Improved storm water treatment resolves community flooding issues & enhances water quality
In Sebring, Fla., the Spring Lake Improvement District’s new lake-wetland marsh system expanded the district’s storage capacity and treatment of its storm water. In September 2017, Hurricane Irma put the new system to the test.
The Florida Legislature created the 4.5-sq-mile Spring Lake Improvement District in 1971. It is home to single- and multi-family residences, some commercially zoned lands along U.S. 98 and a private golf course. Prior to the new 70-acre storm water treatment area, the district had experienced severe flooding issues in recent years, such as major flooding during Tropical Storm Ernesto in 2006, due to an aging system.
The district also received and conveyed storm water runoff off site from more than 620 acres at the Sebring Regional Airport, 20 acres of Florida Department of Transportation (FDOT) right-of-way, and nearly 70 acres of other unimproved lands via FDOT’s storm water system. At that time, storm runoff from the district and from off site, a total of more than 3,000 acres served, received treatment through a series of existing upstream and cascading lakes, a network of canals, and an aging pump station. The pump station consisted of four 65,000-gal-per-minute pumps that controlled the discharge of storm water to Arbuckle Creek.
Arbuckle Creek is a 25-mile scenic waterway through the heart of Highlands County flowing from Lake Arbuckle to Lake Istokpoga. Protecting this natural beauty is vital to the district, Highlands County and all Floridians.
Time for a Change
In early 2014, the district received a Federal Clean Water Act Section 319(h) Grant from the Florida Department of Environmental Protection (DEP) for approximately $1.7 million. The district acquired more than 80 acres of unimproved lands to help with the capture and treatment of storm water before discharge to Arbuckle Creek. More than 70 acres of these lands were contiguous and made up the lake-wetland marsh system that would become the new storm water treatment area (STA). This STA provided additional water quality treatment benefits prior to discharging into the creek by removing more of the total suspended solids and nutrients, such as total nitrogen and phosphorus.
The first phase of the project included design, surveying, permitting, site preparation, partial construction of the overall project, excavation of 32 acres of wet detention ponds, and completion of a portion of the 38 acres of northeast shallow marsh area, a series of connected constructed wetlands and their associated conveyance improvements. The design of the STA was coordinated with a wetland resources biologist to achieve maximum environmental benefits.
The existing storm water system was modified to allow runoff to enter the wet detention pond by way of two large-capacity gravity storm sewers along the northwestern perimeter of the pond. This allows for gentle redistribution of storm water into the pond, which then travels out and through the adjacent marsh portion of the STA for treatment. A control structure was installed at the southeastern perimeter to help ensure flow through the constructed wetlands to optimize treatment. The control structure allows for 6 in. of retention plus 2 ft of detention, for a total gross volume of 150 acre-ft (or approximately 49 million gal). A perimeter ditch, which is a short-compacted shell access road, also was added, along with upgrades at the outfall point. These outfall area upgrades included excavation, grading and erosion control.
At the end of 2014, the DEP’s Clean Water State Revolving Fund awarded the district a $1.9-million, low-interest 20-year-term loan for additional storm water improvement construction within the district. Because the district’s storm water feeds into Arbuckle Creek, a tributary of Lake Istokpoga, it is ultimately transported to Lake Okeechobee. Eventually this water ends up in the Everglades and Florida’s sensitive Atlantic estuaries. The district was not in compliance with the original surface water permit conditions and corrective action was necessary. This next phase of storm water improvements included, among other features, storm water conveyance and treatment to remove silt. Silt not only causes turbidity issues in downstream waters, but also can carry nutrients along with it.
The district also experienced severe flooding for many years due to the age of the surface water system components. Therefore, the existing culverts and master pump station were replaced and lake storage capacity further expanded, providing additional land for treatment capacity.
In state fiscal year 2015/2016, the district received a legislative appropriation of $500,000 to help with the rehabilitation of the pump station that served the storm water system. During Tropical Storm Ernesto, in August 2006 when the pump station was not fully functioning, major flooding occurred within the district due to the heavy rainfall. It became clear that during such major storm events that services within the district, such as use of the roads and the operation of water and wastewater treatment plants, were greatly disrupted. Failure to address the pump station rehabilitation ultimately would impact not only the health and safety of the residential community, but also the neighboring Highlands County communities.
In 2008, emergency repairs were performed at the pump station as the result of both erosion and sheet pile failure at paved areas within, and discharge basin banks adjacent to the site. However, these repairs were only a bandage. Additional erosion within the paved areas became evident and required more permanent action, and the rehabilitation improvements for the 40-year-old storm water pump station were listed in the district’s Water Control Plan as the second highest priority.
Rehabilitation of the storm water pumping station located at the eastern boundary of the district began in early 2016. This work included the repair and reinforcement of the existing pump station foundation, reshaping the existing canal bank and installing rip-rap material, and repairing the existing asphalt and base material within the pump station limits. Importantly, two existing storm water pumps in the station were replaced with two new axial flow pumps and the timing system for all of the pumps was modified for efficiency and to handle peak flows caused by major storm events to help alleviate the flooding issues. A new drainage structure and culvert to interconnect an adjacent canal also were installed. Other useful improvements to assist in the safety and resilience were the removal and replacement of the existing chain link perimeter fence, the installation of a security system at the pumping station, and the addition of hurricane-resistant doors and shutters.
With the addition of the new storm water treatment area, the refurbished pumping station more effectively controls the runoff so it flows into the completed lake-marsh system via two new large-capacity gravity storm sewers. The new lake-marsh system also provides additional storm water treatment by removing sediment and nutrients from the water before it is released into Arbuckle Creek.
Overall, the Florida DEP and the state provided more than $4.1 million to facilitate the planning, design and construction of Spring Lake Improvement District’s new storm water treatment area, including improvements to the existing storm water system and pump station. Over the course of three years, funds were combined from the Department’s Clean Water State Revolving Fund loan program, Federal Clean Water Act Section 319(h) Grant, and an appropriation from the Florida Legislature to help make this necessary project come to fruition.
“Our new storm water treatment area performed beyond expectations during Hurricane Irma,” said Joe DeCerbo, district manager of the Spring Lake Improvement District. “Not one street in Spring Lake flooded, and not one home was flooded. In the aftermath of Irma, the system’s newly refurbished pumping station moved over a billion gallons of water. We are so glad we had this [storm water treatment area] or who knows what my community would have looked like.”