Author(s): Zhang Danrong; J. C. Nonner; N. L. Van Der Moot
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Keywords: Groundwater flow; Brackish water upconing; Pumping; Clay layer; Groundwater management
Abstract: The groundwater system in the eastern part of The Netherlands consists of continental sandy to gravelly deposits, which are alternated with clay and loam lenses, and marine deposits consisting of fine and silty sands. The geohydrological base of the system consists of marine sandy silts and clays. Marine salts, not completely ‘flushed' from the bottom part of the groundwater system, and diffusion, have played a role in establishing a brackish groundwater zone with a high salt concentration. Pumping carried out in the groundwater system accelerates the upward movement of the brackish water, resulting in the deterioration of water quality. For this reason, the licensed production rate for a well field in Hoogeveen City was reduced from 6 Mm3/year to 3.5 Mm3/year. To satisfy the demand for water, the water supply company Waterleidingmaatschappij Drenthe (WMD) intends to bring a new well field into operation at Holtien with a production of 2.5 Mm3/year. The new well field may face the same problems as experienced in Hoogeveen City: the risk of brackish water upconing. Predicting brackish water upconing is critical for groundwater management. Therefore, this research included the simulation of brackish groundwater upconing beneath the existing well fields at Hoogeveen City and the future field at Holtien, and the subsequent assessment of the water quality of the pumped water. The computer codes MODFLOW and MT3D were applied to simulate the groundwater flow and brackish water transport respectively. The regional groundwater flow model was calibrated with both ten-year groundwater levels and pumping test data. The simulations indicated that all pumping wells except 3 in Hoogeveen City and 1 at Holtien would have a salinity increase less than 150mg/l during a fifty-year operation period. The non-continuous presence of a clay layer in the groundwater system below the pumping wells significantly affects the brackish water upconing.
Year: 2001