Hydrogeological overview map of Lower Saxony 1 : 200 000 - Protection potential of groundwater cover

Description

The map "Hydrogeological overview map of Lower Saxony 1 : 200 000 - Groundwater Coverage Protection Potential" assesses the nature and thickness of the upcoming rocks in terms of their ability to protect the upper aquifer from being loaded with potential pollutants. Groundwater is considered to be well protected where low permeable surface layers above the groundwater impede infiltration and where large distances between the terrain and the groundwater surface favour a long residence time. The protective potential is summarily assigned to three classes, in which different substance-reducing properties of the rocks are summarized in the groundwater cover. • low < 1m low permeable rocks (clay, silt) or < 5m well-drained rocks (fine to medium sand) or < 10m very well-drained rocks (gravel sand, gravel, jagged or karstized solid rock) • medium 1 - 5m low permeable rocks (clay, silt) or 5 – 10m of well-drained rocks (fine to medium sand) or > 10m very well-drained rocks (gravel sand, gravel, jagged or karstized solid rock) • high > 5m low permeable rocks (clay, silt) or > 10m well-drained rocks (fine to medium sand) Basically, groundwater is protected against loadings with potential pollutants, which are entered as liquid phases or dissolved with the seepage of precipitation, wherever low-permeable surface layers above the groundwater hinder the seepage and where large distances between the surface of the terrain and the groundwater favor a long residence time, within which depletion processes can be effective. For the substances to be considered, three broad groups can be distinguished: • biodegradable substances (e.g. certain organic compounds, nitrogen compounds) • adsorbable substances (e.g. certain organic compounds, heavy metals, some cations of salts) • Persistent substances (e.g. certain organic compounds) Several criteria need to be taken into account for the depletion processes favoured by long residence times in the unsaturated zone: • viscosity plays a major role in liquid phases, thin phases can easily seep through, while pasty phases are already retained in the soil. • solid phases in the rock or on the surface are washed out differently depending on the solubility • in the adsorption of substances, the available surfaces of clay minerals and the content of organic carbon play an overarching role. The permeability of aqueous solutions is essentially based on the permeability of the permeable rocks. This in turn depends on the effective cavity fractions, which are determined in loose rock by the pore space, in solid rock by cross-linked gaps, layer joints and solution cavities. The ‘small’ category covers areas where, due to very small thicknesses or the absence of potential barrier rocks (clay, silt) or small gaps in the ground, the residence time of intruded pollutants is short and where adsorbent surfaces are scarce or absent. Therefore, depletion processes (degradation, adsorption) can hardly take place. The ‘medium’ class covers the areas where, due to medium thicknesses of potential barrier rocks (clay, silt) or medium distances between landfills, the residence time of infiltrated pollutants is moderate and there are low levels of adsorptive surfaces. Therefore, depletion processes (degradation, adsorption) can take place to a limited extent. Areas classified as ‘high’ are those in which, due to the large widths of potential barrier rocks (clay, silt) or large gaps in permeable rocks, the residence time of intruded pollutants is large and/or adsorptive surfaces are present to a large extent (clay). Therefore, depletion processes (degradation, adsorption) can take place to a particularly high degree. Potential cleaning processes in the groundwater-filled area are not considered. Solid rock areas were assessed on the basis of the groundwater conductivity of the near-surface rocks.

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0 https://nibis.lbeg.de/net3/public/ogc.ashx?NodeId=62&Service=WMS&Request=GetCapabilities&

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  • sgd_hydrogeologie

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