DEGRADATION KINETICS OF AROMATIC ORGANIC SOLUTES INTRODUCED INTO A HETEROGENEOUS AQUIFER

Degradation rates of benzene, p-xylene, naphthalene, and o-dichloroben zene have been measured in a heterogeneous, unconfined aquifer during a pulse injection experiment at Columbus Air Force Base, Columbus, Mis sissippi. Dissolved oxygen in the pulse plume maintained aerobic condi tions. Degradation kinetics calculated from the complete field data se t were approximately first order with the following rate constants: be nzene, 0.0070 d-1; p-xylene, 0.0107 d-1; naphthalene, 0.0064 d-1; and o-dichlorobenzene, 0.0046 d-1. Reaction rates were also calculated fro m a near-field subset of the data using a model based on the hydrologi c characteristics of the aquifer. Shapes of the degradation rate curve s were consistent with microbial degradation processes. Maximum degrad ation rates obtained are presumed to be characteristic of the microbia l population metabolism. Carbon 14-labeled p-xylene was included in th e injection solution to permit detection of degradation products. This technique is suggested for future field experiments, because it disti nguishes solute degradation from solute losses by sorption and evapora tion and allows mass balance to be demonstrated throughout the course of the reaction in the aquifer.