(a) Stormwater Management Plan Required for All Developments.
(1) No application for development will be approved unless it includes a stormwater management plan detailing in concept how runoff and associated water quality impacts resulting from the development will be controlled or managed. This plan must be prepared by an individual approved by the City of Dunbar and must indicate whether storm water will be managed on-site or off-site and, if on-site, the general location and type of practices.
(2) The stormwater management plan(s) shall be referred for comment to all other interested agencies, and any comments must be addressed in a final stormwater management plan. This final plan must be signed by a licensed professional engineer (PE), who will verify that the design of all storm water management practices meet the submittal requirements outlined in the Submittal Checklist found in the stormwater design manual. No building, grading, or sediment control permit shall be issued until a satisfactory final stormwater management plan, or a waiver thereof, shall have undergone a review and been approved by the City of Dunbar after determining that the plan or waiver is consistent with the requirements of this article.
(b) Stormwater Management Concept Plan Requirements.
(1) A stormwater management concept plan shall be required with all permit applications and will include sufficient information (e.g., maps, hydrologic calculations, etc) to evaluate the environmental characteristics of the project site, the potential impacts of all proposed development of the site, both present and future, on the water resources, and the effectiveness and acceptability of the measures proposed for managing stormwater generated at the project site. The intent of this conceptual planning process is to determine the type of storm water management measures necessary for the proposed project, and ensure adequate planning for management of storm water runoff from future development. To accomplish this goal the following information shall be included in the concept plan:
A. A map (or maps) indicating the location of existing and proposed buildings, roads, parking areas, utilities, structural stormwater management and sediment control facilities. The map(s) will also clearly show proposed land use with tabulation of the percentage of surface area to be adapted to various uses; drainage patterns; locations of utilities, roads and easements; the limits of clearing and grading. A written description of the site plan and justification of proposed changes in natural conditions may also be required.
B. Sufficient engineering analysis to show that the proposed storm water management measures are capable of controlling runoff from the site in compliance with this article and the specifications of the Stormwater Design Manual.
C. A written or graphic inventory of the natural resources at the site and surrounding area as it exists prior to the commencement of the project and a description of the watershed and its relation to the project site. This description should include a discussion of soil conditions, forest cover, topography, wetlands, and other native vegetative areas on the site. Particular attention should be paid to environmentally sensitive features that provide particular opportunities or constraints for development.
D. A written description of the required maintenance burden for any proposed storm water management facility.
(2) The City of Dunbar may also require a concept plan to consider the maximum development potential of a site under existing zoning, regardless of whether the applicant presently intends to develop the site to its maximum potential.
(3) For development or redevelopment occurring on a previously developed site, an applicant shall be required to include within the stormwater concept plan measures for controlling existing stormwater runoff discharges from the site in accordance with the standards of this article to the maximum extent practicable.
(c) Final Stormwater Management Plan Requirements. After review of the storm water management concept plan, and modifications to that plan as deemed necessary by the City of Dunbar, a final storm water management plan must be submitted for approval. The final stormwater management plan, in addition to the information from the concept plan, shall include all of the information required in the Final Stormwater Management Plan checklist found in the Stormwater Design Manual. This includes:
(1) Contact Information. The name, address, and telephone number of all persons having a legal interest in the property and the tax reference number and parcel number of the property or properties affected.
(2) Topographic Base Map. A 1" = 200' topographic base map of the site which extends a minimum of feet beyond the limits of the proposed development and indicates existing surface water drainage including streams, ponds, culverts, ditches, and wetlands; current land use including all existing structures; locations of utilities, roads, and easements; and significant natural and manmade features not otherwise shown.
(3) Calculations. Hydrologic and hydraulic design calculations for the pre-development and post-development conditions for the design storms specified in this article. Such calculations shall include:
A. Description of the design storm frequency, intensity and duration,
B. Time of concentration,
C. Soil Curve Numbers or runoff coefficients,
D. Peak runoff rates and total runoff volumes for each watershed area,
E. Infiltration rates, where applicable,
F. Culvert capacities,
G. Flow velocities,
H. Data on the increase in rate and volume of runoff for the design storms referenced in the Storm water Design Manual, and
I. Documentation of sources for all computation methods and field test results.
(4) Soils Information. If a storm water management control measure depends on the hydrologic properties of soils (e.g., infiltration basins), then a soils report shall be submitted. The soils report shall be based on on-site boring logs or soil pit profiles. The number and location of required soil borings or soil pits shall be determined based on what is needed to determine the suitability and distribution of soil types present at the location of the control measure.
(5) Maintenance and Repair Plan. The design and planning of all storm water management facilities shall include detailed maintenance and repair procedures to ensure their continued function. These plans will identify the parts or components of a storm water management facility that need to be maintained and the equipment and skills or training necessary. Provisions for the periodic review and evaluation of the effectiveness of the maintenance program and the need for revisions or additional maintenance procedures shall be included in the plan.
(6) Landscaping Plan. The applicant must present a detailed plan for management of vegetation at the site after construction is finished, including who will be responsible for the maintenance of vegetation at the site and what practices will be employed to ensure that adequate vegetative cover is preserved. This plan must be prepared by a registered landscape architect or by the soil conservation district.
(7) Maintenance Easements. The applicant must ensure access to all stormwater treatment practices at the site for the purpose of inspection and repair by securing all the maintenance easements needed on a permanent basis. These easements will be recorded with the plan and will remain in effect even with transfer of title to the property.
(8) Maintenance Agreement. The applicant must execute an easement and an inspection and maintenance agreement binding on all subsequent owners of land served by an on-site storm water management measure in accordance with the specifications of this article.
(9) Erosion and Sediment Control Plans for Construction of Storm Water Management Measures. The applicant must prepare an erosion and sediment control plan for all construction activities related to implementing any on-site stormwater management practices.
(10) Other Environmental Permits. The applicant shall assure that all other applicable environmental permits have been acquired for the site prior to approval of the final storm water design plan.
(d) Performance Bond/Security.
(1) The City of Dunbar may, at its discretion, require the submittal of a performance security or bond prior to issuance of a permit in order to insure that the stormwater practices are installed by the permit holder as required by the approved stormwater management plan.
(2) The amount of the installation performance security shall be the total estimated construction cost of the stormwater management practices approved under the permit, plus 25%. The performance security shall contain forfeiture provisions for failure to complete work specified in the stormwater management plan.
(3) The installation performance security shall be released in full only upon submission of "as built plans" and written certification by a registered professional engineer that the stormwater practice has been installed in accordance with the approved plan and other applicable provisions of this article. The City of Dunbar will make a final inspection of the stormwater practice to ensure that it is in compliance with the approved plan and the provisions of this article. Provisions for a partial pro-rata release of the performance security based on the completion of various development stages can be done at the discretion of the City of Dunbar.
(Ord. 654. Passed 7-6-10.)