Case Study: Lake Wire

WRS Infrastructure & Environment, Inc. (WRS) performed a source removal corrective action on Lake Wire located in Lakeland, Florida. Lake Wire was identified as an Area of Concern in a RCRA facility assessment. Historical storm water discharges to Lake Wire have resulted in elevated concentrations of metals in sediments (predominately lead).

Remediation/Construction Tasks:

  • Constructed dredged sediment stabilization and staging areas.
  • Installing turbidity silt curtains.
  • Install storm outfall bypass system.
  • Constructed water treatment system for wastes generated from dewatering process and storm water runoff.
  • Mechanically, dry-dredged over 6000 cubic yards of lead contaminated lake bottom sediments.
  • Solidified and stabilized dredged sediments with admixture reagents.
  • Loaded and transported over 6000 tons of stabilized sediments.
  • Backfilled excavated lake areas.
  • Site restoration of landscape and wetlands to pre-construction conditions.

Background and Preparation

WRS mechanically dry-dredged via barge mounted excavators over 9,000 cubic yards of lead impacted sediments from a 12-acre spring fed lake down to a depth of 20-feet. Aerial control was provided with a sub-meter global positioning unit. Vertical elevations were recorded by an independent, licensed surveyor based on area footprints provided by the GPS software.

All dredged sediments were loaded into barge mounted intermodal steel containers and located by pusher motors. The wet sediments were removed with a 65-foot long reach excavator, placed into the steel containers, and transported to the edge of the lake.

Initially, the dredge sediments were dewatered using a plate and frame filter press. However, a number of complications associated with filter pressing the sediments resulted in delayed production. Accordingly, various alternatives were explored to solidify the sludge phase and thus increase the overall production rates.

After examining the various alternatives, it was determined that the addition of ZapZorb (a Super Absorbent Polymer or SAP distributed by ZappaTec) was extremely effective in the rapid and economical solidification of the sediment. The dredged sediments were transferred to a field constructed mechanical mix basin consisting of interlocking concrete lined with an HDPE liner.

After the transfer of approximately 200 tons of wet dredge sediments into the mix basin approximately 2 cubic yards of super absorbent polymer and phosphate-based lead fixating agent were added. The super absorbent polymer was used to solidify the sediments prior to stabilizing the metals (contaminants). Approximately 1-ton of SAP was broadcast within a confined concrete cell to approximately 200 cubic yards of sediments where it was mixed using a long-reach excavator.

Treatment & Restoration

Once the solidified sediment transformed into a cohesive “soil,” the phosphate-based reagent was applied. To treat the sediments for a TCLP lead results below 5 mg/l, dosages ranging from 1% to 3% were applied. Stabilized sediments were transferred to 250-ton stockpiles and then sampled for TCLP metals (RCRA 8). The sediments were loaded into dump trailers for transportation to a Sub-Title D landfill after analytical verification.

Restoration activities included:

  • Importing clean fill and replacing/backfilling the removed sediments in water depths of 4 foot or less
  • Grading and sodding disturbed bank soils
  • Wetland plantings

This removal action was intended to reduce or eliminate exposure risks of impacted sediment to reduce the rate of migration of lead to surface waters. This was accomplished by treating contaminated sediments to below TCLP metal standards to render the dredged sediments non-hazardous for landfill disposal.