PROJECT DESCRIPTION
BACKGROUND
Ground water withdrawals lower the groundwater level. This phenomenon slowly but surely undermines the basis of a healthy and varied natural landscape. In the Netherlands this desiccation process results in the loss of wetlands. One of the four priorities set for the drinking water industry in the Second National Environmental Policy Plan (Ministry of Housing, Regional Development and the Environment, 1993) was to reduce the loss of wetlands. Furthermore, the Utrecht Province outlined a policy for creating new opportunities for the natural environment in its Water Management Plan (Province of Utrecht, 1992). The diminishing water table in the region of Utrecht is attributable to several factors. Abstraction for the production of drinking water was assumed to be one of them.
OBJECTIVES
The beneficiary agreed with the provincial Authorities to reduce the ground water abstraction by 9 million cubic meters in the year 2000 (together with the increasing demand for drinking water). For many years, the beneficiary has only used groundwater as raw water for his drinking water production. The advantages are: 1°) a high basic quality of ground water and only limited post treatment requirements which means that there are little environmental impact (low consumption of water treatment chemicals) and 2°) that the process is relatively cheap. Surface water could also be used for the production of drinking water, but would require a much stronger treatment with all the environmental and financial consequences. Therefore, the beneficiary has developed an innovative concept in which the advantages of groundwater and surface water are combined. This concept is based on a DOuble aquifer PASSage (DOPASS) in which surface water is purified before drinking water production. The objective of the project was a successful implementation of the first stage of the DOPASS concept, e.g. bank filtration, in the Steenwaard, a floodplain of the Rhine river, in order to: • get a sustainable water supply • reduce the dehydration of the Steenwaard • restoration of nature in the Steenwaard
RESULTS
This project has not been implemented as a result of new insights. Prior to implementation, comprehensive research was conducted on the cause of desiccation and the actions that should be taken against it. This research involved the co-operation with three provinces, drinking water companies, water boards and nature conservation societies. The results of this research were unexpected. It appeared that in 50% of the area where desiccation appeared, local measures and changes in surface water management would change the conditions sufficiently and solve the problem. A decrease in groundwater withdrawal by drinking water companies would only contribute to problem solving in an extra 5% of the area. These results generated a new debate as to whether the huge investment (approximately €70.000.000 for 7 million m3 water yearly) in the new water purification system, DOPASS, would still be justified in view of its limited expected contribution to the decrease of desiccation. Also the development in alternative purification systems in general, membrane technology specific, went so quickly that by the end of 2000, the DOPASS method was not competitive anymore. The DOPASS concept (DOuble aquifer PASSage) was anticipated to work as follows: the surface water would be pumped up in floodplains at a short distance (approx. 40 m) from the river (current technologies are located 500 to 1000 metres from the river). The “bank filtrate”, sand layers, originates for about 90% in the surface water - the other 10% is ground water from flood plain. The first aquifer passage in the bank of the river would act as a filter, natural processes would remove various contaminants from the surface water. After extraction, the bank filtrate would undergo pre-treatment after which it would undergo a second aquifer passage in the range of hills known as the Utrechtse Heuvelrug. The virological and bacteriological contaminants would be further broken down during this second passage. The result of this would be that DOPASS would produce new groundwater by natural process and pre-treatment. After re-extraction, a final, marginal post-treatment working on the principles of groundwater treatment would secure drinking water quality before distribution to the consumers. Given these new insights, the project did not take off. Hydron Midden-Nederland thus contributed in other ways to the restoration of the flood plain of the natural area of Steenwaard. This project has not been implemented as a result of new insights. Prior to implementation, comprehensive research was conducted on the cause of desiccation and the actions that should be taken against it. This research involved the co-operation with three provinces, drinking water companies, water boards and nature conservation societies. The results of this research were unexpected. It appeared that in 50% of the area where desiccation appeared, local measures and changes in surface water management would change the conditions sufficiently and solve the problem. A decrease in groundwater withdrawal by drinking water companies would only contribute to problem solving in an extra 5% of the area. These results generated a new debate as to whether the huge investment (approximately €70.000.000 for 7 million m3 water yearly) in the new water purification system, DOPASS, would still be justified in view of its limited expected contribution to the decrease of desiccation. Also the development in alternative purification systems in general, membrane technology specific, went so quickly that by the end of 2000, the DOPASS method was not competitive anymore. The DOPASS concept (DOuble aquifer PASSage) was anticipated to work as follows: the surface water would be pumped up in floodplains at a short distance (approx. 40 m) from the river (current technologies are located 500 to 1000 metres from the river). The “bank filtrate”, sand layers, originates for about 90% in the surface water - the other 10% is ground water from flood plain. The first aquifer passage in the bank of the river would act as a filter, natural processes would remove various contaminants from the surface water. After extraction, the bank filtrate would undergo pre-treatment after which it would undergo a second aquifer passage in the range of hills known as the Utrechtse Heuvelrug. The virological and bacteriological contaminants would be further broken down during this second passage. The result of this would be that DOPASS would produce new groundwater by natural process and pre-treatment. After re-extraction, a final, marginal post-treatment working on the principles of groundwater treatment would secure drinking water quality before distribution to the consumers. Given these new insights, the project did not take off. Hydron Midden-Nederland thus contributed in other ways to the restoration of the flood plain of the natural area of Steenwaard.