SITE CHARACTERIZATION FOR LIL RADIOACTIVE WASTE DISPOSAL IN ROMANIA Page: 4 of 8
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The first three layers, the silty less, clayey less, and red clay, belong to the unsaturated zone. The
degree of saturation increases from 0.1 in the first less horizon to 0.8 in the red clay. The pre-
quaternary clay layer, where the degree of saturation varies between 0.8 and 1 could be considered
as the first saturated zone since many sand lenses are filled with water. The second saturated zone
corresponds to the Baremmian limestone where the main aquifer of the region is found. It is directly
connected to the Danube River and to the Danube - Black Sea canal, which bound the site along the
west and south sides, respectively. The level of the Danube controls the aquifer flow direction.
Therefore, during wet periods when the level of the Danube is higher, the aquifer moves in an eastern
direction, while in dry seasons when the level of the river is lower, there is movement in the opposite
direction [1]. Since the canal is maintained at a constant level, the amplitude of these "come and go"
movements depends only on the variation in the level of the Danube.
The lithological characteristics of the Saligny site had to be refined as a result of statistical analysis of
the experimental results obtained from the analysis of the samples from drill cores, especially from the
less formations. A more refined structure was also demonstrated by the results obtained from the
modelling of underground water flow in the unsaturated zone. In accordance with the previous
lithological observations, the profile of the computed degree of saturation shows a continuously
increasing moisture content while the measured moisture profile, presented in Fig.1, shows the
existence of two peaks of water content at the side of the less horizons.
Therefore the statistical analyse of dried densities and porosity values, the main parameters defining
the layer structure, showed a two-modal distribution in silty less layer and three-modal distribution in
clayey less layer. The points grouped around the lower value of porosity correspond to the less
samples having larger water content. As a structure with small porosity reflects the presence of larger
clay content, proved by experimental data and illustrated in Fig. 1, the conclusion was that in side of
the less formations there are two thin and more consolidated layers, with better properties in water
retention. With this hypothesis, the statistical analyse of data showed, for each new layer, a normal
distribution of experimental values and especially a significant decrease of standard deviation i.e. from
5% in the initial silty less to 2% in the new considered layer.
The presence of these consolidated less was also confirmed
0 20 40 (%) by porosity distribution diagrams and soil-water retention
0 curves, characteristics directly linked to soil-water interaction.
Even if the diagrams of open porosity distribution in the
samples of less and clay collected from Saligny site showed a
large dispersion in porous structure, few characteristics of the
10 - porosity distribution in these geological layers could be
determined. The large percentage of quartz, mica and
feldspars in the less layers determines the large porosity (40-
47%) of these horizons. The pores can generally be grouped
20 - into 4 classes defined by most probable radii of 60pm, 9 pm,
0.8pm and 0.3pm. The clay fraction, with particle size less than
+ 2 pm, is responsible for the fine pores smaller than 0,2pm.
They are usually grouped around 0.07pm, 0.01pm and
30 - 0.003pm. The porosity distribution, quantitatively reflected in
+ the main classes of pores, the mean pore radius (rp) and the
fraction of each pore class in the total porosity (i) is
synthesised in Table I for all horizons. Specific pore volume
40 (Vp), total (n) and open porosity (p) complete the characteristic
of porous structure of the geological layers.
More than 60% of the open pore volume of the silty less layer
lesss A) is due to the pores ranging between 7 and 15pm,
5 - while the fine porosity represents less than 8%. The same
-clay content groups of pores also determine the structure of the clayey
+ moisture content less, but the larger percentage of clay leads to slight
-- -i increases in the percentage of fine pores. The porosity
60 distribution in less Al and less B1 is significantly shifted
Figure 1. Correlation of the towards the smaller radius values, 0.07pm, confirming the
less structure and composition more consolidated structure of these less layers. The porosity
with the moisture content distribution in samples from the red clay layer showed a very
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DIACONU, D. R.; BIRDSELL, K. H. & WITKOWSKI, M. SITE CHARACTERIZATION FOR LIL RADIOACTIVE WASTE DISPOSAL IN ROMANIA, article, August 1, 2001; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc720621/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.