Prospects and Limitations of Surface Runoff Quality Management in the Republic of Serbia - page 03

 

 

Other tests conducted in the U.S. show that the quality of surface runoff depends primarily on surface soil properties and land use (Debo and Reese, 2003):

  • Surface runoff from impervious surfaces, such as pavements and roofs, carries the dissolved or suspended pollution accumulated on surfaces and washed away by the the runoff. After the contaminants have been washed away with the initial surface runoff, the water quality begins to improve. High rainfall intensities and reduced soil infiltration capacity has a major impact on contaminant load levels of suspended solids, heavy metals and oils while the content of BOD5 and nutrients are usually relatively low.
  • Surfaces such as grasses, forests and other vegetation, which are porous and highly permeable to rainfall help to reduce contaminant levels of surface runoff. Runoff from these areas usually does not have highly polluted "first flush", but studies have shown that the pollution loads depends primarily on the intensity and duration of rain. Typical pollutants in runoff from the green areas are suspended solids, BOD5 and nutrients.

The fate and transport of contaminants are very complex. Contaminants that are persistent and that tend to bio accumulate in tissue, like metals, produce long lasting impacts on terrestrial organisms (Lancaster and Beutel, 2011).

As part of the City of Belgrade's Sewer System Master Plan preparation, rainfall-runoff and stormwater quality measurements were taken. Runoff flow and quality measurements were taken from two storm sewers located in New Belgrade. The area covered by storm sewerage is home to about 150,000 inhabitants. Measurements were carried out on two low intensity rainfall events on October 29, 2008 and November 25, 2008. Measured contaminant concentration levels measured at both measuring points in water samples were as follows:

 

BOD5

from 10.0 to 125 mg/l

COD

from 10.2 to 383.3 mg/l

Suspended solids

from 49.4 to 222.0 mg/l

TKN

from 2.1 to 27.5 mg/l

PO43-

from 0.1 to 2.4 mg/l

 

Pollution loads measured during rain events in autumn 2008 were about 300 kg BOD5 per day (5,000 p.e.), and about 1730 kg per day of suspended solids (approx 25,000 p.e). Loads in population equivalents were derived from storm pollution loads divided by unit loads per population equivalent as per the German ATV-DVWK-A 131E guidelines. It can be expected that higher rainfall intensities and longer rainfall durations would produce higher contaminant loads.