Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
It is well known that the areas in the vicinity of roads are polluted due to traffic, mainly in form of heavy metals and
PAHs (polycyclic aromatic hydrocarbons). The pollutions are transported to the surroundings by air, splash or
highway runoff where they either infiltrate into the ground or flow on the surface to a surface water recipient. The
Swedish National Road Administration has the responsibility for the national road networks impact on the environment.
The water protection area of Östra Mälaren contains 230 kilometres governmental roads of which some are
the most busy ones in Sweden (E4, E18 and E20). Due to this a cost effective way is needed to take care of the
polluted highway runoff that may contaminate the water recipients in the surroundings. Soils have capabilities to
retain pollutions which stop the further transport to the groundwater. This capacity of the soil differs between
different sites since the soil material is very heterogonous. The soils texture decides to a large degree the concentration
of the metal in the leachate. A large amount of clay and humic substances gives a high capacity to retain metal
ions, whereas in a more sandy soil the leaching of pollutions is larger. To examine the risk of downward transport in
a drain situated along a busy highway outside Stockholm, samples were taken and analyzed for the total content of
Cd, Cr, Cu, Pb and Zn and the potential leachable amount. The gradients of the total content with depth and distance
from the road showed that the drain was polluted and most obvious was this for Cu, Pb and Zn. Cadmium had
the highest concentration in the bottom of the drain while the concentration in the slope (e.g. closer to the highway)
were significantly lower. The Cr concentration was close to background values and showed no significant trend at all.
The leaching tests showed that only small amounts of the total metal contents were leachable, 0,16 %, 2 % and 8,8 %
for Pb, Cu and Zn. In spite of this the concentrations of Pb and Zn exceeded the drinking water criteria. This indicates
that the groundwater in the area may have enhanced metal concentrations. Cu and Pb occurred in association
with dissolved organic carbon (DOC). The amount of DOC will increase with increasing pH and accordingly the risk
of leaching. Zinc showed high correlations with Mn which indicates that Zn is adsorbed to oxides. This will lead to
that a higher loss of Zn is expected in an environment with low pH and reduced conditions. In this study Lake
Bornsjön is the final recipient and the inflow to the lake is situated 5 kilometres from the studied drain and hence the
impact of the polluted highway runoff will be insignificant due to dilution. Although, in other parts in the water
protection area the situation might be different, as well as in the future and this can lead to a change in the pollution
load on the water reservoir.
2007. , 27 p.