ABSTRACT: The permeable reactive barriers (PRBs) were constructed in the frame of the 1st stage of cleanup activities at Hluk site in 2002. As main contaminants, the chlorinated hydrocarbons (CHC such as 1,2 DCE, TCE and PCE) were identified at the site, partly also with total petroleum hydrocarbons (TPH). The clean-up system was designed as a combination of classic pump & treat method together with soil vapor extraction (SVE) and PRBs located in groundwater flow direction from the contamination hotspots. In total, the system is composed of 4 slurry walls with 8 reactive gates. The gates are filled with zero valent iron – cast iron filings originated from dry metal machinery. The 1st phase of reactive gates efficiency evaluation has been realized from 2002 to 2005. The strong fluctuations of gates efficiency in time was registered, partly caused by unsuitable location of PRBs monitoring system. After completion of the monitoring system, the calculated efficiency of PRBs increased significantly. The average efficiency of reactive gates varied between 57 – 97 % and concentration fluctuations achieved almost 90 %.