Chapter 14.16 STORMWATER MANAGEMENT

B. High volumes of stormwater can harm aquatic resources and their habitats. The frequency, duration and intensity of peak flows can erode and undercut streambanks, scour streambeds, and deposit excessive amounts of sediments.

C. Stormwater pollution is a problem associated with land use and development. If stormwater is not treated, pollutants can degrade surface waters. Common pollutants carried by stormwater runoff include pesticides, herbicides, fertilizers, petroleum products, metals, pathogens, sediments and organic toxins.

D. Stormwater problems and dangers can be reduced or avoided if property owners and future developers follow best management practices (BMPs) when clearing land and install stormwater facilities to control and treat stormwater runoff.

E. In order to perform as intended, stormwater facilities must be properly designed and constructed, and periodically inspected and maintained. If this is not done, these facilities can actually become sources of pollutants to surface water and groundwater. (Ord. 1118 § 1.1, 2001).

14.16.020 Purpose.

The provisions of this chapter are intended to guide and advise all who conduct new development and redevelopment within the city. The provisions of this chapter establish the minimum level of compliance which must be met to permit a property to be developed or redeveloped within the city. It is the purpose of this chapter to:

A. Minimize or eliminate the impacts of increased runoff, erosion and sedimentation caused by land disturbance, development and redevelopment;

B. Promote site planning and construction practices that seek to maintain the natural topographical, vegetative and hydrological conditions;

C. Authorize the city to require that stormwater facilities be operated, maintained and repaired in conformance with this chapter;

D. Guide all that own and/or maintain stormwater facilities within the city. The provisions of this chapter establish the minimum level of compliance that must be met for maintaining stormwater facilities within the city; and

E. Provide for inspection and maintenance of stormwater facilities in the city to provide for an effective, functional stormwater drainage system. (Ord. 1118 § 1.2, 2001).

Article II. Definitions

14.16.030 Definitions.

For the purposes of this chapter, the following definitions shall apply:

“Approval” means proposed or completed work conforms to this chapter in the opinion of the director.

“Best management practice (or BMP)” means a physical, structural, and/or managerial practice that, when used singly or in combination, prevents or reduces pollution of water. BMPs are listed and described in the manual.

“Clearing” means destruction or removal of vegetation by manual, mechanical or chemical methods.

“Commercial agriculture” means activities conducted on lands defined in RCW 84.34.020(2) and activities involved in the production of crops or livestock for wholesale trade. An activity ceases to be considered commercial agriculture when the area on which it is conducted is proposed for conversion to a nonagricultural use or has lain idle for more than five years, unless the idle land is registered in a federal or state soils conservation program, or unless the activity is maintenance of irrigation ditches, laterals, canals, or drainage ditches related to an existing and ongoing agricultural activity.

“Detention” means the release of stormwater runoff from the site at a slower rate than it is collected by the stormwater facility system, the difference being held in temporary storage.

“Detention facility” means an above or below ground facility, such as a pond or tank, that temporarily stores stormwater runoff and subsequently releases it at a slower rate than it is collected by the drainage facility system. There is little or no infiltration of stored stormwater.

“Director” means the city public works director or his or her designee.

“Earth material” means any rock, natural soil or fill and/or any combination thereof.

“Erosion” means the wearing away of the land surface by running water, wind, ice, or other geological agents, including such processes as gravitational creep. Detachment and movement of soil or rock fragments by water, wind, ice, or gravity.

“Excavation” means the mechanical removal of earth material.

“Experimental BMP” means a BMP that has not been approved through a process of using an approved testing protocol.

“Fill” means a deposit of earth material placed by artificial means.

“Forest practice” means any activity conducted on or directly pertaining to forest land and relating to growing, harvesting or processing timber, including but not limited to road and trail construction; harvesting, final and intermediate; precommercial thinning; reforestation; fertilization; prevention and suppression of diseases and insects; salvage of trees and brush control.

“Groundwater” means water in a saturated zone or stratum beneath the surface of land or a water body.

“Illicit discharge” means all nonstormwater discharges to stormwater drainage systems that cause or contribute to a violation of state water quality, sediment quality or groundwater quality standards, including but not limited to sanitary sewer connections, industrial process water, interior floor drains and gray water systems.

“Impervious surface” means a hard surface area which either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development, and/or a hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater. Open, uncovered retention/detention facilities shall not be considered as impervious surfaces.

“Interflow” means that portion of precipitation that infiltrates into the soil and moves laterally through the upper soil horizons until intercepted by a stream channel or until it returns to the surface via a wetland, spring or seep.

“Land disturbing activity” means any activity that results in a change in the existing soil cover (both vegetative and nonvegetative) and/or the existing soil topography. Land disturbing activities include, but are not limited to, demolition, construction, clearing, grading, filling and excavation.

“Large parcel erosion and sediment control (ESC) plan” means a plan to implement BMPs to control pollution generated during land disturbing activity. Guidance for preparing a large parcel ESC plan is contained in the manual.

“Manual” means the current edition of the King County Surface Water Design Manual, as adopted or hereafter amended by King County.

Mitigation Order of Preference. From first to last:

1. Avoid the impact altogether by not taking a certain action or part of an action;

2. Minimize impacts by limiting the degree or magnitude of the action and its implementation, by using appropriate technology, or by taking affirmative steps to avoid or reduce impacts;

3. Rectify the impact by repairing, rehabilitating or restoring the affected environment;

4. Reduce or eliminate the impact over time by preservation and maintenance operations during the life of the action; and

5. Compensate for the impact by replacing, enhancing, or providing substitute resources or environments.

“New development” means land disturbing activities; structural development, including construction, installation or expansion of a building or other structure; creation of impervious surfaces; Class IV – general forest practices that are conversions from timber land to other uses; and subdivision and short subdivision of land as defined in RCW 58.17.020. All other forest practices and commercial agriculture are not considered new development.

“Person” means any individual, partnership, corporation, association, organization, cooperative, public or municipal corporation, agency of the state, or local government unit, however designated.

“Pollution” means contamination or other alteration of the physical, chemical, or biological properties of waters of the state, including change in temperature, taste, color, turbidity, or odor of the waters, or such discharge of any liquid, gaseous, solid, radioactive or other substance into any waters of the state as will or is likely to create a nuisance or render such waters harmful, detrimental or injurious to the public health, safety or welfare, or to domestic, commercial, industrial, agricultural, recreational, or other legitimate beneficial uses, or to livestock, wild animals, birds, fish or other aquatic life.

“Redevelopment” means, on an already developed site, the creation or addition of impervious surfaces, structural development including construction, installation or expansion of a building or other structure, and/or replacement of impervious surface that is not part of a routine maintenance activity, and land disturbing activities associated with structural or impervious redevelopment.

“Site” means a portion of property that is directly subject to development.

“Small parcel erosion and sediment control plan” or “small parcel ESC plan” means a plan for small sites to implement temporary BMPs to control pollution generated during the construction phase only, primarily erosion and sediment. Guidance for preparing a small parcel ESC plan is contained in the manual.

“Soil” means unconsolidated mineral and organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.

“Source control BMP” means a BMP that is intended to prevent pollutants from entering stormwater. Examples include erosion control practices, maintenance of stormwater facilities, roofing storage and working areas, and directing wash water and similar discharges to the sanitary sewer or a dead end sump.

“Stormwater” means that portion of precipitation that does not naturally percolate into the ground or evaporate, but flows overland, via interflow, or through channels or pipes into a defined surface water channel or constructed infiltration facility.

“Stormwater drainage system” means constructed and natural features which function together as a system to collect, convey, channel, hold, inhibit, retain, detain, infiltrate, divert, treat or filter stormwater.

“Stormwater facility” means a constructed component of a stormwater drainage system, designed or constructed to perform a particular function or multiple functions. Stormwater facilities include, but are not limited to, pipes, swales, ditches, culverts, street gutters, detention basins, retention basins, constructed wetlands, infiltration devices, catch basins, oil/water separators, sediment basins and modular pavement.

“Vegetation” means all organic plant life growing on the surface of the earth.

“Water body” means surface waters including rivers, streams, lakes, marine waters, estuaries and wetlands.

“Watershed” means a geographic region within which water drains to a particular river, stream or body of water as identified and numbered by the State of Washington Water Resource Inventory Areas (WRIAs) as defined in Chapter 173-500 WAC.

“Wetlands” means areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas, and areas created, restored or enhanced as part of a mitigation procedure. Constructed wetlands or the following surface waters of the state intentionally constructed from sites that are not wetlands are not included: irrigation and drainage ditches, grass-lined swales, canals, agricultural detention facilities, farm ponds, and landscape amenities. (Ord. 1809 § 4, 2024; Ord. 1666 § 14, 2018: Ord. 1577 § 1, 2016: Ord. 1118 § 2, 2001).

Article III. General Provisions, Requirements, Applicability

14.16.040 Abrogation and greater restrictions.

It is not intended that this chapter repeal, abrogate or impair any existing regulations, easements, covenants or deed restrictions. However, where this chapter imposes greater restrictions, or is in conflict with any other applicable city ordinance or regulation, the provisions of this chapter shall prevail. (Ord. 1464 § 1 (Exh. A (part)), 2012: Ord. 1118 § 3.1, 2001).

14.16.050 Applicability.

The director is authorized to adopt written procedures for the purpose of carrying out the provisions of this chapter, including procedures related to the inspection of stormwater facilities. Prior to fulfilling the requirements of this chapter, the city shall not grant any approval or permission to conduct a regulated activity including but not limited to the following:

Building permit, commercial or residential; binding site plan; conditional use permit; franchise right-of-way construction permit; grading and clearing permit; master plan development; planned unit development; right-of-way permit; shoreline substantial development permit; shoreline variance; shoreline conditional use permit; shoreline environmental redesignation; unclassified use permit; variance; zone reclassification; subdivision; short subdivision; special use permit; utility and other use permit; zone reclassification; or any subsequently adopted permit or required approval not expressly exempted by this chapter. (Ord. 1464 § 1 (Exh. A (part)), 2012: Ord. 1118 § 3.2, 2001).

14.16.060 Manual adopted.

The current edition of the King County Surface Water Design Manual is hereby adopted by reference. (Ord. 1809 § 5, 2024; Ord. 1577 § 2, 2016: Ord. 1464 § 1 (Exh. A (part)), 2012: Ord. 1118 § 3.3.1, 2001).

14.16.070 Stormwater best management practices (BMPs).

Stormwater and drainage features should incorporate low impact development techniques that mimic predevelopment hydrologic conditions, when technically feasible. BMPs shall be used to control runoff flows and treat stormwater for all projects. Approved BMPs are contained in the manual. The city has also adopted by reference the current edition of the King County Stormwater Pollution Control Manual (BMP manual) as now in effect or as subsequently amended. The BMP manual applies to existing facilities and activities and to new development activities not covered by the King County Surface Water Design Manual. The BMP manual describes the types of regulated activities, the types of contaminants generated by each activity, the contaminant’s effect on water quality, the required source control BMPs, and the available treatment BMPs. The BMP manual includes information on design, maintenance, allowable use of alternative BMPs, and a schedule for BMP implementation. (Ord. 1809 § 6, 2024; Ord. 1464 § 1 (Exh. A (part)), 2012: Ord. 1118 § 3.3.2, 2001).

14.16.075 Type C – Conveyance.

A. Type C waters are those natural open ephemeral drainage courses (including where bridged, piped or culverted) that are not Type S, F, Np or Ns waters, which contain flow only during or immediately after periods of precipitation, and which flow generally less than 30 days per year.

B. Type C waters are regulated for the values they provide for conveyance, infiltration, water quality treatment, and flow attenuation of surface waters. It is encouraged that Type C waters be maintained in their existing natural channels to provide these functions. However, subject to conformance to all floodplain management regulations, such channel courses may be altered, piped or realigned, so long as sufficient mitigation is provided that maintains:

1. One-hundred-year conveyance capacity;

2. Infiltration capacity equivalent to that provided by the original channel either within the altered, piped, or realigned system or together with other infiltration accomplished elsewhere on the site; and

3. Comparable water quality treatment per the Manual either within the altered, piped or realigned system or together with other aboveground water quality measures provided for the on-site development that are accomplished elsewhere on the site. (Ord. 1809 § 7, 2024; Ord. 1688 § 8, 2019).

14.16.080 Illicit discharges.

Connections of conveyance systems to the storm drainage system or ground water infiltration systems which were not constructed or intended to convey precipitation runoff, or which have been converted from such usage, are prohibited, with the following exceptions:

A. Allowable discharges as defined in NBMC 14.16.100;

B. Discharges authorized by a NPDES or state waste discharge permit;

C. Connections conveying effluent from an approved onsite sewage disposal system to its drainfield. (Ord. 1118 § 3.3.3, 2001).

14.16.090 Prohibited discharges.

It is unlawful for any person to discharge contaminants into surface water and stormwater, or ground water. Contaminants include, but are not limited to, the following:

1. Trash or debris;

2. Construction materials;

3. Petroleum products including but not limited to oil, gasoline, grease, fuel oil, heating oil;

4. Antifreeze and other automotive products;

5. Metals in either particulate or dissolved form;

6. Flammable or explosive materials;

7. Radioactive material;

8. Batteries;

9. Acids, alkalis, or bases;

10. Paints, stains, resins, lacquers, or varnishes;

11. Degreasers and/or solvents;

12. Drain cleaners;

13. Pesticides, herbicides, or fertilizers;

14. Steam cleaning wastes;

15. Soaps, detergents, or ammonia;

16. Swimming pool or spa filter backwash;

17. Chlorine, bromine, or other disinfectants;

18. Heated water;

19. Domestic animal wastes;

20. Sewage;

21. Recreational vehicle waste;

22. Animal carcasses;

23. Food wastes;

24. Bark and other fibrous materials;

25. Collected lawn clippings, leaves, or branches;

26. Silt, sediment, or gravel;

27. Dyes (except as described in NBMC 14.16.100, Allowable discharges);

28. Chemicals not normally found in uncontaminated water;

29. Any other process associated discharge except as otherwise allowed in this section;

30. Any hazardous material or waste not listed above. (Ord. 1118 § 3.3.4, 2001).

14.16.100 Allowable discharges.

Subject to provisions of the BMP manual, the following types of discharges shall not be considered prohibited discharges for the purpose of this chapter unless the director determines that the type of discharge, whether singly or in combination with others, is causing pollution of surface water and stormwater or ground water.

A. Potable water including water from water line flushing and hydrant maintenance;

B. Uncontaminated water from crawl space pumps or footing drains;

C. Lawn watering;

D. Dechlorinated swimming pool water;

E. Materials placed as part of an approved habitat restoration or bank stabilization project;

F. Natural uncontaminated surface water or ground water;

G. Flows from riparian habitats and wetlands;

H. Common practices for water well disinfection;

I. Discharges resulting from diffuse or ubiquitous sources such as atmospheric deposition;

J. Discharges resulting from dye testing authorized by the director;

K. Discharges which result from emergency response activities or other actions that must be undertaken immediately or within a time too short to allow full compliance with this chapter so as to avoid an imminent threat to public health or safety. (The director may further define qualifying activities in administrative guidance. The person responsible for said emergency response activities should take steps to ensure that the discharges resulting from such activities are minimized and ensure that future incidents are prevented to the greatest extent possible);

L. Other types of discharges as determined by the director. (Ord. 1118 § 3.3.5, 2001).

Article IV. Regulated Activities, Minimum Standards, Maintenance

14.16.110 Regulated activities.

The city shall approve or disapprove all new development and/or redevelopment in accordance with the manual, and the city’s public works standards, unless exempted as discussed in NBMC 14.16.170, Exemptions. (Ord. 1666 § 15, 2018: Ord. 1118 § 4.1, 2001).

14.16.120 Minimum standards for all new development and redevelopment.

All new development and redevelopment shall include minimum standards as described in the manual, and the city’s public works standards. (Ord. 1666 § 16, 2018: Ord. 1118 § 4.2, 2001).

14.16.130 Maintenance required.

All stormwater facilities shall be maintained in accordance with this chapter and the city’s adopted manual. (Ord. 1118 § 4.3, 2001).

14.16.140 Minimum standards for maintenance of facilities.

The following are the minimum standards for the maintenance of stormwater facilities:

A. Facilities shall be inspected at least annually and cleared of all debris, sediment and vegetation in order to ensure continued performance.

B. Where lack of maintenance is causing or contributing to a water quality problem, immediate action shall be taken to correct the problem. Within one month, the director shall revisit the facility to ensure that it is being maintained. (Ord. 1118 § 4.4, 2001).

14.16.150 Disposal of waste from maintenance activities.

Disposal of waste from maintenance activities shall be conducted in accordance with Chapter 173-304 WAC, Minimum Functional Standards for Solid Waste Handling, guidelines for disposal of waste materials from stormwater maintenance activities (when completed), and, where appropriate, Chapter 173-303 WAC, Dangerous Waste Regulations. (Ord. 1118 § 4.5, 2001).

14.16.160 Compliance.

Property owners are responsible for the maintenance, operation and repair of stormwater drainage systems and BMPs. Property owners shall maintain, operate and repair these facilities in compliance with the requirements of this chapter and the adopted manual. (Ord. 1118 § 4.6, 2001).

14.16.170 Exemptions.

The following are exempt from this chapter:

A. Commercial agriculture and forest practices regulated under WAC Title 222, except for Class IV – general forest practices that are conversions from timber land to other uses; and

B. Development undertaken by the Washington State Department of Transportation in state highway rights-of-way. (Regulated by Chapter 173-270 WAC, Puget Sound Highway Runoff Program). (Ord. 1118 § 4.7, 2001).

Article V. Inspection Program

14.16.180 Inspection.

Whenever implementing the provisions of the inspection program or whenever there is cause to believe that a violation of this chapter has been or is being committed, the inspector is authorized to inspect during regular working hours and at other reasonable times all stormwater drainage systems within the city to determine compliance with the provisions of this chapter. (Ord. 1118 § 5.1, 2001).

14.16.190 Procedures.

Prior to conducting inspections, the inspector shall present identification credentials, state the reason for the inspection and request entry.

A. If the property or any building on the property is unoccupied, the inspector shall first make a reasonable effort to locate the owner or other person(s) having charge or control of the property and request entry.

B. If after reasonable effort, the inspector is unable to locate the owner or other person(s) having charge or control of the property, and has reason to believe the condition of the stormwater drainage system creates an imminent substantial hazard to persons or property, the inspector may enter.

C. Unless entry is consented to by the owner or person(s) in control of the property or portion of the property or unless conditions are reasonably believed to exist which create an imminent substantial hazard, the inspector shall obtain a court order, prior to entry, as authorized by the laws of the state of Washington. (Ord. 1118 § 5.2, 2001).

14.16.200 Inspection schedule.

The city may establish a master inspection and maintenance schedule and procedure to inspect appropriate stormwater facilities that are not owned by the city. (Ord. 1118 § 5.3, 2001).

14.16.210 Inspection and maintenance records.

As existing stormwater facilities are encountered, they should be added to the master inspection and maintenance schedule. Records for new stormwater facilities shall include the following:

A. As-built plans and locations;

B. Findings of fact from any exemption granted by the local government;

C. Operation and maintenance requirements and records of inspections, maintenance actions and frequencies; and

D. Engineering reports, as appropriate. (Ord. 1118 § 5.4, 2001).

Article VI. Administration

14.16.220 Director.

The director or a designee shall administer this chapter and shall be referred to as the director. The director shall have the authority to develop and implement administrative procedures to administer and enforce this chapter. (Ord. 1666 § 17, 2018: Ord. 1118 § 6.1, 2001).

14.16.230 Review and approval.

The director may approve, conditionally approve, or deny an application for activities regulated by this chapter. (Ord. 1118 § 6.2, 2001).

14.16.240 Inspection.

All activities regulated by this chapter, except those exempt in NBMC 14.16.170, may be inspected by the director. The director may inspect projects at various stages of completion to determine that adequate controls are being exercised. Stages of completion include, but are not limited to, preconstruction; land disturbing activities; installation of BMPs, utilities, landscaping, and retaining walls; and project completion. Once completed, the director is authorized to develop a regular inspection program for all stormwater facilities in the city. (Ord. 1118 § 6.3, 2001).

Article VII. Enforcement

14.16.250 General.

Enforcement actions shall be in accordance with Chapter 20.10 NBMC. (Ord. 1118 § 7, 2001).