Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

Geological Survey of Finland, Special Paper 46
Volli Kalm
Fig. 3. Heavy metals
distribution in the section
through cultural layer
in the centre (corner of
Küüni and Vanemuise
streets) of the City of
Tartu.
144
HEAVY METALS IN THE CULTURAL LAYER
Chemical analyses of the samples from the cultural
layer exposed in an excavation at the city centre revealed
that the soil contamination from heavy metals
is very high (Fig. 3). The highest concentrations
of Pb were found below the layer of debris from
the Second World War (WW2), although this probably
represents the extensive use of leaded gas after
WW2. The maximum estimated concentration of Pb
(240 mg/kg; Nõges 2006) in the section is 14.6 times
higher than the average amount of Pb in Estonian
humic soils (16.4 mg/kg; Petersell et al. 1997). Zinc
and Cu reach their maximums (150 mg/kg and 96
mg/kg respectively) in the lower half of the cultural
Undesirable urban geological phenomena – subsidence
of buildings, groundwater level fl uctuations,
soil pollution – are mostly restricted to the city
quarters located on the fl oodplain area. Lowering of
the groundwater level in the fl oodplain deposits lead
into soil compaction, decay of timber rafts under the
foundations of buildings and subsidence of buildings.
The highest rate of subsidence (4.9 mm/yr in
CONCLUSIONS
layer, some 1.8-2.6 m below the surface. Concentration
values of Zn and Cu have a good correlation
(r = 0.77 and 0.82 respectively) with the content of
Ca, supporting the conclusion that in Ca-rich soils
Cu and Zn may be sorbed on the surface of CaCO 3
(Dudley et al. 1991). Concentration of Cd in the cultural
layer (average 0.13 mg/kg) remains below the
average Cd content in Estonian humic soils (0.4 mg/
kg; Petersell et al. 1997). In the peat deposits below
the cultural layer, the concentration of heavy metals
decreases rather strongly (Fig. 3) and remains close
to the average values in Estonian soils.
1973) was recorded at the time of the most intensive
groundwater consumption from the Quaternary aquifer.
Since 1974, the groundwater level has risen
and the subsidence decreased to 1.5-2 mm/yr over
a 20 year period. Initial analyses showed that the
cultural layer in the centre of the city is heavily contaminated
with Pb, Zn and Cu, but not with Cd.