Growth FAQ - Engineering

What are the requirements for underground stormwater management facilities?

Sec. 5-86(m), TLDC, establishes the standards for underground stormwater management facilities. That code section is summarized below, but we encourage you to call our engineering staff at 850-891-7001 (option 4) to discuss.

• Underground stormwater management facilities shall only be authorized when the applicant demonstrates the following: 1.) That the use of an on-site above ground stormwater management facility would make the project financially infeasible; and 2.) That positive non-mechanical outfall to an adequate off-site conveyance system deemed adequate can be provided or the site is within an area with a soil texture class of sand.
• Once the director approves an underground stormwater management facility, the following design standards apply:
• The property owner (not the agent) shall agree to and sign the "Underground Stormwater Facility Inspection and Reporting Requirements Acknowledgement Sheet"; and
• Water quality treatment shall be provided using surface ponds and/or mechanical or chemical treatment methods designed in conformance with subsection 5-86(c) prior to discharge to underground storage attenuation cells; and
• Treatment pond control structures shall include skimmers and trash racks to prevent debris from entering underground storage cells; and
• Underground cells shall have a minimum headroom clearance of 6-feet inside cells; and
• Underground storage cells with discharge structures shall have a positive slope to direct flows to said discharge structures; and
• Major structural components shall be designed and constructed to have a minimum 100-year design life; and
• Inspection portholes shall be provided at key locations to ensure that each entire cell is visible in its entirety. A remote/robotic camera system that makes each entire cell visible in its entirety may be provided in lieu of the inspection portholes; and
• Prior to issuance of the building permit for the primary structure that the underground stormwater management facility is designed to serve, a five-year cash bond or irrevocable letter of credit in a form acceptable to the city attorney shall be required in the amount deemed reasonable by the director to assure the completion of required inspections and reports and maintenance of the facility in perpetuity.

Please speak to our engineering staff at 850-891-7001, option 4, to discuss whether project characteristics at a specific site would warrant a headroom clearance of less than 6 feet.