The authors estimated the distribution of chlorinated aliphatic hydrocarbon (CAHs) from groundwater samples collected along three transects in a sand aquifer. Trichloroethylene (TCE) leaked and contaminated the aquifer probably more than a decade before the authors collected the measurements. The data show significant concentrations of TCE, cis-1,2-dichloroethylene (c-DCE), vinyl chloride (VC), and ethene. The authors attributed DCE, VC, and ethene to the reductive dehalogenation of TCE. The CAH concentrations varied significantly with depth and correlate with sulfate and methane concentrations. Anoxic aquifer conditions exist with methane present at relatively high concentrations at depth. The authors estimated that about 20% of TCE has dechlorinated to ethene. The analysis of the data enhanced the authors' knowledge of natural in situ transformation and transport processes of CAHs.