Chapter 18.250 STORMWATER CONTROL AND DRAINAGE

A. Minimize surface and groundwater quality degradation and prevent erosion and sedimentation of creeks, streams, ponds, lakes, wetlands, and other water bodies;

B. Minimize damage to property from increased runoff rates and volumes;

C. Protect the quality of waters for drinking water supply, contact recreation, fishing and other beneficial uses;

D. Establish sound developmental policies which protect and preserve the city’s water resources;

E. Protect city roads and rights-of-way from damage due to inadequately controlled runoff and erosion;

F. Preserve and enhance the aesthetic quality of the city’s water resources;

G. Protect the health, safety and welfare of the inhabitants of the city;

H. Maintain existing groundwater levels, instream flows and available water supply volumes; and

I. Further the goals of no net negative impact caused by quantity of runoff entering streams and no net negative change in the quality of runoff entering streams through the implementation of best management practices. (Ord. 09-16 (part), 2010; Ord. 96-802 § 1, 1996)

18.250.015 Adoption statement.

The city hereby adopts the thresholds, definitions, minimum requirements and exceptions, adjustment and variance criteria found in Appendix I of the NPDES Phase II Municipal Stormwater Permit, including the mandatory incorporated provisions of the 2005 Ecology Stormwater Management Manual for Western Washington. Where provisions of this chapter conflict with the Western Washington Manual or other cited design guidance, the more stringent requirements as determined by the director shall take precedence. (Ord. 09-16 (part), 2010)

18.250.020 Applicability and thresholds.

The provisions of this chapter apply to each of the following development activities:

A. Projects that disturb one acre or more, or projects that are part of a larger common plan of development or sale that will disturb one acre or more, shall comply with the following requirements:

1. Projects that add five thousand square feet or more of new impervious surface, convert three-quarters of an acre or more of native vegetation to lawn or landscape areas, or convert two and a half acres or more of native vegetation to pasture shall comply with Minimum Requirements Nos. 1 through 9 as specified in BGMC 18.250.050;

2. Redevelopment projects that add or replace five thousand square feet or more of impervious surfaces shall comply with Minimum Requirements Nos. 1 through 9 as specified in BGMC 18.250.050;

3. Projects that create more than two thousand five hundred square feet of impervious surface or divide urban single-family residential land that the director determines creates the reasonable potential for more than two thousand five hundred square feet of additional impervious surface shall comply with Minimum Requirements Nos. 1 through 5 as specified in BGMC 18.250.050 and the small project requirements for water quality treatment and quantity control as specified in BGMC 18.250.140 and 18.250.210;

4. Projects that create or add two thousand square feet or greater of new, replaced, or new plus replaced impervious surface area shall comply with Minimum Requirements Nos. 1 through 5 as specified in BGMC 18.250.050;

5. Projects that add more than one thousand square feet of new impervious surfaces, other than buildings, that require oil/water separators as specified in BGMC 18.250.160 shall comply with Minimum Requirements Nos. 1 through 5 as specified in BGMC 18.250.050 and the small project requirements for water quality treatment and quantity control as specified in BGMC 18.250.140 and 18.250.210;

6. Projects that are part of a larger common plan of development or sale that will disturb one acre or more, that individually disturb seven thousand square feet or more, shall comply with Minimum Requirements Nos. 1 through 5 as specified in BGMC 18.250.050.

B. Projects that disturb less than one acre and are not part of a larger common plan of development or sale that will disturb one acre or more, but meet the criteria below, shall comply with Minimum Requirements Nos. 1, 3, 4, and 5 as specified in BGMC 18.250.050 and the small project requirements for water quality treatment and quantity control as specified in BGMC 18.250.140 and 18.250.210.

1. The creation of more than two thousand five hundred square feet of impervious surface or the division of urban single-family residential land that the director determines creates the reasonable potential for more than two thousand five hundred square feet of additional impervious surface;

2. The addition of more than one thousand square feet of new impervious surfaces, other than buildings, that require oil/water separators as specified in BGMC 18.250.160;

3. The replacement of existing structures exceeding five thousand square feet on commercial or industrial parcels.

C. Projects involving a land use requiring an oil/water separator as described in BGMC 18.250.160 must comply with that section. (Ord. 11-06 § 4, 2011; Ord. 09-16 (part), 2010; Ord. 96-802 § 2, 1996)

18.250.025 Exemptions.

A. The following types of projects are exempt from this chapter:

1. Forest practices regulated under WAC Title 222, except for Class IV general forest practices that are conversions from timber land to other uses;

2. Commercial agriculture practices involving working the land for production;

3. Road maintenance practices as follows: pothole and square cut patching, overlaying existing asphalt or concrete pavement with asphalt or concrete without expanding the area of coverage, shoulder grading, reshaping/regrading drainage systems, crack sealing, resurfacing with in-kind material without expanding the road prism, and vegetation maintenance;

4. Previously reviewed and approved sites that are included in an approved stormwater plan that meets the requirements of this chapter;

5. Temporary buildings; provided the buildings utilize roof downspout infiltration or dispersion systems. A final stormwater design detailing the infiltration or dispersion system shall be required.

B. The following types of projects are exempt from this chapter except as described:

1. Residential short plats of lots less than one acre that create less than two thousand five hundred square feet of new impervious surface at the time of platting shall submit a stormwater plan limited to conveyance and disposal.

2. Underground utility projects that replace the ground surface with in-kind material or materials with similar runoff characteristics shall be exempt from all of the minimum requirements as defined in BGMC 18.250.050 except Minimum Requirement No. 2, Construction Stormwater Pollution Prevention Plan.

3. Drainage projects are exempt from the water quality treatment provisions of this chapter as described in BGMC 18.250.130 provided they do not meet the thresholds in BGMC 18.250.020. The director may also waive all or parts of the submittal requirements required by BGMC 18.250.100, ownership and maintenance requirements required by BGMC 18.250.300 and 18.250.310, and bonding requirements required by BGMC 18.250.380 if the project meets the other appropriate parts of this chapter.

4. Redevelopment projects in which the value of the proposed improvements, including interior improvements, does not exceed fifty percent of the assessed or replacement value of the existing structures on the site are exempt from Minimum Requirements Nos. 6 through 9 as specified in BGMC 18.250.050 on replaced impervious surfaces.

5. Road redevelopment projects that increase the impervious surface area by less than five thousand square feet are exempt from Minimum Requirements Nos. 6 through 9 as specified in BGMC 18.250.050. Road redevelopment projects that increase the impervious surface area by less than fifty percent within the project limits are required to apply Minimum Requirements Nos. 6 through 9 as specified in BGMC 18.250.050 to the new impervious surfaces only. (Ord. 09-16 (part), 2010)

18.250.030 Definitions.

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

“Basin” means a topographic region in which all water drains to a common point.

“Basin plan” means a management plan for a basin identified in the most current version of the city of Battle Ground stormwater management plan.

“Best management practices” or “BMPs” means those physical, structural and managerial practices, and prohibitions of practices, that, when used singly or in combination, control stormwater runoff peak flow rates and volumes and prevent or reduce pollution of surface water or groundwater.

“City” means the city of Battle Ground, Washington.

“Construction” means any site-altering activity, including but not limited to grading, utility construction and building construction.

“Continuous runoff model” means the most current version of the Western Washington Hydrology Model (WWHM) or any other equivalent model approved by the Department of Ecology.

“Contributing drainage area” means the subject property together with the basin contributing water runoff to the subject property.

“Council” means the city council of Battle Ground, Washington.

“Department” means the city of Battle Ground public works department.

“Design storm” means the rainfall from a storm of twenty-four-hour duration. For example, “two-year storm” means the two-year, twenty-four-hour storm event.

“Development” means land-disturbing activities, construction, installation or expansion of a building or other structure, creation or replacement of impervious surfaces, and subdivision of properties.

“Director” means the director of the city of Battle Ground public works department.

“Downstream analysis” means an analysis of the stormwater impacts of proposed development activity including the effects on existing upstream and downstream drainage systems and property, and the ability of the natural drainage ways to pass additional flow created by the development.

“Drainage project” means the excavation or construction of pipes, culverts, channels, embankments or other flow altering structures in any stream, stormwater facility, or wetland.

“Effective impervious surface” means those impervious surfaces that are connected via sheet flow or discrete conveyance to a drainage system. Impervious surfaces on residential project sites are considered ineffective if the runoff is dispersed through at least one hundred feet of native vegetation in accordance with BMP T5.30, “Full Dispersion,” as described in Chapter Five of Volume V of the Western Washington Manual.

“Engineering acceptance” means having received completion of construction and all required paperwork has been approved by the engineering division and recorded by the applicant as required.

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

“Impervious surface” means a hard surface area which either prevents or retards the entry of water into the soil. Examples include, but are not limited to, structures, walkways, patios, driveways, carports, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, haul roads and soil surface areas compacted by construction operations, and oiled or macadam surfaces.

“Land-disturbing activity” means any activity that results in movement of earth, or 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 clearing, grading, filling, and excavation. Compaction that is associated with stabilization of structures and road construction shall also be considered a land-disturbing activity. Vegetation maintenance practices are not considered land-disturbing activity.

“Low Impact Development Manual” means the Low Impact Development Technical Guidance Manual for Puget Sound dated January 2005 and updated errata sheets issued or approved by the director as may be necessary to correct clear and obvious mathematical and technical errors in manual criteria.

“Native vegetation” means vegetation comprised of plant species, other than noxious weeds, that are indigenous to the Pacific Northwest and which reasonably could have been expected to naturally occur on the site. Examples include trees such as Douglas Fir, Western Hemlock, Western Red Cedar, Alder, Big-Leaf Maple, and Vine Maple; shrubs such as Willow, Elderberry, Salmonberry, and Salal; and herbaceous plants such as Sword Fern, Foam Flower, and Fireweed.

“Natural location” means the location and elevation of those channels, swales, and other nonmanmade conveyance systems as defined by the first documented topographic contours existing for the site, either from maps or photographs.

“NPDES” means the National Pollutant Discharge Elimination System.

“Peak discharge” means the maximum stormwater runoff rate in cubic feet per second determined for the design storm.

“Pollution-generating impervious surface” or “PGIS” means those impervious surfaces considered to be a significant source of pollutants in stormwater runoff. Such surfaces include those which are subject to: vehicular use, industrial activities or storage of erodible or leachable materials, wastes, or chemicals, and which receive direct rainfall or the run-on or blow-in of rainfall. Metal roofs are also considered to be pollution-generating unless they are coated with an inert, nonleachable material (e.g., baked-on enamel coating).

“Pollution-generating pervious surface” or “PGPS” means any nonimpervious surface subject to use of pesticides and fertilizers or loss of soil.

“Predeveloped condition” means the land cover that existed at a site prior to development or redevelopment. For projects required to comply with Minimum Requirement No. 7 for flow control as defined in BGMC 18.250.050(G) the predeveloped condition shall be assumed to be a forested land cover unless reasonable, historic information is provided that indicates the site was prairie prior to settlement.

“Project engineer” means a registered professional engineer, licensed in the state of Washington, experienced and knowledgeable in the practice of civil engineering related to stormwater runoff control and treatment, who is responsible for design and the preparation of stormwater plans and hydrology report.

“Project site” means that portion of a property, properties, or right-of-way subject to land-disturbing activities, new impervious surfaces or replaced impervious surfaces.

“Redevelopment” means development activity on sites that have thirty-five percent or more impervious surface coverage at the time of the project.

“Regional facility” means a facility designed to treat and control stormwater runoff from multiple project sites.

“Registered soil scientist” means a professional soil scientist certified by the Soil Science Society of America, experienced and knowledgeable in the practice of pedology related to soil survey, who is responsible for design and preparation of soils maps, related soil groups, and identifying soil factors for construction engineering.

“Replaced impervious surface” means the removal and replacement of any exterior impervious surfaces or foundation for structures, or the removal down to bare soil or base course and replacement for other impervious surfaces.

“Road redevelopment project” means any work, whether publicly or privately funded, on an existing roadway.

“Roof downspout system” means infiltration or dispersion systems that meet the requirements stated in Chapter Three of Volume III of the Western Washington Manual.

“Severe and unexpected economic hardship” means site specific constraints that make the strict application of any or all of the minimum requirements economically infeasible and prevent reasonable development of a property to its designated use as defined by the city comprehensive plan.

“Site” means the area defined by the legal boundaries of a parcel or parcels of land that is (are) subject to development. For road projects, the length of the project site and the right-of-way boundaries defining the site.

“Steep slopes” means slopes greater than fifteen percent.

“Stormwater facility” means the natural or constructed components of a stormwater drainage system, designed and constructed to perform a particular function, or multiple functions. Stormwater facilities include, but are not limited to: pipes, swales, ditches, open channels, culverts, stormwater ponds, catch basins, manholes, oil/water separators and sedimentation basins.

“Stormwater utility” means a publicly owned utility responsible for stormwater control.

“Stream” means those areas where surface waters produce a defined channel or bed. For the purposes of this chapter, streams shall include both natural channels and manmade channels which were constructed to replace a natural stream.

“Subregional facility” means a facility designed to treat and control stormwater runoff from more than one development in a contributing drainage area of less than forty acres.

“Temporary building” means buildings that will be in place for one year or less.

“Threshold discharge area” means an on-site area draining to a single natural discharge location or multiple natural discharge locations that combine within one-quarter mile downstream as determined by the shortest flow path.

“Western Washington Manual” means State of Washington Department of Ecology’s “Stormwater Management Manual for Western Washington,” February 2005 Edition, and updated errata sheets issued or approved by the director as may be necessary to correct clear and obvious mathematical and technical errors in manual criteria.

“Wetlands” means those areas defined as wetlands under Chapter 18.270 BGMC.

Any terms not defined in this chapter shall be as defined in Appendix One of the city’s NPDES Phase II permit. (Ord. 09-16 (part), 2010; Ord. 96-802 § 3, 1996)

18.250.035 Construction details.

The city of Battle Ground standard construction details for stormwater are kept on file at the city and maintained by the city engineer. (Ord. 09-16 (part), 2010)

18.250.040 Enforcement.

The director is authorized to enforce the provisions of this chapter utilizing the remedies and procedures under BGMC Title 20. (Ord. 09-16 (part), 2010; Ord. 96-802 § 4, 1996)

18.250.050 Minimum requirements.

A. Minimum Requirement No. 1—Preparation of Stormwater Site Plans.

1. A stormwater site plan is required for all projects. Stormwater site plans shall be prepared in accordance with BGMC 18.250.100.

B. Minimum Requirement No. 2—Construction Stormwater Pollution Prevention Plan (SWPPP).

1. All development projects are responsible for preventing erosion and discharge of sediment and other pollutants into receiving waters.

2. A SWPPP shall be prepared in accordance with Volume II of the Western Washington Manual, implemented prior to initial soil disturbance and kept in place until final stabilization.

3. Sediment and erosion control BMPs shall be consistent with the BMPs contained in Chapters Three and Four of Volume II of the Western Washington Manual, and the requirements of Chapter 18.255 BGMC.

C. Minimum Requirement No. 3—Source Control of Pollution.

1. All known, available and reasonable source control BMPs are required.

2. Source control BMPs must be selected, designed, and maintained in accordance with Volume IV of the Western Washington Manual.

D. Minimum Requirement No. 4—Preservation of Natural Drainage Systems and Outfalls.

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

2. 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 necessitated by this requirement shall require energy dissipation.

E. Minimum Requirement No. 5—On-site Stormwater Management.

1. On-site stormwater management BMPs to infiltrate, disperse, and retain stormwater runoff on site are required to the maximum extent feasible without causing flooding or erosion impacts.

2. Roof downspout control BMPs, functionally equivalent to those described in Chapter Three of Volume III of the Western Washington Manual, and dispersion and soil quality BMPs, functionally equivalent to those in Chapter Five of Volume V of the Western Washington Manual, are required to reduce the hydrologic disruption of developed sites.

F. Minimum Requirement No. 6—Runoff Treatment.

1. The following require construction of stormwater treatment facilities:

a. Projects in which the total of effective, pollution-generating impervious surface is five thousand square feet or more in a threshold discharge area of the project; or

b. Projects in which the total of pollution-generating pervious surfaces (PGPS) is three-quarters of an acre or more in a threshold discharge area, and from which there is a surface discharge in a natural or manmade conveyance system from the site.

2. Treatment facilities shall be selected and designed in accordance with Volume V of the Western Washington Manual.

G. Minimum Requirement No. 7—Flow Control.

1. The following require construction of flow control facilities and/or land use management BMPs:

a. Projects in which the total of effective impervious surfaces is ten thousand square feet or more in a threshold discharge area;

b. Projects that convert three-quarter acres or more of native vegetation to lawn or landscape, or convert 2.5 acres or more of native vegetation to pasture in a threshold discharge area, and from which there is a surface discharge in a natural or manmade conveyance system from the site; or

c. Projects 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 from a threshold discharge area as estimated using a continuous runoff model.

2. Project sites shall match developed discharge durations to predeveloped condition durations for the range of predeveloped discharge rates from fifty percent of the two-year peak flow up to the full fifty-year peak flow, unless a regional facility as described in BGMC 18.250.410 is used to meet the requirements of this chapter.

3. The predeveloped condition to be matched shall be a forested land cover unless reasonable, historic information is available that indicates the site was prairie prior to settlement.

4. For projects that discharge stormwater directly or indirectly to wetlands, Minimum Requirement No. 8 applies.

5. This minimum requirement is waived for sites that will reliably infiltrate all runoff from the one-hundred-year design storm for the project site per BGMC 18.250.200(E).

6. Flow control BMPs shall be selected, designed, and maintained in accordance with Volume III of the Western Washington Manual.

H. Minimum Requirement No. 8—Wetlands Protection.

1. The requirements below apply only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system.

2. Discharges to wetlands shall maintain the hydrologic conditions, hydrophytic vegetation, and substrate characteristics necessary to support existing and designated uses.

3. The hydrologic analysis shall use the existing land cover condition to determine the existing hydrologic conditions.

4. A wetland can be considered for hydrologic modification and/or stormwater treatment in accordance with Guide Sheet 1B in Appendix I-D in the Western Washington Manual. Before modifying a wetland, additional requirements by the Washington State Department of Ecology and the Army Corps of Engineers may apply.

5. Stormwater treatment and flow control facilities shall not be built within native vegetated buffers, except for necessary conveyance systems as approved by the city, as allowed by BGMC 18.270.100(A), or as allowed in wetlands approved for hydrologic modification and/or treatment.

I. Minimum Requirement No. 9—Operation and Maintenance.

1. An operation and maintenance manual consistent with the provisions in Volume V of the Western Washington Manual is required for all proposed private and experimental stormwater facilities and BMPs.

2. The party (or parties) responsible for long-term maintenance and operation shall be identified as required by BGMC 18.250.310(B)(1).

3. For private facilities approved by the city, a copy of the operations and maintenance manual shall be retained on-site or within reasonable access to the site, and shall be transferred with the property to the new owner. A log of maintenance activity that indicates what actions were taken shall be kept and be available for inspection by the city. (Ord. 09-16 (part), 2010)

18.250.100 Submittal requirements.

Stormwater plans shall be designed in accordance with the most current edition of the Standard Specifications for Road, Bridge, and Municipal Construction, as prepared by Washington State Department of Transportation (WSDOT), and the Western Washington Manual. (Ord. 09-16 (part), 2010; Ord. 96-802 § 5, 1996)

18.250.110 Stormwater plan.

A. Purpose. The stormwater plan provides engineering design and construction drawings for the stormwater aspects of a proposed development activity or drainage project.

1. A stormwater plan is required for all projects required to comply with Minimum Requirement No. 1.

B. Contents. The stormwater plan shall consist of two parts, engineering plans as described in BGMC 18.250.600 and a hydrology report as described in BGMC 18.250.610. Both the engineering plans and hydrology report shall be signed and stamped by the project engineer.

1. Preliminary Stormwater Plan. The preliminary engineering plans shall contain all information required by BGMC 18.250.600. The preliminary hydrology report shall contain the information required by BGMC 18.250.610(B), (C), and (D), and preliminary calculations to show feasibility for sections (E), (F), and (G). Information used to create the preliminary stormwater plan may be approximate, but must represent the most current data available at the time of preparation.

2. Final Stormwater Plan. The final engineering plans shall contain all of the information required by BGMC 18.250.600. The final hydrology report shall contain all information required by BGMC 18.250.610.

C. Modification of Content Requirements. The director may waive, in writing, some of the content requirements of the stormwater plan if:

1. The development activity or drainage project is included in an approved final stormwater plan which meets the requirements of this chapter and the applicant demonstrates to the satisfaction of the director that the applicable provisions of the previously approved final stormwater plan will be met;

2. The director determines, upon receipt of a letter of request from the applicant, that less information is required to accomplish the purposes of this chapter; or

3. A basin plan exists that makes some of the information irrelevant.

D. Review and Approval.

1. All final stormwater plans require approval by the director. Approval is only for conformance with city standards and does not relieve the engineer of record of responsibility for the design.

2. Approval of final stormwater plans does not relieve the applicant from the obligation to comply with this chapter and does not prevent the city from recovering for defective work or violation of this chapter.

E. Timing. The preliminary stormwater plan is required at the time of development application, if applicable. The final stormwater plan must be approved by the director prior to beginning utility construction related to a development activity or drainage project. (Ord. 09-16 (part), 2010; Ord. 96-802 § 6, 1996)

18.250.120 As-built drawings.

A. Preliminary as-built plans are required to be submitted and accepted prior to paving over newly constructed public infrastructure. Authorization to pave must be received prior to paving.

1. The preliminary as-built plan submittal shall include two sets of full size drawings plotted on paper.

B. Accepted, final as-built plans shall be submitted prior to engineering acceptance.

1. The final as-built plan submittal shall include the following: One set of full size drawings plotted on Mylar, one set of full size drawings plotted on paper, two sets of drawings plotted on eleven-inch by seventeen-inch paper, and one 3.5-inch disk or compact disc version of the as-built drawings in AutoCAD and TIF format.

C. Information provided on as-built plans shall include, but not be limited to, the following:

1. Invert elevations;

2. Pipe slope;

3. Rim elevations;

4. Pipe diameters;

5. Top of berm elevations;

6. Bottom of pond elevations;

7. Elevations of orifices or weirs in flow control structures; and

8. Emergency spillway elevations.

D. The as-built plans submittal shall be stamped, signed and dated by a licensed professional civil engineer, registered in the state of Washington. (Ord. 09-16 (part), 2010; Ord. 96-802 § 7, 1996)

18.250.130 General standards for water quality treatment.

A. All projects, unless otherwise exempted by this chapter, shall provide treatment of stormwater runoff through the use of BMPs specified in the Western Washington Manual or LID BMPs as specified in BGMC 18.250.170. Alternatively experimental BMPs meeting the requirements of BGMC 18.250.180 may be utilized if approved by the director.

B. All sites with direct discharges to surface waters shall comply with the following state laws: the Water Pollution Control Act (Chapter 90.48 RCW) and Water Quality Standards for Surface Waters of the State of Washington (Chapter 173-201A WAC).

C. Water quality treatment of runoff from sidewalks, separated bike paths, roofs, fenced fire lanes, and infrequently used maintenance access roads is not required if the stormwater drains away from pollution generating surfaces. Runoff from these surfaces that mixes with runoff from pollution generating surfaces will require treatment.

D. For vegetated wet facilities including, but not limited to, wet biofiltration swales, stormwater treatment wetlands, wet ponds and wetpools, plantings are required to be plugs, rootstock or nursery stock. Seeding of wet facilities is not allowed unless it can be demonstrated to the satisfaction of the director that facility vegetation will be fully established before the facility receives stormwater. (Ord. 09-16 (part), 2010; Ord. 96-802 § 8, 1996)

18.250.140 Design methodology for water quality treatment facilities.

A. Treatment BMPs shall be sized to capture, hold and treat the water quality design storm. Treatment BMPs shall be sized based on the following:

1. Water Quality Design Storm Volume. The volume of runoff predicted from a twenty-four-hour storm with a six-month return frequency (a.k.a., six-month, twenty-four-hour storm. This storm may be assumed to be two-thirds of the two-year, twenty-four-hour storm). Alternatively, the ninety-first percentile, twenty-four-hour runoff volume indicated by a continuous runoff model may be used.

2. Water Quality Design Storm Flow Rate.

a. For projects that are required to comply with Minimum Requirement No. 6: the flow rate at or below which ninety-one percent of the runoff volume, as estimated by a continuous runoff model, will be treated. Design criteria for treatment facilities are assigned to achieve the applicable performance goal at the water quality design flow rate (e.g., eighty percent total suspended solids removal).

b. For small projects as defined in BGMC 18.250.020(B): the flow rate predicted from a twenty-four-hour storm with a six-month return frequency (a.k.a., six-month, twenty-four-hour storm).

c. Downstream of detention facilities the water quality design flow rate must be the full two-year release rate from the detention facility. Alternative methods may be used if they identify volumes and flow rates that are at least equivalent.

B. Projects required to follow the small project requirements as defined in BGMC 18.250.020(B) are exempt from the enhanced treatment requirements as defined in Volume V of the Western Washington Manual. (Ord. 09-16 (part), 2010; Ord. 96-802 § 9, 1996)

18.250.160 Oil/water separators.

A. The following development activities require American Petroleum Institute (API) or Coalescing Plate Separator (CPS)-type oil/water separators:

1. Commercial or industrial sites with an expected average daily traffic count greater than or equal to one hundred vehicles per one thousand square feet of gross building area;

2. Commercial or industrial sites subject to petroleum storage and transfer in excess of one thousand five hundred gallons per year, not including routinely delivered heating oil;

3. Commercial or industrial sites subject to parking, storage or maintenance of twenty-five or more vehicles over ten thousand tons gross weight;

4. Roadway intersections with a measured average daily traffic 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 improvements;

5. Log storage and sorting yards;

6. Airfields and aircraft maintenance;

7. Industrial machinery and equipment maintenance;

8. Railroad yards;

9. Fueling stations;

10. Vehicle maintenance and repair;

11. Construction businesses including paving, heavy equipment storage and maintenance, storage of petroleum products (this does not include construction sites); or

12. Other activities that exhibit a significant risk of high oil loading in runoff.

B. The following development activities shall require spill control (SC) type oil/water separators:

1. Restaurants;

2. Multifamily residential projects creating parking spaces for twenty-five or more vehicles;

3. Fleet vehicle yards which have more than twenty-five vehicles parked overnight;

4. Retail/wholesale vehicle and equipment dealers; or

5. Other activities where the risk of oil spills or illegal dumping of oil or grease is significant as determined by the director.

C. For development activities cited in subsections A and B of this section, oil/water separators shall not be required on portions of a site where the risk of oil or grease spills or dumping is minimal.

D. Oil/water separators shall be designed in accordance with Chapter 11 of Volume V of the Western Washington Manual. (Ord. 09-16 (part), 2010; Ord. 96-802 § 11, 1996)

18.250.170 Low impact development best management practices.

A. Acceptable LID BMPs include the following:

1. Bioretention areas.

2. Amended soils.

3. Permeable paving.

4. Vegetated roofs.

B. Additional LID BMPs may be utilized if approved by the director.

C. LID BMPs shall be designed as specified in the Low Impact Development Manual or the low impact development chapter of the Clark County Stormwater Manual.

D. Infiltration testing as required by BGMC 18.250.200(E)(1) must be performed if infiltration will be used to dispose of water from LID BMPs. (Ord. 09-16 (part), 2010; Ord. 96-802 § 12, 1996)

18.250.180 Experimental best management practices.

A. Experimental best management practices are those which have not been fully tested and evaluated by the city or the Department of Ecology and are not included as accepted practices in this code or the Western Washington Manual.

B. Experimental BMPs may be allowed upon approval by the director if the Department of Ecology Technology Assessment Protocol—Ecology (TAPE) program is followed. (Ord. 09-16 (part), 2010; Ord. 96-802 § 13, 1996)

18.250.190 Drainage structure labeling and signage.

A. All catch basins and manholes capable of accepting stormwater shall be stenciled. The stenciling shall read:

Dump No Waste—Drains to Stream

B. Signs shall be installed along all above ground stormwater facilities as required by the city standard detail. (Ord. 09-16 (part), 2010; Ord. 96-802 § 14, 1996)

18.250.200 General standards for runoff quantity control.

A. All projects, unless otherwise exempted by this chapter, shall provide quantity control of stormwater runoff through the use of BMPs specified in the Western Washington Manual or LID BMPs as specified in BGMC 18.250.170. Alternatively experimental BMPs meeting the requirements of BGMC 18.250.180 may be utilized if approved by the city.

B. Facility design shall allow access to all areas within the pond by standard maintenance equipment vehicles.

C. Transfer of runoff from one basin to another shall not be allowed unless otherwise approved by the director.

D. No reduction of existing conveyance capacity and no net loss of existing storage capacity for the one-hundred-year storm is permitted in special flood hazard areas as defined in BGMC 18.310.020(B). This requirement shall also apply to all areas within the limits of the existing one-hundred-year floodplain, as determined by hydrologic/hydraulic computations in accordance with this chapter, for all streams and manmade channels within the city of Battle Ground.

E. Infiltration is the preferred BMP if site conditions are appropriate and groundwater quality will not be impaired. All applicable discharges to groundwater shall comply with the requirements of the Washington State Department of Ecology Underground Injection Control Program.

1. Infiltration systems shall be designed and sized in accordance with Chapter 3.3 of Volume III of the Western Washington Manual or A Review of Infiltration Standards and Practices in Clark County, July 31, 2009, as prepared by the Southwest Washington Branch of the American Society of Civil Engineers.

F. To ensure the standards in this chapter are met, the volume available for storing runoff in a stormwater facility shall be reduced by high seasonal groundwater and/or ordinary high water unless a liner and buoyancy calculations are provided for the facility.

G. Residential and commercial structures meeting the requirements in Chapter 3.1, Volume III of the Western Washington Manual shall direct roof runoff to roof downspout control systems. (Ord. 09-16 (part), 2010; Ord. 96-802 § 15, 1996)

18.250.210 Design methodology for quantity control facilities.

A. Projects required to meet Minimum Requirement No. 7 shall use a continuous runoff model for hydrologic and hydraulic analysis and facility sizing in accordance with Volume III of the Western Washington Manual and the city of Battle Ground NPDES permit.

B. Projects required to meet the small project requirements shall utilize the Santa Barbara Unit Hydrograph (SBUH) method for hydrologic and hydraulic analysis and facility sizing. A Soil Conservation Society (SCS) Type 1A rainfall distribution resolved to a maximum of ten-minute time intervals shall be used. When sizing facilities and calculating the rate and volume of runoff leaving a project site, the following criteria shall be met:

1. The peak release rate for the two-year design storm after development shall not exceed one-half the predeveloped two-year design storm peak runoff rate.

2. The peak release rate for the ten- and one-hundred-year design storms after development shall not exceed the respective predeveloped design storm peak runoff rates.

3. After meeting the requirements of subsections (B)(1) and (B)(2) of this section, the pond volume shall be increased by either the following multiplication factor F: F = (composite curve number /46)-0.6 or by using Figure 18.250.210A. This correction factor is to be applied to the volume of the pond without changing its depth or the design of its outlet structure, which shall result in an increase in surface area.

Figure 18.250.210A

4. Isopluvial maps used for analysis shall be “Isopluvial Maps for Design Storms in Clark County,” as published in National Oceanic and Atmospheric Administration (NOAA) Atlas 2, “Precipitation—Frequency Atlas for the Western United States,” Volume IX, Washington. Isopluvial maps are available from the city of Battle Ground engineering division.

5. Curve numbers used for analysis shall be as specified in “USDA SCS TR-55,” June 1986, published by the SCS.

C. All facilities shall provide emergency overflow routes for storm events that exceed the design capacity of the facility.

D. Infiltration facilities shall be designed to infiltrate the one-hundred-year design storm. Facilities that infiltrate less than the one-hundred-year design storm shall meet the requirements of this section.

E. Soil groups used for analysis shall be as defined in the most current version of “Hydrologic Soil Groups for Soils in Clark County,” published by the SCS. Alternatively, hydrological soil groups from the United States Department of Agriculture (USDA) “Web Soil Survey” can be used, or soil groups can be developed by a registered soil scientist.

F. Closed depression analysis shall be performed as required in Chapter 2.4 of Volume III of the Western Washington Manual for projects required to meet Minimum Requirement No. 7, or section III-1.5 of the Stormwater Management Manual for the Puget Sound Basin, February 1992, as prepared by the Washington State Department of Ecology for projects required to meet the small project requirements. The requirements of subsection C of this section will be waived for projects in closed depressions. (Ord. 09-16 (part), 2010; Ord. 96-802 § 16, 1996)

18.250.230 Conveyance systems.

A. Open channel conveyance systems incorporating water quality treatment, habitat improvement, and emergency overland flood relief routes shall be utilized to the maximum extent practicable.

B. Stormwater conveyance elements to transport water within and from a project site shall be sized to carry flows from the design storm from the contributing drainage area based upon the projected full buildout of that contributing drainage area, and be fully compatible with existing downstream conveyance elements and flow conditions.

C. For stormwater conveyance design the design storms shall be as follows:

1. Ten-year storm: contributing drainage areas less than forty acres;

2. Twenty-five-year storm: contributing drainage areas of forty acres or more;

3. One-hundred-year storm: culverts with contributing drainage areas greater than two hundred acres, culverts in areas of special flood hazard as described in Federal Emergency Management Agency “FIRM” maps and reports for Clark County, culverts where upsizing in order to meet design requirements for the one-hundred-year storm is required.

D. Development sites shall be planned to be able to pass the one-hundred-year storm through the site.

E. Closed conveyance system elements shall be designed to operate in an open flow, not pressure flow regime, for the design storm.

F. A backwater analysis shall be performed under any of the following conditions:

1. Pipes with slopes less than 0.5 percent;

2. Pipes with subcritical flow velocities over 6.5 feet per second;

3. Stormwater main lines forming an angle or forty-five degrees or more at junctions;

4. Pipes with inverts less than three feet deep.

G. When backwater analysis is required, the hydraulic grade line shall be calculated for the required design storm as well as the twenty-five- and one-hundred-year storm events. For the twenty-five-year event there shall be a minimum of one foot of freeboard between the water surface and the top of any manhole or catch basin. For the one-hundred-year event the stormwater flows must meet the requirements of subsections I, J, and K of this section.

H. Backwater analysis shall be performed as described in Section 6.6 of the WSDOT Hydraulics Manual, 2007, as prepared by the Washington State Department of Transportation.

I. Runoff from the one-hundred-year storm may leave pipes and channels but shall not rise to elevations more than two feet below that of the lowest finished floor of buildings.

J. For roadway flooding conditions during the one-hundred-year storm, one travel lane in either direction shall remain open to emergency vehicles at all times. A travel lane will be considered to be open to emergency vehicles if the maximum depth of flow in the travel lane does not exceed 0.5 feet.

K. For parking lot flooding conditions during the one-hundred-year storm, the maximum depth of ponding shall not exceed 1.5 feet. Storage volumes resulting from ponding in street and parking lot areas may be used to meet the storage requirements of BGMC 18.250.210(B) for the maximum design storm.

L. Design of conveyance systems shall be in accordance with the city of Battle Ground stormwater construction requirements. (Ord. 09-16 (part), 2010; Ord. 96-802 § 18, 1996)

18.250.300 Ownership of stormwater facilities.

A. Stormwater facilities located within public road rights-of-way shall be owned by the city.

B. City ownership of stormwater facilities is required where the city will assume long-term maintenance of the facilities.

C. Stormwater facilities which collect, convey, treat, and/or infiltrate runoff from public rights-of-way shall be publicly owned and maintained, unless it is demonstrated to the satisfaction of the director that the stormwater facility can be adequately maintained by private parties.

D. Stormwater facilities that treat runoff from only private property shall be owned and maintained by private parties.

E. Stormwater facilities that treat mixed runoff from public and private property shall be owned and maintained by private parties unless otherwise approved by the director.

F. Stormwater facilities that treat stormwater runoff from single-family residential subdivisions shall be publicly owned and maintained, unless it is demonstrated to the satisfaction of the director that the stormwater facility can be adequately maintained by private parties. (Ord. 09-16 (part), 2010; Ord. 96-802 § 19, 1996)

18.250.310 Maintenance.

A. Initial Maintenance.

1. To ensure satisfactory operation of new public stormwater facilities, the applicant constructing the facility shall maintain it for two years after completion of the project. A maintenance agreement stating that the applicant will be responsible for the maintenance of the facility must be recorded prior to engineering acceptance.

2. The applicant shall post and maintain a maintenance bond or other security acceptable to the director during this two-year initial maintenance period. The purpose of the maintenance bond is to cover the cost of design defects or failures in workmanship of the facilities. The amount of the maintenance bond shall be twenty percent of the construction cost of the stormwater facilities.

B. Long-Term Maintenance.

1. Final plats shall include a note specifying the party(s) responsible for long-term maintenance of stormwater facilities.

2. If private parties are to provide long-term maintenance of a stormwater facility, a maintenance covenant will be required. The covenant shall include an agreement to transfer maintenance responsibilities to future occupants or owners of the property. Said covenant shall be recorded prior to engineering acceptance.

3. If the city provides long-term maintenance of a stormwater facility, all the following requirements shall be met:

a. The facilities shall be inspected and approved by the director prior to acceptance. Required remedial work to correct design, construction, and maintenance deficiencies shall be completed by the project developer prior to acceptance; and

b. All necessary ownerships and easements entitling the city to properly access and maintain the facility shall be conveyed to the city and recorded with the county auditor.

C. The city shall inspect privately maintained facilities for compliance with the requirements of this chapter. Facilities shall be maintained to the standards set forth in the city of Battle Ground stormwater facility maintenance manual, or the design engineer provided maintenance manual as required in BGMC 18.250.610(K). If the parties responsible for long-term maintenance fail to maintain their facilities to acceptable standards, the city shall issue a written notice specifying required actions to be taken in order to bring the facilities into compliance. Following the written warning the city will enforce maintenance requirements as detailed in BGMC 18.250.040. (Ord. 09-16 (part), 2010; Ord. 96-802 §§ 20, 21, 1996)

18.250.320 Tracts, easements, and covenants.

A. All stormwater facilities maintained by the city shall be in a tract dedicated to the city of Battle Ground. In subdivisions and short plats the tracts are recommended, but not required, to meet minimum zoning lot size requirements.

B. Stormwater easements shall be provided to the city for access and maintenance of all conveyance systems within the site, which are to be maintained by the city. The required widths of easements shall be as follows. The director may decrease widths in special cases or require increased widths when necessary to ensure adequate area for equipment access and maintenance:

1. Pipes with inner diameter less than or equal to thirty-six inches: twenty feet.

2. Pipes with inner diameter greater than thirty-six inches: twenty feet plus pipe inner diameter.

3. Pipes shall be located with their centerline no closer than one-quarter of the easement width from an adjacent property line.

4. Streams and channels: top width of channel plus fifteen feet on one side.

C. Private stormwater facilities must have an access and inspection covenant dedicated to the city of Battle Ground encompassing the facility.

D. No buildings or other structures are permitted within easements. Fences crossing easements must cross the easement perpendicularly and shall provide gates that extend across the entire width of the easement for access by maintenance vehicles. (Ord. 09-16 (part), 2010)

18.250.330 Location of stormwater facilities.

A. Runoff treatment and control facilities shall be located prior to the point of discharge into a stream, lake, or fish-bearing water or prior to discharge to groundwater.

B. Unless otherwise approved by the director, infiltration systems shall be located as follows:

1. Fifty feet from the top of any slope greater than fifteen percent;

2. One hundred feet from municipal water supply wells; and

3. One hundred feet from existing or proposed septic drain fields.

C. Infiltration systems shall be located and designed to prevent influencing existing or proposed building foundations.

D. Swales and other stormwater treatment facilities using biofiltration shall be located outside easements and corridors used by phone, electric, water, natural gas, and other utilities unless the utilities are installed prior to construction of the biofiltration system. (Ord. 09-16 (part), 2010; Ord. 96-802 § 22, 1996)

18.250.350 Fencing of stormwater facilities.

A. Stormwater ponds dedicated to the city shall be fenced unless otherwise approved by the director.

B. Privately owned stormwater ponds shall be fenced where they abut the public right-of-way.

C. The size and type of fence, as required by subsections A and B of this section, shall be per the city of Battle Ground standard details. (Ord. 09-16 (part), 2010; Ord. 96-802 § 24, 1996)

18.250.360 Side slopes of stormwater facilities.

A. For maintenance and safety reasons, side slopes of stormwater facilities normally shall be no steeper than three to one.

B. Side slopes steeper than three to one may be allowed by the director where all the following conditions are met:

1. Side slopes do not need to be mowed; and

2. Adequate long-term erosion control is provided.

C. Use of retaining walls greater than four feet in stormwater facilities requires approval of the director. The height of the wall shall be measured from the bottom of the footing to the top of the wall. (Ord. 09-16 (part), 2010; Ord. 96-802 § 25, 1996)

18.250.370 Recovering costs of stormwater facilities.

A. The following costs associated with stormwater facilities may be recoverable through latecomers agreements as described in Article II of Chapter 17.200 BGMC.

B. The costs for constructing a regional stormwater facility included in the approved city of Battle Ground stormwater management plan may be eligible as a credit against applicable system development charges. (Ord. 09-16 (part), 2010; Ord. 96-802 § 26, 1996)

18.250.380 Bonds and insurance.

A. Performance Security. In lieu of completing required stormwater facilities within a preliminary plat prior to recording, the applicant may post a performance bond or other security, if acceptable to the director, in the amount of one hundred twenty-five percent of the approved estimated cost (prepared by the project engineer) of completing construction per the approved stormwater plan. After determination by the director that all facilities are constructed in compliance with the approved plan, are performing their intended functions in a satisfactory manner, and that the requirements of BGMC 18.250.310(A) and subsection B of this section are met, the performance bond or security shall be released.

B. Maintenance Security. In cases identified in BGMC 18.250.310(A)(2), a maintenance bond or other security acceptable to the director shall be posted and maintained throughout the two-year initial maintenance period for a stormwater facility. (Ord. 09-16 (part), 2010; Ord. 96-802 § 27, 1996)

18.250.400 Basin plans.

Adopted basin plans are identified in the most current version of the city of Battle Ground stormwater management plan. (Ord. 09-16 (part), 2010; Ord. 96-811 § 1, 1996: Ord. 96-802 § 28, 1996)

18.250.410 Regional and subregional facilities.

A. The city encourages multiple users of stormwater facilities. If regional or subregional facilities are used to meet some or all of the requirements for stormwater quality treatment and quantity control, the following conditions shall be met:

1. Stormwater runoff shall be transported from a project site to a regional/subregional facility through a pipe or manmade open channel conveyance system, or through a natural drainage way if approved by the director.

2. If the regional/subregional facility does not yet exist, interim quantity control and treatment methods shall be used to meet the requirements of this chapter. All interim methods shall be reviewed and shall require written approval by the director.

3. The facility must have sufficient capacity to provide quality treatment and/or quantity control as required by this chapter.

B. A system development charge will be assessed for use of a regional/subregional facility per the city capital plan. (Ord. 09-16 (part), 2010; Ord. 96-811 § 2, 1996: Ord. 96-802 § 29, 1996)

18.250.510 Variances.

A. Major Variances. If application of the minimum requirements will impose a severe and unexpected economic hardship, an applicant can make a written request for a waiver from some or all of the minimum requirements as specified in BGMC 18.250.050.

1. To determine whether the minimum requirements impose a severe and unexpected economic hardship, the city will consider and document with written findings of fact the following:

a. The current (preproject) use of the site;

b. How the application of the minimum requirement(s) restrict the proposed use of the site compared to the small project requirements;

c. The possible remaining uses of the site if the variance were not granted;

d. The uses of the site that would be allowed under the small project requirements;

e. A comparison of the estimated amount and percentage of value loss as a result of the minimum requirements versus the estimated amount and percentage of value loss as a result of the small project requirements; and

f. The feasibility for the owner to alter the project to apply the minimum requirements.

2. Any major variances must meet the following conditions:

a. The variance will not increase risk to the public health and welfare, nor injurious to other properties in the vicinity and/or downstream, and to the quality of waters of the state; and

b. The variance is the least possible exception that could be granted to comply with the intent of the minimum requirements.

3. Major variances may be granted by the city following legal public notice of an application for the variance, legal public notice of the city’s decision on the application, and written findings of fact that documents the city’s determination to grant the variance.

4. Major variances shall not allow projects to discharge stormwater to standards less than those required by the small project requirements.

5. Major variances shall be processed as a Type III land use action as set forth in BGMC 17.200.035.

B. Minor Variances. The director may grant minor variances to the numerical standards of this chapter prior to permit approval and construction. Minor variances deal with the design and construction of facilities and are not limited to any percentage change.

1. Requirements that may be changed by minor variances include, but are not limited to, the following:

a. Conveyance system analysis and design;

b. Off-site analysis;

c. Materials;

d. Facility side slopes;

e. Easements;

f. Percent of facility made up of retaining wall;

g. Fencing requirements; and

h. Varying from the standard details.

2. Major variances shall be processed as a Type I land use action as set forth in BGMC 17.200.035. (Ord. 09-16 (part), 2010; Ord. 96-811 § 3, 1996: Ord. 96-802 § 31, 1996)

18.250.520 Other governmental agency projects.

As required by RCW 35A.21.250, the performance bonding requirements of BGMC 18.250.380(A) shall be waived for projects undertaken by governmental agencies. (Ord. 09-16 (part), 2010; Ord. 96-802 § 32, 1996)

18.250.600 Contents of engineering plans.

The engineering plans required pursuant to BGMC 18.250.110 shall contain the information listed below. All maps shall contain a scale and north arrow. Ensuring the accuracy of all the information is the applicant’s responsibility.

A. Site Location Map. A site location map (minimum USGS 1:24000 Quadrangle Topographic Map), shall be required. The site location map may be placed on a cover sheet if the stormwater plan is part of a larger set of plans.

B. The engineering plans shall show the character of the existing site and proposed features, including but not limited to:

1. Existing and proposed property boundaries, easements and rights-of-way;

2. Existing contours of the project site and adjacent properties with a one-foot maximum contour interval, unless the director determines a lesser interval is sufficient to show drainage patterns;

3. Existing on-site water wells, known agricultural drain tiles, areas of potential slope instability, structures, utilities, and septic tanks and drainfields;

4. Location of the one-hundred-year floodplain and floodways and shoreline management area limits on the site;

5. Proposed impervious surfaces outside of single-family residential lots;

6. Existing water resource features on and adjacent to the site including streams, wetlands, springs, sinks and stormwater facilities;

7. Drainage flow routes and existing discharge points to and from the site;

8. Location and size and design of proposed stormwater facilities, including typical cross-sections of proposed facilities, storage volumes of detention facilities, water level elevations for all design storms, elevations and dimensions of all structures, and, for vegetated facilities, planting plan including plant species, spacing and total number of plants required;

9. Wetland delineation if wetlands exist on the site;

10. A conceptual grading plan verifying the constructability of a stormwater facility; and

11. Additional site or vicinity information required by the director, if needed, to determine the feasibility of the proposed stormwater plan. (Ord. 09-16 (part), 2010; Ord. 96-802 § 37, 1996)

18.250.610 Contents of the hydrology report.

The hydrology report required pursuant to BGMC 18.250.110 shall contain the following information:

A. Certificate of completeness and feasibility that reads as follows:

This Technical Information Report includes all information required by the City of Battle Ground Municipal Code Chapter 18.250—Stormwater Control and Drainage, for (Name of Project). The facilities, as designed, are feasible to construct and maintain and conform to the City Code requirements.

B. Table of Contents.

1. List section headings and their respective page numbers;

2. List of tables with page numbers;

3. List of figures with page numbers;

4. List of attachments, numbered; and

5. List of references.

C. Vicinity Maps. All vicinity maps shall clearly show the site of the development activity or drainage project.

1. Site Location Map. Minimum USGS 1:24000 Quadrangle Topographic Map showing (and labeling where appropriate):

a. Surrounding roadways;

b. Contributing drainage areas and acreage; and

c. Natural and manmade drainage features adjacent to site including existing and proposed (if known) stormwater facilities;

2. Soils Map.

a. The soils map shall show soils within the contributing area draining to the site and the site itself. Copies of Clark County soil survey maps may be used; however, if the maps do not appear to accurately represent the soils for a site, the applicant is responsible for verifying the actual soil types existing on a site.

b. Where unstable or complex soil conditions exist which may significantly impact the design of stormwater facilities, the director may require a preliminary soils report to be completed that addresses stormwater design considerations arising from soil conditions. The preliminary soils report shall be prepared by a registered professional engineer proficient in geotechnical investigation and engineering, or a soil scientist. The preliminary soils report shall include a soils map, developed using the criteria set in the USDA, SCS National Soils Handbook and USDA, SCS Title 430 Soil Survey Manual at a minimum scale of one to five thousand;

3. Site basin map, showing:

a. Pre- and postdevelopment conditions and contributing areas of pollution generating and nonpollution generating pervious and impervious areas;

b. Existing and proposed contours (one-foot maximum contour interval); and

c. Directions and lengths of overland, pipe and channel flow;

4. Other Maps. The following additional vicinity maps shall be required in the situations noted below:

a. Conveyance System. If a direct surface water discharge of stormwater is proposed from the site, a map showing the conveyance system downstream to a point where the stormwater enters a stream, wetland, or other natural water body shall be required.

b. Wellhead Protection. If the site lies within the ten-year zone of contribution of a public water supply well, maps showing all the zones of contribution that overlap the site are required.

c. Floodplains. If a floodplain mapped by Federal Emergency Management Agency exists on or adjacent to the site, a map showing the floodplain is required.

d. Shoreline Management Area. If the site contains or is adjacent to a stream or lake regulated under the State Shorelines Management Act, a map showing the boundary of the shoreline management area in relation to the site is required.

D. Project Overview.

1. Describe the requirements that apply to the project. Include flow charts from the city of Battle Ground and/or the Western Washington Manual showing assumptions used to find project requirements;

2. Describe drainage to and from adjacent properties;

3. Describe any known flooding or drainage issues;

4. Describe proposed site construction, applicable minimum requirements, and proposed methods of mitigating stormwater runoff quantity and quality impacts;

5. Include a table showing amount of land-disturbing activity, existing and proposed impervious surface area, amount of new and replaced impervious surface in each threshold discharge area, amount of lawn and landscaping in each threshold discharge area, and amount of pollution generating pervious and impervious surfaces; and

6. Discuss water table elevations, and data on seasonal water table fluctuations with minimum and maximum water table elevations in areas of high groundwater.

E. Quantity Control Analysis and Design.

1. Hydrologic Analysis, Existing and Developed Conditions.

a. Tabulate acreage; imperviousness; curve number; length and grade of overland, pipe and channel flow, off-site flows; and other hydrologic parameters used in completing analyses;

b. Complete detailed hydrologic analysis for existing and developed site conditions in accordance with the requirements of BGMC 18.250.200 through 18.250.230. Compute existing and developed peak flows and volumes for the design storms for all site basins. Refer to labeled points shown on the site location map and development plan;

c. Include and reference all hydrologic and hydraulic computations in the technical appendix; and

d. Include all maps, exhibits, graphics and references used to determine existing and developed site hydrology.

2. Quantity Control System Design.

a. Compute inflow and outflow hydrographs and peak flows and storage volumes. Reference conveyance and stormwater control facilities to labeled points shown on the development plan;

b. Tabulate existing proposed peak flows and storage volumes; and

c. Show all hydrologic and hydraulic computations, equations, ratings curves, stage/storage/discharge tables, and graphs necessary to show methodology and results.

3. Quantity Control System Plan.

a. Provide illustrative sketch of quantity control facility and its appurtenances;

b. Show basic measurements necessary to confirm storage volumes;

c. Show all orifice, weir and flow restrictor dimensions and elevations;

d. Tabulate peak flow rates, storage volumes and ponding elevations for all design storms.

F. Water Quality Design.

1. Identify best management practices used in design and their sources;

2. Identify and discuss initial conditions including groundwater elevations, beginning storage elevations, and other data or assumptions used to determine initial conditions in order to complete analyses;

3. Identify and discuss assumptions used in completing analysis;

4. Complete detailed analysis and design of all proposed water quality system elements in accordance with BGMC 18.250.130 through 18.250.190;

5. Include and reference all computations, equations, charts, nomographs, detail drawings and other tabular or graphic aids used to design water quality system elements;

6. Summarize results of water quality design and describe how the proposed design meets the requirements of this chapter.

G. Conveyance Systems Analysis and Design.

1. Identify criteria used in completing analyses and their sources;

2. Complete detailed hydraulic analysis of all proposed collection and conveyance systems. Compute and tabulate design flows and velocities and conveyance element capacities for all conveyance elements within the development;

3. Include and reference all hydraulic computations, equations, pipe flow tables, flow profile computations, charts, and nomographs;

4. Downstream Analysis. The analysis shall be extended downstream to points where the impact is insignificant.

H. Soils Evaluation.

1. Identify on-site soil types and their erosive potential and discuss their suitability for implementation of proposed best management practices (BMPs) and quantity control facilities;

2. Identify seasonal high water table elevations in cases where this will impact the stormwater facilities;

3. Identify and discuss soil parameters, testing, and design methods used in hydrologic and hydraulic design of proposed facilities; and

4. Where infiltration BMPs are proposed, complete soil tests to determine the infiltration rates. In some cases the director may require additional geotechnical investigation, in accordance with the requirements of Chapter 3.3 of Volume III of the Western Washington Manual.

I. Special Reports and Studies. Where specific site characteristics including, but not limited to steep slopes, wetlands, and sites located in wellhead protection areas pose difficult drainage and water quality design problems, the director may require additional information or the preparation of special reports and studies which further address the specific site characteristics, the potential for impacts associated with the development, and the measures which would be implemented to mitigate impacts. Special reports shall be prepared by professional persons with expertise in the particular area of analysis, who shall date, sign, stamp and otherwise certify the report. Subjects of special reports may include, but not be limited to, the following:

1. Geotechnical/pedological;

2. Wetlands;

3. Floodplains and floodways;

4. Groundwater;

5. Structural design; and

6. Fluvial geomorphology (erosion and deposition).

All special reports and studies shall be included as an attachment to the hydrology report.

J. Other Permits. Construction of roads, stormwater facilities, and infiltration facilities may require additional water-related permits from other agencies. These additional permits may contain requirements which impact design of the stormwater system. This subsection of the hydrology report shall list the titles of all other required permits, the agencies requiring the permits, and identify the permit requirements, if known, that affect the stormwater plan. Approved permits that are critical to the feasibility of the stormwater facility design shall be included in this section. Examples of other permits are as follows:

1. Developer/local agency agreement: Washington State Department of Transportation;

2. Short-term water quality modification approval: Washington State Department of Ecology;

3. Hydraulic project approval: Washington State Departments of Fisheries and Wildlife;

4. Dam safety permit: Washington State Department of Ecology;

5. Section 10, 103 and 404 permits: U.S. Army Corps of Engineers;

6. Surface mining reclamation permits: Washington State Department of Natural Resources;

7. Underground injection control registration: Washington State Department of Ecology.

K. Maintenance and Operations Manual.

1. The standards set forth in the city of Battle Ground stormwater facility maintenance manual shall be used for all standard BMPs. If the city manual is to be used it may be adopted by reference in the hydrology report.

2. For any stormwater control or treatment facility which constitutes an experimental system under BGMC 18.250.180, or for any facility that does not have maintenance standards set forth in the city of Battle Ground stormwater facility maintenance manual, the project engineer shall prepare a maintenance and operations manual. The manual shall provide an outline of required maintenance tasks with recommended frequencies at which each task should be performed. (Ord. 09-16 (part), 2010; Ord. 96-802 § 38, 1996)

18.250.620 Severability.

The provisions of this chapter are hereby declared to be severable. If any provision, clause, sentence, or paragraph of this chapter or the application thereof to any person, establishment, or circumstances shall be held invalid, such invalidity shall not affect the other provisions or application of this chapter. (Ord. 09-16 (part), 2010)

18.250.630 Effective date.

This chapter shall be in full force and effective five days after approval and shall be published according to law. This chapter is necessary for the immediate preservation of public peace, health and safety and for the support of city government and its existing public institutions and is urgent due to the requirements of the Washington State Department of Ecology. (Ord. 09-16 (part), 2010)