HELCOM RECOMMENDATION 11/2

(supersedes HELCOM Recommendation 9/9)

Adopted 14 February 1990, having regard to Article 13, Paragraph b) of the Helsinki Convention

REDUCTION OF DISCHARGES FROM URBAN AREAS BY PROPER MANAGEMENT OF STORMWATER

THE COMMISSION,

RECALLING Paragraph 1 of Article 6 of the Convention on the Protection of the Marine Environment of the Baltic Sea Area, 1974 (Helsinki Convention), in which the Contracting Parties undertake to take all appropriate measures to control and minimize land-based pollution of the marine environment of the Baltic Sea Area,

RECALLING ALSO HELCOM Recommendation 5/1 regarding limitation of oil in stormwater systems,

RECOGNIZING the, need for limiting the harmful effects caused by the stormwater discharged to the Baltic Sea,

RECOMMENDS to the Governments of the Contracting Parties to the Helsinki Convention that:

  a)         measures should be taken already at the source to prevent the deterioration of the quality of stormwater (e.g. efficient dry street cleaning and reduction of lead in petrol);

  b)         where a stormwater in a separate sewer system district is collected from areas with high traffic

     (i)         flow equalization units should be provided whenever possible for the first flush of stormwater; and

     (ii)        this water be conveyed to a sewage treatment plant;

  c)         contaminated stormwater from heavily polluted industrial areas (loading, unloading, storing) should be treated as polluted wastewater;

  d)         all possible means should be taken to minimize the volume of stormwater entering combined sewer systems (minimization of the volume, reached e.g. by local infiltration);

  e)         in areas with combined sewer systems, overflow should not be allowed more than on the average 10 times per year or limited to 10 percent of the total amount of pollutants conveyed in the sewer system (several overflow occasions during one single day are regarded as one), which aim may be reached by means of appropriate design of the sewerage system and by providing retention facilities; *) the aim should be further to catch the first (most polluted) volume of overflow for conveying it to the treatment plant, and to decrease the amount of overflowing pollutants, combined sewer outflows should be equipped with some treatment facilities such as swirl concentrators,

RESOLVES that a decision on the date from which paragraph e) of this Recommendation should be implemented will be taken in 1995.**)

*)         Experience shows that the easiest way to express pollution load caused by combined sewer overflow is to use the indirect figure of frequency, i.e. number of times per year, because thus it is not necessary to undertake the difficult task of determining the quality of the combined sewer overflow water in each case.

**)       The aim is to have paragraph e) implemented in 1998, but lack of knowledge makes it impossible to set this date definitely as of today.  National projects, however, are believed to produce the information needed to take a decision by 1995.