Sensitive areas
Another major provision is that of Article 5 which lays down a specific additional requirement that applies to “sensitive areas.” Member States shall ensure that urban waste water entering collecting systems shall before discharge into such sensitive areas be subject to “more stringent treatment”, sometimes called “tertiary treatment” for all discharges from agglomerations of more than 10,000 p.e. (Article 5(2)). By and large, sensitive areas are freshwater bodies, estuaries and coastal waters “which are found to be eutrophic or which in the near future may become eutrophic if protective action is not taken”, surface freshwater intended for the abstraction of drinking water “which could contain an excessive concentration of nitrate (…) if action is not taken”, and, as per some sort of a “catch-all clause”, all other “areas where further treatment than that prescribed in Article 4 of this Directive is necessary to fulfill Council Directives” (Annex II).
Waters must only be designated as sensitive areas if discharges contribute to the aquatic environment’s eutrophic nature or to the risk that the waters may become eutrophic. In a given instance, the existence of a causal link between nutrient input and the accelerated growth of phytoplankton was considered to be sufficiently probable to require the adoption of measures based on the precautionary principle, even though the ecological model on which it was based was not perfect (Case C-282/02 Commission v France, para. 34). For example, sensitive areas were found to exist for the purpose of the requirement of more stringent treatment with respect to the whole of Finnish territory (Case C-335/07 Commission v Finland, para. 31) as well as with respect to the whole of Swedish territory (Case C-438/07 Commission v Sweden, para. 34).
Italy was found to be in breach because it did not submit urban waste-waters in the Milan area to more stringent treatment than the regular secondary treatment although they were discharged into the sensitive areas of the “Pô Delta” and the coastal areas of the North West Adriatic: it makes no difference whether the waste-water discharges directly into a sensitive area rather than indirectly, e.g. by going through the water basin of the Po (Case C-396/00 Commission v Italy). However direct or indirect discharges from urban waste-water treatment plants situated in the same catchment area of a sensitive area, are required to meet the requirements applicable to sensitive areas only to the extent that those discharges contribute to the pollution of that area and a causal link is established between those discharges and the pollution of the sensitive areas (Case C-335/07 Commission v Finland, paras. 41-44; Case C-438/07 Commission v Sweden, paras. 45-47).