HELCOM RECOMMENDATION 17/7
Adopted 12 March 1996 having regard to Article 13, Paragraph b) of the Helsinki Convention
This Recommendation supersedes HELCOM Recommendation 11/2
REDUCTION OF DISCHARGES FROM URBAN AREAS BY PROPER MANAGEMENT OF STORMWATER
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 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 discharges 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) contaminated stormwater from heavily polluted industrial areas (loading, unloading, storing) should be treated separately; measures can be based on local research and consideration case by case;
c) if a stormwater in a separate sewer system district is collected from traffic areas where the first flush of stormwater is highly polluted
- flow equalization units should be provided whenever possible for the first flush of stormwater; and
- when possible this water should be treated separately in stormwater treatment facilities or in a sewage treatment plant, as appropriate;
d) depending on the characteristics of the contamination of the stormwater, possible means should be taken to minimize the volume of stormwater entering combined and separate sewer systems (minimization of the volume, reached e.g. by local infiltration if allowed by geological conditions);
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 flow conveyed in the sewer system (several overflow occasions during one single day are regarded as one), which aim may be reached by appropriate design of the sewerage system and by providing retention facilities*); the aim should further be to catch the first (most polluted) volume of overflow for separate treatment. In order to decrease the amount of overflowing pollutants combined sewer outflows should be equipped with some treatment facilities such as swirl concentrators,
RECOMMENDS that this Recommendation will be in force as from 1 January 1998, with provisions b) - e) applying only to new and retrofitted sewerage systems,
RECOMMENDS ALSO that the Contracting Parties report to the Commission every three years starting in 2000,
DECIDES that this Recommendation should be reconsidered in 2000.
*) 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 outflow in each case.
REPORTING FORMAT FOR HELCOM RECOMMENDATION 17/7 CONCERNING REDUCTION OF DISCHARGES FROM URBAN AREAS BY PROPER MANAGEMENT OF STORMWATER
1. Have steps been taken to prevent the deterioration of the quality of the stormwater at the source, e.g.
a) dry street cleaning?
b) reduction of lead in petrol?
2. Are flow equalization units used; to what extent and what is the experience?
3. Is heavily polluted stormwater conveyed to special waste water treatment plants?
4. Are local infiltration systems used to minimize the volume of stormwater entering the combined systems? If so, describe the systems and your experience of applications.
5. Are there any national, regional or local regulations or guidelines for the proper management of stormwater? If so, describe them and your experience of applications. Please, describe also recording and estimations of overflows.