Clauson-Kaas, J.

Dam Joensen, S.

Mose Poulsen, B.

Skov, J.

I-Revues

NOVATECH 2016 
1 
Copenhagen: Rainwater quality and handling of 
urban run-off 
Copenhague : qualité des eaux pluviales et maitrise des 
rejets urbains de temps de pluie 
 
Jes Clauson-Kaas1, Bodil Mose Pedersen 2, Jette Skov 3, Sølvi 
Dam Joensen3 
 
1
 Greater Copenhagen Utility (HOFOR), Orestads Boulevard 35, DK- 
Copenhagen 2300S, Denmark, jecl@hofor.dk   
2Danish Hydraulic Institute (DHI), Agern Allé 5, DK-2970 Hørsholm 
Denmark, bmp@dhigroup.com    
3Copenhagen Municipality, Njaldsgade 13, DK-2300 Copenhagen S, Denmark, 
B98A@tmf.kk.dk  
 
RÉSUMÉ 
Copenhague est actuellement en train de mettre en œuvre un programme de prévention contre les 
inondations de plus d'un milliard d'euros, afin de protéger la ville lors de pluies torrentielles. Le réseau 
de tunnels, de canaux, de zones vertes ainsi que plusieurs plans d’eau facilitent la déconnexion des 
eaux de ruissellement du réseau d'égout offrant une alternative plus économique à l'augmentation de 
la capacité hydraulique du système d'égout actuelle. En se basant sur des analyses des eaux de 
ruissellement provenant de toits, de cours, de places et de rues, la qualité de l'eau de chaque surface 
urbaine est caractérisée. La qualité de l'eau de ruissellement provenant d'une zone urbaine composée 
de différents types de surfaces peut ainsi être estimée. Cette qualité de l'eau est comparée à la qualité 
des eaux réceptrices grâce à une évaluation des risques. Si les critères de rejet ne sont pas remplis, 
le choix est soit de mettre en place un traitement des eaux, soit d’empêcher les ruissellements les plus 
pollués (provenant par exemple des rues à forte circulation) en les évacuant dans le réseau d'égout. 
L'article propose une méthode de calcul de la qualité de l'eau de ruissellement d'une zone urbaine, la 
mise à disposition des données et identifie les éléments critiques dans les types de surfaces 
sélectionnées. De plus, des recommandations sont faites pour améliorer la qualité des données et la 
prise de décision dans la gestion des eaux de ruissellement urbaines. 
ABSTRACT 
Copenhagen is presently implementing an over one bill. EUR flood protection program to protect the 
city against cloud burst. The system of tunnels, canals, green areas and various water bodies 
facilitates disconnection of the urban run-off from the combined sewer as a cheaper alternative to 
increasing the hydraulic capacity of the existing sewer. Based on analyses of run-off from roofs, yards, 
squares and streets, the typical water quality of run-off from each type of urban surface is 
characterized. The resulting water quality of run-off from an urban area consisting of various types of 
surfaces can thus be estimated. This water quality is compared with the sensitivity of the receiving 
water using risk assessment. If discharge requirement are not met, the choice is either to introduce 
treatment or to avoid run off from the most polluted areas by continued discharging to the sewer (i.e. 
streets with heavy traffic). The paper proposes a method to calculate the water quality of run-off from 
an urban area, the availability of data and identifies critical compounds in the selected surface types. 
Further, recommendations are given on how to improve data quality and to improve decision making in 
handling of urban run-off.  
KEYWORDS 
Urban surface types, Urban run-off, water quality  
SESSION 
2 
1 INTRODUCTION 
1.1 Background 
Copenhagen is presently implementing an over one bill. EUR flood protection program to protect the 
city against cloud burst. The program also includes the necessity to disconnect 30% of the areas 
connected to the combined sewers, to compensate the fact that it presently is estimated that the 
rainfall intensity in DK will increase by 30%. A system of tunnels, canals, green areas and various 
water bodies will facilitate disconnection of the urban run-off from the combined sewer as it is a far 
cheaper alternative to increasing the hydraulic capacity of the existing sewer.  
However, there is a need for a better estimation of the quality of the disconnected run-off to minimize 
the potential impact on receiving water bodies. The most important environmental regulation for water 
bodies include: 
• The EU water framework directive implemented in National law (The Danish Water 
Management Plans) 
The EU water framework directive is in Denmark implemented in national water plans. In these 
management plans many water bodies shall meet the requirement in the form of good ecological and 
good chemical quality no later than in 2027. While working with climate adaption and the aim to 
increase discharge of run-off to the recipients, it is important to focus on the water quality of the run-off 
to maintain the goals of both the ecological and chemical quality in the water management plans. To 
make sure of this, the developed screening tool is used to assess if negative impacts on the water 
bodies are supposed to take place. 
• Bathing water 
Copenhagen municipality wishes to maintain bathing water quality and continuously improve the 
ecological and chemical conditions in the harbour. Bathing water requires that discharge of E coli and 
enterococci from CSO's are reduced, which is followed by a decrease of impacts from other pollutants 
 
1.2 Objective 
The water quality of a separate rain water discharge is determined by the materials used in the 
different urban surfaces (streets, roofs, square, etc.) and the activities on these surfaces (traffic, street 
cafés, etc.). A screening tool is therefore developed to assist environmental authorities in evaluation of 
potential environmental impacts from discharge of disconnected run-off. Gaining knowledge about the 
water quality of the run-off can also help the utility in finding more efficient ways of managing 
stormwater. 
The objectives of developing the screening tool were more specific: 
• To collect data on run-off quality from city surfaces like streets, roofs and squares during daily 
rain 
• To identify the most environmentally critical compounds 
• To identify the most critical surface types in a run-off catchment 
• To develop a method for screening of environmental risks from surface run-off which is 
discharged to a water body 
This paper describes the approach to developing the screening tool and how it can be applied in the 
work of making cities with combined sewer systems more climate proof by disconnection of run-off 
from roofs and other areas.  
 
NOVATECH 2016 
3 
2 METHOD 
2.1 Types of urban surfaces 
When dividing the city surface into categories the recommendations in the standard developed by the 
German Association for Water, Wastewater and Waste has inspired to the following divisions into 
surface types: 
1. Inner yards and playgrounds 
2. Roofs with copper 
3. Roofs with zinc 
4. Other roofs 
5. Streets with less than 5.000 vehicles/day 
6. Streets with 5.000-15.000 vehicles/day 
7. Streets with traffic more than 15.000 vehicles/day 
8. Parking lots for more than 80 cars 
The environmental authorities in Copenhagen has chosen to discharge road runoff to the sewer when 
the dally traffic exceed 5000 AADT.  
2.2 Choice of parameters 
Based on literature reviews, collected run-off quality data in Denmark (DK) and internationally and 
requirements in Danish environmental regulation, 30 indicators are included in the tool. These consist 
of common wastewater parameters like BOD and COD, nutrients like Tot-P and Tot-N, heavy metals, 
PAH, phthalates and pesticides. 
To assess if discharge of urban runoff might have negative environmental impact on the water quality 
in the water body it is relevant to compare the PNEC (predicted no effect concentration) for pollutants 
with the current concentration in urban runoff. If the concentration of pollutants are lower than PNEC in 
discharged water after initial dilution the urban runoff is not expected to have negative environmental 
effects  
Because introduction of new building materials and change in pollution from cars (e.g. no lead in fuel, 
copper in brakes, less oil leakage) it was decided only to include data from year 2000 and onwards.  
2.3 Calculating the water quality at a discharge point 
Based on analyses of run-off from roofs, yards, squares and streets, the typical water quality of run-off 
from each type of urban surface is characterized and the water quality at a discharge point is 
calculated by multiplying the size of each area type by the concentration of each compound and the 
sum it all up : 
Concxyz = ((Areax/AreaTotal)*Concx)+((Areay/AreaTotal)*Concy)+((Areaz/AreaTotal)*Concz) 
Arealxyz : The impermeable area (red. ha) of surface type X, Y and Z 
ArealTotal : The total area, i.e. the sum of Arealx, Arealy og Arealz 
Concxyz: The concentration of a compound in surface type X, Y and Z 
The resulting water quality of run-off from an urban area consisting of various types of surfaces can 
thus be estimated. This water quality is compared with the sensitivity of the receiving water using risk 
assessment. If discharge requirement are not met, the choice is either to introduce treatment or to 
avoid discharge of the most polluted areas (i.e. streets with heavy traffic).  
3 RESULTS AND DISCUSSION 
3.1 Availability of data 
There is plenty of data on roof water and some on street water, whereas there is no data on inner 
squares, pedestrian pavement and inner yards. The following table shows the availability of data 
where red means: no reportings, orange: less than 5 and green more than 5 reportings. 
 
SESSION 
4 
Table 1. Number of reported data of water quality 
  Ro
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Wastewater 
parameters 12-16 12-19 12-16 4-8 3-4 0-10 0-6 
Total-N and Total-P 15-19 15-20 15-19 8 3-4 10-11 0-6 
Metals total 2-20 2-20 15-20 4-8 4 13 6 
Metals dissolved 0-1 3-4 1 4-8 4 0 6 
PAH 15-18 15-22 15-18 8 3 0 2 
DEHP 0 0 0 5 3 9 2 
Other phthalates 0 0 0 0 0 0-9 0 
Bisphenol A 0 0 0 5 3 0 2 
Pesticides 0 0 0 0 0 0 0 
The majority of the water quality reporting is from DHI investigations in Denmark. 
3.2 Critical compounds 
3.2.1 Roof water 
The main problem with roof water in DK is the widely use of zinc for roofing pans, flashing at windows 
and gutters. To a lesser extent, copper used on older buildings is similarly problematic. Zinc and 
copper are environmental toxic compounds that accumulate in the food chain and hamper the 
biomass. 
PAH can also appear in roof water when asphalt roofing is used. Roofs with trees overhanging and/or 
birds, as well as atmospheric deposition can lead to elevated levels of nutrients in the water.  
3.2.2 Street water 
The quality of street water depends partly on traffic intensity. Over time the most dramatic change has 
been observed in compounds originating from the exhaust (earlier it contained lead), from engines 
(less oil spill today), the brakes and from various car care products. The brakes earlier contained 
asbestos, but now contains significant amount of copper. PAH in street water originate from the tyres 
and the asphalt surface, especially during acceleration and braking. 
Overview of critical compounds for selected surface types. For each type of recipient the 
recommended dilution factor included in evaluating impact is shown. 
NOVATECH 2016 
5 
 
 
Table 2. Critical compounds for selected surface types 
Surface Marine waters 
(Dilution 10x) 
Fresh waters 
(Dilution 2 x) 
Groundwater 
(No dilution) 
Roofs (other materials than 
copper and zinc)  Cu 
Zn, DEHP, 
glyphosat 
Zinc roofs Zn, Pb Zn, Cu, Pb,  Zn, glyphosat 
Roads  < 5,000 AADT PAH, bisphenol A 
Cu, PAH, DEHP, 
bisphenol A 
Pb, PAH, DEHP, 
glyphosat 
Roads 5-15,000 AADT PAH, bisphenol A 
Zn, Cu, PAH, 
bisphenol A 
Zn, Cu, Pb, PAH, 
DEHP, glyphosat 
Parking lots 
Cu, PAH, 
bisphenol A 
Zn, Cu, PAH, 
DEHP, bisphenol 
A 
Zn, Pb, PAH, 
DEHP, glyphosat 
 
In relation to improvement of water quality in lakes and achieving good ecological conditions, 
phosphorous is the most critical parameter. Therefore the load of phosphorous coming from urban 
runoff is an important parameter to control. Generally roof water and street water contain Total-P at 
intervals of 0.1-0.3 mg/l and Total-N of 2-3 mg/l.) 
 
Table 3. Concentrations of Total-P, Total-N and BOD for selected surface types (75% percentile) 
Surface Total-P 
(mg/l) 
 
Total-N 
(mg/l) 
 
BOD 
(mg/l) 
Roofs (other materials than 
copper and zinc) 
0.11 2.2 - 
Zinc roofs 0.26 - 12 
Roads  < 5,000 AADT 0.13  2.4  3.7 
Roads 5-15,000 AADT 1.1  4.6  12 
Parking lots 0.24 2.8 - 
 
4 CONCLUSION 
4.1 Screening tool 
It was found possible to develop a screening tool which is useful for storm water planners and 
environmental authorities in deciding how separated run-off water is handled with the best possible 
protection of the receiving waters. The project team identified areas where further data shall be 
collected to strengthen the tool and identified more clearly which surface materials and urban activities 
influence the content of critical compounds in run-off water. 
Therefore, intensified data collection will take place over the coming years especially focussing on 
street run-off water from streets, squares and inner yards. 
4.2 Need for data collection 
4.2.1 Surface types 
There is an obvious need for data on run-off water from non-motorized areas like squares, pavement 
and court yards. The water quality from these areas appears to be in close compliance with the 
environmental criteria for the three types of recipients (inland waters, other waters and groundwater). 
Analysis of run-off water from local streets with low traffic intensity shows low concentrations of critical 
compounds, whereas the level of critical traffic intensity where minimal treatment is sufficient needs to 
SESSION 
6 
be identified. 
4.2.2 Critical compounds 
There are very few data on dissolved metals (Zn, Cu, Pb) in run-off water. The environmental quality 
parameters for Zn, Cu, Pb in fresh and marine waters are expressed as dissolved metals. Therefore, it 
is recommended to include dissolved metals in future data collection programs. 
For all surface types, data on eco toxic compounds like phthalates, bisphenol A and pesticides as well 
as for total ammonium (total NHx-N) and fee ammonia (free NH3-) are virtually non-existent. The need 
for including these parameters must be clarified as they are important environmental quality 
parameters. 
4.3 Surface materials 
When developing new urban areas in Copenhagen regulation on roofing material has been introduced 
the last 10 years in DK. Materials of zinc, copper and tar-products have been banned, unless it is 
sealed and it is documented that the run-off contains only low levels of critical compounds. 
Widening this regulation to also including renovation of existing buildings could in time lead to gradual 
decrease in content of critical compounds in run-off. 
4.4 Traffic 
As it appears today, communication between car manufactures and water environmental authorities 
does not exist. To minimize the produced street waste from cars, the authors therefore urge car 
manufactures to focus on exhaust emissions and the materials used both in and on the cars, which is 
critical to the city water bodies.  
 
LIST OF REFERENCES 
Birch, H., Mikkelsen, P.S., Jensen, J.K., Lützhøft, H-C.H: Micropollutants in stormwater runoff and combined 
sewer overflow in the Copenhagen area, Denmark. Water Science & Technology 2011: 64 (2): 485-493 
Davis, B., Birch, G.: Comparison of heavy metal loads in stormwater runoff from major and minor 
urban roads using pollutant yield rating curves. Environmental Pollution 2010: 158: 2541-2545 
Deffontis, S., Breton, A., Vialle, C., Montréjaud-Vignoles, M., Vignoles, C., Sablayrolles, C.: 
Impact of dry weather discharges on annual pollution from a separate storm sewer in Toulouse, 
France. Science of the Total Environment 2013: 452-453: 394-403 
DHI, Danish Hydraulic Institute, Water quality analyses of surface run-off from varius areas in Copenhagen, 2010-
14. 
DIRECTIVE 2013/39/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 12 August 2013 
amending Directives 2000/60/EC and 2008/105/EC as regards priority substances in the field of water policy 
DWA Deutche Vereinigung fü Wasserwirtschaft, Abwasser und Abfal e.V. Advisory Leaflet DWA-M 153E: 
Recomended Actions for Dealing with Stormwater. August 2007 
Sally Zgheib, Régis Moilleron, Mohamed Saad, Ghassan Chebbo. Partition of pollution between dissolved and 
particulate phases: What about emerging substances in urban stormwater catchments? Water Research 45 
(2011) pp. 913-925 
 


Copenhague : qualité des eaux pluviales et maitrise des rejets urbains de temps de pluie

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Copenhague : qualité des eaux pluviales et maitrise des rejets urbains de temps de pluie

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