EPA's Region 6 Office
Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations
Creosote is a complex mixture of chemical constituents encompassing diverse chemical structures. Of the 150 to 200 chemicals in creosote, only a few are present in amounts of 1% or more. Creosote is a highly insoluble dense non-aqueous phase liquid (DNAPL) that tends to collect in "pools" within the soil matrix. Groundwater tends to flow around these "pools" because the oil is highly hydrophobic, and as a result only a small fraction of the total contained polynuclear aromatic hydrocarbon (PAH) mass is actually exposed to the groundwater. The solubilities of the PAHs identified at the Popile site vary from insoluble to 31 milligrams per liter (mg/L).
The PAH compounds have various physical and chemical characteristics. The lower molecular weight PAHs are more biodegradable, volatile, and water-soluble than the heavier compounds. PAHs are biodegradable, especially under aerobic conditions (in the presence of oxygen). Several of the lower molecular-weight PAHs are also biodegradable under anaerobic conditions (in the lack of oxygen).
Commercial grade pentachlorophenol (PCP) is a white crystalline solid with low solubility in water (14 mg/L), but more soluble in diesel oil (3,100 mg/L). When PCP is used in wood preserving, it is applied in carrier oil to assist in penetration into the wood. PCP does not readily partition from the oil into the groundwater, so it can slowly leach into the groundwater for long periods of time. PCP in an aqueous phase (dissolved in water) can be rapidly biodegraded through both aerobic and anaerobic processes.
Organic contaminants are biodegrading at the Popile site, because the following basic factors are present: (1) an appropriate microbial community; (2) degradable PCP and PAHs; and (3) favorable environmental parameters such as temperature, redox potential, oxygen, and nutrient availability.