Groundwater is currently monitored by EU laboratories to control the level of contamination by major or trace elements in particular in support to EC Directives (80/68/CEE, 80/778/CEE and 91/676/CEE) which prescribe the determination of a range of elements and compounds. In monitoring groundwater, it is essential to ensure that the data produced are of sufficient accuracy and precision so that results of different laboratories obtained over a number of years can be compared which requires the availability of representative CRMs.

The project aimed to carry out an interlaboratory study to check the feasibility of groundwater material preparation and evaluate the analytical state of the art, and to organise a certification campaign of two groundwater CRMs to be certified for their contents of a range of trace elements (CRMs 609 and 610) and two other CRMs to be certified for their contents of bromide and iodide (CRMs 611 and 612).
The interlaboratory study (organised in 1995) was successfully conducted and enabled to pursue the project. The certification campaign was carried out with 22 laboratories from EU and Associated Member States; it was successfully concluded for the CRMs 609 and 610 which were certified for their contents of Al, As, Cd, Cu and Pb. The CRMs 611 and 612 could only be certified for their bromide content based on ion-chromatographic measurement, owing to the lack of techniques available; iodide could not be certified.
The different tasks were the following: (1) preparation of reference materials containing natural groundwater (in bottles for trace elements and in ampoules for bromide and iodide), (2) organisation of an interlaboratory study, (3) preparation of large batches of candidate reference materials, (4) organisation of a certification campaign, and (5) technical and statistical evaluation of the results followed by writing of the certification report.