FATE AND TRANSPORT A LINEAR ALKYLBENZENESULFONATE IN A SEWAGE-CONTAMINATED AQUIFER - A COMPARISON OF NATURAL-GRADIENT PULSED TRACER TESTS

Two natural-gradient tracer tests were conducted to determine the tran sport and biodegradation behavior of linear alkylbenzenesulfonate (LAS ) surfactant under in situ conditions in a sewage-contaminated aquifer . The tests were conducted in two biogeochemically distinct zones of t he aquifer: (1) an aerobic uncontaminated zone (oxic zone) and (2) a m oderately aerobic, sewage-contaminated zone (transition zone). Chromat ographic separation of the surfactant mixture was observed in both zon es and attributed to the retardation of the longer alkyl chain homolog ues during transport. No significant loss of LAS mass was observed for the oxic zone while 20% of the LAS mass injected into the transition zone was removed due to biodegradation. Biodegradation preferentially removed the longer alkyl chain homologues and the external isomers (i. e., 2- and 3-phenyl), The removal of LAS mass coincided with a decreas e in dissolved oxygen concentrations, the appearance of LAS metabolite s, and an increase in the number of free-living bacteria with a concom itant change in bacteria morphology, The formation of LAS metabolites accounted for 86% of the LAS mass removed in the transition zone. Over the duration of the test, sorption and biodegradation enriched the LA S mixture in the more water-soluble and biologically resistant compone nts.