Cleanup Criteria and Disposal Requirements

Because of the large volume of contaminated material, it was critical that reasonable cleanup levels and disposal options be established for the site.  Although the Tampa Mill site contained the largest volume of contaminated material, this was not AmeriSteel’s first remediation project.  AmeriSteel had gained experience  with two smaller but otherwise similar sites.  All of the lead-contaminated  fill not meeting the cleanup criteria at the two previously remediated sites had been solidified/stabilized using Portland cement prior to disposal.  Data collected for these two sites were consistent with studies performed for the Tampa Mill and confirmed that fill materials and soil with lead concentrations below 1,000 mg/kg generally complied with the federal leachability criteria as non-hazardous waste.  Shredder residue even at concentrations in excess of 1,000 mg/kg also complied with the leachability criteria.  In addition, groundwater concentrations even directly beneath the fill with the highest lead concentrations were consistently complied with the strict regulatory standards.  For these reasons, a cleanup level for lead in the fill and soil of 1,000 mg/kg and chemical fixation prior to disposal of only those materials which failed the federal leachability criteria were proposed for the Tampa Mill site.

At the time the investigation began at the Tampa Mill, regulations stipulated that PCB-contaminated soils would have to be destroyed in a special type of incinerator prior to disposal.  In 1987, AmeriSteel had used such an incinerator to treat some 20,000 tons of PCB-contaminated soil at another of its mills.  However, even if incineration were limited to PCB concentrations exceeding 25 mg/kg, estimates of the cost to remediate the Tampa Mill site, assuming the precedent set at prior sites, were in excess of US$45 million.  If all of the PCB-contaminated material required incineration, cost estimates were in excess of US$100 million.  It was clear that the incineration option would have been prohibitively expensive for the Tampa Mill site.

Approved Remedy

After more than five years of collaboration, a remedial action plan was approved by the state and federal regulatory agencies. By this time, AmeriSteel had decided to close the mill for economic reasons.  The approved remedy involved excavating and disposing of all fill within the remediation areas and all sediments in the storm water ditches.  In addition, native soil that exceeded the cleanup criteria would also be removed.  The native soil cleanup criterion for lead was 1,000 mg/kg.  For PCBs, the criteria were 3.5 mg/kg within 0.6 meters of final grade and 44 mg/kg at depths greater than 0.6 meters.  No separate criteria were established for other contaminants, such as other metals, because the studies had conclusively demonstrated that lead was the controlling heavy metal, i.e., if the criterion for lead were satisfied, the other metals would also be within approved limits.

The approved plan required chemical fixation prior to disposal of all excavated materials with a leachable lead concentration exceeding 5.0 mg/l.  The final approved treatment standards for lead-contaminated material were: (i) a leachability lead concentration less than 5.0 mg/l; and (ii) an unconfined compressive strength equal to or greater than 340 kPa for the stabilized waste.  Both the state and federal regulatory agencies agreed that if all of the fill were excavated and disposed of on-site in an approved landfill (discussed below), incineration would not be required prior to disposal.

A contractor was selected on the basis of competitive bidding for a lump sum contract to complete the approved remedy.

The average depth of excavation for removal of the artificial fill and underlying contaminated soils was approximately 0.75 meters.  In some places, the excavation had to be extended to 1.5 meters.  The boundary between the artificial fill and the underlying native soils was relatively distinct allowing a high degree of control in the field, as shown on the photograph in Figure 4.

 Verification sampling of the native soils underlying the artificial fill was performed on a 15-meter square grid system.  If the verification sample exceeded the cleanup requirements, an additional 15 cm of material from that grid was excavated and the procedure repeated until the requirements were achieved.

Vault Base Design and Construction

The on-site vault was designed to exceed all federal and state requirements for a hazardous waste landfill.  It was constructed in the western part of the Tampa Mill property, where the automobile shredding facility once operated. The vault occupies an area of approximately 4 hectares. The bottom liner and leachate collection system consists of the following components in ascending order:

• A 30-cm thick compacted soil liner with a hydraulic conductivity less than 2.0x10-8 cm/sec
  
• Two 1.5-mm thick high density polyethylene (HDPE) geomembrane liners separated by a 5-mm thick geonet
  
• A 60-cm thick sand layer drained by HDPE prefabricated drainage panels on 7-meter centers.

Figure 5 is a photograph of the vault base under construction

Solidification/Stabilization

Portland cement was used to solidify/stabilize the excavated materials that exceeded the treatment standards. The operation involved screening of the excavated fill to remove particles larger than 2.5 cm, and mixing the screened material with 8% to 10% cement and water in a pug mill.  The ratio of the mixture had been derived from the results of a long series of treatability tests.  Prior to full scale production,  test runs were performed using the field equipment to confirm the appropriate cement content and water-cement ratio.  During the full-scale operation, confirmatory testing was performed to document that the treatment criteria had been achieved.  Less than 15,000 metric tons of the excavated material required treatment. A photograph of the pug mill operation is shown on Figure 6.

Final Cover Design and Construction

After  the excavated and treated materials  had been placed in the vault, a final cover was constructed to prevent infiltration.  The grass layer of the final cover serves as an aesthetic cover and minimizes the potential for water and wind erosion.  The final cover for the on-site vault consists of the following components in ascending order:

•  A 30-cm thick compacted soil liner with a hydraulic conductivity less than 2.0x10-8

• cm/sec. A 1-mm thick HDPE geomembrane.

• A 45-cm thick protective soil cover.

• A 15-cm thick topsoil soil layer with sod cover.

  Figure 7 is a photograph of the top cover during construction.  The height of the completed vault is approximately 11 meters.

QA/QC Program

A comprehensive construction quality assurance (CQA) program, which included full-time third-party inspection of all remediation and construction activities, and field and laboratory testing of the treated soil and all liner components, was implemented to assure that the remediation was performed in compliance with the remedial design.

Approximately 800,000 liters of leachate were removed from the leachate collection system approximately four months after the final cover was in place.  The leachate collection system was checked again two months later, and was found to be empty.  No leachate has been detected in the leak detection system.

Conclusions

The environmental restoration of the Tampa Mill site has been considered a huge success by the government, the community and AmeriSteel.

Remediation of the Tampa Mill was completed in approximately 15 months, approximately 9 months ahead of the original schedule, with a total remediation cost of approximately US$7 million.  This translates to an average cost of approximately US$12 to $15 per metric ton of excavated material, which is substantially lower than any of the remediation options that had originally been considered for the project.  A photograph of the site after remediation is shown in Figure 8.

 The restored site has been subdivided into nine parcels to form an industrial park.  One of the parcels has been sold, and three other parcels have prospective buyers.

 Several important lessons were learned from this project that can be applied to remediation projects in other countries, other regulatory contexts, and other industries.

• Cleanup projects that are under the control of one party will proceed more efficiently, more rapidly, and at lower cost than projects where several parties are involved.

• Cleanup projects where all operations can be confined to the affected property, including final disposal, will be more acceptable to everyone involved, especially the local community, will cost less, and will proceed with fewer delays than projects where offsite operations such as incinerators, landfills, etc., are involved.

• Provided that additional capacity can be planned for in advance, having final disposal take place on the property will result in much lower total and marginal costs per unit of material disposed.  This will allow the owner to make significant concessions with respect to the cleanup levels and thus provide a much more comprehensive cleanup than the minimum required by the regulators.

• When contaminated materials must be hauled off-site, the unit cost is so great that considerable effort must be expended to reduce the total quantity of excavated material to the absolute minimum required to satisfy the regulatory limits.  The residual contamination will not only reduce the value of the property for future development, but will likely require ongoing surface and ground water monitoring.