RAINWATER POLLUTION

Characteristic of pollutants

In urban areas, the level of pollution is dependent on many factors (traffic intensity, type of pavement, etc.). The pollutants present can be classified into two categories: pollutants in particulate form and pollutants in dissolved form. Pollutants in particulate form including Suspended Solids (SS) are an important part of stormwater pollution. In fact, at the scale of a watershed, the pollutants transported during rainy weather (hydrocarbons, PAHs, heavy metals, COD, and to a lesser extent BOD5, nitrogen, etc.) are partly fixed on the SS. In addition, much of this pollution is associated with fine particles less than 100 microns. As an indication, the table below illustrates the average proportions of pollutants present in runoff in dissolved and undissolved form.

Distribution of rainwater pollutants 63

Depending on the nature of the watershed (road, industrial, etc.), the concentration of different pollutants can vary significantly and may also lead to a risk of accidental oil pollution, as illustrated by the table below.

Activity / Parameters MES
mg/l
DCO
mg/l
Hydrocarbons
µg/l 
HAP's
µg/l 
Lead
µg/l
Zinc
µg/l
Residential area 53 - 190 79 - 142 <200 - 500 2'819 - 3'718 12 - 56 92 - 170
Ind. Zone access road 540 - 590 156 - 177 200 - 1'200 5'024 - 13'473 79 - 100 700 - 1'100
Heavy traffic road 180 - 600 79 - 617 700 - 2'000 3'409 - 40'745 40 - 71 430 - 1'150
Office carpark 22 - 500 12 - 175 <100 - 1'100 460 - 12'479 <5 - 90 <50 - 530
Commercial zone carpark 45 - 242 93 - 395 <20 - 2'400 640 - 3'890 50 - 280 220 - 1'000

Table 1: Pollutant concentration according to the watershed type

Therefore, the use of a treatment system adapted to the case (nature of the watershed, hydraulic pipelines, discharge objectives and treatment flow) must be studied.

This control of discharge in rainy weather is framed by:

  • The European Water Framework Directive which sets a clear objective: to reach by 2015 the ecological and chemical "good state" of all natural aquatic environments and to preserve those in very good condition.
  • The regulatory requirements defined by the discharge agreements (STORM directive)

For this purpose we offer different technical options such as:

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