Since mid January 2012, within the framework of the Knowledge for Climate programme (Climate Proof Fresh Water Supply theme), at an orchid grower’s in Nootdorp, KWR researchers have injected about 14,000 m3 of roof-collected and treated rainwater into a brackish groundwater aquifer located at a depth of 10-40 m. The recovery of this stored fresh water this summer met the needs for high-quality irrigation water of this and a neighbouring grower.
Because the summer of 2012 was a wet one, the orchid grower had, by early September, only recovered about 2,700 m3 of the 13,700 m3 stored fresh water. To test the system further, in September-October, extra fresh water was recovered and piped over to fill the (empty) reservoir basin of a neighbouring company. As a result, this company’s water shortage problem also vanished. In the end, by 10 October, 5,500 m3 of fresh water was recovered, water that was not too saline for use. Afterwards, all the basins were full and the recovery was stopped.
First test a success
During the first year, 40% of the injected water was therefore recovered. This yield is several times higher than that of conventional aquifer storage, which makes use of one long well screen. In Nootdorp four short screens were used, positioned one above the other, for the injection (below) and recovery (above) of fresh water from the saline underground. In this way, the rising of the (more buoyant) fresh water to the shallow recovery filters is postponed as much as possible. The model calculations predicted this “gain”, but it had not yet been demonstrated in practice.
Higher yields next year
Possible “pitfalls” are clearly preventable – for example, the short-circuit flow of brackish water through the borehole can be avoided by tightly sealing it with clay plugs. Because a great deal of the injected water (partly mixed with brackish water) remained behind in the aquifer, the conditions for fresh water storage next season will be significantly better, thus further increasing yields. In the meantime, the changes in water quality that were observed – for example through column experiments – are being further examined and interpreted.
The animation shows the model results for the first season at Nootdorp. You see a cross-section of the aquifer, including the brackish groundwater (orange). Fresh water (light blue) is being injected through the four well screens (left) when the screens turn dark blue, and recovered when they turn red. It is clear that the brackish groundwater presses the fresh water upwards, but that a substantial proportion of the fresh water is available for recovery.