EFFECT OF COMMON ORGANIC CONTAMINANTS ON HYDRAULIC CONDUCTIVITY OF AQUIFER SAND

A series of laboratory experiments were conducted to study the effects of some commonly-occurring but widespread chemical contaminants in the environment on the hydraulic conductivity of aquifer sand. Bulk sand samples from the Missouri Valley aquifer— a major source of groundwater supply in the U.S. Midwest— were used in the experiment. The experiment was designed to expose sand to gasoline and trichloroethylene (TCE) for varying periods of time at different levels of saturation (v/v %) to simulate physical and chemical changes in sand caused by oil tanker spill and leaking gas lines. In order to ascertain the degree of saturation and duration of exposure, a series of trial runs were initially performed on sand sample (-2.36mm fraction) using benzene, toluene, ethylbenzene, xylenes (BTEX) and isooctane which are the main constituents of gasoline. Geotechnical properties were measured before and after exposing sand samples with BTEX and isooctane for 4 weeks. This was done to assess the effect of these contaminants on the hydraulic conductivity of sand, and to establish exposure time. Fifty-four sand samples comprising the -2.36mm and -0.425mm fractions were then contaminated with TCE and gasoline at 25, 50 and 100% concentration for 2, 4, 8, 16, and 32 weeks. The grain size parameters of sand along with its density, void ratio, porosity, and hydraulic conductivity were determined before and after contaminating them with gasoline and TCE for the above durations. Hydraulic conductivities were measured, following the American Society for Testing and Materials’ test method D2434–68. The results show a decrease of up to 48% in the hydraulic conductivity of sand upon contamination. Microscopic examination did not reveal any change in the physical features of sand which leads to the conclusion that the decrease in hydraulic conductivity is controlled by the retention characteristic of the chemicals, causing an increase in surface tension and other forces. Further work is in progress.