chapter  3
10 Pages

Predictive Models for VOC Partitions in Soils

Chloroorganic solvents, such as 1,1,1-trichloroethane (TCA), trichloroethylene (TCE) and tetrachloroethylene (or perchloroethylene, PCE), have been found in many contaminated sites and groundwaters. The outward migration of these chemicals in saturated soils is largely dependent upon their interactions with the soil particles. In general, the adsorption of these volatile organic compounds (VOC) by most soils are only slight to moderate since plumes of the VOC's have been detected quite far away from the initial sites of contaminat i~n. '~~

In today's engineering practice, it is often necessary to estimate the rate of transport of these VOC's in the subsurface environment. Many engineers attempt to solve the problem by taking numerous soil cores and water samples surrounding the contaminated site. After sample analyses, iso-concentration curves (contour) for both water and soil are "roughly" sketched. The results are then used for modelling the movement of these VOC's in their future outward migration. Although this approach of solving the problem seems to be quite logic, it is expensive and tedious because of the need for making numerous soil borings. In addition, the organic solvents are extremely volatile. As such, they can be easily lost into the atmosphere during the boring, handling and chemical extraction of the water and soil samples unless extreme precautions are taken. Therefore, many iso-concentration curves which are plotted from "less than satisfactory" data are not truly representative of those existing in the field. If the future transport were estimated according to such inaccurate iso-concentration curves, significant errors would undoubtedly be introduced.