Subsurface contamination by trichloroethene (TCE) was detected at the St. Joseph, Michigan site in 1982. Investigation of the site revealed the presence of TCE degradation products, including three dichloroethene isomers, vinyl chloride and ethene. The plume was found to be depeleted of oxygen and methanogenic at certain depths. In August of 1994, water samples were tkaen from a barge situated about 100 m off-shore in Lake Michigan. Each round of samples were taken along transects that crossed the width of the plume; as determined in the field by gas chromatography. From the data set, the average concentration of each chemical and net apparent loss coefficients between appropriate pairs of transects were calculated. The loss rates were calculated from the solution of the one-dimensional advective-dispersive-reactive transport equation. The net apparent rate coefficients and a set of coupled reaction rate equations were used to extract the apparent loss coefficients from the field data.