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(A) Standards generally. Design standards are established for the purpose of promoting sound development practices which respect, preserve and enhance the county’s watercourses and are not intended to prohibit the use of innovative and alternative techniques which can be demonstrated to have the potential for successfully achieving the objectives stated in § 52.01.
(B) Design storm.
(1) The measures shall control and treat the difference in stormwater runoff volume leaving the project site between the pre- and post-development conditions for, at a minimum, the one-year, 24-hour storm. Runoff volume drawdown time shall be a minimum of 48 hours, but not more than 120 hours.
(2) All structural stormwater treatment systems used to meet the requirements of this chapter shall be designed to have a minimum of 85% average annual removal for total suspended solids (TSS).
(3) The hillside development standards of Ch. 70 of the county’s code of ordinances (§ 20-70-68) apply. This chapter limits the density of disturbed area and impervious surfaces on steep slopes.
(4) The design of drainage facilities in flood hazard areas shall be consistent with the requirements of the county’s flood damage prevention ordinance. No stormwater controls shall be allowed within the floodway. No built upon area shall be within 30 feet landward of any perennial and intermittent surface water.
(5) The computation of stormwater runoff shall follow established engineering practice. Acceptable methods of computation include the rational method, the peak discharge method as described in U.S.D.A. Technical Release Number 55 (TR-55), and U.S. Geological Survey regression equations, where applicable. If an alternate method is proposed, the method should be described and justification for using this method should be provided. The same method must be used for both the pre- and post-development conditions.
(6) Runoff coefficients shall be based on full development of the project and of the watershed to the extent of the current zoning or land use patterns, and shall include the complete development of the site through build-out, including roof tops and other impervious areas that may be proposed.
(7) (a) Stormwater detention shall be provided to ensure that the rate of discharge does not exceed the pre-development rate of discharge.
(b) In order to demonstrate this, pre- and post-development hydrographs will be submitted that demonstrate no increase in flow leaving the site during the one-year 24-hour storm. Inflow-outflow calculations shall also be submitted for any stormwater detention ponds.
(8) Stormwater controls that drain in whole or part to designated trout waters shall be designed
and shall implement the best stormwater practices that do not result in a sustained increase in the receiving water temperature, while still meeting the other requirements of this chapter.
(2013 Code, § 20-12)
The County Planning and Development Department may furnish additional guidance and standards for the proper implementation of the regulations of this chapter and may provide such information in the form of a Stormwater Design Manual. Stormwater management practices that are designed, constructed, or maintained in accord with the Stormwater Design Manual must be presumed to comply with these regulations; however, the Stormwater Administrator shall have the right to consult other engineers and duly qualified professionals, and to impose any conditions or require any modifications deemed necessary to meet the purpose, intent and requirements of this chapter.
(2013 Code, § 20-13)
(A) Stormwater management facilities shall be constructed in accordance with approved plans and maintained in proper working condition. The applicant/property owner is responsible for ensuring that the construction of drainage structures and stormwater management measures are completed in accordance with the approved plan and specifications. Inspections which may be performed by the county during construction will not relieve the developer of the responsibility to install stormwater management and drainage facilities in accordance with the approved plan.
(B) In response to a complaint, or as a compliance check with the requirements of the ordinance, the Stormwater Administrator or the designee shall perform a physical inspection of the construction of drainage structures and stormwater management measures, or monitor long-term maintenance procedures.
(C) The property owner will be notified in writing of any substandard and/or non-conforming work identified by the Stormwater Administrator. The notification shall state the specific work that is out of compliance, the specific reasons for noncompliance, and the corrective measures necessary to bring the work into compliance.
(D) Failure of the property owner or developer to correct substandard and/or nonconforming work identified by the Stormwater Administrator shall be sufficient reason to refuse or revoke building permits, and/or deny occupancy permits for buildings serviced by said work. Appeals on determination of nonconforming or substandard work and/or the adequacy of the corrective measures executed shall be made in accordance with § 52.06. Pending the ruling on the appeal, the determination of the Stormwater Administrator remains in effect.
(E) Revisions which affect the intent of the design or the capacity of the system shall require prior written approval by the Stormwater Administrator.
(2013 Code, § 20-14)
(A) The county will require the submittal of a surety performance bond made by a surety bonding company licensed and authorized to do business in the state, a bond of the owner/developer with an assignment to the county of a certificate of deposit as security for the bond, a bond of the owner/developer by an official bank check drawn in favor of the county and deposited with the county, or cash or an irrevocable letter of credit deposited with the county prior to issue of a permit in order to ensure that the stormwater system is installed by the developer and functions as required by the approved stormwater plan.
(B) The amount of an installation performance security shall be the total estimated construction cost of the system and devices approved under the permit, plus 25%.
(C) The performance security shall contain forfeiture provisions for failure, after proper notice, to complete work within the time specified, or to initiate or maintain any actions which may be required of the applicant in accordance with this chapter.
(D) Upon default of the applicant to construct, maintain, repair, and if necessary reconstruct any stormwater device in accordance with the applicable permit, the Stormwater Administrator shall obtain and use all or any portion of the security to make necessary improvements based on an engineering estimate. Such expenditure of funds shall only be made after requesting the applicant to comply with the permit. In the event of a default triggering the use of installation of performance security, the county shall not return any of the unused deposited cash funds or other security, which shall be retained for maintenance.
(E) If the county takes action upon such failure by the applicant, the county may collect the difference should the amount of the reasonable cost of such action exceed the amount of the security held. This difference will be collected from the applicant.
(F) Within 60 days of the final approval, the installation performance security shall be refunded to the applicant or terminated.
(2013 Code, § 20-15)
(A) The county may not approve a record plat, or in the case of single-lot development not requiring a record plat may not issue a building permit, until those stormwater improvements required of the developer have been completed or a performance guarantee has been provided.
(B) Upon completion of required improvements, the design professional must submit as-built plans, or certify the existing plans as-built if no changes have occurred, of the installed stormwater improvements to the Stormwater Administrator. These plans must indicate that stormwater improvements were constructed in accordance with the county ordinance and approvals.
(2013 Code, § 20-17)
All stormwater improvements must be maintained so they will continue to serve their intended functions.
(A) The developer must maintain stormwater improvements until accepted by a property owners association or lot owner. The developer must disclose which party will be responsible for continued maintenance on the record plat and on the stormwater management plan. The developer will be responsible for the installation, operations, and maintenance of the stormwater controls until ownership is conveyed. The responsibility and agreement for operations and maintenance for the stormwater system is transferred with title, as each property is conveyed.
(B) Before improvements are accepted for maintenance by the property owner’s association or lot owner, the developer or the developer’s engineer or landscape architect must certify to the property owners association or lot owner and to the county that improvements are complete and functioning as designed.
(C) The developer must record, and reference on the record plat, an operations and maintenance plan that instructs the property owners association or lot owner about the annual operations and maintenance tasks for at least a 20-year period.
(D) (1) The person responsible for maintenance of any stormwater structure or feature installed pursuant to this chapter shall submit to the Stormwater Administrator an inspection report annually from a qualified registered state professional engineer, surveyor, or landscape architect performing services only in their area of competence.
(2) The report shall contain the following:
(a) The name and address of the laud owner;
(b) The recorded book and page number of the lot of each stormwater control;
(c) A statement that an inspection was made of all stormwater controls and features;
(d) The date the inspection was made;
(e) A statement that all inspected controls and features are performing properly and are in compliance with the terms and conditions of the approved maintenance agreement required by this chapter; and
(f) The signature and seal of the engineer, surveyor, or landscape architect.
(3) All inspection reports shall be on forms supplied by the Stormwater Administrator. An original inspection report shall be provided to the Stormwater Administrator beginning one year from the date of as-built certification and each year thereafter on or before the date of the as-built certification.
(4) It will be the responsibility of the property owners association or lot owner to update the plan annually.
(E) The developer must record and reference on the record plat a maintenance agreement, or restrictive covenant that sets forth the property owner’s association’s or lot owner’s continuing responsibilities for maintenance, including specifying how cost will be apportioned among lot owners served.
(F) The maintenance agreement must provide that the association and its individual members are jointly and severably liable for maintenance.
(G) The developer must record easements for access, maintenance, and inspections by any property owners association and by county government.
(H) All maintenance documents required by this chapter must be submitted to the Stormwater Administrator before record plat approval, and such documents must be referenced on the record plat, or, in the case of single-lot developments not requiring record plats, documentation must be submitted to the Stormwater Administrator before building permit issuance.
(2013 Code, § 20-18)
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