(1) Interpretation of the term "existing combustion plant". The Directive is clear that new combustion plants which share a common stack, or in the judgement of the competent authority could share a common stack, are to be regarded as a single plant for the purposes of the Directive. This means that their capacities are aggregated, for example for the purpose of determining whether the Directive applies and the applicable emission limit values. Similarly, existing plants whose waste gases are de facto discharged through a common stack should be considered as a single plant. Therefore, when a group of boilers discharge their waste gases through a common stack, the term "existing combustion plant" should be interpreted as that group of boilers. However, this aggregation approach does not apply to existing plants which potentially could share a common stack, but as a matter of fact do not. In other words the requirement to consider the possibility of sharing a common stack where one is not currently used, taking technical and economic factors into account, only applies to new plant.
(2) Interpretation of the term "stack". The Directive uses the term "stack" which should not be confused with the term "flue". A "flue" is a compartment or division of a stack (or chimney) for conveying combustion gases to the outer air. A "stack" refers to the structure (providing a conduit for combustion gases) rising above roof level which may embody one or more "flues". As a result, a "common stack" cannot be interpreted as a "common flue".
(3) Interpretation of the derogation in Article 4.4 of the Directive. Article 4.4 allows a plant to be exempted from compliance with the emission limit values of the Directive or inclusion in a national emission reduction plan, provided that the operator undertakes not to operate the plant for more than 20,000 operational hours starting from 1 January 2008 and ending no later than 31 December 2015. After this time the plant must close. A plant is considered to be operating for the purposes of this derogation when any part of it operates, irrespective of the load factor. Therefore, when several boilers discharge their waste gases through a common stack, and any of these boilers operates at any load factor for, say, one hour, it will be considered that the whole plant is operating for one hour for the purposes of the derogation.
(4) Conditions for combined approaches. If a Member State decides to use a "combined approach", in view of the added complexity that this entails the Commission will request two lists of plants from the Member State: those that would be subject to ELVs; and those included in the plan. In addition, in order to ensure compliance with the emission limit values, the Commission will ask to receive every year from 2008 (or the year when the ELVs begin to apply) the inventory of emissions from those existing plants to which they apply. In order to confirm compliance with the targets of the plan, Member States are also strongly recommended to set up the annual national reporting system foreseen in Commission Recommendation 2003/47/EC.