3.1.3 Runoff
The PAH flux related to runoff on roads and roofs (F12e) was quantified considering
the volume of runoff collected in the sewer system. To estimate this flux, the
PAH concentrations were gathered from four studies depicting 31 samples collected
in separate sewer systems of urban areas [10, 24–26]. The samples covered an
extended area across the Paris conurbation, providing a good spatial representativeness of the database. Moreover, they were in good agreement with previously
reported values for similar urban or suburban areas [27, 28]. However, the temporal
representativeness was not as good. Indeed, samples were collected at various
times over the year, but the relationship between PAH concentrations and the
characteristics of the rain event considered (rainfall intensity or duration of
the previous dry periods) could not be investigated. Consequently, this flux was
estimated as the sum over the year of 12-day periods of runoff volumes multiplied by
PAH concentrations randomly drawn within the runoff database. The flux totalled
F12e ¼ 300 Æ 40 kg year
À1 (Σ15). This result was in good agreement with fluxes
reported for other French urban areas [29]. However, the quality grade of this flux
was reduced to 3 because of the lack of information on the temporal changes in the
runoff contamination.
In addition, the PAH flux during the street cleaning process (F12f) was quantified.
According to the SIAAP, the amount of water used for street cleaning reached
59 Mm
3 year
À1 . A previous study showed that the PAH concentration in water
samples ranged from 0.1 to 2.2 μg L
À1 (Σ13) [30]. This study used data from
21 samples collected at various places within the Paris city limits. Although the
spatial database was spatially representative, all samples were collected from May to
June 2002, and neither temporal changes nor the influence of meteorological parameters could be investigated. Consequently, and although the order of magnitude of
the contamination was supported by the concentrations reported in runoff samples,
the quality rate was downgraded to 2. The flux estimated in this way was
F12f ¼ 93 Æ 3 kg year
À1 (Σ16, naphthalene included), and it amounted to 32% of
the atmospheric deposition and 29% of the PAH runoff from roads and roofs.
However, the influence of meteorological parameters could not be tested, and a
redundancy between F12e (street runoff) and F12f (street cleaning) cannot be
excluded because both remobilise pollutants from roads.
3.1.4 Domestic and Industrial Wastewater
The flux related to domestic wastewater (F22a) was quantified using 35 measurements either in domestic effluents or in combined sewers during dry weather periods
[30, 31]. Specific attention was paid to using only samples collected close to
domestic sources to avoid dilution by infiltration waters. Using data from combined
sewers provided a better spatial representativeness, especially within the city of Paris
itself, where there were exclusively combined sewers. However, this might have
Mass Balance of PAHs at the Scale of the Seine River Basin
171
The PAH flux related to runoff on roads and roofs (F12e) was quantified considering
the volume of runoff collected in the sewer system. To estimate this flux, the
PAH concentrations were gathered from four studies depicting 31 samples collected
in separate sewer systems of urban areas [10, 24–26]. The samples covered an
extended area across the Paris conurbation, providing a good spatial representativeness of the database. Moreover, they were in good agreement with previously
reported values for similar urban or suburban areas [27, 28]. However, the temporal
representativeness was not as good. Indeed, samples were collected at various
times over the year, but the relationship between PAH concentrations and the
characteristics of the rain event considered (rainfall intensity or duration of
the previous dry periods) could not be investigated. Consequently, this flux was
estimated as the sum over the year of 12-day periods of runoff volumes multiplied by
PAH concentrations randomly drawn within the runoff database. The flux totalled
F12e ¼ 300 Æ 40 kg year
À1 (Σ15). This result was in good agreement with fluxes
reported for other French urban areas [29]. However, the quality grade of this flux
was reduced to 3 because of the lack of information on the temporal changes in the
runoff contamination.
In addition, the PAH flux during the street cleaning process (F12f) was quantified.
According to the SIAAP, the amount of water used for street cleaning reached
59 Mm
3 year
À1 . A previous study showed that the PAH concentration in water
samples ranged from 0.1 to 2.2 μg L
À1 (Σ13) [30]. This study used data from
21 samples collected at various places within the Paris city limits. Although the
spatial database was spatially representative, all samples were collected from May to
June 2002, and neither temporal changes nor the influence of meteorological parameters could be investigated. Consequently, and although the order of magnitude of
the contamination was supported by the concentrations reported in runoff samples,
the quality rate was downgraded to 2. The flux estimated in this way was
F12f ¼ 93 Æ 3 kg year
À1 (Σ16, naphthalene included), and it amounted to 32% of
the atmospheric deposition and 29% of the PAH runoff from roads and roofs.
However, the influence of meteorological parameters could not be tested, and a
redundancy between F12e (street runoff) and F12f (street cleaning) cannot be
excluded because both remobilise pollutants from roads.
3.1.4 Domestic and Industrial Wastewater
The flux related to domestic wastewater (F22a) was quantified using 35 measurements either in domestic effluents or in combined sewers during dry weather periods
[30, 31]. Specific attention was paid to using only samples collected close to
domestic sources to avoid dilution by infiltration waters. Using data from combined
sewers provided a better spatial representativeness, especially within the city of Paris
itself, where there were exclusively combined sewers. However, this might have
Mass Balance of PAHs at the Scale of the Seine River Basin
171