An approach is presented to determine groundwater flow in unconsolidated aquifers with a heat pulse response test using a heating cable and a fiber-optic cable. The cables are installed together using direct push so that the cables are in direct contact with the aquifer. The temperature response is measured for multiple days along the fiber-optic cable with Distributed Temperature Sensing (DTS). The new approach fits a two-dimensional analytical solution to the temperature measurements, so that the specific discharge can be estimated without knowledge of the position of the fiber-optic cable relative to the heating cable. Two case studies are presented. The first case study is at a managed aquifer recharge system where fiber-optic cables are inserted 15 m deep at various locations to test the fitting procedure. Similar and relatively large specific discharges are found at the different locations with little vertical variation (0.4–0.6 m/day). The second case study is at a polder, where the water level is maintained 2 m below the surrounding lakes, resulting in significant groundwater flow. The heating and fiber-optic cables are inserted to a depth of 45 m. The specific discharge varies 0.07–0.1 m/day and is significantly larger in a thin layer at 30-m depth. It is shown with numerical experiments that the estimated specific discharge is smoother than in reality due to vertical conduction, but the peak specific discharge is estimated correctly for layers thicker than ∼1.5 m.

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Soil passage of (pretreated) surface water to remove pathogenic microorganisms is a highly efficient process under oxic conditions, reducing microorganism concentrations about 8 log¹⁰ within tens of meters. However, under anoxic conditions, it has been shown that removal of microorganisms can be limited very much. Setback distances for adequate protection of natural groundwater may, therefore, be too short if anoxic conditions apply. Because removal of microorganisms under suboxic conditions is unknown, this research investigated removal of bacteriophage MS2 and PRD1 by soil passage under suboxic conditions at field scale. At the field location (dune area), one injection well and six monitoring wells were installed at different depths along three suboxic flow lines, where oxygen concentrations ranged from 0.4 to 1.7 mg/l and nitrate concentrations ranged from 13 to 16 mg/L. PRD1 and MS2 were injected directly at the corresponding depths and their removal in each flow line was determined. The highest bacteriophage removal was observed in the top layer, with about 9 log removal of MS2, and 7 log removal of PRD1 after 16 meters of aquifer transport. Less removal was observed at 12 m below surface, probably due to a higher groundwater velocity in this coarser grained layer. MS2 was removed more effectively than PRD1 under all conditions. Due to short travel times, inactivation of the phages was limited and the reported log removal was mainly associated with attachment of phages to the aquifer matrix. This study shows that attachment of MS2 and PRD1 is similar for oxic and suboxic sandy aquifers, and, therefore, setback distances used for sandy aquifers under oxic and suboxic conditions provide a similar level of safety. Sticking efficiency and the attachment rate coefficient, as measures for virus attachment, were evaluated as a function of the physico-chemical conditions.

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An approach is presented to determine the specific discharge in an unconsolidated aquifer with a heat pulse response experiment using a heating cable and a fiber optic cable. The cables are installed using direct-push so that the cables are in direct contact with the aquifer and the disturbance of the aquifer due to installation is small. The temperature increase and decrease are measured for multiple days along the fiber optic cable with a Distributed Temperature Sensing system (DTS). A two-dimensional analytical solution is fitted to each of the measurement points along the fiber optic cable and the specific discharge is estimated, resulting in a profile of the specific discharge over depth. With the suggested approach it is not needed to specify the distance between the heating cable and the fiber optic cable. Two case studies are presented. The first case study contains a setup with one heating cable and multiple fiber optic cables inserted at various distances. Similar specific discharges are measured independent of the distance between the heating cable and the fiber optic cable, thereby showing that the approach gives consistent results. The second case study focusses on the ability to measure vertical variation in the specific discharge and the effect of neglecting vertical conduction. A heating cable and a fiber optic cable are installed as a pair up to a depth of 47 m. A thin layer was found at 30 m depth where groundwater moves 2.5 times faster. Variations in specific discharge of such magnitude result in vertical heat exchange. Numerical simulations are used to quantify the effect of vertical heat exchange on the estimated specific discharge. @en

Artificial recharge of aquifers can be performed for various purposes and under varying hydrogeological conditions. We present an overview of deep-well recharge applications which have taken place in the Netherlands over the last two decades. We present the purpose of each application, the issues which had to be resolved, the preventive measures which were taken to improve performance and the lessons learned from each experience. Examples are given of applications which aimed at the storage of water for drinking and other purposes such as irrigation, achieving environmental goals and disposal of wastewater. Applications aiming at drinking water production usually faced issues related to the quality of the abstracted water not meeting drinking water standards with respect to various elements, such as iron, manganese and arsenic. Storage of water in brackish aquifers was complicated by buoyancy effects making part of the recharged water irrecoverable. Recharge of water with the purpose of recovering declined groundwater tables and fighting seawater intrusion was hindered by clogging of the injection well while the disposal of wastewater was limited to aquifers of lower groundwater quality.@en

As the public water authority of the city of Amsterdam and surrounding areas, Waternet makes use of both steady-state and transient groundwater models for a variety of purposes involving urban groundwater management. For instance when determining the effect of planned measures on the occurrence of groundwater levels that are too low or too high, potentially resulting in degradation of wooden pile foundations or mold in houses, respectively. One of the challenges we face in that modelling, is the discrepancy between the physical processes that play a part in the city, influencing groundwater measurements, and the extent to which we are able to quantify those processes in groundwater models. We addressed this discrepancy with automated Time Series Analysis (TSA). In the over 3000 time series of groundwater measurements that were analyzed, TSA often identified one or more disturbances, such as groundwater extractions and measurement error. Along with identifying disturbances and artifacts, TSA offers a way to structurally address these issues. Incorporating (automated) TSA in generating model observations also results in a uniform, reproducible approach, and the ability to evaluate enormous amounts of monitoring wells. We argue that this approach is preferable to visual inspection and evaluation of measurement series, and discuss ways to incorporate these insights into groundwater models.@en

In the area that is managed by the waterboard Amstel, Gooi and Vecht, some deep polders are located. Most of them attract large amounts of brackish seepage. This seepage not only contains salt, but also nutriënts. Without hydrological intervention, the waterquality in the area would suffer significantly from the brackish seepage. To prevent this, each year about 140 million cubic meter of water from the lake Markermeer, which equals a column of 20 cm, is let in at the river Vecht. This water is used to dilute the brackish water and flush it as soon as possible to the bigger parts of the watersystem like the Amsterdam-Rijncanal. However, this supply of a huge volume of water from the Markermeer is the reason that the water quality objectives, as set in the European Water Framework Directive, are not met in the area around the northern part of the river Vecht. Ecologically, this area needs local, fresh seepage from the hills of the Utrechtse Heuvelrug and not the foreign water from the Markermeer, which contains a lot of sulphate. Furthermore, the available amount of fresh water in the Markermeer is expected to become less due to the predicted climate change and the involved waterboards have agreed to reduce the intake from the Markermeer. Waternet is the merged organisation of: 1) the Waterboard Amstel, Gooi and Vecht, 2) the Surface Water and Sewerage Management of the City of Amsterdam, 3) the Amsterdam Water Supply. Because Waternet, as a governmental organisation, covers the complete watercycle, innova-tive solutions for the classic problems with brackish seepage can be thought of... Currently Waternet works on the following research questions: Can the brackish ground-water be extracted by wells, to prevent the brackish seepage to reach the surface water sys-tem of the deep polder? Does this save fresh water from the Markermeer? Can this brackish groundwater be used as a new source for the drinking water supply for the city of Amster-dam? And if so, how can the concentrate be disposed that is created with the purification of the brackish groundwater by the process of reverse osmosis? What are the benefits, the costs and the risks of such a system? We would like to present a concise but colorful introduction of the current system with the brackish seepage from the polder Horstermeer, and the ideas for using it as a new source for drinking water. Contact Information: Frank Smits, Waternet, Production Plant Leiduin, Vogelenzangseweg 21, 2114 BA, Vogelenzang, the Netherlands, Mobile Phone: +31 6 532 714 39, Phone: +31 20 608 7546, Email: frank.smits@waternet.nl @en