HBM for remediation - introduction

Methods of remediation
Methods of contaminated land remediation include:

1. Dig & dump
2. Soil washing
3. Bioremediation
4. Phyto-remediation
5. Stabilization/solidification.

The use of HBM in remediation belongs to the latter method of stabilization / solidification.

Stabilization/solidification (S/S)
In remediation terms, as distinct from road construction terms, stabilization is a process where additives are mixed with waste to minimize the rate of contaminant migration from the waste and to reduce the toxicity of the waste. Thus stabilization may be described as a process by which contaminants are fully-bonded or partially-bound by the addition of supporting media, binders, or other modifiers.

Likewise, solidification is a process employing additives by which the physical nature of the waste – as measured by the engineering properties of strength, compressibility, and/or permeability - is improved during the process. (Note that in road construction, this would be called, confusingly, stabilization.)

Thus the objectives of S/S encompass both the reduction in waste toxicity and mobility as well as an improvement in engineering properties.

Application of S/S
The 3 major areas of application for S/S and thus HBM are:

1. Land disposal - the remediation of wastes prior to secure landfill disposal
2. Site remediation – the remediation of contaminated sites
3. Solidification of industrial wastes - the treatment of residues such as sludge from other treatment processes.

S/S for land disposal
The land disposal of liquid waste increases the likelihood of contaminant migration. Liquid waste, along with wet sludges, must be stabilized prior to land-filling. To effectively stabilize liquids, the stabilization agent cannot just be an absorbent (such as sawdust) since the absorbed liquids could be squeezed out (desorbed) under the weight of overlying material in the landfill. Therefore the liquids must be chemically and physically bound by the stabilization reagents so that they are not squeezed out or leached out by the downward percolation of precipitation.

S/S for site remediation
The remediation of contaminated sites may be accomplished by S/S.
S/S is employed to:

1. improve the handling and physical characteristics of the contaminated material
2. decrease the rate of contaminant migration by decreasing the surface area across which the transfer of pollutants can occur
3. limit the solubility of pollutants
4. reduce the toxicity of certain contaminants.

S/S may be considered a more permanent solution than say containment.

S/S is particularly suited to the treatment of sites where the hazard involves large quantities of soils contaminated at low levels since it may not be environmentally sound nor cost-effective to excavate, transport, and landfill or incinerate soils contaminated with low levels of pollutants.

Solidification of industrial wastes
As a legacy from our past, a wide variety of organic and inorganic wastes can be found in pits, ponds, and lagoons. Solidification improves the engineering properties and may reduce the rate at which contaminants migrate into the environment. Although many of the non-hazardous waste materials may not endanger health or the environment, the materials are frequently structurally unstable, aesthetically unsuitable, and their condition precludes other uses of the site area. Thus the primary goal of solidification is structural integrity that can be evaluated simply by measurement of strength.

Mechanisms of S/S
In order to understand how to use S/S and thus HBM for remediation purposes, it is necessary to understand fully the physical and chemical mechanisms of remediation. Detailed information on the process is available (reference) which covers;

• risk assessment
• treatment design
• implementation
• monitoring and validation.

Reference
The essential guide to stabilization/solidification for the remediation of brown-field land using cement and lime. 2004. BCA publication 46.112. enquiries@concretebookshop.com