Section 90-149. Water quality requirements.
Stormwater management systems will be evaluated based on the ability of the system to prevent degradation of receiving waters, to prevent adverse impacts on the site's natural systems, to remove pollutants and to conform to state water quality standards, as set forth in chapters 17-3 and 17-4, Florida Administrative code. The following criteria are based on the principle that the first flush of runoff contains the majority of the pollutants and that pollutant removal efficiencies differ according to the method of stormwater management and land use:
(1) retention and wet detention requirements. retention and wet detention in the overall system shall be provided for the first flush removal of pollutants with one of the two following criteria or equivalent combinations thereof:
a. Wet detention treatment volume shall be the first inch of runoff from the developed project and offsite areas draining into the treatment facility or the total runoff of 2.5 inches times the percentage of imperviousness, whichever is greater. No more than one-half the volume may be discharged in the first 60 hours. The volume in the permanent pool must provide for a residence time of at least 14 days. A littoral shelf shall be provided by extending and gently sloping the sides of the facility (at least 6:1) out to a point two to three feet below the normal water level or control elevations.
b. retention volume shall be provided equal to 50 percent of the amounts stated in subsection (1)a. of this section, computed for wet detention or runoff from the first inch of rainfall, whichever is greater. The storage must be recovered within 72 hours following rainfall.
(2) Intense land uses.
a. commercial or industrial projects shall provide at least one-half inch of pretreatment dry detention or retention.
b. Stormwater discharge facilities which receive stormwater from areas with greater than 50 percent impervious surface or which are a potential source of oil and grease contamination in concentrations exceeding applicable water quality standards shall include a baffle, skimmer, grease trap or other mechanism suitable for preventing oil and grease from leaving the discharge facility in concentrations that would contribute to violations of the water quality standards.
(3) Credit for systems with inlets in grassed areas. Systems with inlets in grassed areas will be credited with up to 0.2 inches of the required wet detention amount for the contributing areas. Full credit will be based on an impervious area to pervious area ratio of 1:10, with proportional credit granted for greater ratios.
(4) Area of special concern. All projects which discharge directly into the Indian River Lagoon or any watercourse connecting with the lagoon shall include an additional level of treatment equal to 50 percent of the regular treatment criteria, shall provide off-line treatment of the first one-half inch of runoff and shall utilize a trash collection device in the stormwater management system.
(5) Single-family and duplex sites. Facilities to accommodate only one single-family or duplex unit, unless included in section 90-132, shall provide on-site treatment equal to one-half inch of runoff over the entire site. Prior to issuance of a building permit for such sites, a stormwater permit must be approved by the building official.
Secs. 90-150--90-160. Reserved.
DIVISION 4. DESIGN STANDARDS