Conversion of Process Pond to OnSite Disposal Cell at Superfund Site

Chemical manufacturing at the site used remnant mining pits as process lagoons and storm water holding ponds receiving process water overflows. We completed remedial investigation of soil, sediment, surface water and groundwater that identified large volumes of contaminated source material resistant to chemical, biological or physical treatment. WSP USA conducted the removal action to consolidate contaminated soil and sediment under the cap of a process lagoon converted for use as a disposal cell.



  • Central Florida, USA



Project Status

  • Ongoing, 2004 – present

Strategic Advice, Technical Expertise

WSP is the prime engineering contractor for the demolition and remediation of a 1,000-acre phosphate chemical plant in Central Florida. After completion of the first phase of the remedial investigation, WSP evaluated soil and sediment removal technologies under the Engineering Evaluation/Cost Analysis (EE/CA) process of the National Contingency Plan to address the imminent risk to public health and safety. Chemicals present in site media include mining and chemical processing constituents including arsenic, boron and technologically enhanced radioactive material (TENORM).

To address the site contamination, we proposed remedial action to consolidate contaminated soil and sediment under the cap of a process lagoon which would be converted for use as a disposal cell. WSP gained acceptance from the Florida Department of Environment (FDEP) and the U.S. EPA to utilize the existing process pond before installing an impervious cap and groundwater hydraulic control system.

The process pond selected as the on-site consolidation cell was a 60-acre mining pit filled with phosphatic clay, a semi-solid sludge exhibiting low shear strength. WSP’s design called for reinforcement of the sludge by placement of a high-strength woven geotextile over the sludge. The geotextile was seamed on-site and deployed in four 15-acre panels, providing a platform for placement of lifts of contaminated soil and sediment from the site.  The design was reviewed and approved by the Corps of Engineers, and the implementation, which was the largest single deployment of geotextile at the time, was awarded the Outstanding Achievement Award by the Industrial Fabrics Association International.


On-Site Process Pond

After completion of contaminated material placement, the cell was capped with high density polyethylene (HDPE) and a soil cover to provide a vegetated layer for erosion protection after closure. The closure of the process pond and consolidated sediments included closure-in-place of contaminated process sludge, including sludge in contact with groundwater. WSP provided a hydrogeological evaluation of future leaching to demonstrate low potential for vertical leaching of contaminants to groundwater, and designed a perimeter hydraulic control system to contain horizontal migration of contamination.

The use of the on-site process pond as a disposal cell for consolidation of contaminated site materials addressed the imminent threat to public health and safety in a cost effective and low risk manner.  Operation, maintenance and monitoring of the cell and surrounding groundwater conditions have resulted in a decreasing trend in the concentrations and footprint of groundwater contamination.

WSP is implementing a five-year plan to complete the remediation of the remaining areas of contamination at the site under the terms of a Cleanup Agreement Document negotiated with the FDEP.