Chapter 18.250 STORMWATER CONTROL AND DRAINAGE

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

B. Prevent 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. 96-802 § 1, 1996)

18.250.020 Applicability.

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

1. The creation of more than two thousand five hundred square feet of impervious surface or the division of urban single-family residential land creating the reasonable potential for more than two thousand five hundred square feet of additional impervious surface, except residential short plats creating less than two thousand five hundred square feet of new impervious surface at the time of platting shall submit a final stormwater plan limited to conveyance and disposal;

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, to be shown on final engineering plans;

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

B. The provisions of this chapter also apply to drainage projects, as defined in BGMC 18.250.030. (Ord. 96-802 § 2, 1996)

18.250.030 Definitions.

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

“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.

“Basin” means a watershed as shown on the map attached to the ordinance codified in this chapter on file in the office of the city clerk.

“Basin plan” means a stormwater management plan adopted by the city of Battle Ground.

“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.

“Contributing drainage area” means the subject property together with the watershed 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.

“Development activity” means:

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

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

“Development site” means the property or portion thereof on which a development activity is proposed.

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

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

“Groundwater” means water in a saturated zone or stratum beneath the surface of land or below a surface water body (source: WAC 173-200-020).

“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. Open, uncovered stormwater facilities are not considered impervious surfaces.

“Natural location” means the location and elevation of those channels, swales, and other non-man-made conveyance systems as defined by the first documented topographic contours existing for the development 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.

“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.

“The Puget Sound Manual” means state of Washington Department of Ecology’s “Stormwater Management Manual for the Puget Sound Basin,” February 1992 edition and updated errata sheets issued by the director as may be necessary to correct clear and obvious mathematical and technical errors in manual criteria.

“Regional facility” means a facility designed to treat and control stormwater runoff from a contributing drainage area of at least forty acres.

“Registered soil scientist” means a professional soil scientist registered with the American Registry of Certified Professionals in Agronomy, Crops and Soils, 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.

“Roof downspout systems” mean disposal systems that infiltrate stormwater runoff from roofs into the ground and meet the requirements stated in BGMC 18.250.140(B) for these systems.

“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, storage basins, infiltration devices, catchbasins, manholes, dry wells, oil/water separators and sediment basins.

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

“Stream” means those areas of year-round base flow or where surface waters produce a defined channel or bed at least two feet in width between ordinary high water marks. 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.

“Wetlands” means those areas defined as wetlands under Chapter 18.200 BGMC. (Ord. 96-802 § 3, 1996)

18.250.040 Enforcement.

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

18.250.100 Submittal requirements.

Stormwater plans shall be designed in accordance with 1994 Standard Specifications for Road, Bridge, and Municipal Construction, and updates as prepared by Washington Department of Transportation (WDOT), Puget Sound Manual, and the Washington State Chapter of the American Public Works Standards (APWA), current edition. (Ord. 96-802 § 5, 1996)

18.250.110 Stormwater plan.

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

B. Types of Projects. A stormwater plan is required for the following activities:

1. Short plats and site plan reviews subject to SEPA review;

2. Subdivisions;

3. Conditional use permits;

4. Planned unit developments.

C. Contents. The stormwater plan shall be prepared in the standardized format described in BGMC 18.250.600. The stormwater plan shall consist of two parts:

1. Final engineering plans which provide sufficient detail to allow construction of the stormwater facilities. These plans shall be stamped, signed and dated by the engineer(s) registered in the state of Washington, responsible for hydrologic, hydraulic, geotechnical, structural and general civil engineering design and by the project engineer responsible for the preparation of the final stormwater plan. Additionally, the final engineering plan shall show all utilities to insure conflicts between proposed utility lines do not exist.

2. A hydrology report.

a. The hydrology report shall be a comprehensive report containing all technical information and analysis necessary to complete final water quantity and quality engineering plans based on sound engineering practices.

b. The hydrology report shall be stamped, signed and dated by the professional engineer(s), registered in the state of Washington, responsible for hydrologic, hydraulic, geotechnical, structural and general civil engineering design.

c. The contents and format of the hydrology report are specified in BGMC 18.250.610. This format is intended to serve as a guide to the type of information appropriate in the hydrology report. The level of detail in the hydrology report is dependent on the complexity and size of the project.

D. Modification of Content Requirements. The director may waive, in writing, some of the content requirements in the final 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; or

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;

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

E. Review and Approval.

1. All final stormwater plans require approval by the director. Approval is only for conformance with city of Battle Ground 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.

F. Timing. The stormwater plan is required and must be approved by the director prior to beginning clearing and grading and construction related to a development activity or drainage project. (Ord. 96-802 § 6, 1996)

18.250.120 As-built drawings.

A. As-built plans shall be provided prior to: the issuance of building permits for single-family residential subdivisions, the issuance of occupancy permits for projects subject to site plan review, and within sixty days following completion of construction for other projects; and

B. All plans submitted shall be reproducible and on mylar; and

C. The as-built plans submittal shall be stamped, signed and dated by licensed professional engineer, registered in the state of Washington.

D. As-built plans shall be maintained and updated on-site during construction. (Ord. 96-802 § 7, 1996)

18.250.130 General standards for water quality treatment.

A. All projects shall provide treatment of stormwater runoff through the use of BMPs specified in this section.

B. Treatment BMPs shall be sized to capture, hold and treat the water quality design storm, defined as one-third of the two-year, twenty-four-hour storm precipitation.

C. If site conditions are appropriate and groundwater quality will not be impaired, infiltration is the preferred BMP. All discharges to groundwater shall comply with the following state laws: the Water Pollution Control Act (Chapter 90.48 RCW), the Water Resources Act (Chapter 90.54 RCW), and Water Quality Standards for Ground Waters of the state of Washington (Chapter 173-200 WAC). Infiltration may be limited near public water supply wells.

D. The BMPs cited in this section shall be cited, designed and constructed in accordance with the requirements detailed in the Puget Sound Manual for each BMP, with the following exceptions:

1. For biofiltration swales (RB.05) and vegetative filter strips (RB.10) alternative design criteria from the publication “Biofiltration Swale Performance, Recommendations, and Design Considerations - Appendix G” by the municipality of metropolitan Seattle, water pollution control department, dated October 5, 1992 shall be used.

2. Where provisions of this chapter conflict with the Puget Sound Manual or other cited design guidance, this chapter shall take precedence.

E. All 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).

F. Treatment of runoff from sidewalks and bike paths is not required if the stormwater drains away from roadways. Runoff from sidewalks and bike paths that mix with roadways will require treatment. (Ord. 96-802 § 8, 1996)

18.250.140 Standard best management practices.

A. Standard stormwater treatment BMPs shall be used to treat stormwater in the city.

B. Acceptable standard treatment BMPs include the following from the Puget Sound Manual (Chapters III-3, III-4 and III-6):

1. RI.05 - WQ infiltration basin;

2. RI.10 - WQ infiltration trench;

3. RI.15 - Roof downspout system;

4. RD.09 - Constructed wetland;

5. RD.06 - Wet pond with marsh;

6. RD.05 - Wet pond without marsh;

7. RB.05 - Biofiltration swale;

8. RB.10 - Vegetative filter strip;

9. RF.05 - Sand filtration basin;

10. RF.10 - Sand filtration trench.

C. Sand filtration BMPs (RF.05 and RF.10) are not allowed on commercial or industrial sites where the effluent from the treatment systems will drain to groundwater.

D. For biofiltration swales and vegetative filter strips, the hydraulic residence shall be between five and nine minutes. Swale slopes may not be less than 0.5 percent.

E. Infiltration BMPs shall not be used as temporary erosion control devices.

F. Alternative roof downspout systems that provide an equivalent level of performance to the system in the Puget Sound Manual (RI.15) may be approved by the director. (Ord. 96-802 § 9, 1996)

18.250.150 Source control best management practices.

In addition to the other water quality treatment requirements in this section, commercial, industrial and public works development activities shall meet the source control BMPs specified in Chapters IV-2, IV-3 and IV-4 of the Puget Sound Manual. (Ord. 96-802 § 10, 1996)

18.250.160 Oil/water separators.

A. The following development activities require API or CPS-type oil/water separators:

1. Industrial machinery and equipment, trucks and trailer, aircraft, parts and aerospace, railroad equipment;

2. Log storage and sorting yards;

3. Airfields and aircraft maintenance;

4. Fleet vehicle yards;

5. Railroads;

6. Gas stations;

7. Retail/wholesale vehicle and equipment dealers;

8. Vehicle maintenance and repair;

9. Construction businesses such as paving, heavy equipment storage and maintenance, storage of petroleum products (this does not include construction sites);

10. 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. Multi-family residential projects creating parking spaces for twenty-five or more vehicles;

3. Other activities where the risk of oil spills or illegal dumping of oil or grease is significant.

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 III, Section III-7 of the Puget Sound Manual. (Ord. 96-802 § 11, 1996)

18.250.170 Infiltration best management practices on industrial and commercial sites.

A. Infiltration of stormwater runoff may not be allowed on commercial industrial sites which, due to location or the proposed use, pose a significant threat of contamination to groundwater.

B. Approval for use of infiltration BMPs (RI.05-30 in the Puget Sound Manual) on industrial and commercial sites, including gas stations, shall be conditioned on all the following criteria, unless found inappropriate by the director:

1. Analysis of the potential for groundwater contamination from the site. This analysis shall include a soils and groundwater evaluation if deemed appropriate by the director;

2. Demonstration that no other feasible alternative exists for disposing of stormwater from the site;

3. A state waste discharge permit, as described in WAC 173-216, obtained from the state of Washington Department of Ecology, where required by the state, and other state permits and approvals as appropriate.

C. The requirements of subsection A of this section shall not apply to runoff from portions of a site where the risk of groundwater contamination is no greater than single-family residential sites. Examples of these areas include rooftop drainage, runoff from undeveloped portions of a site, and drainage from portions of parking lots where the risk of illegal dumping is minimal.

D. In cases where infiltration is allowed on commercial and industrial sites and a significant risk of groundwater contamination exists, the director may require groundwater monitoring to insure against groundwater contamination. The director may also require an agreement from the applicant for full mitigation in the event of groundwater contamination.

E. The provisions of this section do not apply to nonindustrial and noncommercial sites that are defined under the NPDES permit system as industrial due to temporary construction activity. (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 Puget Sound Manual.

B. Experimental BMPs may be allowed if all the following conditions are met:

1. The experimental BMP usage is part of a Department of Ecology or city of Battle Ground research project.

2. Monitoring of the effluent quality produced by the BMP, as well as influent quality, will be conducted for at least two years.

3. Results of the research will be published.

4. Financing is available to construct the BMP, conduct the testing, and publish the results. (Ord. 96-802 § 13, 1996)

18.250.190 Drainage structure labeling and signage.

A. All catchbasins and manholes capable of accepting stormwater shall be stenciled. For infiltration systems stenciling shall read:

Please protect — Drains to drinking water

For facilities draining to surface waters the stenciling shall read:

Please protect — Drains to (name of waterbody)

B. Signs shall be installed along water quality biofiltration systems that read:

Water Quality Filter — Please Leave Vegetated

(Ord. 96-802 § 14, 1996)

18.250.200 General standards of quantity control.

A. All projects shall provide quantity control of stormwater runoff in accordance with the requirements of this section.

B. Natural drainage flow routes through streams shall be maintained, and discharges from the site shall occur at the natural location and elevation, to the maximum extent practical.

C. Transfer of runoff from one basin to another shall not be allowed.

D. Surface water exiting a parcel shall be discharged with adequate energy dissipators within the development site to prevent downstream damage.

E. 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. 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 man-made channels within the city of Battle Ground.

F. Where provisions of this chapter conflict with the Puget Sound Manual or other cited design guidance, this chapter shall take precedence. (Ord. 96-802 § 15, 1996)

18.250.210 Hydrologic and hydraulic analysis.

A. Hydrologic and hydraulic analysis shall be in accordance with Chapters III-1 and III-2 of the Puget Sound Manual, with the following exceptions:

1. Table III-1.6, “Hydrologic Soil Groups for Soils in the Puget Sound Basin” is replaced by “Hydrologic Soil Groups for Soils in Clark County,” (Exhibit B). (Source: SCS TR-55, Second Edition, June 1986, Exhibit A-1. Revisions made from SCS, Soils Interpretation Record, Form #5, September 1988.) Alternatively, hydrological soil groups can be developed by a registered soil scientist using criteria set in the USDA, SCS National Soils Handbook.

2. Appendix AIII-1.1, “Isopluvial Maps for Design Storms” is replaced by “Isopluvial Maps for Design Storms in Clark County,” (Exhibit C). (Source: NOAA Atlas 2, “Precipitation - Frequency Atlas for the Western United States,” Volume IX, Washington.)

3. The “HEC-1 Flood Hydrograph Package” computer program, developed by the Hydrologic Engineering Center, U.S. Army Corps of Engineers is an acceptable hydrologic computation program for use in the city.

4. Design of stormwater collection systems shall be in accordance with Hydraulic Engineering Circular #12, “Drainage of Highway Pavements,” 1984 edition, published by the United States Department of Transportation, Federal Highway Administration (FHWA).

B. Table III-1.3, “SCS Western Washington Runoff Curve Numbers” of the Puget Sound Manual shall be used to calculate predevelopment and postdevelopment runoff. (Ord. 96-802 § 16, 1996)

18.250.220 Design methodology for quantity control facilities.

A. Except as limited by BGMC 18.250.170 for commercial and industrial sites, infiltration of the one-hundred-year storm is required for all stormwater discharges from development sites where local soil types and groundwater conditions are suitable (in general, soils from hydrologic groups “A” and “B” with low seasonal water table); provided, that water quality treatment as detailed in BGMC 18.250.130 is provided prior to infiltration.

B. The design infiltration rate for infiltration systems shall be limited to half the percolation rate. Percolation rates shall be tested on-site for all soils.

C. The director may allow the base of infiltration facilities to be less than three feet above seasonal high water or an impermeable layer if the quality and quantity control requirements of this chapter can be met.

D. For surface runoff leaving a development 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 predevelopment design storm peak runoff rates.

3. After meeting the requirements of subsections (D)(1) and (D)(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 III-1.1 in Section III of the Puget Sound Manual. 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.

E. To insure the standards in this section are met, the volume available for storing runoff in a stormwater facility shall be reduced by high seasonal groundwater and/or ordinary high water.

F. Residential and commercial structures shall be designed to direct roof runoff to downspout roof systems in areas that contain soil groups A, B and C, where the infiltration rate is equal to or greater than four inches per hour. The system shall be designed to discharge the two-year developed storm into the ground. For design purposes one-half of the infiltration rate shall be used. Percolation tests shall be provided for all proposed roof downspout systems prior to final stormwater plan approval. Short plats, subdivisions of four lots or less and single-family home construction on lots of record may utilize the SCS infiltration rates for design purposes. Infiltration is not required in areas having steep slopes as defined in BGMC 18.250.030.

G. Design of stormwater control facilities shall be in accordance with the following methods from the Puget Sound Manual (Chapters III-1 and III-3):

1. Section III-1.4.4 - Hydrograph Routing;

2. Section III-1.4.5 - Hydrograph Summation and Phasing;

3. Section III-1.4.6 - Computer Applications;

4. Section III-1.5 - Closed Depression Analysis;

5. Section III-3.3 - Feasibility Analysis and General Limitations for Infiltration BMPs;

6. Section III-3.4 - General Design Criteria for Infiltration and Filtration BMPs;

7. Section III-3.5 - Construction and Maintenance;

8. Section III-4.3 - General Design Criteria;

9. Section III-4.4 - Standards and Specifications for Detention Ponds. (Ord. 96-802 § 17, 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 a 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.

F. 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.

G. For the ten-year storm, street ponding shall be limited to one-half of the roadway area and shall not exceed the capacity of the inlet or produce a flow depth of greater than 0.12 feet at the edge of the travel lane.

H. 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.

I. 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 18.250.220 for the one-hundred-year storm.

J. Design of conveyance systems shall be in accordance with Chapter III-2 of the Puget Sound Manual.

K. Design of bridges shall be in accordance with the state of Washington Department of Transportation Bridge Design Standards, 1991 edition.

L. Stormwater easements shall be provided to the city for access and maintenance of all conveyance systems within the development site which are to be maintained by the city. The minimum widths of easements shall be as follows, although the director may require increased widths when necessary to insure adequate area for equipment access and maintenance:

1. Pipes with I.D. less than or equal to thirty-six inches: twenty feet;

2. Pipes with I.D. greater than thirty-six inches: twenty feet plus pipe I.D.;

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.

M. No buildings or other structures which prevent access are permitted within easements. Fences crossing easements shall provide gates of sufficient width over the easement for access by maintenance vehicles. (Ord. 96-802 § 18, 1996)

18.250.300 City 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 outside public road rights-of-way is not required where the applicant demonstrates to the satisfaction of the director that the stormwater facilities can be adequately maintained by private parties.

C. City ownership of stormwater facilities is required where the city will assume long-term maintenance of the facilities. (Ord. 96-802 § 19, 1996)

18.250.310 Initial maintenance.

A. To insure satisfactory operation of new stormwater facilities, the applicant constructing the facility shall maintain it for two years after completion of the project.

B. In cases where the stormwater facility is within a public road right-of-way or on land owned by the city, the applicant constructing the facility, after satisfactory completion of the stormwater facilities and as a condition of acceptance of such facilities by the city, shall commence a two-year period of maintenance of the facility. The applicant shall satisfactorily maintain the facility and repair any failure within this two-year period. Additionally, 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 ten percent of the construction cost of the stormwater facilities. (Ord. 96-802 § 20, 1996)

18.250.320 Long-term maintenance.

A. The city shall provide long-term maintenance of new stormwater facilities under any of the following situations:

1. Facilities located in public road rights-of-way; or

2. Facilities dedicated to the city.

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

1. The requirements in BGMC 18.250.310 shall be completed;

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

3. 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 city auditor.

C. For stormwater facilities for which the city will not provide long-term maintenance, the applicant shall make arrangements with the existing or future (as appropriate) occupants or owners of the subject property for assumption of maintenance in a manner subject to the approval of the director. Such arrangements shall be approved prior to city approval of the final stormwater plan and completed prior to the end of the two-year initial maintenance period of the applicant’s responsibility or in the case of plats, prior to the time of recording.

D. The city shall inspect privately maintained facilities for compliance with the requirements of this chapter. 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.

E. Easements or a covenant acceptable to the director shall be provided to the city for purposes of inspection of privately maintained facilities. The minimum dimensions of easements for stormwater facilities are as follows:

1. Sufficient width around a treatment or storage pond to encompass the pond plus the additional area necessary for equipment access;

2. Pond design and easements shall allow access to all areas within the pond by standard maintenance equipment vehicles;

3. Widths of easements for conveyance facilities shall be as detailed in BGMC 18.250.230(L).

F. Final plats shall include a note specifying the party(s) responsible for long-term maintenance of stormwater facilities. (Ord. 96-802 § 21, 1996)

18.250.330 Location of stormwater facilities.

A. Treatment, runoff control, and recharge 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. Stormwater facilities, other than closed conveyance systems, shall be located at least one hundred feet from existing and proposed on-site sewage system drainfields.

C. Infiltration systems used for stormwater disposal shall be located at least one hundred feet from domestic water supply wells.

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.

E. Sites used for stormwater treatment and runoff control facilities shall be owned by the applicant, city or state, and:

1. If the site is owned by the city or state, a letter from the responsible agency allowing use of the site for stormwater control shall be submitted with the stormwater plan.

2. If the site is not owned by the city or state and the proposal involves a development activity, the stormwater control site shall be included for consideration with the land use application for the development activity.

F. Stormwater treatment and control facilities in urban residential subdivisions and short plats shall be located on separate tracts which are recommended, but not required, to meet minimum zoning lot size requirements. The plat or other dedication instrument shall indicate tract disposition in the event of city abandonment or vacation. (Ord. 96-802 § 22, 1996)

18.250.340 Protection of infiltration systems from erosion.

Stormwater infiltration systems shall be isolated and protected from sedimentation due to erosion during the construction phase of a development activity or drainage project. Furthermore, use of infiltration systems shall be minimized until the erodible parts of a site are stabilized with adequate vegetation. (Ord. 96-802 § 23, 1996)

18.250.350 Fencing of stormwater facilities.

A. Stormwater treatment and runoff control facilities located in or adjacent to residential areas shall be fenced unless these facilities are constructed as part of a project amenity such as a park or the director waives the fencing requirement due to special circumstances.

B. Stormwater treatment and runoff control facilities, other than those described in subsection A of this section, shall be fenced if they pose safety risks to the public.

C. The size and type of fence shall be determined by the director. (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 3:1.

B. Side slopes steeper than 3:1 may be allowed by the director for specialized projects, such as streambank reconstruction, where all the following conditions are met:

1. Side slopes do not need to be mowed,

2. Adequate long-term erosion control is provided. (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 (See RCW 35.91.010):

1. Oversizing on-site facilities above their existing capacity or the capacity required for the proposed development;

2. A proportionate share of the total cost of off-site facilities.

B. If a stormwater utility exists, the costs for building or oversizing a stormwater facility may be eligible as a credit against applicable system development charges. (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 shall post a performance bond or other security acceptable to the director in the amount of the 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 maintenance bonding requirements of Sections 18.250.310 and 18.250.320 are met, the performance bond or security shall be released.

B. Maintenance Security. In cases identified in BGMC 18.250.310, 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. 96-802 § 27, 1996)

18.250.400 Basin plans.

Adopted basin plans are identified in the storm drainage master plan of the city of Battle Ground of August, 1983. (Ord. 96-811 § 1, 1996: Ord. 96-802 § 28, 1996)

18.250.410 Regional and subregional facilities.

A. If regional or subregional facilities are used to meet some or all of the standard requirements of Sections 18.250.100 through 18.250.380, the following conditions shall be met:

1. Stormwater runoff shall be transported from a development site to a regional/subregional facility through a pipe or manmade open channel conveyance system.

2. If the regional/subregional facility does not yet exist, interim quantity control and treatment methods shall be used to meet the standard requirements of Sections 18.250.100 through 18.250.380. All interim methods shall be reviewed and shall require written approval by the director.

3. The facility must have sufficient capacity to provide the treatment and quantity control specified in Sections 18.250.100 through 18.250.380

4. A written commitment from the owner of the facility, or the director in the case of city-owned facilities, shall be; provided, that allows use of the facility by the applicant.

5. The city encourages multiple users of stormwater facilities. Review of designs of these types of facilities shall be expedited by the city and receive priority review.

B. Where a stormwater utility exists, a system development charge can be assessed for use of a regional/subregional facility. (Ord. 96-811 § 2, 1996: Ord. 96-802 § 29, 1996)

18.250.500 General.

A. Variance requests require a public hearing before the planning commission. Notice and appeal requirements will be the same as those provided for preliminary subdivision plat.

B. Variances shall be valid only for the life of the land use application permit or approval. (Ord. 96-802 § 30, 1996)

18.250.510 Variances—Hardship.

If application of the standard requirements of Sections 18.250.100 through 18.250.380 will preclude all reasonable use of a parcel, an applicant can make a written request for a waiver from some or all of the standard requirements found in said sections. For the variance request to be considered, the applicant must demonstrate all of the following:

A. The proposed activities will not cause significant degradation of groundwater or surface-water quality;

B. The proposed activities comply with all state, local and federal laws, including those related to sediment control, pollution control, floodplain and floodway restrictions, and wetland protection;

C. No material damage to nearby public or private property nor significant threat to the health or safety of people on or off the property will occur; and

D. The inability to derive any reasonable use of the property is not the result of actions by the applicant in segregating or dividing the property and creating the undevelopable condition after the effective date of the ordinance codified in this chapter. (Ord. 96-811 § 3, 1996: Ord. 96-802 § 31, 1996)

18.250.520 Other governmental agency projects.

The bonding and insurance requirements of BGMC 18.250.380 shall be waived for development activities and drainage projects undertaken by governmental agencies. (Ord. 96-802 § 32, 1996)

18.250.530 Single-family home construction.

The construction of single-family homes, duplexes, triplexes, and their accessory structures that fall into one of the categories below and meet the conditions stated for that category, are exempt from the provisions of this chapter.

A. Previously Reviewed and Approved Site. The development site or parcel is included in an approved final stormwater plan that meets the requirements of this chapter or a stormwater plan was approved that provided for detention or retention of runoff from residential lots.

B. Existing Lots of Record. All residential structures built on A, B or C soils shall be constructed with roof downspout systems in accordance with BGMC 18.250.220(F). (Ord. 96-811 § 4, 1996: Ord. 96-802 § 33, 1996)

18.250.540 Small residential projects.

A. Qualifying Projects. Small residential projects include single-family residential short plats and subdivisions of four lots or less.

B. Treatment and Runoff Control Requirements. Small residential projects that create less than two thousand five hundred square feet of new impervious surface, after deducting houses that utilize roof downspout systems, shall be exempt from the quantity and quality control requirements of this chapter. A final stormwater plan is required if stormwater is conveyed off-site.

C. Information Requirements. The submittal requirements (Sections 18.250.100 through 18.250.190) for small residential projects are modified as follows:

1. A hydrology report (BGMC 18.250.110(C)(2)) shall not be required, however, sufficient information and data shall be provided with the final stormwater plan to allow the director to determine conformance with the applicable provisions of this chapter. (Ord. 96-802 § 34, 1996)

18.250.550 Portable school buildings.

Temporary portable school buildings shall be exempt from the quantity and quality provisions of this chapter, provided the buildings utilize roof downspout systems. A final stormwater design that addresses disposal of stormwater shall be required. (Ord. 96-802 § 35, 1996)

18.250.560 Other exemptions.

A. Drainage Projects.

1. Drainage projects that are not a part of a development activity are exempt from the water quality treatment provisions of this chapter (BGMC 18.250.130).

2. For drainage projects that are not part of a development activity, the director may waive all or parts of the submittal requirements (Sections 18.250.100 through 18.250.190), maintenance and ownership requirements (BGMC 18.250.300), and bonding and insurance requirements (BGMC 18.250.380) if the project meets the other appropriate parts of this chapter. (Ord. 96-802 § 36, 1996)

18.250.600 Contents of a stormwater plan.

The stormwater plan required pursuant to BGMC 18.250.110 shall contain the information listed below. All maps shall contain a scale and north arrow. Insuring 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.

B. Development Plan. The development plan 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 with a two-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; and

8. Approximate location and size of proposed stormwater facilities, including typical cross-sections of proposed facilities.

C. Additional Site and Vicinity Information.

1. If wetlands exist on the site and will be impacted by the proposal, a wetland delineation report shall be required.

2. In areas of high groundwater, water table elevations, flow directions (where available), and data on seasonal water table fluctuations with minimum and maximum water table elevations (where available) shall be required.

3. For sloping sites, a conceptual grading plan verifying the constructability of a stormwater facility shall be required.

4. The director may require additional site or vicinity information if needed to determine the feasibility of the stormwater proposal.

D. Signatures. All plans and reports shall be stamped, signed and dated by the professional civil engineer(s), registered in the state of Washington, and registered soil scientist, if appropriate. (Ord. 96-802 § 37, 1996)

18.250.610 Contents of the hydrology report.

The hydrology report, which is part of the final stormwater plan, shall contain the following information:

A. 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;

5. List of references.

B. 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. Contributing drainage areas and acreage,

b. Natural and man-made drainage features adjacent to site including existing and proposed (if known) stormwater facilities; and

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 registered 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 1:5000 (twelve and seven-tenths in./mi.).

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

a. Conveyance System. If a 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 waterbody 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 FEMA 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.

C. Development Plan. The development plan, which can be combined with the final engineering plans, shall include the following additional information:

1. Delineate subbasins and show sub-basin acreage used in hydraulic/hydrologic calculations;

2. Existing and proposed contours (two-foot maximum contour interval);

3. Show directions and lengths of overland, pipe and channel flow;

4. Indicate outfall points and overflow routes for the one-hundred-year storm;

5. Show storage volumes, pipe and weir invert elevations, and lengths of weir for stormwater control facilities;

6. Show all existing and proposed easements and rights-of-way;

D. Project Overview.

1. Describe drainage to and from adjacent properties.

2. Generally describe proposed site construction, size of improvements, and proposed methods of mitigating stormwater runoff quantity and quality impacts.

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; 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 subbasins. 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;

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;

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. 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.

G. 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.

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 and design methods for use in hydrologic and hydraulic design of proposed facilities;

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 Section III-3.3.3 of the Puget Sound Manual.

I. Special Reports and Studies. Where specific site characteristics such as 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;

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 and stormwater 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 shall list the titles of all other required permits, the agencies requiring the permits, and identify the permit requirements, if known, that affect the final 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.

K. Maintenance and Operations Manual. For each stormwater control or treatment facility which is to be privately maintained and for those which constitute an experimental system under BGMC 18.250.180 to be maintained by the city, 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. Use of the maintenance procedures outlined in the Puget Sound Manual for various BMPs is encouraged. (Ord. 96-802 § 38, 1996)