COMPARISON OF DISCHARGES FROM
URBAN STORM-WATER RUN-OFF,
MIXED STORM OVERFLOW
AND TREATED SEWAGE
G. SÖDERLUND and H. LEHTINEN
AJlmänna Ingenjörsbyran, Stockholm, Sweden
INTRODUCTION
The rapid migration of the Swedish population to a few urban areas is resulting in
intense development around the major towns. In all these expanded population centres
the sewage is collected in separate systems for storm-water and domestic sewage. This
process of urbanization leads to a reduction in the natural infiltration capacity, and the
volume of storm-water run-off is thus increased. As the storm-water is conducted through
its own sewer system to the nearest discharge point without treatment, its contribution to
the water recipients can be considerable. Storm-water run-off from heavily trafficated
urban areas contains large quantities of pollutants (1) and large numbers of bacteria
(2-11).
Because of the more more widespread treatment of domestic sewage, the storm-water
run-off becomes relatively more important as a source of water pollution and the
question is whether this source is important enough to require treatment.
The prime purpose of this study was to determine and compare the pollutant content
of urban storm-water run-off with that of the treated effluents, and also with that of the
storm overflow water from combined systems.
SAMPLING AND EXPERIMENTAL METHOD
Sampling areas
As sampling areas two urban drainage districts with separate sewer systems located in
the southern part of Stockholm were used. The first district has a population of 11,000
and is 1000 hectares* in extent, 220 hectares of which is developed, with 145 hectares
(66%) residential, 10 hectares (5%) industrial, and 65 hectares (29%) open space. The
locations chosen for closer analysis were:Terrace housing — 25 hectares, of which 9 ha open space (population 700)
Suburban service centre — 25 hectares, of which 8 ha open space (population 2,600)
A cloverleaf junction — 3.3 hectares, with a traffic density of 65.000 vehicles a day
The second district, having a population of 30,000 is 530 hectares in extent, which
consists of 315 hectares (59%) residential, 35 hectares (7%) industrial, and 180 hectares
(34%) open space.
Meteorological data
The rainfall intensity and total rainfall were registered on pluvigraphs. The flow in the
storm-water sewers serving the two areas was registered continuously with a water-level
recorder calibrated against flow meters.
* 1 hectare = 2Vi acres, approx.
309
URBAN STORM-WATER RUN-OFF,
MIXED STORM OVERFLOW
AND TREATED SEWAGE
G. SÖDERLUND and H. LEHTINEN
AJlmänna Ingenjörsbyran, Stockholm, Sweden
INTRODUCTION
The rapid migration of the Swedish population to a few urban areas is resulting in
intense development around the major towns. In all these expanded population centres
the sewage is collected in separate systems for storm-water and domestic sewage. This
process of urbanization leads to a reduction in the natural infiltration capacity, and the
volume of storm-water run-off is thus increased. As the storm-water is conducted through
its own sewer system to the nearest discharge point without treatment, its contribution to
the water recipients can be considerable. Storm-water run-off from heavily trafficated
urban areas contains large quantities of pollutants (1) and large numbers of bacteria
(2-11).
Because of the more more widespread treatment of domestic sewage, the storm-water
run-off becomes relatively more important as a source of water pollution and the
question is whether this source is important enough to require treatment.
The prime purpose of this study was to determine and compare the pollutant content
of urban storm-water run-off with that of the treated effluents, and also with that of the
storm overflow water from combined systems.
SAMPLING AND EXPERIMENTAL METHOD
Sampling areas
As sampling areas two urban drainage districts with separate sewer systems located in
the southern part of Stockholm were used. The first district has a population of 11,000
and is 1000 hectares* in extent, 220 hectares of which is developed, with 145 hectares
(66%) residential, 10 hectares (5%) industrial, and 65 hectares (29%) open space. The
locations chosen for closer analysis were:Terrace housing — 25 hectares, of which 9 ha open space (population 700)
Suburban service centre — 25 hectares, of which 8 ha open space (population 2,600)
A cloverleaf junction — 3.3 hectares, with a traffic density of 65.000 vehicles a day
The second district, having a population of 30,000 is 530 hectares in extent, which
consists of 315 hectares (59%) residential, 35 hectares (7%) industrial, and 180 hectares
(34%) open space.
Meteorological data
The rainfall intensity and total rainfall were registered on pluvigraphs. The flow in the
storm-water sewers serving the two areas was registered continuously with a water-level
recorder calibrated against flow meters.
* 1 hectare = 2Vi acres, approx.
309