FDOT, FDEP and the Southwest Florida Water Management District (SWFWMD)) and various other stakeholders joined forces and took a proactive approach to produce a Reasonable Assurance Plan (RAP) to guide the management of water quality in Tampa Bay. The RAP requires an estimated 85 tons of additional nitrogen load reduction projects for each five-year planning period, equal to a 17-ton- per-year reduction. The most widely adopted stormwater treatment system in Florida, wet detention ponds, remove only about 30 to 40 percent of incoming nitro- gen loads from stormwater. Dry retention ponds have nitrogen removal efficiencies in excess of 90 percent, but they often require much larger construction costs or areas of land to meet design standards and are often impossible in areas with poor soils or high-water tables. However, the Florida legislature passed House Bill 559 in 2012 which included direction to the water management districts and the FDEP to “…allow alternatives to onsite treatment, including, but not limited to (emphasis added) regional stormwater treatment systems.” Upon the governor’s signature, this provision was enacted into law as Section 373.413(6), Florida Statutes (F.S.). Additionally, Section 4.0 of the SWFWMD Applicant’s Handbook Volume II (AH Vol II) states that “The applicant may also provide reasonable assurance of compliance with state water quality standards by the use of alternative methods that will provide treatment equivalent to systems designed using the criteria specified in this section.”
Ecological Uplift Through Engineering Tidal Circulation and Old Tampa Bay
By Shayne Paynter, PhD, PE, PG, Ed Cronyn, PWS, Daniel Lauricello, PE, Virginia Creighton, PWS, David Tomasko, PhD, and Mike Salisbury, PE
In highly urban areas, large transportation projects often spend tens of millions of dollars purchasing right-of-way for stormwater manage- ment, including the purchase of developed property to be demolished to construct ponds. In lieu of traditional stormwater best management practices, Atkins, a member of the SNC-Lavalin Group and the Florida Department of Transportation (FDOT) looked at an area of Old Tampa Bay (OTB) that historically has had poor water quality and evaluated improving this offsite area to compensate for other projects that drain to Tampa Bay. The Florida Department of Environmental Protection (FDEP) placed OTB on its list of impaired water bodies in 1998. For waterbodies cat- egorized as having impaired water quality, the typical management ap- proach has been to transition towards the development of a total maxi- mum daily load (TMDL). Rather than waiting for FDEP to produce a TMDL for Tampa Bay, local governments, state agencies (including
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csengineermag.com
may 2020
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