The consequences of mixing water from the Arrenaes Artificial Recharge (AR) trial plant with groundwater from existing well fields have been investigated. The potential problems of interest are bacterial regrowth, precipitation of iron, and corrosion in the raw water distribution system. The AR trial plant is located on the Arrenaes peninsula on Zealand, Denmark. A large-scale production plant for drinking water (4 million m3/year) is proposed at the locality. To test the microbial properties of the mixed water, laboratory experiments have been carried out. Based on the results, it has been concluded that introducing water from the proposed large-scale AR plant to the distribution system will not cause problems with undesirable regrowth of bacteria in the pipelines, as long as the content of AOC in the abstracted AR water stays within the current range, between 3 and 15 μg/L. Chemical modelling (PHREEQC) shows that the mixed water is supersaturated with iron oxides, which may precipitate as iron sludge. Furthermore, the model shows that the hardness of the water in the pipelines will decrease when abstracted AR water is added. This is not expected to cause corrosion, due to a simulated supersaturation with calcite in all water types. However, long-term operation of the proposed large-scale AR plant, and thereby leaching of calcite from the aquifer, may lead to corrosion of the pipelines.

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