The following criteria shall control when designing stormwater quality control structures:
(A) Water quality control structures. In addition to carrying pollutants, stormwater runoff from developed areas increases the frequency and duration of full-bank flows in the receiving streams, causing increased erosion of the stream banks and further degradation of in-stream water quality, on-site infiltration, designed for the increased runoff due to development, is the preferred solution to this impact. A water quality control facility must capture and treat the 80th percentile rainfall event "first flush", or the runoff volume corresponding with a 0.61 - inch rainfall event. The water quality volume for sizing green infrastructure BMPs shall be computed as follows:
Rv = 0.009(1) + 0.05
Where:
Rv = volumentric runoff coefficient; and
I = the percent imperviousness of the drainage area.
WQV = 3,630 x Rv x P x A
Where:
3,630 = conversion factor from acre - inches to cubic feet;
WQV = water quality volume (ft3);
Rv = volumetric runoff coefficient;
P = rainfall depth associated with the 80th percentile precipitation event (in.), equivalent to a rainfall event of 0.61 inches; and
A = drainage area to BMP (acres).
(B) Stormwater quality plan. The final stormwater quality plan for the entire development shall include, but not be limited to, the following:
(1) All calculations, assumptions and criteria used in the design of the stormwater quality control structures.
(2) Location, dimensions and design details required for the construction of all facilities.
(3) A description of the operation and maintenance needs for the stormwater quality control structures.
(4) All deed restrictions, easements and rights-of-way.
(5) The ownership and maintenance responsibilities for all stormwater quality control structures during and after development. The identity of the responsible individual, corporation, association or other specific entity and the specific maintenance activities and schedule must be outlined on the plan.
(6) Stormwater quality management facilities shall be designed to effectively treat the required amount of water quality runoff volume for the developed site.
(7) Project narrative and summary from existing conditions to proposed conditions showing that applicable ordinances are met.
(C) Design certification. Design of all stormwater quality facilities shall be prepared and stamped by a licensed professional engineer (Kentucky registration required). Design methods shall be in accordance with the Kentucky Department of Highways' Manual of Instructions for Drainage Design, latest edition and City of Madisonville Standards Guidance for Development.
(D) Construction certification. Prior to final approval of the development, the licensed professional engineer must submit certification that the stormwater quality control structures were constructed in accordance with the approved plan. Final approval shall also provide evidence of the recording of all stormwater conveyance, management, and water quality facilities deed restrictions, easements and rights-of-way. Any request for deviation from the approved plan during construction shall be submitted to the City Engineer in writing for approval.
(E) Ownership, operation and maintenance of stormwater control and water quality management facilities. For all developments requiring stormwater control and water quality management facilities, ownership and maintenance responsibilities remain with the property owner/developer. The Stormwater Management/BMP Facilities Long-term Maintenance Agreement must be signed, notarized, and submitted with the stormwater quality management plan.
(F) Additional treatment and monitoring may be required. The city reserves the right to require for new and redeveloped properties superseding or additional treatment criteria or objectives for specific pollutant(s) as necessary to meet overall stormwater quality management program objectives or directives under a watershed improvement or Total Maximum Daily Load (TMDL) program or KPDES/NPDES permit program as administered by the USEPA or Commonwealth of Kentucky.
(G) Self inspection required. The property owner shall provide annual self-inspection documentation for water quality management facilities as outlined in the Stormwater Management/BMP Facilities Agreement. The City Engineer or his/her designee will periodically inspect water quality management facilities for the purpose of identifying maintenance and structural deficiencies and if required proof of monitoring. If additional treatment and or monitoring is required, the property owner shall be fully responsible for monitoring their stormwater management and water quality facilities in accordance with the most recent directives under a watershed improvement or Total Maximum Daily Load Program or KPDES/NPDES permit program as administered by the USEPA or Commonwealth of Kentucky. In the event a deficiency is discovered a notice of violation will be issued and shall be enforced under this code.
(H) In lieu of fee or off site mitigation program may be established. The City of Madisonville Engineering Department may develop a payment-in-lieu program to allow property owners/developers to make payment to the city in lieu of constructing stormwater quality management structures. The in lieu of fee funds shall be applied to public stormwater projects. Another option is to allow the property owner/developer to provide off site mitigation in the same watershed. Both of these options may be developed by the City of Madisonville Engineering Department following the permit requirements of the KPDES Permit For Small Municipal Separate Storm Sewer Systems.
(Ord. O-2019-20, passed 12-16-19)