HELCOM RECOMMENDATION 9/9

Adopted 17 February 1988, having regard to Article 13, Paragraph b) of the Helsinki Convention

Supersedes the present HELCOM Recommendation 7/5

RECOMMENDATION CONCERNING MEASURES AIMED AT THE REDUCTION OF DISCHARGES FROM URBAN AREAS BY THE TREATMENT 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 harms caused by the quality of stormwater discharged to the Baltic Sea Area,

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 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 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 could be reached for instance by local infiltration);

e) in areas with combined sewer systems, overflow should not be allowed more than on the average during 10 days per year or be limited to 10 % of the total amount of pollutants conveyed in the sewer system. This aim may be reached by means of appropriate design of the sewerage system and by providing retention facilities. The time when this part of the recommendation should be implemented will be decided within one year after adoption. For the volumes overflowing it is recommended to try to catch the first (most polluted) volume and convey it to the treatment plant. It is further recommended to use for example swirl concentrators at the combined sewer overflows to decrease the amount of pollutants overflowing,

RECOMMENDS FURTHER that the action taken by the Contracting Parties should be reported to the Commission one year after the adoption of this Recommendation and thereafter every five years.