Two parallel pilot experiments were performed at Kurivody (Czech Republic) in order to compare two reductive remedial technologies for chlorinated ethenes - microbial dehalogenation assisted by lactate and chemical dehalogenation with zero-valent iron (nZVI) nanoparticles. The methods were applied at a site contaminated by tetrachlorethylene (PCE) and trichlorethylene (TCE), with total concentrations from 10 to 50 mg/l. Concentrations of chlorinated ethenes, inorganic components of interest, pH and oxidation reduction potential (ORP) were monitored at the site for a period up to 650 days. The method of biological reductive dechlorination supported by lactate showed a considerable removal of PCE and TCE, but temporary accumulation of transient reaction product 1,2-cis-dihloroethene. Reductive dechlorination with nZVI showed a significant reduction in the concentration of chlorinated ethenes without a formation of intermediate products. The development of pH showed only small changes due to the high buffering capacity of the aquifer. Both methods differ in the initial development of ORP, but over the long term showed similar values around 100 mV. Significant differences were observed for chemical oxygen demand, where groundwater after the application of nZVI showed no change in comparison to the application of lactate. The reductive effects of both agents were verified by changes in inorganic compound concentrations.