" Based on the data of Wood (64) and Levin and Gealt (35).

" Based on the data of Wood (64) and Levin and Gealt (35).

contaminated soil has changed dramatically in the United Kingdom. In mid-July 2004, the implementation of the Landfill Directive classified soil contamination as nonhazardous (<10,000 mg of toxic material kg"1, <1,000 mg of carcinogenic material kg^1) or hazardous (>10,000 and 1,000 mg kg-1, respectively). The cost of landfilling nonhazardous soil has gone to $21 per ton plus a landfill tax of $27 per ton (total, £27.00 per ton, or roughly $48.50). The cost for hazardous soil is £45 ($80) per ton plus a landfill tax of £15 ($27) per ton, making a total of £60, or roughly $107. However, another result of the implementation of the Landfill Directive is that the number of landfill sites in the United Kingdom that can accept contaminated soil has been greatly reduced, which has significantly increased the transportation costs. In some areas of the United Kingdom, it is not unlikely that contaminated soil would have to be transported 200 miles to a suitable landfill site, and the cost for transportation alone might amount to another $72 per ton. This has opened up much greater prospects for bioremediation since the transport cost is immediately removed from the economics.

Risk-Based Remedial Design

The outcomes of the risk assessment exercise feed into the next step in the contaminated land management process, which is selection of the remedial technology appropriate to nullifying the risks. It should be remembered that land remediation should be designed to break the pollutant linkage between source and receptor. In reality, several factors are likely to interplay in the eventual choice of technologies. In the United Kingdom, the four main factors that influence decision-making are as follows:

1. remedial objectives and treatment targets (for the purpose stated above);

2. environmental merit, e.g., incineration destroys contaminants but also destroys the soil;

3. cost-effectiveness; and

4. local factors, e.g., public opinion and local waste license regulations.

There now exist a large variety of treatment technologies, either established or innovative. It is beyond the scope of this book to look at all of these in detail. Therefore, a brief description of technologies classed as physical, chemical, thermal, or solidification is given. Landfill is not discussed, since it is not a remedial technology. Although in many countries it remains the cheapest option, it is merely a disposal option, as the anaerobic environment of the landfill is not conducive to biodégradation of many common contaminants.

Bioremediation has to compete successfully with these technologies, so for a screening exercise choices of which ones to compare it with have to be made. To narrow the field down, use has been made of U.S. EPA data on remedial technologies (60). The most frequently used established technologies in the United States are incineration (thermal), thermal desorption (thermal), solidification/stabilization (physical), and SVE (physical) and, for groundwater, pump-and-treat technologies. SVE and thermal desorption are interesting cases, as they were until recently classed as innovative technologies, but they have crossed the barrier to implementation and are now established. The EPA has defined innovative technologies as those whose use is limited by lack of data on cost and performance. They have only limited full-scale application, and in situ and ex situ bioremediation thus remains classed as innovative.

Bioremediation techniques together (for the fiscal year 1997) had been used in 11% of all Superfund remedial actions. For comparison, SVE had been used in 28%. For remedial treatment trains, in which two or more techniques are used in sequence, bioremediation was used in 6 of 17. Contaminated sites treated by bioremediation have mostly been BTEX (benzene, toluene, ethyl-benzene, and xylene) containing. Tables 2.5 and 2.6 compare the applications of different techniques with respect to contaminant types, soil types, cost, and remediation times, and they contain data compiled from the work

TABLE 2.5 Comparative data on established remedial treatments"

Compound or parameter


Thermal desorption




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