ALLOWING TIME FOR ACTIVATED CARBON CONDITIONING IN CONTAMINATED SOILS INCREASES THE EFFECTIVENESS OF STABILIZATION/SOLIDIFICATION

Stabilization and Solidification (S/S) can be a cost-effective remediation tool for contaminated soils and sediments, and is considered an accepted technology by the US EPA. S/S involves mixing amendments into the contaminated material which reduce the leachability of the contaminants. Though originally designed for inorganic contaminants, S/S is increasingly being used for sites contaminated with organic compounds.

Two amendments commonly used for organics are Portland cement (or other pozzolanics like quick lime or fly ash) and powdered activated carbon (PAC). Cementing agents reduce the leaching of organic contaminants by reducing the permeability of leachate, and by encapsulating soil particles to which contaminants are adsorbed. The PAC serves as surface area to which organic contaminants adsorb very strongly. Ideally, PAC should be given time to adsorb contaminants before cementing agents are added, called PAC conditioning. However, in practice both amendments are typically added at the same time to reduce costs. Laboratory studies conducted on phenol suggest that there is no benefit by allowing PAC conditioning before adding cementing agents. However, these studies were done on soils artificially contaminated with phenols, whereas aged contaminated soils tend to behave quite differently. Moreover, phenols are not very common contaminants of soils.

We will present results from laboratory studies on 6 different soils with aged contamination from BTEX (i.e., benzene, toluene, ethyl benzenes, and xylenes). The studies measured leaching (using the synthetic precipitation leaching procedure, or SPLP) in soils amended with PAC and Portland cement simultaneously, and compared PAC conditioning times of 1 month, 3 months, 6 months, 9 months, and 1 year. Results demonstrate that pre-treatment with PAC before cement dosing dramatically reduces leaching and increases the effectiveness of S/S for organic contaminants.