Natural in situ bioprocesses as a basis for cost-effective remediation : examples of 16 contaminated sites in The Netherlands

The feasibility of intrinsic and enhanced bioremediation approaches for 16 contaminated sites in the Netherlands are discussed. At at least five out of 10 chlorinated solvent sites, natural attenuation can be used as one of the tools to prevent further dispersion of the plume. At two sites stimulation of the intrinsic dechlorination processes in a bioactived zone is required, and pilot field tests are currently under way. In three sulphate-reducing/methanogenic aquifers contaminated with aromatic compounds, natural anaerobic degradation of the risk causing benzene was demonstrated not to occur spontaneously by microcosm studies. Benzene biodegradation could be initiated by feeding small amounts of oxygen (in all samples) or nitrate (only in one sample). Investigations at two locations contaminated with hexachlorocyclohexanes indicated significant intrinsic bioattenuation of HCHs under very low field-redox conditions, and of the HCH-degradation products chlorophenol and benzene under sulphate/iron reducing conditions. Biostimulated zones are still required to complete the degradation of HCH and the degradation product monochlorobenzene.