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ENVIRONMENTAL RESTORATION OF A STEEL MILL (Page 1 of 2)
J.E. Garlanger1, A.J. Turner2, C. Stern3 and F.K. Cheung1 |
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1Ardaman & Associates, Inc., 8008 South Orange Avenue, Orlando, Florida 32809, USA e-mail: jgarlanger@ardaman.com; fcheung@ardaman.com
2AmeriSteel Corporation, 5100 West Lemon Street, Tampa, Florida 33609, USA e-mail: jturner@ameristeel.com
3Carlos Stern Associates, Inc., 1406 North Johnson Street, Arlington, Virginia 22201, USA e-mail: carloste@starpower.net |
Abstract
This paper describes the regulatory and technical background of the successful remediation of a 32-hectare steel mill in Florida, USA. The project site had, over the early years of its 30-year operating history, become contaminated with by-products and wastes from the steel mill operations that, unknown to the company at the time, contained levels of lead and PCBs in excess of subsequently-established government limits. Starting with the initial discovery of the problem in 1986, a comprehensive investigation was undertaken consisting of more than 600 test pits and borings and the analysis of several thousand samples. The results of the nine-year study that characterized the extent, thickness and level of contamination showed conclusively that the problem was confined to approximately 200,000 cubic meters of fill material that had been deposited at varying thicknesses on top of the native soil across virtually the entire site. Because of the huge volume involved, negotiations with the State and Federal environmental agencies on cleanup criteria for the site and disposal options for the contaminated fill continued for over five years. This paper discusses the evolution of the cleanup criteria and treatment and disposal requirements for PCBs and lead, and the agreement that was finally reached between the owner and the regulatory agencies. The actual remediation and future use of the site will also be described. Our goal in presenting this case study is to show that the principal lessons learned as a result of our experience at the Tampa site, as well as several similar environmental cleanup projects we have successfully concluded, may be generally applicable to other types of industries and to the conditions experienced in nations other than the USA.
Introduction
The AmeriSteel Corporation Tampa Mill is located in a major industrial area in Tampa, Florida. Between 1958 and 1994, AmeriSteel manufactured new steel products at this facility by recycling scrap steel, principally junk automobiles, through the use of electric arc furnace technology. An aerial photograph of the Tampa Mill just prior to remediation is shown in Figure 1. Most of the Tampa Mill property and some adjacent areas had been filled with materials that were generated by the steel mill, primarily slag, with lesser but still significant amounts of mill scale and dust from the air pollution control system (referred to as EC dust from “emission control”), and residues from the scrap steel shredding operation. The fill had an average thickness of approximately 0.6 to 0.75 meters, and a volume of more than 200,000 cubic meters.
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In the USA, neither the mill scale nor the slag is regulated as a hazardous waste because they are considered valuable by-products. However, since 1980, many years after the mill began operating, EC dust has been regulated as a hazardous waste. Prior to shutdown of the steel mill melt shop in 1994, an automobile shredder and scrap processing operation had been located in the western portion of the Tampa Mill facility to prepare scrap steel for the furnace. Most of the automobile shredder residue (ASR), sometimes called “fluff”, was shipped off-site as it was generated; however, some ASR remained on the property. Analyses of the scrap processing residue showed it to exceed the permissible regulatory level for lead.
Another complication was the result of the discovery that there were polychlorinated biphenyls (PCBs) present in the soil in some areas of the site. These were the result of the fact that for a brief period in the early 1970s, the mill had used hydraulic shears to cut the hot steel from the continuous caster into billets and that some of the hydraulic oil used in the shears contained PCBs. Some of hydraulic oil had entered the cooling water system and thus contaminated the mill scale with PCBs. The mill scale was periodically removed from the process water system and used as fill on the site. In1976 with the enactment of the Toxic Substances Control Act (TSCA), PCBs became a regulated hazardous waste.
More than 600 test pits/borings and several thousand samples were analyzed during the contamination assessment for the site. The results of the assessment indicated that the fill layer and the sediments in the existing stormwater ditches at the Tampa Mill contained elevated concentrations of lead and PCBs. The lead concentrations ranged from less than 200 to greater than 20,000 mg/kg, and the concentrations of PCBs ranged from less than 10 to greater than 2,500 mg/kg. The areas with lead concentrations greater than 1,000 mg/kg and PCB concentrations greater than 25 mg/kg are shown on Figures 2 and 3, respectively.
Hydrologic Setting
The Tampa Mill site is relatively flat with land surface elevations between +5 and +6 meters above sea level. Storm water runoff from the developed portion of the site was collected by a system of storm drains and ditches. The site is underlain by two aquifers separated by a confining stratum. The surficial aquifer consists of unconsolidated sediments, primarily fine sand with some silt and clay. The thickness of the surficial aquifer ranges from approximately 6 meters in the western part of the site to 3 meters in the eastern part. The surficial aquifer is not a source of potable water in the vicinity of the site. At the base of the surficial aquifer is a 2- to 4-meter thick clayey confining layer containing variable quantities of sand and silt. Below the confining layer is the confined Floridan Aquifer. The upper part of the Floridan Aquifer consists predominantly of variably weathered limestone with some silts and clays. The hydraulic connection between the surficial aquifer and the Floridan Aquifer is limited.
Groundwater in the surficial aquifer was generally encountered within 1 meter below land surface. Groundwater flow in the surficial aquifer was generally to the east toward the Tampa Bypass Canal; however, it also occurred toward the North Ditch and the South Ditch in their immediate vicinity. The general direction of groundwater flow in the Floridan Aquifer was to the southeast toward the tidal portion of the Tampa Bypass Canal.
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