There are over 400 old wood treatment sites in United States of America with pentachlorophenol (PCP) contamination of soils and water. The role of the physical properties of soil on the bioremediation of PCP, a very toxic, high molecular weight chlorinated organic compound was investigated. Experimental results showed that clay minerals and certain soil properties play a very important role in sorption and desorption of pentachlorophenol and, subsequently bioremediation of the compound. A Colorado soil sample containing only 9% clay was shown to have great sorbing power (80%) due to the presence of swelling clay, soil organic matter, iron and aluminum oxides it contained as shown in the results from the physiochemical properties. Biodegradation experiments showed the Colorado soil having the least overall degradation (10%). This was expected since this soil desorbed only 2% of the contaminant, and since bioavailability is important for biodegradation, less desorption ultimately would affect degradation.