Soil characteristics

The basic features of the ground and its surface are given in the scheme and expla-nations inFigure 3.14.

Components of the soil

The original natural relief is no longer present. It began to disappear when the topography of the area was restructured during the economic development of the site; this includes an original ravine being filled in. The absolute height of the surface of the ground ranges from 145 to 149 m.

Almost all the natural soil in the area of interest has been destroyed. Where it remains, it resembles the sod–podsolic type or urban soil (Table 3.2).

A layer of development debris (technogenic ground), which has been formed over several decades, covers the whole area of the site. In some cases it differs sharply from the natural bedrock that lies below; in others it does not. This ground is extraordinarily non-uniform in its structure, comprising 10–20% (and in some

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Figure 3.18. Relief of the RRC-KI radioactive waste storage site and adjacent area, and contours of the inner and the outer walls; axes X and Y are in meters; numbers on the isolines show the elevation in meters.

Figure 3.19. Isometric drawing of the digital elevation map, showing walls, build-ings, and other constructions. The X and Y axes are in meters.

The thickness of the technogenic layer varies widely—from several centimeters to several meters, depending on the relief and other factors.

The technogenic ground needs to be investigated thoroughly, as its composi-tion, condicomposi-tion, and properties have not been quantified. For most of the area, the technogenic ground and soil areas are covered by buildings, constructions, con-crete, and asphalt.

Granulometric structure of the soil

Among the basic parameters of an engineering and geological assessment of sandy bedrocks are heterogeneity and characteristics of water penetration. In most cases, the technogenic ground is composed of natural soil and rocks that were dug out of the trenches and foundation ditches when the construction and planning works were being carried out. It is thus fair to assume that its condition and properties are similar to those of the natural ground beneath it.

The natural ground comprises alluvial sand that formed the top layer of an above-floodplain terrace. The water permeability of the sand, whose particles mostly exceed 0.1 mm, is characterized by an infiltration coefficient of greater than 1 m per day. Sand with particles that are predominantly less than 0.1 mm have an infiltration coefficient of less than 1 m per day.

InTable 3.3data are given for the granulometric structure and infiltration factor that summarize the bulk ground bedding in a sublayer of alluvial sands of average dimension. The contents of the humus and the porosity of the urbanized soil are given in accordance with literature values.

Table3.3.Granulometricstructureofthesoil. Infiltration DepthHumusPorosityfactorKf (cm)Granulometricstructureofground(%)(%)(m/day) Diameterofparticles(mm) >1010–5–2–1–0.25–0.1–0.05–0.01–<0.005 5210.250.10.050.010.005 Urbanizedsoilssimilartobulkgroundofthesite,summarized(%) 0–220.2–0.3–0.6–1.5–5.2–25.9–13.6–1.2–2.1–0.4–1.330–401–4 1.84.02.87.817.258.239.18.15.75.7 22–400.4 40–500.4 Naturalsod–averagepodsolicsandygroundliteraturedata(%) 0–20275072132.3 20–28275174101.9 28–3556268270.2 Naturalsod–semipodsolicsandygroundliteraturedata(%) 3–89142033.7 45–559231130.4 85–95917003notpresent 210–220869205notdefined

Table 3.4b. Infiltration rate from literature search.

Ground Permeability coefficientKf(m/day)

Sands of average fineness 10–25

Fine Sand 2–10

Sandy loam 0.61–0.67

Loam 0.005–0.4

Organic content in surface soil layer

There is practically no soil cover in the area concerned. There is no layer of soil buried under the technogenic deposits. No studies of what remains of the soil have been carried out.

Whether there were organic compounds in the technogenic soil was not sys-tematically determined. The presence of wood remains has sometimes been noted in descriptions of the technogenic deposits over boreholes.

Porosity

The porosity of sod–podsolic soil is about 50% and that of urban soil is 30–40%

(Jakubov, 1999). The porosity of the technogenic deposits was not determined, nor was that of the alluvial sand bedding beneath them.

Permeability of soil surface layer

The water permeability of the technogenic deposits was not studied. The infiltra-tion coefficients of the alluvial sand bedding beneath them vary from 1.8 to 13.8 according to laboratory data and from 1.61 to 6.43 according to data obtained by pumping out water (Table 3.4a). The results of the literature search for this soil property are given inTable 3.4b.

Moisture of the soil

The moisture of the soil was determined qualitatively by analysis of soil samples taken from the wells at the site. According to reference data (Stroganova et al., 2000), the following three categories of soil moisture were used depending on the degree of moisture content (Sr):

Low 0.0< Sr<0.5 Normal 0.5< Sr<0.8 Saturated 0.8< Sr<1.0 3.3.3 Vegetation cover

Figures 3.14, 3.16, and3.17present a general scheme of the distribution of vege-tation cover at the radioactive waste storage site and adjoining area. At the time of the case study (2003–2004) about 30% of the storage site was covered with grass.

This was mostly over the waste burial places (spots) within the site. The rest of the general area is occupied by earth roads, buildings, asphalted sites, and storehouses.

Height of vegetation

The overall height of the grass at the site is low (about 20 cm). The grass areas have a grass coverage of around 70% (see alsoFigure 3.7). About 20% of the grassed area is covered with tansy to a height of about 40 cm.

Trees, reaching 4 m in height, were cut down in 2002. Their stumps and the bushes that have grown up to 2 m occupy the remaining 10% of the vegetated area.

The height of the trees growing on the adjoining city area vary from 4 to 8 m.

The grass cover there is quite poor and of various types, with a height of 15–30 cm.