Water purification subsoil

Water treatment of the subsurface is about different aspects and processes; denitrification, mobilisation of metals in the groundwater compartment and leaching of metals from the soil, biodegradation of contaminants (e.g. oil contaminants), degradation of microbiological contaminants (e.g. viruses). For this card we choose the potential for denitrification as an example of ‘water treatment of the substrate’. The redox state of the groundwater gives a first indication of the potential for denitrification. The map is a land-covering point map that shows the average redox state (in time) in the upper filter of the groundwater well location. Groundwater samples are divided into 4 classes: • Aerobic and/or nitrate-containing groundwater, • Mix groundwater with nitrate and iron; • Anaerobic groundwater (benefit for denitrification); • Highly anaerobic groundwater (benefit for denitrification); The criteria for the classification of groundwater samples by redox class are described (Vermooten et al., 2006) where readability has been chosen to include the category SO4-reducing groundwater and SO4-reduced/methanogenic groundwater in the category ‘Strong anaerobic groundwater’. In addition, an additional point map is added below which shows the pH for the same filters. The pH is a first indication of the extent to which trace elements (e.g. heavy metals) are mobile or not. These can be metals that rinse out of the soil and metals that are mobilised in the groundwater compartment, for example with pyrite oxidation.