Preserving the Peace | PCL

Preserving the Peace

As part of the upper Peace River watershed in Polk County, Florida, the waters of Lake Hancock flow south down the Peace River, through Charlotte Harbor, and into the Gulf of Mexico. Years of pollution and stormwater runoff from the surrounding phosphate-rich soils of central Florida have made Lake Hancock one of the most polluted and nutrient rich water bodies in the state. The poor quality of the water in Lake Hancock impacts the Peace River water quality and threatens Charlotte Harbor—one of the most productive estuaries in the state.

The Lake Hancock Outfall Wetland project required
 the reclamation of 1,000 acres of land.

Treated effluent water cascades down the aeration
structure before being released into the Peace River
via Saddle Creek.

To improve water quality and protect the estuary and surrounding ecology, the Southwest Florida Water Management District established a plan to reclaim the settling area of a former phosphate mine and establish a 1,000-acre treatment wetland to reduce the amount of harmful nutrients from the water. This ultimately lowers nutrient levels in the water that passes through to the Peace River and effectively protects the estuary in Charlotte Harbor.

More Than 750 Football Fields of Work

The Lake Hancock project is enormous. With 1,000 acres of land to reclaim (more than 750 football fields), it covers an immense physical space; careful planning and coordination were required to ensure the work was accomplished safely and efficiently.
Because it was not possible to see the entirety of the site from a single location, a number of safety stations were established, with first-aid equipment and water for all employees and crews on-site. Numbered markers were installed around the perimeter to ensure workers would not get lost in the project’s vast expanse. In addition, the work areas were further broken down into a grid system of 30-acre blocks; each block could be monitored and tracked as its own smaller project, making it easier to fulfill time and budget commitments.

Pinpoint Grading in Challenging Soil Composition

In addition to the sheer size of the project, creating a wetland from an old mine-setting area presents its own challenges. Because the wetland water depths had to be carefully controlled to ensure wetland plant survivability, the bottom grade of the entire 1,000-acre wetland needed to have a differential of plus or minus three inches—leaving little to no room for error. To complicate matters, the soil in this area comprises largely waste phosphatic clay, a highly plastic material that is subject to shrinkage and expansion and, when wet, has the consistency of silly putty. With daily rainfall common in central Florida during the summer, work crews had to move to higher elevations and to areas with less of the waste material during the rainy season.
The consistency of the soil meant that fine grading activities using traditional earthwork equipment could not be sustained during Florida’s summer rainy season. After extensive research and planning, the team decided on the use of agricultural tractors using scraper pans, which use very low ground pressure and could effectively traverse the gooey material. The work was then subcontracted to a group with extensive experience in scraper pan grading, and the area was successfully graded to standard.

“This project is the largest of its kind undertaken by our district,” said Janie Hagberg, project manager, Southwest Florida Water Management District. “It addresses nutrients at the source and should have immediate benefits for the Peace River system."

 

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