Saturday, 15 July 2006

Remediation of Petroleum Contaminated Soils by Lime Addition.

Chris D. Collins1, Dan Lothian1, and Vito Schifano2. (1) Reading Univ, Dept Soil Science, Whiteknights, Reading, United Kingdom, (2) Arcadis GMI, Craven Court, Willie Snaith Road, Newmarket, United Kingdom

The use of lime reagents to treat inorganic contaminated sites is an established technique, as part of stabilisation/solidification technology. The success in treating organic contaminants using lime has varied; scepticism surrounds the type of organics that can be treated, and the various interferences these contaminants induce. Successful insitu or non-insitu application of lime binders can render contaminants stable, inhibiting migration, therefore removing the risk to groundwater. In terms of the UK definition of contaminated land, breaking the pollution linkage by rendering the contaminants immobile is a potential means of cost-effectively treating contaminated sites. A twenty-one day study was conducted to evaluate the effect that the addition of quicklime and hydrated lime would have on clay soil spiked with two pollutants commonly encountered at contaminated sites; petrol and diesel. Quicklime and hydrated lime were mixed at five and ten percent of the dry weight of soil. Each treatment concentration was prepared in triplicate, and placed in individual microcosms. Alterations in the physical parameters of the soil were quantified by examining moisture content, liquid limit and plastic limit changes over the twenty-one day testing program. Several immediate and longer-term physico-chemical changes were initiated following mixing by quicklime and hydrated lime. More than ninety-percent of light petrol fractions (C5-C12) were volatilised almost instantaneously. Additionally flocculation and pozzolanic reactions reduced the concentration of petrol and diesel compounds migrating from the soil system to the aqueous phase by 80-95%; but temporal variations were apparent, indicative of long-term encapsulation interferences. The addition of both quicklime and hydrated lime induced the immediate loss of toxic indicator species (e.g. BTEX), and the stabilisation/solidification of less volatile species. The elevated levels of petroleum hydrocarbons did not retard the physical parameters of the soil, as plasticity of the soil was improved by between 5 and 30%; producing a more manageable material.

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