The effect of residual kerosene on the transport of ammonium and nitrate ions in sandy soil

Field and laboratory work have shown that the availability of electron acceptors such as oxygen and/or nitrogen as well as of nutrients such as nitrogen and phosphorus is necessary for effective biodegradation of hydrocarbon compounds. Therefore, these compounds are frequently injected into the contaminated subsurface to enhance in situ biodegradation. The effect of residual subsurface hydrocarbon (kerosene) contamination on the transport of an electron acceptor (NO3−) and a nutrient (NH4+) was investigated. Soil column experiments were conducted using uncontaminated and contaminated soil, and a one-dimensional solute transport model with multiprocess nonequilibrium sorption was used to predict the breakthrough curves. The presence of kerosene contamination was found to decrease the volumetric water content which in turn increased the pore-water velocity. An earlier breakthrough time for NO3− relative to the uncontaminated soil was observed and predicted by the transport model. The exchange isotherm involving NH4+ was not affected by the presence of kerosene; therefore, no significant difference in NH4+ transport was observed or predicted. The results of this study indicate that the transport of NO3− will be increased by residual subsurface hydrocarbon contamination whereas NH4+ transport will be unaffected. Therefore the presence of residual subsurface contamination by hydrocarbons will have to be taken into account in NO3− transport models.