Benefits and limits of isotope investigations in groundwater protection and remediation

An example is given for the application of isotope methods to improve the database in an area with groundwater pollution due to a waste dumping site. Contamination by chlorinated and aromatic hydrocarbons was detected in all three aquifers despite the fact that there was no evidence from geological data for a hydraulic connection between the two upper aquifers and the lower aquifer. By measuring H-2, O-18, H-3, He-3 and C-14 in groundwater samples from all three aquifers it could be shown that the two upper aquifers are well connected, with groundwater ages of less than 10 a and less than 15 a, respectively. In the lower aquifer a young water component was detected by tritium/He-3 dating (age about 20 a), while the C-14 dating gave an age of several thousand years, indicating a mixture between an old and a very young groundwater component. This sufficiently explained the groundwater contamination in the lower aquifer. The isotope investigation enhanced the site specific database derived from hydrogeological and hydrochemical data. A greatly improved basis for the development of a remediation concept was achieved. (author)