Article 6

within two years of notification of the Directive, monitor the nitrate concentration in freshwaters over a period of one year:

1. (i)

   at surface water sampling stations, laid down in Article 5 (4) of Directive 75/440/EEC and/or at other sampling stations which are representative of surface waters of Member States, at least monthly and more frequently during flood periods;

2. (ii)

   at sampling stations which are representative of the groundwater aquifers of Member States, at regular intervals and taking into account the provisions of Directive 80/778/EEC;

repeat the monitoring programme outlined in (a) at least every four years, except for those sampling stations where the nitrate concentration in all previous samples has been below 25 mg/l and no new factor likely to increase the nitrage content has appeared, in which case the monitoring programme need be repeated only every eight years;

review the eutrophic state of their fresh surface waters, estuarial and coastal waters every four years.