The successful realisation of the greenhouse horticulture area of AFC Nieuw Prinsenland (Dinteloord) requires that the supply of irrigation water be made sustainable. Rainwater is not enough to meet the needs of the greenhouse horticulturalists. Moreover, water supply from industry in the area does not dovetail with demand, because the periods of water supply and water demand do not coincide. High-quality irrigation water can be produced from effluent when the WWTP of the neighbouring sugar manufacturing plant is in operation (September to January). The water demand of the horticulturalists however is concentrated in the spring and summer. There is therefore a need to temporarily store the supplementary water. The subsurface storage of the irrigation water produced presents a promising possibility. But the groundwater in the greenhouse horticultural area is brackish, which can have an impact on the quality of the recovered irrigation water.
Aquifer storage and recovery (ASR) involves the storage and recovery of excess freshwater, through the use of wells, to satisfy later periods of demand. ASR-coastal is a special form of ASR in which several well screens are installed above each other in a single borehole, and can be independently operated. This enables the optimisation of the recovery of freshwater during ASR in aquifers with brackish groundwater. The buoyancy movement of the freshwater into the brackish groundwater can be overcome through deep infiltration and shallow recovery.
Little is known about the local soil structure and groundwater quality in the study area. Yet these soil conditions are of crucial importance for the successful storage and recovery of high-quality irrigation water. The challenge is to obtain sufficient information for an initial, small-scale ASR system. This would then enable a close study of a test cycle of infiltration, storage and recovery, and a reliable model simulation of the storage and recovery. On the basis of this information, a full-scale, reliable ASR system should be realised.
The extracted material from the test drilling showed that an appropriate aquifer is located at a depth of 6 to 30 m NAP (Normal Amsterdam Water Level). The aquifer consists of medium-fine to medium-coarse sand, and is adequately confined between clay/peat layers. The groundwater at the test drilling site is lightly brackish and shows that the aquifer has been saltier in the past. Modelling with SEAWAT shows that the application of ASR-coastal would allow for the annual abstraction of the targeted volume of freshwater.
On the basis of the results of this study, the concept design for the ASR system was developed (total of 8 ASR wells) and its hydrological impact on the surroundings calculated. A licence was then requested to roll out the ASR wellfield somewhat to the southeast of the test drilling site. Following approval, the first ASR-coastal was installed with four separate well screens. It was put into operation for a short test cycle with the storage of high-quality irrigation water. The well was equipped with extensive online monitoring and a monitoring well at a distance of 10 m. During the test cycle the movement of the groundwater and changes in the water quality during its residence in the subsurface were monitored. The test cycle was then simulated in a model. This provides the basis for the definitive implementation of the full-scale ASR system in Nieuw Prinsenland.