Chapter 12.18
MINIMUM SITE DEVELOPMENT REQUIREMENTS
Sections:
12.18.010 Plans and reports (minimum requirement No. 1).
12.18.020 Construction storm water pollution prevention plan (SWPPP) (minimum requirement No. 2).
12.18.030 Source control of pollution (minimum requirement No. 3).
12.18.040 Preservation of natural drainage systems and outfalls (minimum requirement No. 4).
12.18.050 On-site storm water management (minimum requirement No. 5).
12.18.060 Runoff treatment (minimum requirement No. 6).
12.18.070 Oil control treatment requirements.
12.18.080 Phosphorus treatment requirements.
12.18.090 Enhanced treatment requirements.
12.18.100 Basic treatment requirements.
12.18.110 Flow control (minimum requirement No. 7).
12.18.120 Flow control exemption.
12.18.130 Wetlands protection (minimum requirement No. 8).
12.18.140 Operation and maintenance (minimum requirement No. 9).
12.18.010 Plans and reports (minimum requirement No. 1).
All development and redevelopment projects meeting the thresholds contained in this chapter shall submit plans and reports in accordance with the criteria stipulated in the manual.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.020 Construction storm water pollution prevention plan (SWPPP) (minimum requirement No. 2).
All new development and redevelopment projects are responsible for preventing erosion and discharge of sediment and other pollutants into receiving waters. The SWPPP shall include a narrative and drawings. All BMPs shall be clearly referenced in the narrative and marked on the drawings. The SWPPP narrative shall include documentation to explain and justify the pollution prevention decisions made for the project.
The construction site operator shall include each of the twelve elements below in the SWPPP and ensure that they are implemented, from initial soil disturbance until final stabilization, unless site conditions render the element unnecessary and the exemption from that element is clearly justified in the SWPPP:
1. Preservation of vegetation/marking of clearing limits;
2. Construction access;
3. Controlling flow rates;
4. Installing sediment controls;
5. Stabilizing soils;
6. Protecting slopes;
7. Protecting drain inlets;
8. Stabilizing channels and outlets;
9. Controlling pollutants;
10. Controlling dewatering;
11. Maintaining best management practices;
12. Management of the project.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.030 Source control of pollution (minimum requirement No. 3).
Source control best management practices (operational and/or structural) are required for all projects. Those practices listed in the source control chapter of the manual as applicable operational or structural source controls for a particular pollutant source are required under this minimum requirement.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.040 Preservation of natural drainage systems and outfalls (minimum requirement No. 4).
A. Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and down-gradient properties. All outfalls require energy dissipation.
B. Downstream Analysis. The following projects shall conduct an analysis of downstream water quality impacts resulting from the project and shall provide for mitigation of these impacts:
1. All major developments; and
2. Any minor developments located within critical drainage areas.
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 excessive sedimentation, erosion, discharges to ground water contributing or recharge zones, violations of water quality standards, and spills and discharges of priority pollutants.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.050 On-site storm water management (minimum requirement No. 5).
All projects that add two thousand square feet or more of impervious surface shall maintain the average annual volume of water that infiltrates on a site at or above pre-development levels as predicted by an approved hydrologic model.
Project proponents may use prescriptive pre-designed best management practices contained in the manual to fulfill this requirement.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.060 Runoff treatment (minimum requirement No. 6).
The following require construction of storm water treatment facilities designed in accordance with the manual:
1. Projects in which the total of effective, pollution-generating impervious surface (PGIS) is five thousand square feet or more; or
2. Projects in which the total of pollution-generating pervious surfaces (PGPS) is three-fourths of an acre or more, and from which there is a surface discharge in a natural or manmade conveyance system from the site.
3. The level of treatment for each project will be determined by Sections 12.18.070 through 12.18.100.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.070 Oil control treatment requirements.
1. Treatment to achieve oil control applies to projects that have high-use sites.
“High-use sites” are those that typically generate high concentrations of oil due to high traffic turnover or the frequent transfer of oil. High-use sites include:
A. An area of a commercial or industrial site subject to an expected average daily traffic (ADT) count equal to or greater than one hundred vehicles per one thousand square feet of gross building area;
B. An area of a commercial or industrial site subject to petroleum storage and transfer in excess of one thousand five hundred gallons per year, not including routinely delivered heating oil;
C. An area of a commercial or industrial site subject to parking, storage or maintenance of twenty-five or more vehicles that are over ten tons gross weight (trucks, buses, trains, heavy equipment, etc.);
D. A road intersection with a measured ADT count of twenty-five thousand vehicles or more on the main roadway and fifteen thousand vehicles or more on any intersecting roadway, excluding projects proposing primarily pedestrian or bicycle use improvements.
2. Oil/Water Separators. All storm water from impervious areas subject to motor vehicle traffic shall flow through a spill-containment type oil/water separator prior to surface discharge off site.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.080 Phosphorus treatment requirements.
Phosphorus treatment is required for the following:
a. Kitsap Lake;
b. Those waterbodies reported under Section 305(b) of the Clean Water Act, and designated as not supporting beneficial uses due to phosphorus;
c. Those listed in Washington State’s nonpoint source assessment required under Section 319(a) of the Clean Water Act due to nutrients.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.090 Enhanced treatment requirements.
Enhanced treatment for reduction in dissolved metals (primarily copper and zinc) is required for the following project sites that discharge to fish-bearing streams, lakes, or to waters or conveyance systems tributary to fish-bearing streams or lakes:
1. Industrial project sites;
2. Commercial project sites;
3. Multifamily project sites; and
4. High AADT roads as follows:
A. Within Urban Growth Management Areas.
(1) Fully controlled and partially controlled limited access highways with annual average daily traffic (AADT) counts of fifteen thousand or more;
(2) All other roads with an AADT of seven thousand five hundred or greater.
B. Outside of Urban Growth Management Areas.
(1) Roads with an AADT of fifteen thousand or greater unless discharging to a fourth Strahler order stream or larger;
(2) Roads with an AADT of thirty thousand or greater if discharging to a fourth Strahler order stream or larger (as determined using 1:24,000 scale maps to delineate stream order).
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.100 Basic treatment requirements.
Basic treatment applies to:
1. Project sites that discharge to the ground, unless:
A. The soil suitability criteria for infiltration treatment are met (see the manual for soil suitability criteria); or
B. The project uses infiltration strictly for flow control and not treatment and the discharge is within one-fourth mile of a phosphorus sensitive lake (use a phosphorus treatment facility), or within one-fourth mile of a fish-bearing stream, or a lake (use an enhanced treatment facility); and
2. Residential projects not otherwise needing phosphorus control as designated by USEPA, the Department of Ecology, or by Kitsap County; and
3. Project sites discharging directly to salt waters; and
4. Project sites that drain to streams that are not fish-bearing, or to waters not tributary to fish-bearing streams; and
5. Landscaped areas of industrial, commercial, and multifamily project sites, and parking lots of industrial and commercial project sites that do not involve pollution-generating sources (e.g., industrial activities, customer parking, storage of erodible or leachable material, wastes or chemicals) other than parking of employees’ private vehicles. For developments with a mix of land use types, the basic treatment requirement shall apply when the runoff from the areas subject to the basic treatment requirement comprise fifty percent or more of the total runoff.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.110 Flow control (minimum requirement No. 7).
Except as provided in Section 12.18.120, the following require construction of flow control facilities and/or land use management BMPs that result in storm water discharges that match developed condition discharge durations to pre-developed condition durations for the range of pre-developed discharge rates from fifty percent of the two-year peak flow up to the full fifty-year peak flow:
1. Projects in which the total of effective impervious surfaces is ten thousand square feet or more; or
2. Projects that convert three-fourths acre or more of native vegetation to lawn or landscape, or convert two and one-half acres or more of native vegetation to pasture, and from which there is a surface discharge in a natural or manmade conveyance system from the site; or
3. Projects located within urban growth areas or census defined urbanized areas that through a combination of effective impervious surfaces and converted pervious surfaces cause a 0.1 cubic feet per second increase in the one-hundred-year flow frequency as estimated using the Western Washington hydrology model or other approved model.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.120 Flow control exemption.
A. Flow control is not required for projects that discharge directly to the Puget Sound if all the following are satisfied:
1. Direct discharge to the exempt receiving water does not result in the diversion of drainage from any perennial stream classified as Type 1, 2, 3, or 4 in the State of Washington Interim Water Typing System, or Type “S,” “F,” or “Np” in the Permanent Water Typing System, or from any Category I, II, or III wetland; and
2. Flow splitting devices or drainage BMPs are applied to route natural runoff volumes from the project site to any downstream Type 5 stream or Category IV wetland:
(a) Design of flow splitting devices or drainage BMPs will be based on continuous hydrologic modeling analysis. The design will assure that flows delivered to Type 5 stream reaches will approximate, but in no case exceed, durations ranging from fifty percent of the two-year to the fifty-year peak flow;
(b) Flow splitting devices or drainage BMPs that deliver flow to Category IV wetlands will also be designed using continuous hydrologic modeling to preserve pre-project wetland hydrologic conditions unless specifically waived or exempted by regulatory agencies with permitting jurisdiction; and
3. The project site must be drained by a conveyance system that is comprised entirely of manmade conveyance elements (e.g., pipes, ditches, outfall protection, etc.) and extends to the ordinary high water line of the exempt receiving water; and
4. The conveyance system between the project site and the exempt receiving water shall have sufficient hydraulic capacity to convey discharges from future build-out conditions (under current zoning) of the site, and the existing condition from nonproject areas from which runoff is or will be collected; and
5. Any erodible elements of the manmade conveyance system must be adequately stabilized to prevent erosion; and
6. Shoreline erosion is avoided through the use of appropriate energy dissipation or other protective measures.
B. Flow control for a project that disturbs an area of less than one acre in size and is not part of a larger scale of development or sale may use the following flow control standard if the site cannot mitigate flows without relying predominantly on underground centralized detention. Assertions that the site cannot mitigate flows without relying predominantly on underground centralized detention will be determined by the director or designee using the Kitsap County small site centralized detention verification checklist approved by the board of county commissioners.*
1. The post-development peak storm water discharge rates from the development site for the two-, ten- and one-hundred-year, twenty-four-hour duration storm events shall at no time exceed the pre-development peak storm water runoff rates for the same design storm events, except as expressly permitted by this title. Also, where storm water directly or indirectly discharges to open channels or streams, streambank erosion protection is required; the post-development peak storm water discharge rate from the development site for the two-year, twenty-four-hour duration storm event shall not exceed fifty percent of the pre-development peak storm water runoff rate for the same design storm event.
2. The methodology used to determine the peak storm water discharge rates may be an event model based on the Santa Barbara Urban Hydrology method using the rainfall and site characteristic numbers obtained in the manual.
3. Under these circumstances the predevelopment conditions shall be those that existed on September 21, 1987.
(Ord. 451 (2010) § 2, 2010: Ord. 448 (2010) § 2, 2010; Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
* Editor’s Note: The Kitsap County small site centralized detention verification checklist, as adopted by Ordinance 451 (2010), may be found on file in the clerk of the board’s office.
12.18.130 Wetlands protection (minimum requirement No. 8).
1. Discharges to wetlands shall maintain the hydrologic conditions, hydrophytic vegetation, and substrate characteristics necessary to support existing and designated uses. The hydrologic analysis shall use the existing land cover condition to determine the existing hydrologic conditions unless directed otherwise by a regulatory agency with jurisdiction.
2. Storm water treatment and flow control facilities shall not be built within a natural vegetated buffer, except for:
(a) Necessary conveyance systems as approved by the permittee; or
(b) As allowed in wetlands approved for hydrologic modification and/or treatment in accordance with Guidesheet 1B in Appendix I-D of the Stormwater Management Manual for Western Washington (2005).
3. An adopted and implemented basin plan prepared in accordance with the provisions of Section 12.20.130 may be used to develop requirements for wetlands that are tailored to a specific basin.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)
12.18.140 Operation and maintenance (minimum requirement No. 9).
All storm water facilities shall be operated and maintained in accordance with Chapter 12.24.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 33 (part), 2009)