Hydrogeological overview map of Lower Saxony 1: 200 000 — Groundwater Coverage Protection Potential (WMS Service)

The map "Hydrogeological overview map of Lower Saxony 1: 200 000 — Protection potential of groundwater cover" assesses the impending rocks according to their nature and thickness in terms of their ability to protect the upper aquifer from being loaded with potential pollutants. The groundwater is considered well protected where low-permeable top layers over the groundwater hinder the leakage and where large corridor distances between terrain and groundwater surface favour a long dwell time. The protection potential is summarised three classes in which different material-reducing properties of the rocks are summarised in the groundwater cover. • low < 1 m low-permeable rocks (tone, sludge) or < 5 m well-permeable rocks (fine to medium sand) or < 10 m very well permeable rocks (grabsand, gravel, smart or karst solid rock) • funds 1-5 m low permeable rocks (tone, sludge) or 5-10 m well-permeable rocks (fine to medium sand) or > 10 m very well permeable rocks (grabsand, gravel, smart or karst solid rock) • high > 5 m low-permeable rocks (tone, sludge) or > 10 m well-permeable rocks (fine to medium sand) In principle, groundwater is protected against cargoes with potential pollutants that are entered as liquid phases or dissolved with the leaching precipitation, wherever low-permeable top layers above groundwater impede the leaching and where large corridor distances between terrain and groundwater surface favour a long dwelling time, within which substance reduction processes can become effective. For the substances to be considered, it is possible to distinguish roughly three groups: • 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) A number of criteria should be taken into account in the substance reduction processes which are favoured by long periods of residence in the unsaturated zone: • viscosity plays a major role in liquid phases; thin-fluid phases can easily leak through, while pastous phases are already retained in the soil. • solid phases in the rock or 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 overriding role. The infiltration capacity of aqueous solutions is essentially based on the permeability of the leaked rocks. This, in turn, depends on the effective cavity fractions that are determined in the looser rock through the pore space, in solid rock by cross-linked crevices, layer joints and solution cavities. The ‘low’ class is classified as areas where, due to very small widths or the absence of potential barrier rocks (tone, sludge) or low corridor distances, the dwelling time of intruded pollutants is short and adsorptive surfaces are scarce or absent. Therefore, substance reduction processes (degradation, adsorption) can hardly take place. The “medium” class is classified as areas in which, due to medium widths of potential barrier rocks (tone, mud) or mean corridor distances, the dwelling time of intruded pollutants is moderate and where adsorptive surfaces are present on a small scale. Therefore, substance reduction processes (degradation, adsorption) can take place to a limited extent. The “high” class is classified as areas where, due to large widths of potential barrier rocks (tone, sludge) or large corridor distances for permeable rocks, the dwelling time of intruded pollutants is large and/or astringent surfaces are present to a high extent (tone). Therefore, substance reduction processes (degradation, adsorption) can take place to a particularly strong extent. Potential cleaning operations 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.