(A) In order to comply with the city's permanent stormwater standards for new development and redevelopment projects, design and install SCMs as established by Tennessee Rule 0400-40-10-.04 and comply with other requirements of Tennessee Rule 0400-40-10-.04. Note that for design purposes, total suspended solids (TSS) may be used as the indicator for the reduction of pollutants.
(B) SCMs must be designed to provide full treatment capacity within 72 hours following the end of the preceding rain event for the life of the new development or redevelopment project. The designer may select from the most appropriate alternatives listed in the city's BMP Manual.
(C) Designs shall be based on the 24-hour design storm adopted by the city:
(1) The city has adopted, for use in designing water quality SCMs, the design storm requirements as established in Tennessee Rule 0400-40-10-.04. The post construction/permanent water quality design storm is a 1-year, 24-hour storm event for water quality SCMs. See definition of design storm event for the municipality's rainfall amounts for each return period interval.
(a) Anyone disturbing one or more acres: 1-year 24-hour Water Quality= 3.02
(2) Any commercial or industrial site must submit calculations for the 2-year, 5-year, and 10-year storm designs. If post construction runoff flows are increased by two cubic feet per second (cfs) from pre development flows, the following storm designs are required:
(a) 2-year: Water Quantity= 3.61
(b) 5-year: Water Quantity = 4.40
(c) 10-year: Water Quantity = 5.02
(D) Water quality riparian buffers. Post construction/permanent water quality riparian buffers shall be those buffers defined in § 14-802 and shall meet the requirements described in this chapter. The criteria for the width of the post construction/permanent buffer zone can be established on an average width basis at a project, as long as the minimum width of the buffer zone is more than the required minimum width at any measured location. If the new development or redevelopment site encompasses both sides of a stream, buffer averaging can be applied to both sides, but must be applied independently. Water quality riparian buffer widths are measured from the top of bank also referred to as the "ordinary high-water mark." Stormwater discharges should enter the post construction/permanent water quality riparian buffer as sheet flow, not as concentrated flow, where site conditions allow.
(E) Post construction/permanent buffers for waters with available parameters for siltation or habitat alteration or unassessed waters:
(1) Average buffer width: 30 feet.
(2) Minimum buffer width: 15 feet.
(F) The designer/operator must comply with the vegetation requirements and the permissible land uses set forth for buffers in the MS4 permit.
(Ord. 7122, passed 8-13-2024)