parties are required to employ procedures to minimize the potential for flooding on the site and to minimize the potential for the project to increase the risk of floods on adjacent or nearby properties. Flood control measures shall include those set forth in other titles of the Seattle Municipal Code and rules promulgated thereunder, including, but not limited to, Chapter ((23.60 (Shoreline District))) 23.60A (Seattle Shoreline Master Program Regulations), Chapter 25.06 (Floodplain Development), and Chapter 25.09 (Regulations for Environmentally Critical Areas).
D. Minimum requirements for construction stormwater pollution prevention plan. Temporary and permanent construction controls shall be used to accomplish the following minimum requirements. All projects are required to meet each of the elements below or document why an element is not applicable. Additional controls may be required by the Director when minimum controls are not sufficient to prevent erosion or transport of sediment or other pollutants from the site.
1. Mark clearing limits and environmentally critical areas. Within the boundaries of the project site and prior to beginning land disturbing activities, including clearing and grading, clearly mark all clearing limits, easements, setbacks, all environmentally critical areas and their buffers, and all trees and drainage courses that are to be preserved within the construction area.
2. Retain top layer. Within the boundaries of the project site, the duff layer, topsoil, and native vegetation, if there is any, shall be retained in an undisturbed state to the maximum extent feasible. If it is not feasible to retain the top layer in place, it should be stockpiled on-site, covered to prevent erosion, and replaced immediately upon completion of the land disturbing activities to the maximum extent feasible.
3. Establish construction access. Limit construction vehicle access, whenever possible, to one route. Stabilize access points and minimize tracking sediment onto public roads. Promptly remove any sediment tracked off site.
4. Protect downstream properties and receiving waters. Protect properties and receiving waters downstream from the development sites from erosion or flooding due to increases in the volume, velocity, duration, and peak flow rate of drainage water from the project site. If it is necessary to construct flow control facilities to meet this requirement, these facilities shall be functioning prior to implementation of other land disturbing activity. If permanent infiltration facilities are used to control flows during construction, these facilities shall be protected from siltation during the construction phase of the project.
5. Prevent erosion and sediment transport from the site. Pass all drainage water from disturbed areas through a sediment trap, sediment pond, or other appropriate sediment removal BMP before the water leaves the site or prior to discharge to an infiltration facility. Sediment controls intended to trap sediment on site shall be constructed as one of the first steps in grading and shall be functional before other land disturbing activities take place. BMPs intended to trap sedimentation shall be located in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages. Provide and maintain natural buffers around surface waters, direct stormwater to vegetated areas to increase sediment removal and maximize stormwater infiltration where feasible.
6. Prevent erosion and sediment transport from the site by vehicles. Whenever construction vehicle access routes intersect paved roads, the transport of sediment onto the paved road shall be minimized. If sediment is transported onto a paved road surface, the roads shall be cleaned thoroughly at the end of each day. Sediment shall be removed from paved roads by shoveling or sweeping and shall be transported to a controlled sediment disposal area. If sediment is tracked off site, roads shall be cleaned thoroughly at the end of each day, or at least twice daily during wet weather. Street washing is allowed only after sediment is removed, and street wash wastewater shall be prevented from entering the drainage system and receiving waters.
7. Stabilize soils. Prevent on-site erosion by stabilizing all exposed and unworked soils, including stock piles and earthen structures such as dams, dikes, and diversions. From October 1 to April 30, no soils shall remain exposed and unworked for more than two days. From May 1 to September 30, no soils shall remain exposed for more than seven days. Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Soil stockpiles shall be stabilized from erosion, protected with sediment trapping measures, and be located away from storm drain inlets, waterways, and drainage channels. Before the completion of the project, permanently stabilize all exposed soils that have been disturbed during construction.
8. Protect slopes. Erosion from slopes shall be minimized. Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion. Off-site stormwater run-on or groundwater shall be diverted away from slopes and undisturbed areas with interceptor dikes, pipes, and/or swales. Pipe slope drains or protected channels shall be constructed at the top of slopes to collect drainage and prevent erosion. Excavated material shall be placed on the uphill side of trenches, consistent with safety and space considerations. Check dams shall be placed at regular intervals within constructed channels that are cut down a slope.
9. Protect storm drains. Prevent sediment from entering all storm drains, including ditches that receive drainage water from the project. Storm drain inlets protection devices shall be cleaned or removed and replaced as recommended by the product manufacturer, or more frequently if required to prevent failure of the device or flooding. Storm drain inlets made operable during construction shall be protected so that drainage water does not enter the drainage system without first being filtered or treated to remove sediments. Storm drain inlet protection devices shall be removed at the conclusion of the project. When manufactured storm drain inlet protection devices are not feasible, inlets and catch basins must be cleaned as necessary to prevent sediment from entering the drainage control system.
10. Stabilize channels and outlets. All temporary on-site drainage systems shall be designed, constructed, and stabilized to prevent erosion. Stabilization shall be provided at the outlets of all drainage systems that is adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches.
11. Control pollutants. Measures shall be taken to control potential pollutants and shall include, but not be limited to, the following measures:
a. All pollutants, including sediment, waste materials, and demolition debris, that occur on site shall be handled and disposed of in a manner that does not cause contamination of drainage water and pursuant to all applicable disposal laws.
b. Containment, cover, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment.
c. On-site fueling tanks shall include secondary containment.
d. Maintenance, fueling, and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into drainage water runoff shall be conducted using spill prevention and control measures.
e. Contaminated soils shall be removed and surfaces shall be cleaned immediately following any discharge or spill incident.
f. Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system that prevents discharge to surface water, or to the sanitary sewer or combined sewer system with approval of the Director of SPU. Temporary discharges or connections to the public sanitary and combined sewers shall be made in accordance with Chapter 21.16 (Side Sewer Code).
g. Application of fertilizers and pesticides shall be conducted in a manner and at application rates that will not result in loss of chemical to drainage water. Manufacturers' label requirements for application rates and procedures shall be followed.
h. BMPs shall be used to prevent or treat contamination of drainage water by pH-modifying sources. These sources include, but are not limited to, recycled concrete stockpiles, bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters. Construction site operators may be required to adjust the pH of drainage water if necessary to prevent a violation of water quality standards.
i. Construction site operators must obtain written approval from Ecology prior to using chemical treatment other than carbon dioxide (CO 2 ) dry ice, or food grade vinegar, to adjust pH.
j. Uncontaminated water from water-only based shaft drilling for construction of building, road, and bridge foundations may be infiltrated provided the wastewater is managed in a way that prevents discharge to surface waters. Prior to infiltration, water from water-only based shaft drilling that comes into contact with curing concrete must be neutralized until pH is in the range of 6.5 to 8.5 (su).
k. Train all employees on proper BMPs for preventing illicit discharges, including spills.
12. Control dewatering. When dewatering devices discharge on site, to a public drainage system, or to the public combined sewer, dewatering devices shall discharge into a sediment trap, sediment pond, gently sloping vegetated area of sufficient length to remove sediment contamination, or other sediment removal BMP. Foundation, vault, and trench dewatering waters must be discharged into a controlled drainage system prior to discharge to a sediment trap or sediment pond. Clean, non-turbid dewatering water, such as unpolluted well-point groundwater, that is discharged to systems tributary to ((state)) surface waters must not cause erosion or flooding. Highly turbid or contaminated dewatering water shall be handled separately from drainage water. For ((any project)) all projects with an excavation depth of 12 feet or more below the existing grade, all projects with an excavation depth of less than 12 feet located in an area expected to have shallow groundwater depths, and ((for)) all ((large)) projects with 5,000 square feet or more of new plus replaced hard surface or one acre or more of land disturbing activity, a dewatering ((flows)) analysis must be ((determined)) performed to determine dewatering flows and ((it must be verified)) to verify that there is sufficient capacity in the downstream system (e.g., public drainage system ((and)) or public combined sewer) ((prior to discharging)) for review and approval or disapproval by the Director.
13. Maintain BMPs. All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. All temporary erosion and sediment controls shall be removed within five days after final site stabilization is achieved or after the temporary controls are no longer needed, whichever is later. Trapped sediment shall be removed or stabilized on site. Disturbed soil areas resulting from removal shall be permanently stabilized.
14. Inspect BMPs. BMPs shall be periodically inspected. For projects with 5,000 square feet or more of new plus replaced hard surface or 7,000 square feet or more of land disturbing activity, site inspections shall be conducted by a Certified Erosion and Sediment Control Lead who shall be identified prior to construction and shall be present on-site or on-call at all times.
15. Execute ((Construction Stormwater Control Plan)) construction stormwater control plan. Construction site operators shall maintain, update, and implement their ((Construction Stormwater Control Plan)) construction stormwater control plan. Construction site operators shall modify their ((Construction Stormwater Control Plan)) construction stormwater control plan to maintain compliance whenever there is a change in design, construction, operation, or maintenance at the site that has, or could have, a significant effect on the discharge of pollutants to waters of the state.
16. Minimize open trenches. In the construction of underground utility lines, where feasible, no more than 150 feet of trench shall be opened at one time, unless soil is replaced within the same working day, and where consistent with safety and space considerations, excavated material shall be placed on the uphill side of trenches. Trench dewatering devices shall discharge into a sediment trap or sediment pond.
17. Phase the project. Development projects shall be phased to the maximum extent feasible in order to minimize the amount of land disturbing activity occurring at the same time and shall take into account seasonal work limitations.
18. Install flow control and water quality facilities. Development projects required to comply with Section 22.805.080 (Minimum requirements for flow control) or Section 22.805.090 (Minimum requirements for treatment) shall install permanent flow control and water quality facilities to prevent erosion or transport of sediment or other pollutants from the site during construction.
19. Protect stormwater BMPs
a. Protect all stormwater BMPs from sedimentation through installation and maintenance of erosion and sediment control BMPs. Restore the BMPs to their fully functioning condition if they accumulate sediment during construction. Restoring the stormwater BMP must include removal of sediment and any sediment-laden stormwater BMP soils, and replacing the removed soils with soils meeting the design specification.
b. Prevent compacting ((on-site)) infiltration BMPs by excluding construction equipment and foot traffic. Protect completed lawn and landscaped areas from compaction due to construction equipment.
c. Control erosion and avoid introducing sediment from surrounding land uses onto permeable pavements. Do not allow muddy construction equipment on the base material or pavement. Do not allow sediment-laden runoff onto permeable pavements or base materials.
d. Permeable pavements fouled with sediments or no longer passing an initial infiltration test must be cleaned until infiltrating per design or replaced.
e. Keep all heavy equipment off existing soils under ((on-site)) infiltration BMPs, especially those that have been excavated to final grade, to retain the infiltration rate of the soils.
* * *
G. Protect shorelines. All projects discharging directly or indirectly through a drainage system into the shoreline district as defined in Chapter ((23.60)) 23.60A (Seattle Shoreline Master Program Regulations) shall prevent impacts to water quality and stormwater quantity that would result in a net loss of shoreline ecological functions as defined in WAC 173-26-020(13).
H. Ensure sufficient capacity. All ((large)) projects with 5,000 square feet or more of new plus replaced hard surface or one acre of land disturbing activity, all projects with an excavation depth of 12 feet or more below the existing grade, ((and)) all projects with an excavation depth of less than 12 feet located in an area expected to have shallow groundwater depths, and all projects that alter the drainage pattern from 5,000 square feet or more of an existing, new, or replaced hard surface or 3/4 of an acre or more of a pervious surface from a site to a downstream system not previously connected via discrete conveyance shall ensure that sufficient capacity exists in the ((public)) drainage system and public combined sewer to carry existing and anticipated loads, including any flows from dewatering activities. Capacity analysis shall extend to at least 1/4-mile from the discharge point of the site. Sites at which there is insufficient capacity may be required to install a flow control facility or improve the drainage system or public combined sewer to accommodate flow from the site. Unless approved otherwise by the Director as necessary to meet the purposes of this subtitle:
1. Capacity analysis for discharges to the ((public)) drainage system shall be based on peak flows with a 4 percent annual probability (25-year recurrence interval); and
2. Capacity analysis for discharges to the public combined sewer shall be based on peak flows with a 20 percent annual probability (5-year recurrence interval).
* * *
K. Comply with Side Sewer Code
1. All privately owned and operated drainage control facilities or systems, whether or not they discharge to a public drainage system or public combined sewer, shall be considered side sewers and subject to Chapter 21.16 (Side Sewer Code), SPU Director's Rules promulgated under Title 21, and the design and installation specifications and permit requirements of SPU ((and SDCI)) for side sewer and drainage systems.
2. Side sewer permits and inspections shall be required for constructing, capping, altering, or repairing privately owned and operated drainage systems as provided for in Chapter 21.16. When the work is ready for inspection, the permittee shall notify the Director of ((SDCI)) SPU. If the work is not constructed according to the plans approved under this Subtitle VIII, Chapter 21.16, the SPU Director's Rules promulgated under Title 21, and SPU ((and SDCI)) design and installation specifications, then the Director may issue a stop work order under Chapter 22.808 and require modifications as provided for in this Subtitle VIII and Chapter 21.16.
* * *
O. Minimum requirements for treatment. All projects that connect flows from 5,000 square feet or more of an existing, new, or replaced pollution-generating hard surface from the site not previously connected via discrete conveyance to a drainage system that discharges to a receiving water or a receiving water, and all projects that convert an existing hard surface of 5,000 square feet or more to a pollution-generating hard surface (e.g., an existing slab not previously subject to vehicular use) and direct flows from the site not previously connected via discrete conveyance to a drainage system that discharges to a receiving water or a receiving water, shall comply with the minimum requirements for treatment contained in Section 22.805.090 to treat flows from those pollution-generating hard surfaces. When stormwater flows from other areas, including non-pollution generating surfaces (e.g., roofs), dewatering activities, and off-site areas, cannot be separated or bypassed, treatment BMPs shall be designed for the entire area draining to the treatment facility.
((22.805.030 Minimum requirements for single-family residential projects
A. Soil amendment. Retain and protect undisturbed soil in areas not being developed, and prior to completion of the project, amend all new, replaced, and disturbed topsoil (including construction lay-down areas) with organic matter to the extent required by and in compliance with the rules promulgated by the Director.
B. On-site stormwater management. Single-family residential projects shall meet the minimum requirements for on-site stormwater management contained in Section 22.805.070, to the extent allowed by law, if:
1. For a project on a lot most recently created, adjusted, altered, or otherwise amended by a plat or other lawful document recorded with the King County Recorder on or after January 1, 2016, and where that document either created the lot or altered the size of the lot, either the total new plus replaced hard surface is 750 square feet or more or land disturbing activity is 7,000 square feet or more; or
2. For any other project, either the total new plus replaced hard surface is 1,500 square feet or the land disturbing activity is 7,000 square feet or more.))
22.805.040 Minimum requirements for trail and sidewalk projects
* * *
B. On-site stormwater management. All trail and sidewalk projects with 2,000 square feet or more of new plus replaced hard surface or 7,000 square feet or more of land disturbing activity shall meet the minimum requirements for on-site stormwater management contained in Section 22.805.070, to the extent allowed by law.
22.805.050 Minimum requirements for parcel-based projects
* * *
C. Flow control. Parcel-based projects shall meet the minimum requirements for flow control contained in Section 22.805.080, to the extent allowed by law, as prescribed below.
1. Discharges to wetlands. Parcel-based projects discharging into a wetland, or to the drainage basin of a wetland, shall:
a. Comply with Section 22.805.020 (Minimum requirements for all projects), including, but not limited to subsection 22.805.020.E (Protect wetlands).
b. Comply with the minimum requirements for wetland protection contained in subsection ((22.805.080.B.1)) 22.805.080.C (Wetland protection standards) if:
1) The total new plus replaced hard surface is 5,000 square feet or more; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture and from the project there is a surface discharge into a natural or constructed conveyance system from the site.
2. Discharges to listed creek basins. Parcel-based projects discharging into Blue Ridge Creek, Broadview Creek, Discovery Park Creek, Durham Creek, Frink Creek, Golden Gardens Creek, Kiwanis Ravine/Wolfe Creek, Licton Springs Creek, Madrona Park Creek, Mee-Kwa-Mooks Creek, Mount Baker Park Creek, Puget Creek, Riverview Creek, Schmitz Creek, Taylor Creek, or Washington Park Creek, or to the drainage basin of such creek, shall:
a. Comply with subsection ((22.805.080.B.2)) 22.805.080.D (Pre-developed forested standard) if the existing hard surface coverage is less than 35 percent and one or more of the following apply:
1) The project adds 5,000 square feet or more of new hard surface and the total new plus replaced hard surface is 10,000 square feet or more; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
4) The project adds 5,000 square feet or more of new hard surface and, through a combination of effective hard surfaces and converted pervious surfaces, causes a 0.15 cubic feet per second increase in the 100-year recurrence interval flow frequency as estimated using a continuous model approved by the Director.
b. Comply with subsection ((22.805.080.B.3)) 22.805.080.E (Pre-developed pasture standard) if the criteria in subsection 22.805.050.C.2.a do not apply and one or more apply:
1) The total new plus replaced hard surface is 5,000 square feet or more; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture, and from the project there is a surface discharge into a natural or constructed conveyance system from the site.
3. Discharges to non-listed creek basins. Parcel-based projects discharging into a creek not listed in subsection 22.805.050.C.2, or to the drainage basin of such creek, shall:
a. Comply with subsection ((22.805.080.B.2)) 22.805.080.D (Pre-developed forested standard) if the existing land cover is forested and one or more of the following apply:
1) The project adds 5,000 square feet or more of new hard surface and the total new plus replaced hard surface is 10,000 square feet or more; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
4) The project adds 5,000 square feet or more of new hard surface and, through a combination of effective hard surfaces and converted pervious surfaces, causes a 0.15 cubic feet per second increase in the 100-year recurrence interval flow frequency as estimated using a continuous model approved by the Director.
b. Comply with subsection ((22.805.080.B.3)) 22.805.080.E (Pre-developed pasture standard) if the criteria in subsection 22.805.050.C.3.a do not apply and one or more of the following apply:
1) The total new plus replaced hard surface is 5,000 square feet or more; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture, and from the project there is a surface discharge into a natural or constructed conveyance system from the site.
4. Discharges to small lake basins. Parcel-based projects discharging into Bitter Lake, Green Lake, or Haller Lake, or to the drainage basin of such lake, shall comply with subsection ((22.805.080.B.5)) 22.805.080.G (Peak control standard) if the total new plus replaced hard surface is ((2,000)) 5,000 square feet or more.
5. Discharges to public combined sewer. Unless the Director of SPU has determined that the public combined sewer has sufficient capacity to carry existing and anticipated loads, parcel-based projects discharging into the public combined sewer or its basin shall comply with subsection ((22.805.080.B.5)) 22.805.080.G (Peak control standard) if the total new plus replaced hard surface is 5,000 square feet or more.
6. Discharges to a capacity-constrained system. In addition to applicable minimum requirements for flow control in subsection 22.805.050.C.1 through subsection 22.805.050.C.5, parcel-based projects discharging into a capacity-constrained system or its basin shall also comply with subsection ((22.805.080.B.5)) 22.805.080.G (Peak control standard) if the total new plus replaced hard surface is ((2,000)) 5,000 square feet or more unless the downstream system only includes ditches or culverts and the system has been determined to have sufficient capacity as specified in subsection 22.805.020.H (Ensure sufficient capacity).
7. Discharges from groundwater. In addition to applicable minimum requirements for flow control in subsection 22.805.050.C.1 through subsection 22.805.050.C.6, parcel-based projects that will permanently discharge groundwater to a public drainage system or to a public combined sewer shall also comply with subsection ((22.805.080.B.5)) 22.805.080.G (Peak control standard) if the total new plus replaced hard surface is 2,000 square feet or more.
D. Treatment. Parcel-based projects not discharging to the public combined sewer shall comply with the minimum requirements for treatment contained in Section 22.805.090 for flows from the total new plus replaced pollution-generating hard surface and the new plus replaced pollution-generating pervious surface, to the extent allowed by law, if:
1. The total new plus replaced pollution-generating hard surface is 5,000 square feet or more; or
2. The total new plus replaced pollution-generating pervious surfaces is 3/4 acres or more, and from ((the project)) which there is a surface discharge in a natural or constructed conveyance system from the site.
22.805.060 Minimum requirements for roadway projects
* * *
B. ((On-Site)) On-site stormwater management. All roadway projects with 2,000 square feet or more of new plus replaced hard surface or 7,000 square feet or more of land disturbing activity shall meet the requirements for on-site stormwater management contained in Section 22.805.070, to the extent allowed by law, except as provided in subsection 22.805.060.E.
C. Flow control. Roadway projects shall meet the minimum requirements for flow control contained in Section 22.805.080, to the extent allowed by law, as prescribed below, except as provided in subsection 22.805.060.E.
1. Discharges to wetlands. Roadway projects discharging into a wetland or to the drainage basin of a wetland, shall:
a. Comply with Section 22.805.020 (Minimum requirements for all projects), including, but not limited to subsection 22.805.020.E (Protect wetlands).
b. Comply with the minimum requirements for wetland protection contained in subsection ((22.805.080.B.1)) 22.805.080.C (Wetland protection standards) if the existing hard surface coverage is less than 35 percent and one or more of the following apply:
1) The total new plus replaced hard surface is 5,000 square feet or more; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture and from the project there is a surface discharge into a natural or constructed conveyance system from the site.
c. Comply with the minimum requirements for wetland protection contained in subsection ((22.805.080.B.1)) 22.805.080.C (Wetland protection standards) if the existing hard surface coverage is greater than or equal to 35 percent and one or more of the following apply:
1) The total new plus replaced hard surface is 10,000 square feet or more. If the new plus replaced hard surfaces total 50 percent or more of the existing hard surfaces within the project limits, comply with subsection 22.805.080.C for the flows from the total new plus replaced hard surfaces; if the new plus replaced hard surfaces total less than 50 percent, comply with subsection 22.805.080.C for the flows from the total new hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way; or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture and from the project there is a surface discharge into a natural or constructed conveyance system from the site.
2. Discharges to listed creek basins. Roadway projects discharging into Blue Ridge Creek, Broadview Creek, Discovery Park Creek, Durham Creek, Frink Creek, Golden Gardens Creek, Kiwanis Ravine/Wolfe Creek, Licton Springs Creek, Madrona Park Creek, Mee-Kwa-Mooks Creek, Mount Baker Park Creek, Puget Creek, Riverview Creek, Schmitz Creek, Taylor Creek, or Washington Park Creek, or to the drainage basin of such creek, shall:
a. Comply with subsection ((22.805.080.B.2)) 22.805.080.D (Pre-developed forested standard) if the existing hard surface coverage is less than 35 percent and one or more of the following apply:
1) The project adds ((5,000)) 10,000 square feet or more of new plus replaced hard surface ((and the total new plus replaced hard surface is 10,000 square feet or more)); or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
4) The project adds 5,000 square feet or more of new hard surface and, through a combination of effective hard surfaces and converted pervious surfaces, causes a 0.15 cubic feet per second increase in the 100-year recurrence interval flow frequency as estimated using a continuous model approved by the Director.
b. Comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) if the criteria in subsection 22.805.060.C.2.a do not apply and the total new plus replaced hard surface is 10,000 square feet or more, and:
1) If the new plus replaced hard ((surface adds)) surfaces total 50 percent or more ((to)) of the existing hard surfaces within the project limits, comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) for the flows from the total new plus replaced hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way; or
2) If the new plus replaced hard ((surface adds)) surfaces total less than 50 percent ((to)) of the existing hard surfaces within the project limits, comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) for the flows from the total new hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way.
3. Discharges to non-listed creek basins. Roadway projects discharging into a creek not listed in subsection 22.805.060.C.2, or to the drainage basin of such creek, shall:
a. Comply with subsection ((22.805.080.B.2)) 22.805.080.D (Pre-developed forested standard) if the existing land cover is forested and one or more of the following apply:
1) The project adds ((5,000)) 10,000 square feet or more of new plus replaced hard surface ((and the total new plus replaced hard surface is 10,000 square feet or more)); or
2) The project converts 3/4 acres or more of vegetation to lawn or landscaped areas, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
3) The project converts 2.5 acres or more of native vegetation to pasture, and from the project there is a surface discharge into a natural or constructed conveyance system from the site; or
4) The project adds 5,000 square feet or more of new hard surface and, through a combination of effective hard surfaces and converted pervious surfaces, causes a 0.15 cubic feet per second increase in the 100-year recurrence interval flow frequency as estimated using a continuous model approved by the Director.
b. Comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) if the criteria in subsection 22.805.060.C.3.a do not apply and the total new plus replaced hard surface is 10,000 square feet or more, and:
1) If the new plus replaced hard ((surface adds)) surfaces total 50 percent or more ((to)) of the existing hard surfaces within the project limits, comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) for the flows from the total new plus replaced hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way; or
2) If the new plus replaced hard ((surface adds)) surfaces total less than 50 percent ((to)) of the existing hard surfaces within the project limits, comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) for the flows from the total new hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way.
4. Discharges to small lake basins. Roadway projects discharging into Bitter Lake, Green Lake, or Haller Lake, or to the drainage basin of such lake, shall comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) if the total new plus replaced hard surface is 10,000 square feet or more, and:
a. If the new plus replaced hard ((surface adds)) surfaces total 50 percent or more ((to)) of the existing hard surfaces within the project limits, comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) for the flows from the total new plus replaced hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way; or
b. If the new plus replaced hard ((surface adds)) surfaces total less than 50 percent ((to)) of the existing hard surfaces within the project limits, comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) for the flows from the total new hard surfaces. The project limits are defined by the length of the project and the width of the right-of-way.
5. Discharges to a capacity-constrained system. In addition to applicable minimum requirements for flow control in subsection 22.805.060.C.1 through subsection 22.805.060.C.4, roadway projects discharging into a capacity-constrained system or its basin shall also comply with subsection ((22.805.080.B.4)) 22.805.080.F (Existing condition standard) if the total new hard surface is 10,000 square feet or more unless the downstream system only includes ditches or culverts and has been determined to have sufficient capacity as specified in 22.805.020.H (Ensure sufficient capacity).
D. Treatment. Roadway projects not discharging to the public combined sewer shall, to the extent allowed by law, except as provided in subsection 22.805.060.E:
1. If the site has less than 35 percent existing hard surface coverage, and the project's total new plus replaced pollution-generating hard surface is 5,000 square feet or more, comply with the minimum requirements for treatment contained in Section 22.805.090 for flows from the total new plus replaced pollution-generating hard surface and new plus replaced pollution-generating pervious surface; and
2. If the site has greater than or equal to 35 percent existing hard surface coverage and the project's total new plus replaced pollution-generating hard surface is 5,000 square feet or more, and
a. If the new plus replaced pollution-generating hard ((surface adds)) surfaces total 50 percent or more ((to)) of the existing hard surfaces within the project limits, comply with the minimum requirements for treatment contained in Section 22.805.090 for flows from the total new plus replaced pollution-generating hard surface and new plus replaced pollution-generating pervious surface. The project limits are defined by the length of the project and the width of the right-of-way; or
b. If the new plus replaced pollution-generating hard ((surface adds)) surfaces total less than 50 percent ((to)) of the existing hard surfaces within the project limits, comply with the minimum requirements for treatment contained in Section 22.805.090 for flows from the total new pollution-generating hard surface and new pollution-generating pervious surface. The project limits are defined by the length of the project and the width of the right-of-way; and
3. If the total new plus replaced pollution-generating pervious surfaces is 3/4 acres or more, and from ((the project)) which there is a surface discharge in a natural or constructed conveyance system from the site, comply with the minimum requirements for treatment contained in Section 22.805.090 for flows from the total new plus replaced pollution-generating pervious surface and the new plus replaced pollution-generating hard surface.
E. For a roadway project that adds less than 50 percent to the existing hard surface within the project limits on a site having greater than 35 percent existing hard surface coverage, the requirements of subsections 22.805.060.B, 22.805.060.C, and 22.805.060.D to install drainage control facilities are modified based on infeasibility to the degree that (1) complete installation would require that an existing major publicly or privately owned infrastructure or utility element be relocated, or (2) the drainage control facility cannot be built and operated to discharge stormwater from the site under gravity flow conditions while meeting the applicable engineering standards. Compliance with subsections 22.805.060.B, 22.805.060.C, and 22.805.060.D is required to the degree that the project can avoid the infeasibility described in this subsection 22.805.060.E. Standard drainage review and approval shall be required whenever this subsection is used, whether or not Section 22.800.070 applies. ((1.)) The following are considered existing major infrastructure or utility elements:
((a.)) 1. Gravity flow pipe greater than or equal to 24 inches in diameter or gravity flow pipe which cannot be relocated to discharge under gravity flow conditions;
((b.)) 2. High-pressure gas pipe;
((c.)) 3. Pressure gas pipe greater than 8 inches in diameter;
((d.)) 4. Any other pressure pipe greater than 12 inches in diameter (e.g., water or steam);
((e.)) 5. Duct banks, vaults, or handholes, for underground electrical, fiber optic, or telecommunication services;
((f.)) 6. Bridge, building, or tunnel structural foundations; and
((g.)) 7. Foundations for walls greater than 6 feet in height or 15 feet in length.
22.805.070 Minimum requirements for on-site stormwater management
A. Applicability. The requirements of this Section 22.805.070 apply as required in Section ((22.805.030)) 22.805.040 to Section 22.805.060.
B. Requirements. On-site stormwater management shall be installed to the extent allowed by law and maintained in compliance with the rules promulgated by the Director to receive flows from that portion of the site being developed and shall:
1. Comply with either:
a. Subsection 22.805.070.C (On-site performance standard); or
b. Subsection 22.805.070.D (On-site lists).
C. On-site performance standard:
1. If the existing hard surface coverage is less than 35 percent and the project discharges to a listed creek, or to the drainage basin of such creek:
a. The post-development discharge durations shall match the discharge durations of a pre-developed forested condition for the range of pre-developed discharge rates from 8 percent of the 2-year peak flow to 50 percent of the 2-year peak flow.
2. For all other projects:
a. The post-development discharge durations shall match the discharge durations of a pre-developed pasture condition for the range of pre-developed discharge rates between the 1 percent and 10 percent exceedance values.
D. On-site lists
1. For each project surface, follow the appropriate project table in this subsection 22.805.070.D((.2 to subsection 22.805.070.D.5)) to evaluate on-site BMPs shown for that type of surface, by category. The project tables apply to roofs and other hard (non-roof) surfaces. All on-site BMPs used must comply with the rules promulgated by the Director. For each surface, consider all ((of)) the applicable on-site BMPs in the first category. Use any that is considered feasible. If none is feasible for that surface, move on to each successive category and repeat the selection process as necessary. Once one on-site BMP is used for a surface, no other on-site BMP is necessary for that surface. If no BMP in the appropriate categories is feasible, then no further evaluation is required for that surface under this subsection 22.805.070.D.1. Feasibility shall be determined by evaluation against:
a. Design criteria, minimum size, limitations, and infeasibility criteria identified for each BMP in this subsection 22.805.070.D and the rules promulgated by the Director; and
b. Competing needs. ((Subsection)) This subsection 22.805.070.D (((On-site lists) can)) may be superseded or reduced by the Director if the installation of the BMPs is in conflict with:
1) Any of the following federal or state laws, rules, and standards, as may be amended or superseded: Historic Preservation and Archaeology Laws identified in subsection 22.805.070.E (Historic preservation and archaeology laws), Federal Superfund or Washington State Model Toxics Control Act, Federal Aviation Administration requirements for airports, the Americans with Disabilities Act, and related rules and standards; or
2) Special zoning district design criteria adopted and being implemented pursuant to a community planning process. Special zoning districts include, for example, historic and preservation districts, pedestrian zone overlays, station area overlays, special review districts, multifamily residential zones, urban centers and urban villages, and master planned communities. Specific criteria in these areas include, but are not limited to, minimum Floor Area Ratio standards; zero lot line development; usable open space requirements; minimum sidewalk width and required bicycle facilities; alley, loading, and access requirements; pitched roof standards; and street-level development standards for modulation and projections; or
3) Public health and safety standards; or
4) Transportation regulations to maintain the option for future expansion or multi-modal use of public rights-of-way; or
5) Chapter 15.43 (Tree and Vegetation Management in Public Places); Chapter 25.09 (Regulations for Environmentally Critical Areas); Chapter 25.11 (Tree Protection); and Chapter 23.60A (Standards for Vegetation in the Shoreline Master Plan).
((2. For single-family residential projects, Table A for 22.805.070 applies.
|
Table A for 22.805.070 On-site List for Single-family Residential Projects |
|
Category |
BMPs |
All Discharge Locations |
|
1 |
Full Dispersion |
R, S |
|
1 |
Infiltration Trenches |
R, Sd |
|
1 |
Drywells |
R, Sd |
|
2 |
Rain Gardens a |
R, S |
|
2 |
Infiltrating Bioretention |
R, S |
|
2 |
Rainwater Harvesting-Category 2 Sizing |
Xb |
|
2 |
Permeable Pavement Facilities |
R, S |
|
2 |
Permeable Pavement Surfaces |
S |
|
2 |
Sidewalk/Trail Compost-Amended Strip g |
S |
|
3 |
Sheet Flow Dispersion |
R, S |
|
3 |
Concentrated Flow Dispersion |
S |
|
3 |
Splashblock Downspout Dispersion |
R |
|
3 |
Trench Downspout Dispersion |
R |
|
4 |
Non-infiltrating Bioretention |
R, S |
|
4 |
Rainwater Harvesting-Category 4 Sizing |
Xc |
|
4 |
Vegetated Roofs |
X |
|
5 |
Single-family Residential Cisterns |
R |
|
5 |
Perforated Stub-out Connections |
R |
|
5 |
Trees |
S |
Note that subsection 22.805.070.D.1 requires consideration of all on-site BMPs in a category for feasibility before moving on to each successive category as necessary. Within a category, BMPs may be considered in any order.
Key to Table A for 22.805.070
R = Evaluation is required for all roof runoff from Single-family residential projects.
S = Evaluation is required for all other hard (non-roof) surfaces of Single-family residential projects, unless otherwise noted below.
X = Evaluation is not required but is allowed.
a Installation is only allowed for projects with less than 5,000 square feet of hard surface infiltrating on the project site.
b Category 2 rainwater harvesting shall be sized to meet the on-site performance standard, subsection 22.805.070.C.
c Category 4 rainwater harvesting shall be sized to reduce the runoff volume by 25 percent or more on an annual average basis.
d Evaluation of other hard (non-roof) surfaces is not required but is allowed.))
3. For trail and sidewalk projects, Table B for 22.805.070 applies.
Table B for 22.805.070 On-site List for Trail and Sidewalk Projects
|
((Table B for 22.805.070 On-site List for Trail and Sidewalk Projects)) |
|
Category |
BMPs |
Projects Discharging to a Receiving Water Not Designated by Section 22.801.050, or its Basin |
Projects Discharging to a Public Combined Sewer or Capacity-constrained System,c or its Basin |
Projects Discharging to a Designated Receiving Water, or its Basin |
|
1 |
Full Dispersion |
S |
S |
S |
|
2 |
Rain Gardens With or Without Tree |
S |
S |
X |
|
2 |
Infiltrating Soil Cell Bioretention With Tree d |
X |
X |
X |
|
2 |
Permeable Pavement Facilities |
X |
Xa |
Xa, b |
|
2 |
Permeable Pavement Surfaces e |
S |
Sa |
Xa, b |
|
2 |
Sidewalk/Trail Compost-Amended Strip e |
S |
S |
X |
|
3 |
Sheet Flow Dispersion |
S |
S |
S |
|
3 |
Concentrated Flow Dispersion |
S |
S |
S |
|
4 |
Trees |
S |
S |
S |
Note that subsection 22.805.070.D.1 requires consideration of all on-site BMPs in a category for feasibility before moving on to each successive category as necessary. Within a category, BMPs may be considered in any order.
Key to Table B for 22.805.070
S = Evaluation is required for all surfaces of trail or sidewalk projects.
X = Evaluation is not required for trail or sidewalk projects.
a Minimum permeable pavement area allowed in right-of-way is 2,000 square feet of pavement within the project site.
b Installation is not allowed in the right-of-way if new plus replaced pollution-generating hard surface area is less than 2,000 square feet of pavement within the project site.
c Does not include any project discharging to a receiving water not designated by Section 22.801.050, or its basin, even if the project discharges to a capacity-constrained system or its basin.
d Tree is required unless considered infeasible per rules promulgated by the Director.
e Infiltration testing is not required to use for the on-site list approach, it is only necessary to prove infeasibility.
((4.)) 2. For parcel-based projects, Table ((C)) A for 22.805.070 applies.
Table A for 22.805.070 On-site List for Parcel-based Projects
|
((Table C for 22.805.070 On-site List for Parcel-based Projects)) |
|
Category |
BMPs |
Projects Discharging to a Receiving Water Not Designated by Section 22.801.050, Public Combined Sewer, or Capacity-constrained System, or its Basin |
Projects Discharging to a Designated Receiving Water or its Basin |
|
1 |
Full Dispersion |
R, S |
R, S |
|
1 |
Infiltration Trenches |
R, Sg |
R, Sg |
|
1 |
Drywells |
R, Sg |
R, Sg |
|
1 |
Rainwater Harvesting-Category 1 Sizing |
Xe |
Xe |
|
2 |
Rain Gardens With or Without Tree |
Ra , Sa |
Ra , Sa |
|
2 |
Infiltrating Bioretention With or Without Tree |
R, S |
R, S |
|
2 |
Infiltrating Soil Cell Bioretention With Tree |
X |
X |
|
((2)) |
((Rainwater Harvesting-Category 2 Sizing)) |
((Xe)) |
((Xe)) |
|
2 |
Permeable Pavement Facilities or approved equivalent |
R, S |
R, S |
|
2 |
Permeable Pavement Surfaces or approved equivalenth |
S |
S |
|
2 |
Sidewalk/Trail Compost-Amended Striph |
S |
S |
|
3 |
Infiltrating Soil Cell Bioretention Without Tree |
X |
X |
|
3 |
Sheet Flow Dispersion |
R, S |
R, S |
|
3 |
Concentrated Flow Dispersion |
S |
S |
|
3 |
Splashblock Downspout Dispersion |
R |
R |
|
3 |
Trench Downspout Dispersion |
R |
R |
|
4 |
Non-infiltrating Bioretention |
Rd , Sd |
Rd , Sd |
|
4 |
Non-Infiltrating Soil Cell Bioretention With Tree |
X |
X |
|
4 |
Rainwater Harvesting-Category 4 Sizing |
Rb, f |
Xf |
|
4 |
Vegetated Roofs |
Rc |
((X)) Rc |
|
4 |
Residential Cistern |
X |
X |
|
5 |
Perforated Stub-out Connections |
R |
R |
|
5 |
Treesi |
S |
S |
Note that subsection 22.805.070.D.1 requires consideration of all on-site BMPs in a category for feasibility before moving on to each successive category as necessary. Within a category, BMPs may be considered in any order.
Key to Table ((C)) A for 22.805.070
R = Evaluation is required for all roof runoff from parcel-based projects.
S = Evaluation is required for all other hard (non-roof) surfaces of parcel-based projects, unless otherwise noted below.
X = Evaluation is not required but is allowed.
a Rain gardens cannot be used to meet Section 22.805.080 (Minimum Requirements for Flow Control) or Section 22.805.090 (Minimum Requirements for Treatment) or for projects with areas of 5,000 square feet or more hard surface infiltrating on the project site.
b Evaluation is not required for projects with less than 20,000 square feet of new plus replaced rooftop surface.
c Evaluation is not required for projects with less than 5,000 square feet of new plus replaced rooftop surface.
d Water quality treatment BMPs sized to meet Section 22.805.090 (Minimum Requirements for Treatment) may be installed in lieu of non-infiltrating bioretention unless the project discharges to a public combined sewer basin.
e Category ((2)) 1 rainwater harvesting shall be sized to meet the on-site performance standard, subsection 22.805.070.C.
f Category 4 rainwater harvesting shall be sized to reduce the runoff volume by 25 percent or more on an annual average basis.
g Evaluation of other hard (non-roof) surfaces is not required but is allowed.
h Infiltration testing is not required to use for the on-site list approach; it is only necessary to prove infeasibility.
((5.)) 4. For roadway projects, Table ((D)) C for 22.805.070 applies.
Table C for 22.805.070 On-site List for Roadway Projects
|
((Table D for 22.805.070 On-site List for Roadway Projects)) |
|
Category |
BMPs |
Projects Discharging to a Receiving Water Not Designated by Section 22.801.050, or its Basin |
Projects Discharging to a Public Combined Sewer or Capacity-constrained System,g or its Basin |
Projects Discharging to a Designated Receiving Water or its Basin |
|
1 |
Full Dispersion |
S |
S |
S |
|
2 |
Rain Gardens With Treeh |
Sa |
Sa |
Sa |
|
2 |
Infiltrating Bioretention With Treeh |
S |
Sb |
Sb, c |
|
2 |
Infiltrating Soil Cell Bioretention With Tree h |
X |
X |
X |
|
2 |
Permeable Pavement Facilities |
Xd |
Xe, f |
Xc, e, f |
|
2 |
Permeable Pavement Surfacesi |
Sd |
Se, f |
Xc, e, f |
|
2 |
Sidewalk/Trail Compost-Amended Stripi |
Se |
Se |
Se |
|
3 |
Sheet Flow Dispersion |
S |
S |
S |
|
3 |
Concentrated Flow Dispersion |
S |
S |
S |
|
4 |
Trees |
S |
S |
S |
|
4 |
Non-Infiltrating Soil Cell Bioretention With Treeh |
X |
X |
X |
Note that subsection 22.805.070.D.1 requires consideration of all on-site BMPs in a category for feasibility before moving on to each successive category as necessary. Within a category, BMPs may be considered in any order.
Key to Table ((D)) C for 22.805.070
S = Evaluation is required for all surfaces of Roadway Projects.
X = Evaluation is not required for Roadway Projects, but is allowed.
a Rain gardens cannot be used to meet Section 22.805.080 (Minimum Requirements for Flow Control) or Section 22.805.090 (Minimum Requirements for Treatment) or for projects with areas of 5,000 square feet or more hard surface infiltrating on the project site.
b Minimum bioretention cell size top area in right-of-way is 500 square feet (including pre-settling area). Evaluation is only required and installation only allowed when contributing area is sufficient to warrant minimum bioretention cell size in right-of-way.
c Evaluation is not required, and installation is not allowed, if new plus replaced pollution-generating hard surface is less than 2,000 square feet.
d Evaluation of roadway surfaces is not required, and installation is not allowed, if roadway is an arterial street/collector.
e Evaluation of roadway surfaces, including alleys, is not required and installation is not allowed.
f Minimum permeable pavement area allowed in right-of-way is 2,000 square feet of pavement within the project site.
g Does not include any project discharging to a receiving water not designated by Section 22.801.050, or its basin, even if the project discharges to a capacity-constrained system or its basin.
h Tree is required unless considered infeasible per rules promulgated by the Director.
i Infiltration testing is not required to use for the on-site list approach; it is only necessary to prove infeasibility.
* * *
22.805.080 Minimum requirements for flow control
* * *
B. Requirements. Flow control facilities shall be installed to the extent allowed by law and maintained pursuant to rules promulgated by the Director to receive flows from that portion of the site being developed. Post-development discharge determination must include flows from dewatering activities. All projects shall use on-site BMPs identified in subsection 22.805.070.D or other infiltration BMPs authorized by rule to the maximum extent feasible to meet the minimum requirements. Flow control facilities that receive flows from less than that portion of the site being developed may be installed if the total new plus replaced impervious surface is less than 10,000 square feet, the project site uses only on-site BMPs to meet the requirement, and the on-site BMPs provide substantially equivalent environmental protection as facilities not using on-site BMPs that receive flows from all of the portion of the site being developed.
((1.)) C. Wetland protection standards((.))
1. Protect the functions and values of wetlands and their buffers from all projects discharging stormwater directly or indirectly to them. The hydrologic conditions, vegetative community, and substrate characteristics of the wetlands shall be protected, and impacts caused by changes in water flows and pollutants shall be prevented. The introduction of sediment, heat, and other pollutants and contaminants into wetlands shall be minimized through the selection, design, installation, and maintenance of temporary and permanent controls.
2. Before authorizing new discharges to a wetland, alternative discharge locations shall be evaluated and infiltration options outside the wetland shall be maximized unless doing so will adversely impact the functions and values of the affected wetlands.
3. If the wetland protection standard cannot be met due to Sections 22.805.070 or 22.805.090, the wetland protection standard shall be met to the maximum extent feasible while fully meeting the on-site stormwater management and water quality treatment requirements, unless an analysis by a wetland professional per rules promulgated under subsection 25.09.330.C (Technical Reports) is conducted that demonstrates that the functions and values of the affected wetland are not protected.
4. If one or more of the flow control requirements contained in subsections ((22.805.080.B.2 through 22.805.080.B.4)) 22.805.080.D through 22.805.080.F also applies to the project, the wetland standard must be met ((an analysis shall be conducted)) to ensure that the functions and values of the affected wetland are protected before implementing these flow control requirements to the full extent.
5. Notwithstanding any provision in this subtitle, no net loss of wetland functions or values shall result from actions regulated by this subtitle.
6. Refer to the Washington State Wetland Rating System for Western Washington: 2014 Update, Version 2.0 (Hruby, ((2014)) 2023) to determine the category, characteristics, and habitat score of the wetland. Wetland classification shall be determined by a wetland professional per rules promulgated under subsection 25.09.330.C (Technical reports).
7. Projects triggering Method 1 or Method 2 in this subsection 22.805.080.C shall refer to I-C.4, Wetland Hydroperiod Protection and I-C-5, Wetland Hydroperiod Data Collection, Evaluation Procedures, and Strategies presented in Appendix I-C of Ecology’s Stormwater Management Manual for Western Washington (Ecology 2024) for additional guidance.
((a.)) 8. Comply with subsection ((22.805.080.B.1.c)) 22.805.080.C.10 (Wetland Protection Standard-Method 1: Monitoring and Wetland Stage Modeling) if the following applies:
((1))) a. The project discharges to a Category I or II depressional or riverine impounding wetland; and
((2))) b. The project owner has legal access to the entire wetland for purposes of conducting monitoring in the wetland.
((b.)) 9. Comply with subsection ((22.805.080.B.1.d)) 22.805.080.C.11 (Wetland Protection Standard-Method 2: Site Discharge Modeling) if the criteria in subsection ((22.805.080.B.1.a)) 22.805.080.C.8 do not apply and one or more of the following applies (or applicability is unknown):
((1))) a. The wetland is Class I or II and does not meet the requirements of subsection ((22.805.080.B.1.a)) 22.805.080.C.8.
((2))) b. The wetland is Class III or IV and:
((a))) 1) Has a habitat score greater than 5;
((b))) 2) Is interdunal and has special characteristics;
((c))) 3) Provides habitat for rare, threatened, endangered, or sensitive species; or
((d))) 4) Contains breeding population of any native amphibian. Per Ecology's guidance, wetlands with permanent or seasonal ponding or inundation are assumed to have breeding population of native amphibian.
((c.)) 10. Wetland Protection Standard-Method 1: Monitoring and Wetland Stage Modeling. Comply with I-C.4, Wetland Hydroperiod Protection, presented in Appendix I-C of Ecology's Stormwater Management Manual for Western Washington (Ecology ((2019)) 2024).
((Projects triggering Method 1 shall refer to I-C-5, Wetland Hydroperiod Data Collection and Evaluation Procedures, presented in Appendix I-C of Ecology's Stormwater Management Manual for Western Washington (Ecology 2019) for additional guidance.))
((d.)) 11. Wetland Protection Standard-Method 2: Site Discharge Modeling. The total volume of stormwater discharging from the project site into a wetland shall not be more than:
((1))) a. On a daily basis, 20 percent higher or lower than the pre-project volume, and
((2))) b. On a monthly basis,
1) 20 percent higher or lower than the pre-project volumes for the months of October, November, and December, and
2) 15 percent higher or lower than the pre-project ((volume)) volumes for all other months (January through September).
((Projects triggering Method 2 shall refer to I-C-5, Wetland Hydroperiod Data Collection and Evaluation Procedures, presented in Appendix I-C of Ecology's Stormwater Management Manual for Western Washington (Ecology 2019) for additional guidance.))
((2.)) D. Pre-developed forested standard. The post-development discharge durations from the project site shall match the discharge durations of a pre-developed forested condition for the range of pre-developed discharge rates from 50 percent of the 2-year peak flow to the 50-year peak flow.
((3.)) E. Pre-developed pasture standard. The post-development discharge durations from the project site shall match the discharge durations of a pre-developed pasture condition for the range of pre-developed discharge rates from 50 percent of the 2-year peak flow to the 2-year peak flow.
((4.)) F. Existing condition standard. ((a.)) The post-development discharge durations from the project site shall be limited as follows:
((1))) 1. Match the discharge durations of the existing land cover condition for the range of discharge rates from 50 percent of the 2-year peak flow to the 25-year peak flow; and
((2))) 2. For discharges to a creek or a creek drainage basin or to a small lake or a small lake basin, also match the discharge durations of the existing land cover condition for the range of discharge rates from 50 percent of the 2-year peak flow to the 50-year peak flow.
((5.)) G. Peak control standard. ((a.)) The post-development release rates from the project site shall be limited as follows:
((1))) 1. The peak flow with a 50 percent annual probability (2-year recurrence flow) shall not exceed 0.07 cubic feet per second per acre;
((2))) 2. The peak flow with a 20 percent annual probability (5-year recurrence flow) shall not exceed 0.10 cubic feet per second per acre; and
((3))) 3. The peak flow with a 4 percent annual probability (25-year recurrence flow) shall not exceed 0.40 cubic feet per second per acre.
((C.)) H. Inspection and maintenance schedule. Temporary and permanent flow control facilities shall be inspected and maintained according to rules promulgated by the Director to keep these facilities in continuous working order.
22.805.090 Minimum requirements for treatment
* * *
B. Requirements. Water quality treatment facilities shall be installed to the extent allowed by law and maintained pursuant to rules promulgated by the Director to treat flows from the pollution-generating pervious and hard surfaces on the site being developed. When stormwater flows from other areas, including non-pollution generating surfaces (e.g., roofs), dewatering activities, and off-site areas, cannot be separated or bypassed, treatment BMPs shall be designed for the entire area draining to the treatment facility. All projects shall use on-site BMPs identified in subsection 22.805.070.D, or other infiltration BMPs authorized by rule, to the maximum extent feasible to meet the minimum requirements. For pollution-generating pervious surfaces other than artificial turf, a landscape management plan developed according to rules promulgated by the Director may be utilized in lieu of installing water quality treatment facilities.
1. Runoff volume. Stormwater treatment facilities shall be designed based on the stormwater runoff volume from the contributing area or a peak flow rate as follows:
a. The daily runoff volume at or below which 91 percent of the total runoff volume for the simulation period occurs, as determined using an approved continuous model. It is calculated as follows:
1) Rank the daily runoff volumes from highest to lowest.
2) Sum all the daily volumes and multiply by 0.09.
3) Sequentially sum daily runoff volumes, starting with the highest value, until the total equals 9 percent of the total runoff volume. The last daily value added to the sum is defined as the water quality design volume.
b. Different design flow rates are required depending on whether a treatment facility will be located upstream or downstream of a detention facility:
1) For facilities located upstream of detention or when detention is not required, the design flow rate is the flow rate at or below which 91 percent of the total runoff volume for the simulation period is treated, as determined using an approved continuous runoff model.
2) For facilities located downstream of detention, the design flow rate shall be the full 2-year release rate, as determined using an approved continuous runoff model.
c. Infiltration facilities designed for water quality treatment must infiltrate 91 percent of the total runoff volume as determined using an approved continuous runoff model. To prevent the onset of anaerobic conditions, an infiltration facility designed for water quality treatment purposes must be designed to drain the water quality design treatment volume (the 91st percentile, 24-hour volume) within 48 hours.
2. Basic treatment. A basic treatment facility ((shall be)) is required for all projects. The requirements of subsection 22.805.090.B.3 (Oil control treatment), subsection 22.805.090.B.4 (Phosphorus treatment), and subsection 22.805.090.B.5 (((Enhanced)) Metals treatment) are in addition to this basic treatment requirement.
3. Oil control treatment. An oil control treatment facility ((shall be)) is required for high-use sites, as defined in this subtitle.
4. Phosphorus treatment. A phosphorus treatment facility ((shall be)) is required for projects discharging into nutrient-critical receiving waters.
5. ((Enhanced)) Metals treatment. ((Unless a project discharges)) Except for landscaped areas (unless containing crumb rubber) and projects that discharge to a basic treatment receiving water (((Section 22.801.030 "B"))), ((an enhanced)) a metals treatment facility for reducing concentrations of dissolved metals ((shall be)) is required for projects that discharge, directly or through conveyance systems, to fresh waters designated for aquatic life use or having an existing aquatic life use, or that use infiltration strictly for flow control (not treatment) and discharge within ((one-quarter)) 1/4 mile of fresh waters designated for aquatic life use or having an existing aquatic life use, if the project meets one of the following criteria:
a. For a parcel-based project, the project is industrial, is commercial, or proposes four or more dwelling units, or the site is subject to industrial activities.
b. For a roadway project, the site ((is either)) includes a road:
1) ((A fully controlled or a partially controlled limited access highway with Annual Average Daily Traffic counts of 15,000 or more; or 2) Any other road with)) With an expected Annual Average Daily Traffic count of 7,500 or greater; or
2) That provides on-street parking for commercial or industrial areas.
6. Discharges to groundwater. Direct discharge of untreated drainage water from pollution-generating hard surfaces to groundwater is prohibited.
* * *
Section 6. Chapter 22.807 of the Seattle Municipal Code, last amended by Ordinance 126336, is amended as follows:
Chapter 22.807 Drainage Control Review And Application Requirements
* * *
22.807.020 Drainage control review and application requirements
A. Thresholds for drainage control review. Drainage control review and approval as described in subsection 22.807.020.B is required for any of the following:
1. Preliminary drainage review and approval is required for applications for the following approvals:
a. Subdivisions (Chapter 23.22);
b. Short plats (Chapter 23.24);
c. Unit lot subdivisions (Sections 23.22.062 and 23.24.045);
d. Lot boundary adjustments (Chapter 23.28); or
e. Master use permits that would allow development that includes 750 square feet or more of new plus replaced hard surface or 5,000 square feet of land disturbing activity where the Director has determined that a preliminary drainage review is required considering, but not limited, to the following attributes of the site:
1) Location within an environmentally critical area or buffer;
2) Proximity and tributary to an environmentally critical area or buffer; and
3) Proximity and tributary to an area with adequacy, erosion, water quality, or flooding problems.
2. Standard drainage review and approval is required for the following:
a. Applications other than those listed in subsection 22.807.020.A.1 that include any land disturbing activity encompassing an area of 5,000 square feet or more, including demolition permits;
b. Applications for a building permit or other construction permit that authorizes the construction or installation of 750 square feet or more of new plus replaced hard surface;
c. Applications for which a grading permit or approval is required pursuant to Chapter 22.170;
d. Applications for street use permits for the cumulative addition of 750 square feet or more of new plus replaced hard surface and land disturbing activity;
e. City public works projects or construction contracts, including contracts for day labor and other public works purchasing agreements, for the cumulative addition of 750 square feet or more of new plus replaced hard surface and/or land disturbing activity to the site, ((except for projects in a City-owned right-of-way and)) except for work performed for the operation and maintenance of park lands under the control or jurisdiction of the Department of Parks and Recreation;
f. Applications for approvals and contracts that include any new or replaced hard surface or any land disturbing activity on a site deemed a potentially hazardous location, as specified in Section 22.800.050 (Potentially Hazardous Locations);
g. Applications for approvals that include any new hard surface in a Category I peat settlement-prone area delineated pursuant to Section 25.09.012;
h. Whenever an exception to a requirement set forth in this Subtitle VIII or in a rule promulgated under this Subtitle VIII is desired, whether or not review and approval would otherwise be required, including, but not limited to, alteration of natural drainage patterns or the obstruction of watercourses;
i. Whenever roadway project infeasibility pursuant to subsection 22.805.060.E is applied, whether or not review and approval would otherwise be required; or
j. Applications for approvals for activities or projects for:
((1.)) 1) Fueling at dedicated stations, for new or substantially altered fueling stations.
((2.)) 2) In-water and over-water fueling.
((3.)) 3) Maintenance and repair of vehicles and equipment.
((4.)) 4) Concrete and asphalt mixing and production.
((5.)) 5) Recycling, wrecking yard, and scrap yard operations.
((6.)) 6) Storage of liquids in aboveground tanks.
((7.)) 7) Other projects that the Director determines pose a hazard to public health, safety, or welfare; endanger any property; adversely affect the safety and operation of City right-of-way, utilities, or other property owned or maintained by the City; or adversely affect the functions and values of an environmentally critical area or buffer.
3. Comprehensive drainage review and approval is required for applications other than those listed in subsection 22.807.020.A.1 that include:
a. ((Five thousand)) 5,000 square feet or more of new plus replaced hard surface;
b. ((One acre)) 10,000 square feet or more of land disturbing activity;
c. ((Conversion of 3/4 acres or more of vegetation to lawn or landscaped area)) A project that has no available off-site point of discharge for stormwater as determined by the Director; ((or))
d. ((Conversion of 2.5 acres or more of native vegetation to pasture;)) An infiltration facility that is designed to fully infiltrate all stormwater runoff directed to it;
e. An installation of a new outfall to a receiving water; or
f. Demolition of a building with a roof area of 5,000 square feet or greater, even if the existing building slab remains.
B. For purposes of applying the thresholds in subsection 22.807.020.A, all closely related projects, projects under a common plan of development or sale, subdivisions, and short plats as determined according to subsection 22.805.010.B shall be counted towards the threshold.
* * *
D. Submittal requirements for drainage control review and approval
1. Information required for preliminary drainage review. The following information shall be submitted to the Director for all projects for which preliminary drainage review is required:
a. Preliminary site plan. A site plan as set forth in rules promulgated by the Director.
b. Preliminary drainage control plan. A drainage control plan that identifies all new and replaced hard surfaces, new and replaced pollution-generating hard surfaces, drainage control facilities, and best management practices for each lot, parcel, and tract of land within the project.
1) The preliminary drainage control plan shall include all drainage control facilities required to meet the minimum requirements for flow control (Section 22.805.080), water quality treatment (Section 22.805.090), and on-site stormwater management (Section 22.805.070), as well as all other best management practices to ensure drainage adequacy.
2) The preliminary drainage control plan shall be prepared by a licensed civil engineer in accordance with standards adopted by the Director, for projects that meet the thresholds for comprehensive drainage control review per subsection 22.807.020.A.3. ((include any one or more of the following:
a. Five thousand square feet or more of new plus replaced hard surface;
b. One acre or more of land disturbing activity;
c. Conversion of 3/4 acres or more of vegetation to lawn or landscaped area;
d. Conversion of 2.5 acres or more of native vegetation to pasture; or
e. No accessible off-site discharge point.
c. Submittals identified by rule. Additional information shall be submitted to the Director to comply with the requirements of this subtitle and rules promulgated hereunder and to accomplish the purposes of this subtitle.))
2. Information required for standard drainage review. The following information shall be submitted to the Director for all projects for which standard drainage review is required.
a. Site plan. A site plan shall be submitted to the Director.
b. Standard drainage control plan. A drainage control plan shall be submitted to the Director. Standard designs for drainage control facilities as set forth in rules promulgated by the Director may be used. ((For a project with no accessible off-site discharge point or that includes development conducted in or near a receiving water requiring a Hydraulic Project Approval (chapter 220-660 WAC), the drainage control plan shall be prepared by a licensed civil engineer in accordance with standards adopted by the Director.))
c. Construction stormwater control plan. A construction stormwater control plan demonstrating controls sufficient to determine compliance with subsection 22.805.020.D shall be submitted. The Director may approve a checklist in place of a plan, pursuant to rules promulgated by the Director.
d. Memorandum of drainage control. The owner(s) of the site shall sign a "memorandum of drainage control" that has been prepared by the Director of SPU. Completion of the memorandum shall be a condition precedent to issuance of any permit or approval for which a drainage control plan is required. The applicant shall file the memorandum of drainage control with the King County Recorder's Office so as to become part of the King County real property records. The applicant shall give the Director of SPU proof of filing of the memorandum. The memorandum shall not be required when the drainage control facility will be owned and operated by the City. A memorandum of drainage control shall include:
1) The legal description of the site;
2) A summary of the terms of the drainage control plan, including any known limitations of the drainage control facilities, and an agreement by the owners to implement those terms;
3) An agreement that the owner(s) shall inform future purchasers and other successors and assignees of the existence of the drainage control facilities and other elements of the drainage control plan, the limitations of the drainage control facilities, and of the requirements for continued inspection and maintenance of the drainage control facilities;
4) The side sewer permit number and the date and name of the permit or approval for which the drainage control plan is required;
5) Permission for the City to enter the property for inspection, monitoring, correction, and abatement purposes;
6) An acknowledgment by the owner(s) that the City is not responsible for the adequacy or performance of the drainage control plan, and a waiver of any and all claims against the City for any harm, loss, or damage related to the plan, or to drainage or erosion on the property, except for claims arising from the City's sole negligence; and
7) The owner(s)' signatures acknowledged by a notary public.
e. Submittals identified by rule. Additional information shall be submitted to the Director to comply with the requirements of this subtitle and rules promulgated hereunder and to accomplish the purposes of this subtitle.
3. Information required for comprehensive drainage review. In addition to the submittal requirements for standard drainage review, the following information is required to be submitted to the Director for projects for which comprehensive drainage review is required:
a. Comprehensive drainage control plan. A comprehensive drainage control plan, in lieu of a standard drainage control plan, to comply with the requirements of this subtitle and rules promulgated hereunder and to accomplish the purposes of this subtitle shall be submitted with the permit application. It shall be prepared by a licensed civil engineer in accordance with standards adopted by the Director unless otherwise not required per rules promulgated by the Director.
b. Inspection and ((Maintenance)) maintenance schedule. A schedule shall be submitted that provides for inspection of temporary and permanent flow control facilities, treatment facilities, and source ((controls)) control facilities to comply with Section 22.803.040 (Minimum source controls for specific activities), Section 22.805.070 (Minimum requirements for on-site stormwater management), Section 22.805.080 (Minimum requirements for flow control), and Section 22.805.090 (Minimum requirements for treatment).
c. Construction stormwater control plan. A construction stormwater control plan prepared in accordance with subsection 22.805.020.D shall be submitted.
4. Applications for drainage control review and approval shall be prepared and submitted in accordance with provisions of this subsection, with Chapter 21.16 (Side Sewer Code), and with associated rules and regulations adopted ((jointly)) by the Directors of SDCI and SPU.
5. The Director may require additional information necessary to adequately evaluate applications for compliance with the requirements and purposes of this subtitle and other laws and regulations, including, but not limited to, Chapter 25.09 (Regulations for Environmentally Critical Areas) and Chapter 23.60A (Seattle Shoreline Master Program Regulations). The Director may also require appropriate information about adjoining properties that may be related to, or affected by, the drainage control proposal in order to evaluate effects on the adjacent property. This additional information may be required as a precondition for permit application review and approval.
* * *
Section 7. The Code Reviser is requested to reorder material in subsections and tables of Seattle Municipal Code subsection 22.805.070.D as appropriate, after the amendments made by this ordinance.
Section 8. This ordinance shall take effect on July 1, 2026.
Passed by the City Council and signed in open session in authentication of its passage on .
President of the City Council
on .
Katie B. Wilson, Mayor
Scheereen Dedman, City Clerk