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60 Second Street
PO Box 219
98250

 

 

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Storm Water Technical Manual

Section 1. Purpose

The provisions of this Stormwater Technical Manual are intended to guide and advise all who conduct new development or redevelopment within the Town. The provisions of this Manual establish the minimum level of compliance which must be met to permit a property to be developed or redeveloped within the Town.

It is the purpose of this Manual to:

A. Minimize water quality degradation and sedimentation in streams, ponds, lakes, wetlands, Puget Sound and other water bodies.

B. Minimize the impact of increased runoff, erosion and sedimentation caused by land development and maintenance practices.

C. Maintain and protect groundwater resources;

D. Minimize adverse impacts of alterations on ground and surface water quantities, locations and flow patterns;

E. Decrease potential landslide, flood and erosion damage to public and private property;

F. Promote site planning and construction practices that are consistent with natural topographical, vegetational and hydrologic conditions;

G. Maintain and protect the Town’s stormwater management infrastructure and those downstream;

H. Provide a means of regulating clearing and grading of private and public land while minimizing water quality impacts in order to protect public health and safety; and

I. Provide minimum development regulations and construction procedures which will preserve, replace or enhance, to the maximum extent practicable, existing vegetation to preserve and enhance the natural quality of lands, wetlands and water bodies.

Section 2. Definitions.

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

1. "American Public Works Association" or "APWA" means the adopted edition of the Washington State Chapter of the American Public Works Association.

2. "Approval" means the proposed work or completed work conforms to this Chapter in the opinion of the Town Administrator or his designee.

3. "As-graded" means the extent of surface conditions on completion of grading.

4. "Basin plan" means a plan and all implementing regulations and procedures including but not limited to land use management adopted by ordinance for managing surface and stormwater management facilities and features within individual sub-basins.

5. "Bedrock" means the more or less solid rock in place either on or beneath the surface of the earth. It may be soft, medium, or hard and have a smooth or irregular surface.

6. "Bench" means a relatively level step excavated into earth material on which fill is to be placed.

7. "Best Management Practice" or "BMP" means physical, structural, and/or managerial practices that, when used singly or in combination, prevent or reduce pollution of water or prevent or reduce increased rate of stormwater runoff. BMPs are listed and described in the DOE Manual.

8. "Civil engineer" means a professional engineer licensed in the State of Washington in Civil Engineering.

9. "Civil engineering" means the application of the knowledge of the forces of nature, principles of mechanics and the properties of materials to the evaluation, design and construction of civil works for the beneficial uses of mankind.

10. "Clearing" means the destruction and removal of vegetation by manual, mechanical, or chemical methods.

11. "Commercial agriculture" means those 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 (5) 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.

12. "Compaction" means densification of a fill by mechanical means.

13. "Critical areas" means, at a minimum, areas which include wetlands, areas with a critical recharging effect on aquifers used for potable water, fish and wildlife habitat conservation areas, frequently flooded areas, geologically hazardous areas, including unstable slopes, and associated areas and ecosystems.

14. "Design storm" means a prescribed hyetograph and total precipitation amount (for a specific duration recurrence frequency) used to estimate runoff for a hypothetical storm of interest or concern for the purposes of analyzing existing drainage, designing new drainage facilities or assessing other impacts of a proposed project on the flow of surface water. (A hyetograph is a graph of percentages of total precipitation for a series of time steps representing the total time during which the precipitation occurs.)

15. "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.

16. "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.

17. "Drainage basin" means a geographic and hydrologic subunit of a watershed.

18. "Earth material" means any rock, natural soil or fill and/or any combination thereof,

19. "Ecology" means the Washington State Department of Ecology (DOE).

20. "Engineering geologist" means a geologist experienced and knowledgeable in engineering geology.

21. "Engineering geology" means the application of geologic knowledge and principles in the investigation and evaluation of naturally occurring rock and soil for use in the design of civil works.

22. "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 rock fragments by water, wind, ice or gravity.

23. "Excavation" means the mechanical removal of earth material.

24. "Existing site conditions" means:

A. For developed sites with stormwater facilities that have been constructed to meet the standards in the Minimum Requirements of this manual, existing site conditions shall mean the existing conditions on the site.

B. For developed sites that do not have stormwater facilities that meet the Minimum Requirements, existing site conditions shall mean the conditions that existed prior to local government adoption of a stormwater management program. If in question, the existing site conditions shall be documented by aerial photograph records, or other appropriate means.

C. For all sites in water quality sensitive areas as identified under Minimum Requirement #7, Water Quality Sensitive Areas, existing site conditions shall mean undisturbed forest, for the purpose of calculating runoff characteristics.

D. For all undeveloped sites outside of water quality sensitive areas, existing site conditions shall mean the existing conditions on the site.

25. "Experimental "BMP" means a BMP that has not been tested and evaluated by the Department of Ecology in collaboration with local governments and technical experts.

26. "Fill" means a deposit of earth material placed by artificial means.

27. "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 :

(1) Road and trail construction.

(2) Harvesting, final and intermediate.

(3) Precommercial thinning.

(4) Reforestation.

(5) Fertilization.

(6) Prevention and suppression of diseases and insects.

(7) Salvage of trees.

(8) Brush control

28. "Frequently flooded areas" means the 100-year floodplain designations of the Federal Emergency Management Agency and the National Flood Insurance Program.

29. "Geologically hazardous areas" means areas that because of their susceptibility to erosion, sliding, earthquake or other geological events, are not suited to the siting of commercial, residential or industrial development consistent with public health or safety concerns.

30. "Grade" means the slope of a road, channel, or natural ground: The finished surface of a canal bed, roadbed, top of embankment, or bottom of excavation; any surface prepared for the support of construction such as paving or the laying of a conduit.

(a) Existing Grade. The grade prior to grading.

(b) Rough Grade. The stage at which the grade approximately conforms to the approved plan.

(c) Finish Grade. The final grade of the site which conforms to the approved plan.

31. "Gradient terrace" means an earth embankment or a ridge-and-channel constructed with suitable spacing and an acceptable grade to reduce erosion damage by intercepting surface runoff and conducting it to a stable outlet at a stable non-erosive velocity.

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

33. "Hydroperiod" means the seasonal occurrence of flooding and/or soil saturation; it encompasses depth, frequency, duration, and seasonal pattern of inundation.

34. "Impervious surface" means a 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 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, rooftops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads and parking areas, 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.

35. "Illicit discharge" means all non-stormwater 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, car washing and greywater systems.

36. "Interflow" means that portion of rainfall 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 for example, in a wetland, spring or seep.

37. "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.

38. "Large Parcel Erosion and Sediment Control Plan" or "Large Parcel 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 DOE Manual.

39. "Mitigation" means, in the following order of preference:

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

B. Minimizing 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.

C. Rectifying the impact by repairing, rehabilitating or restoring the affected environment;

D. Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action; and

E. Compensation for the impact by replacing, enhancing, or providing resources or environments.

40. "Natural location" means the location of those channels, swales, and other non-manmade conveyance systems as defined by the first documented topographic contours existing for the subject property, either from maps or photographs, or such other means as appropriate.

41. "New development" means the following activities: 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 of land. All other forest practices and commercial agriculture are not considered new development.

42. "Permanent Stormwater Quality Control (PSQC) Plan" means a plan which includes permanent BMPs for the control of pollution from stormwater runoff after construction and/or land disturbing activity has been completed. For small sites this requirement is met by implementing a Small Parcel Erosion and Sediment Control Plan. Guidance on preparing a PSQC Plan is contained in the DOE manual.

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

44. "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 likely to crease a nuisance or render such waters harmful, detrimental or injurious 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.

45. "Regional retention/detention system" means a stormwater quantity control structure designed to correct existing excess surface water runoff problems of a basin or sub-basin. The area downstream has been previously identified as having existing or predicted significant and regional flooding and/or erosion problems. This term is also used when a detention facility is used to detain stormwater runoff from a number of different businesses, developments or areas within a catchment

46 "Retention/detention facility" means a type of drainage facility designed either to hold water for a considerable length of time and then release it by evaporation, plant transpiration, and/or infiltration into the ground; or to hold surface and stormwater runoff for a short period of time and then release it to the surface and stormwater management system.

47. "Site" means the portion of a piece of property which is directly subject to development.

48. " Slope" means the degree of deviation of a surface from the horizontal; measured as a numerical ratio, percent, or in degrees. Expressed as a ratio, the first number is the horizontal distance (run) and the second is the vertical distance (rise), as 2:1. A 2:1 slope is a 50 percent slope. Expressed in degrees, the slope is the angle from the horizontal plane, with a 90° slope being vertical (maximum) and a 45° being a 1:1 or 100 percent slope.

49. "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 DOE Manual.

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

51. "Source control BMP" means a BMP that is intended to prevent pollutants from entering stormwater. A few examples of source control BMPs are erosion control practices, maintenance of stormwater facilities, constructing roofs over storage and working areas, and directing wash water and similar discharges to the sanitary sewer or a dead end sump.

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

53. "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.

54. "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. The DOE Manual contains BMPs to prevent or reduce pollution.

55. "Stormwater Management Manual" or "DOE Manual" means the 1992 edition or latest version of the State of Washington, Department of Ecology's "Stormwater Management Manual for the Puget Sound Basin" and all amendments and additions thereto. The DOE Manual contains BMPs to prevent or reduce pollution.

56. "Stormwater Site Plan" means a plan which includes an Erosion and Sediment Control (ESC) Plan and/or a Permanent Stormwater Quality Control Plan (PSQCP). For small sites, this plan is the equivalent of a Small Parcel Sediment Control Plan. Guidance on preparing a Stormwater Site Plan is contained in the DOE Manual.

57. "Toe of slope" means a point or line of slope in an excavation or cut where the lower surface changes to horizontal or meets the existing ground slope.

58. "Top of slope" means a point or line on the upper surface of a slope where it changes to horizontal or meets the original surface.

59. "Treatment BMP" means a BMP that is intended to remove pollutants from stormwater. A few examples of treatment BMPs are detention ponds, oil/water separators, biofiltration swales and constructed wetlands.

60. "Unstable slopes" means those sloping areas of land which have in the past exhibited, are currently exhibiting, or will likely in the future exhibit, mass movement of earth.

61. "Water body" means surface waters including rivers, streams, lakes, marine waters, estuaries, and wetlands.

62. "Watershed" means a geographic region within which water drains in 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.

63. "Wetlands" means those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal conditions do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas. This includes wetlands created, restored or enhanced as part of a mitigation procedure. This does not include constructed wetlands or the following surface waters of the state intentionally constructed from sites that are not wetlands: Irrigation and drainage ditches, grass-lined swales, canals, agricultural detention facilities, farm ponds, and landscape amenities.

64. "Vegetation" means all organic plant life growing on the surface of the earth.

Section 3. General Provisions.

A. It is not intended that this manual repeal, abrogate, or impair any existing regulations, easements, covenants, or deed restrictions. However, where this manual imposes greater restrictions, the provisions of this manual shall prevail.

B. The provisions of this manual shall be held to be minimum requirements in their interpretation and application and shall be liberally construed to serve the purposes of this manual.

Section 4. Applicabilitv.

A. When any provision of any other regulation of the Town conflicts with this manual, that which provides more environmental protection shall apply.

B. The Town shall not grant any approval or issue a permit to construct any of the following regulated activities until the requirements of this manual are fulfilled:

1. Building permit;

2. Grading and clearing permit;

3. Right-of way permit;

4. Subdivision.

C. Regulated activities shall be conducted only after the Town approves a Stormwater Site Plan which includes one or more of the following as required by this manual:

1. Small Parcel Erosion and Sediment Control Plan

2. Large Parcel Erosion and Sediment Control Plan

3. Permanent Stormwater Quality Control (PSQC) Plan

Section 5. Regulated Activities.

5.01 Regulated Activities.

A. Consistent with the minimum requirements contained in this manual, the Town shall approve or disapprove the following activities, unless exempted in Section 5.02 below:

1. New development

a. land disturbing activities including grading and clearing;

b. structural development, including construction; installation of a building or other structure;

c. creation of impervious surfaces including roadways and walkways;

d. 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, land disturbing activity 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.

5.02 Exemptions.

A. Development undertaken by the Washington State Department of Transportation in state highway rights-of way is regulated by Chapter 173-270 WAC, the Puget Sound Highway Runoff Program.

Section 6. General Requirements.

A. The latest edition of State of Washington, Department of Ecology's Stormwater Management Manual is hereby adopted by reference and is hereinafter referred to as the DOE Manual.

B. General: BMPs (Best Management Practices) shall be used to control pollution from stormwater. BMPs shall be used to comply with the standards in this Ordinance. BMPs are in the DOE Manual.

C. Illicit discharges to stormwater drainage systems are prohibited.

Section 7. Approval Standards.

7.01 Small Parcel Erosion and Sediment Control Plan applicability.

A. The following new development shall be required to control erosion and sediment during construction, to permanently stabilize soil exposed during construction and to comply with Small Parcel Requirements 1 through 5:

1. Individual, detached, single family residences and accessory buildings.

2. Creation or addition of less than 5,000 square feet of impervious surface area.

3. Land disturbing activities of less than one acre.

B. Compliance shall be demonstrated through the implementation of an approved Small Parcel ESC Plan. Information regarding the preparation of a Small Parcel ESC Plan is contained in the DOE Manual.

7.02 Small Parcel Minimum Requirements.

7.02.1 Small parcel requirement # 1 - Construction access route.

A. Construction vehicle access shall be, whenever possible; limited to one route. Access points shall be stabilized with quarry spall or crushed rock to minimize the tracking of sediment onto public roads.

7.02.2 Small parcel requirement #2 - Stabilization of denuded areas.

A. Soil stabilization. All exposed soils shall be stabilized by suitable application of BMPs including but not limited to sod or other vegetation, plastic covering, mulching, or application of ground base on areas to be paved. From October 1 through April 30, no soils shall remain exposed for more than 2 days. From May 1 through September 30, no soils shall remain exposed for more than 7 days.

7.02.3 Small parcel requirement #3 - Protection of adjacent properties.

A. Adjacent properties shall be protected from sediment deposition by appropriate use of vegetative buffer strips, sediment barriers or filters, dikes or mulching, or by a combination of these measures and other appropriate BMPs.

7.02.4 Small parcel requirement #4 - Maintenance

All erosion and sediment control BMPs shall be regularly inspected and maintained to ensure continued performance of their intended function.

7.02.5 Small parcel requirement #5 - Other BMPs.

A. The Administrator or his designee shall attach such conditions to the Small Parcel Erosion and Sediment Plan as are necessary to control erosion and runoff including but not limited to:

1. Installing french drains (drywells) or other on-site facilities for disposal of runoff from roofs and other impervious surfaces; and/or

2. Routing storm drainage as necessary and appropriate for the size of the project; and/or

3. Installing erosion control devices (such as construction entrances, filter fabric fences, stockpile protection buffers for critical areas).

7.03 Large Parcel Erosion and Sediment Control Plan applicability.

A. The following new development shall be required to control erosion and sediment during construction, to permanently stabilize soil exposed during construction, and to comply with Large Parcel Requirements 1 through 11:

1. All new development that includes the creation or addition of 5,000 square feet, or greater, of new impervious surface area shall comply.

2. Land disturbing activities of one acre or greater.

B. Compliance shall be demonstrated through the implementation of an approved Stormwater Site Plan consisting of a Large Parcel ESC Plan and a PSQC Plan as appropriate. Information concerning the preparation of a Large Parcel ESC Plan and PSQC Plan is contained in the DOE Manual.

7.04 Large Parcel Minimum Reguirements.

7.04.1 Large parcel requirement #1 - Erosion and sediment control.

A. All exposed and unworked soils shall be stabilized by suitable application of BMPs From October 1, to April 30, no soils shall remain unstabilized for more than 2 days. From May 1 to September 30, no soils shall remain unstabilized for more than 7 days. Prior to leaving the site, stormwater runoff shall pass through a sediment pond or sediment trap, or other appropriate BMPs.

B. In the field, mark clearing limits and/or any easements, setbacks, sensitive/critical areas and their buffers, trees and drainage courses.

C. Properties adjacent to the project site shall be protected from sediment deposition.

D. Sediment ponds and traps, perimeter dikes, sediment barriers, and other BMPs intended to trap sediment on-site shall be constructed as a first step in grading. These BMPs shall be functional before land disturbing activities take place. Earthen structures such as dams, dikes, and diversions shall be seeded and mulched according to the timing indicated in Requirement #1.

E. Cut and fill slopes shall be designated and constructed in a manner that will minimize erosion.

F. Properties and waterways downstream from development site shall be protected from erosion due to increases in the volume, velocity, and peak flow rate of stormwater runoff from the project site.

G. All temporary on-site conveyance channels shall be designed, constructed, and stabilized to prevent erosion from the expected velocity of flow from a 2 year, 24-hour frequency storm for the developed condition. Stabilization adequate to prevent erosion of outlets, adjacent streambanks, slopes and downstream reaches shall be provided at the outlets of all conveyance systems.

H. All storm drain inlets made operable during construction shall be protected so that stormwater runoff shall not enter the conveyance system without first being filtered or otherwise treated to remove sediment.

I. The construction of underground utility lines shall be subject to the following criteria:

1. Where feasible, no more than 200 feet of trench shall be opened at one time.

2. Where consistent with safety and space considerations, excavated material shall be placed on the uphill side of trenches.

3. Trench dewatering devices shall discharge into a sediment trap or sediment pond.

J. Wherever construction vehicle access routes intersect paved roads, provisions must be made to minimize the transport of sediment (mud) onto the paved road. If sediment is transported onto a road surface, the roads shall be cleaned thoroughly at the end of each day. Sediment shall be removed from roads by shoveling, or sweeping and be transported to a controlled sediment disposal area. Street washing shall be allowed only after sediment is removed in this manner.

K. All temporary erosion and sediment control BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil areas resulting from removal shall be permanently stabilized.

L. Dewatering devices shall discharge into a sediment trap or sediment pond.

M. All pollutants other than sediment that occur on-site during construction shall be handled and disposed of in a manner that does not cause contamination of stormwater.

N. 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 maintenance and repair shall be conducted in accordance with the DOE Manual.

0. Performance bonding, or other appropriate financial instruments, shall be required for all projects to ensure compliance with the approved erosion and sediment control plan.

7.04.2 Large Parcel requirement #2 - Preservation of natural drainage systems.

A. Natural drainage patterns shall be maintained, and discharges from the site shall occur at the natural location, to the maximum extent practicable.

7.04.3 Large Parcel requirement #3 - Source control of pollution.

A. Source control BMPs shall be applied to all projects to the maximum extent practicable. Source control BMPs shall be selected, designed, and maintained according to the DOE Manual.

B. An adopted and implemented basin plan (Requirement #9) may be used to develop source control requirements that are tailored to a specific basin, however, in all circumstances, source control BMPs shall be required for all sites.

7.04.4 Large Parcel requirement #4 - Run off treatment BMPs.

A. All projects shall provide permanent treatment of stormwater. Treatment BMPs shall be sized to capture and treat the water quality design storm, defined as the 6-month, 24-hour return period storm. The first priority for treatment shall be to infiltrate as much as possible of the water quality design storm, only if site conditions are appropriate and groundwater quality will not be impaired. Direct discharge of untreated stormwater to groundwater is prohibited. All treatment BMPs shall be selected, designed, and maintained according to the DOE Manual.

B. Stormwater treatment BMPs shall no be built within a structural vegetated buffer, except for necessary conveyance systems as approved by the Town.

C. An adopted and implemented basin plan (Requirement #9) may be used to develop runoff treatment requirements that are tailored to a specific basin.

7.04.5 Large Parcel requirement #5 - Streambank erosion control.

A. The requirement below applies only to situations where stormwater runoff is discharged directly or indirectly to a stream, and must be met in addition to meeting Large Parcel Requirement #4.

B. Stormwater discharges to streams shall control streambank erosion by limiting the peak rate of runoff from individual development sites to 50 percent of the existing condition 2-year, 24-hour design storm while maintaining the existing condition peak runoff rate for the 10-year, 24-hour and 100-year, 24-hour design storms. As the first priority streambank erosion control BMPs shall utilize infiltration to the fullest extent practicable only if site conditions are appropriate and groundwater quality is protected. Streambamk erosion control BMPs shall be selected, designed, and maintained according to the DOE Manual.

C. Stormwater treatment BMPs shall not be built within a natural vegetated buffer, except for necessary conveyance systems as approved by the Town.

D. An adopted and implemented basin plan (Requirement #9) may develop streambank erosion control requirements that are tailored to a specific basin.

7.04.6 Large Parcel requirement #6 - Wetlands.

A. The requirements below apply only to situations where stormwater discharges directly or indirectly through a conveyance system into a wetland, and must be met in addition to meeting the requirements in Large Parcel requirement #4.

1. Stormwater discharges to wetlands must be controlled and treated to the extent necessary to meet the State Water Quality Standards, Ch. 173-201 WAC, or Groundwater Quality Standard, Ch. 173-200 WAC, as appropriate

2. Discharges to the wetlands shall maintain the hydroperiod and flows of existing site conditions to the extent necessary to protect the characteristic uses of the wetland.

3. Prior to discharging to a wetland, alternative discharge locations shall be evaluated, and natural water storage and infiltration opportunities outside the wetland shall be maximized.

4. Created wetlands that are intended to mitigate the loss of wetland acreage function and value shall not be designed to also treat stormwater.

5. In order for constructed wetlands to be considered treatment systems they must be constructed on sites that are not wetlands and they must be managed for stormwater treatment. If these systems are not managed and maintained in accordance with an approved manual for a period exceeding three years these systems may no longer be considered constructed wetlands. Discharges from constructed wetlands to waters of the state (including discharges to natural wetlands) are regulated under Ch. 90.48 RCW, Ch. 173-20 1 WAC, and Ch. 173-200 WAC.

6. Stormwater treatment BMPs shall not be built within a natural vegetated buffer except for necessary conveyance systems as approved by the Town.

7. An adopted and implemented basin plan (Requirement #9) may be used to develop requirements for wetlands that are tailored to a specific basin.

7.04.7 Large Parcel requirement #7 - Water quality sensitive areas.

A. Where local governments determine that the minimum requirements do not provide adequate protection of water quality sensitive areas, either on-site or within the basin more stringent controls shall be required to protect water quality.

B. Stormwater treatment BMPs shall not be built within a natural vegetated buffer, except for necessary conveyance systems as approved by the Town.

C. An adopted and implemented basin plan (Requirement #9) may be used to develop requirements for water quality sensitive areas that are tailored to a specific basin

7.04.8 Large Parcel requirement #8 - Off site analysis and mitigation.

A. All development projects shall conduct an analysis of off site water quality and quantity impacts resulting from the project and shall mitigate these impacts. The analysis shall extend a minimum of one-fourth of a mile downstream from the project. The existing or potential impacts to be evaluated and mitigated shall include, at a minimum, but not be limited to:

1. Excessive sedimentation.

2. Streambank erosion.

3. Discharges to groundwater contributing or recharge zones.

4. Violations of water quality standards.

5. Spills and discharges of priority pollutants.

6. Adverse impacts to downstream facilities.

All development projects shall provide water quantity control of stormwater runoff from the newly created impervious surface. Infiltration is the preferred method of reducing the quantity of stormwater runoff. If infiltration cannot be used at the project site, then the peak rate of runoff from the project site after project completion shall be no greater during the 10-year and 100-year design storms than the existing condition 10-year peak runoff and 100-year peak runoff respectively. In addition, any development project tributary to the streets listed below, shall provide peak rate runoff control such that runoff from the project site shall be no greater during the 2-year design storm than the existing conditions 2-year peak runoff:

Basin No. 2 – Frank Street

Linder Street

Nelson Street

Hunt Street

C Street

Basin No. 4 – Argyle Avenue

Caines Street

Spring Street

Price Street

Blair Avenue

Park Street

Reed Street

Second Street

First Street

Court Street

Basin No. 7 – Carter Street north of Harbor Street

C. Whenever the development project utilizes a detention BMP a factor of safety must be applied to the BMP volume. The factor is safety is dependent on the percentage of total area that is impervious which is contributing flow to the BMP. The factor of safety is obtained from Figure 2.1, Volume III of the 2001 Ecology Stormwater Management Manual. The factor of safety will be applied by first designing the BMP using the Santa Barbara Urban Hydrograph Method and then multiplying the initial design volume by the factor of safety to obtain the final volume. The BMP’s volume must be increased from the initial design volume to the final volume without increasing the average depth.

7.04.9 Large Parcel requirement #9 - Basin planning.

A. Adopted and implemented watershed-based basin plans may be used to modify any or all of the large parcel requirements, provided that the level of protection for surface or groundwater achieved by the basin plan will equal or exceed that which would be achieved by the large parcel requirements in the absence of a basin plan. Basin plans shall evaluate and include, as necessary, retrofitting of BMPs for existing development and/or redevelopment in order to achieve watershed-wide pollutant reduction goal. Standards developed from basin plans shall not modify any of the above requirements until the basin plan is formally adopted and fully implemented by the Town.

B. A Stormwater Site Plan is required for the proposed project. The Stormwater Site Plan should be a comprehensive report containing all the technical information and analysis necessary to evaluate the proposed stormwater facilities. In addition to the requirements for a Stormwater Site Plan described in the DOE Manual, the following items must be addressed in the Stormwater Site Plan.

1 Offsite Analysis. The Stormwater Site Plan shall,

a. Provide a detailed qualitative analysis of the flow path of the discharge from the project site (including those with retention facilities) to the receiving water but in no case less than 1/4 mile downstream of the site. If the flow path crosses private property before reaching receiving waters, include property owner names and/or parcel numbers;

b. Describe flow routing and provide existing pipe and channel sizes and estimated capacities;

c. Discuss any known or reasonably anticipated downstream erosion, flooding or water quality problems, including those that may be caused by interflow from the proposed retention facility; and

d. Describe emergency services located along the flow path such as fire police and hospital services.

e. Describe the upstream tributary area, including the adjacent ground cover, soil type and mode that surface water currently enters the project site. Note any existing, potential or predicted problems that may occur due to development of the project site.

C. Based on the downstream analysis required by the Stormwater Site Plan, the Administrator, or his designee, may impose stricter discharge and or detention standards if the discharge from the project, evaluated within the context of other existing conditions in the drainage area, is reasonably expected to result in any of the following:

1. Flooding;

2. Loss of aquatic habitat due either to high or low flows;

3. Property damage;

4. Water quality problems;

5. Erosion; or

6. An unacceptable interruption of vital services.

D. If the Administrator or his designee determines that greater treatment, infiltration and/or storage volumes lower release rates, or downstream improvements are required, he shall specify project design criteria or other means necessary to relieve the downstream problems; provided that such criteria will not violate the minimum standards established in this Chapter. For purposes of this section, "other means" may include increases in downstream flow capacity and/or off site detention and infiltration facilities, plans and financing for which are subject to the approval of the Administrator or his designee.

7.04.10 Large Parcel requirement #10 - Operation and maintenance.

A. An operation and maintenance schedule shall be provided for all proposed stormwater facilities and BMPs, and the party (or parties) responsible for maintenance and operation shall be identified, in accordance with Section 7.06 of this manual.

7.04.11 Large Parcel requirement #11 - Financial liability.

A. Performance bonding or other appropriate financial instruments shall be required for all projects to ensure compliance with these standards.

7.05 Variances

A. The Town Council shall have the authority to grant a variance from the requirements of Section 7 of the Stormwater Technical Manual in accordance with Chapter 17.84 FHMC

7.06 Maintenance of facilities.

7.06.1 Maintenance Agreement.

A. Prior to the issuance of any permit for any regulated activity for which a storm drainage plan is required, the Town shall require the applicant and owner to execute an inspection and maintenance agreement binding on all subsequent owners of land served by the private storm drainage system. Such agreement shall provide for access to the system at reasonable times for regular inspection by the Town or its authorized representative and for regular or special assessments of property owners to ensure that the facility is maintained in proper working condition to meet design standards and any provisions established.

B. The agreement shall be recorded by the applicant and owner in the land records of San Juan County.

C. The agreement shall also provide that, if after notice by the Town to correct a violation requiring maintenance work and satisfactory corrections are not made by the owner(s) within a reasonable period of time (30 days maximum), the Town may perform all necessary work to place the facility in proper working condition. The owner(s) of the facility shall be assessed the cost of the work and any penalties and there shall be a lien on the property, which may be placed on the tax bill and collected as ordinary taxes by the Town.

7.06.2 Maintenance Responsibility.

A. The owner of the property on which work has been done pursuant to these regulations for private storm drainage systems, or any other person or agent in control of such property, shall maintain in good condition and promptly repair and restore all grade surfaces, walls, drains, dams and structures, vegetation, erosion and sediment control measures, and other protective devices. Such repair or restorations, and maintenance shall be in accordance with approved plans.

B. An operation and maintenance schedule shall be developed for any storm drainage system and shall state the required maintenance to be performed, the equipment and skill level necessary to perform the maintenance, and the required frequency of maintenance. The operation and maintenance schedule shall either be printed on the stormwater management agreement or submitted under a separate cover.

C. The maintenance and operation of private storm drainage systems shall be the responsibility of the property owner. Furthermore, the property owner shall, in accordance with the operation and maintenance schedule, record and log maintenance performed and date. Operation and maintenance records shall be retained by the property owner for a minimum of three (3 ) years and shall be available to the Town for inspection at all reasonable times.

D. The Town shall be responsible for the maintenance and operation of all public storm drainage facilities located within public easements and rights-of-way following the completion of the successful maintenance period and the acceptance of such facilities by the Town.

Section 8. Administration.

8.01 Administrator.

The Town Administrator or his designee shall administer the regulations in the Technical Manual.

8.01.1 Inspection.

All activities regulated by this Manual, except those exempt in Section 5.02, shall be inspected by the Town or it's authorized representative. The Town shall inspect projects at various stages of the work requiring approval to determine that adequate control is being exercised. Stages of work requiring inspection include, but are not limited to, preconstruction; installation of BMPs; land disturbing activities; installation of utilities, landscaping, retaining walls and completion of project. When required by the Town, a special inspection and/or testing shall be performed.

8.01.2 Fees

The Town's fee for review of a Stormwater Site Plan shall be reviewed annually by the Council who shall direct the Town Clerk to adjust the fee appropriately and post said fee in a conspicuous place within Town Hall and make such list available to the public upon request,

Section 9. Enforcement

9.01 Enforcement Authority.

The Town Administrator or his designee shall enforce the regulations in the Technical Manual.

9.02 Stop work order.

The Town Administrator or his designee shall have the authority to serve a person a stop work order if action is being undertaken in violation of the requirements of this Manual.

A. Content of Order. The order shall contain:

(1) A description of the specific nature, extent, and time of violation and the damage or potential damage; and

(2) A notice that the violation or the potential violation cease and desist, and in appropriate cases, the specific corrective action to be taken within a given time.

B. Notice. A stop work order shall be imposed by a notice in writing, either by certified mail with return receipt requested, or by personal service, to the person incurring the same.

C. Effective date. The stop work order issued under this Section shall become effective immediately upon receipt by the person to whom the order is directed.

D. Compliance. Failure to comply with the terms of a stop work order shall result in enforcement actions including, but not limited to, the issuance of a civil penalty

9.03 Violation.

A. Failure to comply with the requirements of this Manual, failure to conform to the terms of an approval or order issued, undertaking new development without first obtaining Town approval, failure to comply with a stop work order issued under these regulations shall be declared both a public nuisance and a Class I civil infraction as defined in Title 1 FHMC.

B. Except in circumstances where there is a serious and imminent threat to public health or safety, prior to filing a public nuisance abatement action in San Juan County Court, the Town shall attempt to gain compliance by use of the civil infraction procedures set forth in Title 1, FHMC.

9.04 Penalty

The penalty for committing a civil infraction shall be as set forth in Title 1, FHMC.

 08/08/2007

 

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