Case Study: SR-676 Hillsborough County

Real-time water level and rain sensor data enable NST engineers to monitor a Smart Pond’s actual performance compared to predicted performance. This analysis is performed and submitted in an annual report to the Water Management District each year to confirm that each operational Smart Pond achieves the permit-required performance.  

NST retrofitted an FDOT pond on SR 676 in Hillsborough County with Continuous Monitoring and Adaptively Controlled (CMAC) equipment in December 2022. The pond was originally permitted and constructed as a wet detention facility as part of FDOT’s 2010 SR 676 road widening project. The facility receives runoff from an 11.57-acre drainage basin consisting mostly of roadway and commercial land uses.   

After the first full year of operation as a Smart Pond, the annual monitoring data demonstrated more than double the treatment efficiency prior to its upgrade. 

As initially designed and constructed, the stormwater facility provided the required 0.55 inches of wet detention treatment for the road project’s added impervious area. The permitted CMAC modification increased the efficiency of the treatment facility to a predicted treatment efficiency of 67.2% for Total Nitrogen removal, resulting in 2.02 acre-feet of additional equivalent treatment volume. 

The CMAC monitoring system tracks and records rainfall, pond elevation, pond volume, and valve opening data in real time. The initial 12 months of operational data ending in December 2023 demonstrates the pond site received a total of 38.07 inches of rain and fully captured (retained without discharge) 87.5% of the annual rainfall volume. While the total rainfall was less than predicted, the pond still significantly outperformed its modeled and permitted TN removal efficiency as shown in the following summary table:  

Resiliency Grants Available Now!

The Resilient Florida Program is a State grant program available to government entities to address impacts of flood and sea level rise. The National Stormwater Trust, Inc. is partnering with local governments to pursue grant funding for several stormwater improvements. For more information, please Click Here to See Florida Resilient Grants Website.

For assistance qualifying your project or meeting grant deadlines, please contact Erin Klores at eklores@nationalstormwater.com

ENGINEERING TIP: Follow the New Rule!

Get ready, there’s a new rule coming!

 

In 2020, the Florida Legislature passed Senate Bill 712, also known as the Clean Waterways Act, that included a wide range of water-quality protection provisions aimed at minimizing the impact of known sources of nutrient pollution and strengthening regulatory requirements. As directed by section 5 of the Act, the Florida Department of Environmental Protection (FDEP) and water management districts (WMDs) initiated rulemaking to update the stormwater design and operation regulations for environmental resource permitting.

 

FDEP and the WMDs formed a Technical Advisory Committee that met 13 times from December 2020 to November 2021, resulting in a Recommendations Report that was released in March 2022.  FDEP and the WMDs held a series of rule workshops from May 2022 to March 2023 to present and discuss proposed rule language. The rule was adopted April 14, 2023 but, due to the cost of implementation, requires ratification by the Florida Legislature. It is anticipated the rule will be ratified during the 2024 legislative session and will be effective no later than July 1, 2024.

 

The rule is long and complex, including Chapter 62-330, Florida Administrative Code, and the incorporated Applicants Handbook I, effective statewide, and the respective Applicant’s Handbook II for each WMD. Most of the rule remains unchanged; however, significant change is proposed that will affect the design, construction, and operation of stormwater treatment facilities, making most facilities larger and more complex to operate and maintain.

 

A very brief overview of the most notable proposed changes is presented below.

1.  Increase treatment requirements across the board:  

a) BMP presumptive treatment will be discontinued.

b) All new development must meet the maximum of:

i) Post nutrient discharge less than pre nutrient discharge

ii) 55%/80% reduction of post development TN/TP load

iii) Greater reductions for discharges to OFWs or impaired waters

c) Redevelopment

i) 45%/80% reduction of TN/TP for all sites

ii) 60%/90% reduction of TN/TP in OFW watersheds

2.  Expand criteria for compensatory and off-site treatment removing the “last resort” and “less than 10%” criteria, enabling the new treatment requirements to be achieved in any combination of on-site and off-site treatment.

3.  Increase monitoring, inspection, and reporting requirements for all facilities.

4.  Provide for inspector training and certification along with an inspection checklist.

5.  Require as-builts, an O&M plan, cost estimate, and more documentation of financial capability to transfer to O&M phase.

 

The implications to development are significant. Utilizing conventional stormwater BMPs, it is estimated that stormwater facilities could increase in size 2-3 times. This may not work in many locations, requiring the consideration of off-site treatment, more advanced treatment technologies, or a combination of these.

For current projects that already require some enhanced treatment, such as those discharging to impaired water bodies, or future projects under the proposed rule, we recommend increasing the efficiency of standard wet detention and retention BMPs with Smart Pond Technology provided by NST. Ponds equipped with that technology can meet requirements under the new rule for all new development.

Mark Thomasson, P.E.

WEBINAR: Smart Ponds 101

Join the National Stormwater Trust, Inc. for a complimentary webinar, “Smart Ponds 101,” featuring Jeff Littlejohn, P.E., and special guest Dayton Marchese, P.E., from OptiRTC.

📅 Date: Thursday, August 24

🕒 Time: 11 AM to 12 PM (EDT)

🔗 Register Now: Click here

Don’t miss this opportunity to engage with industry leaders shaping the future of water management!

We’ll share case studies on a traditional pond versus a Smart Pond, plus insights on how you can save money and land, while better protecting people, property, and the environment. 

National Stormwater Trust, Inc. is an approved Florida Board of Professional Engineers Florida Continuing Education Provider.  Registered P.E.s can earn 1 Professional Development Hour (PDH) for attending the live webinar. 

For more information, please contact Erin Klores at eklores@nationalstormwater.com.

“Smart Pond” A.K.A. Continuous Monitoring and Adaptive Control (CMAC) at Babcock Ranch