Eawag and the Canton Basel-Landschaft are investigating the problems and challenges of water supply, and working out plans and concrete solutions to ensure the quality of drinking water  for the future. The results obtained from the project “Regional Water Supply Basel-Landschaft 21” serve as a model for other regions in Switzerland.

Eawag-Postdoc Tony Merle, Dr Adrian Auckenthaler and Prof. Urs von Gunten (from left to right) are checking the distributed control system of the pilot facility.

The Canton of Basel-Landschaft (BL, “Basel-Country”) is characterised by karst areas used for agriculture, urban settlements in the valleys, and industry with its long history in the urban agglomeration of Basel. “This local setting has a great influence on the quality of the drinking water, and indeed also on the way the water supply utilities are organised and cooperate”, says Dr. Adrian Auckenthaler, Director of the Water and Geology department at the Office for Environmental Protection and Energy of the Canton Basel-Landschaft. Dr Adrian Auckenthaler is leading the joint project together with Professor Urs von Gunten, Director of the Potable Water Chemistry Group and the Potable Water Competence Center at Eawag, and the Laboratory for Water Quality and Treatment (LTQE) at the EPFL in Lausanne. This project was started in March 2013 and is set to run for three years. Besides Eawag and the Canton BL, the University of Basel and University of Bern are also involved in the project.

Microbes in spring water

The karst substrate in the rural regions is not very effective as a filter. “It is a well-known fact that karst springs constantly give rise to problems”, says Adrian Auckenthaler. Especially when there is a heavy rainfall, the water becomes cloudy and microorganisms get into the water. To continuously monitor the quality of the drinking water, until now one of the main methods was to measure the turbidity of the water. If it increases, it is also likely that there are more germs present. Now, by using a device known as a flow cytometer, which was developed at Eawag, the specialists can continuously measure the actual bacteria. “Using this device we are able to obtain a highly resolved view of the dynamics of the bacteria populations in the spring water”, explains the environmental expert. What is more, the findings obtained from case studies made at certain selected springs can be applied to other locations as well. “A karst spring reacts in a similar way in the various different regions, even though the time it takes for the number of microbes and the degree of turbidity to rise following heavy rain may differ”, Adrian Auckenthaler says.

These measurements are expensive, though, and they have to be interpreted by specialists. “We have a large number of small water supply facilities, which cannot afford such an expensive infrastructure”, Urs von Gunten says. But it is hoped that the transfer of expertise from Eawag to the Food Safety and Veterinary Office BL will now make it possible for the new measuring method to get established.

The data that is being collected over an extended period of time by flow cytometry, from certain water supplies in Basel-Country, will show whether the potable water treatment – which is usually a single-stage UV disinfection – is adequate. “UV disinfection is very efficient”, says Urs von Gunten. “Carried out correctly, the resulting drinking water is completely safe and healthy.” However, after a rainfall bacteria may still be concealed in the cloudy water and pass through the system intact. A second safety stage with a filter would provide clean drinking water that is guaranteed to be safe. But such a system requires a higher level of investment and staff expenditure, which not every municipality can afford.

From river to drinking water

Many drinking water collection points are built near rivers where there is a plentiful supply. However, this quantitative advantage brings with it a certain qualitative risk. A fact that becomes all the more apparent when there are contaminants in the rivers. In such cases, which also occur repeatedly in the Canton BL, the collecting points have to be shut down and the consumers supplied via neighbouring supplies or cisterns.

The river water infiltration during dry weather and during periods of precipitation is being investigated at three model sites. “In the course of this investigation we found many types of medicines, household chemicals and pesticides in the rivers and in the groundwater”, says Adrian Auckenthaler. Although the concentrations were mostly very low, of the order of a few nanograms per litre, which is well below the legal limits, these substances are undesirable in drinking water.

To understand the systems at work, groundwater models have been developed for the selected model sites. These models allow one to describe how the old regional groundwater mixes with the new river water infiltrate. “In this way a better water man-agement system can be set up, and the drinking water collecting points can be protected against critical situations”, says Urs von Gunten.

Use of drinking water in urban areas

The Hardwald forest in Muttenz, which is flanked by industry, a railway freight depot and a storage tank, is a popular recreational area for walkers, joggers and dog owners. And this is also where the drinking water to supply over 130,000 consumers in Basel-Country and the city of Basel is obtained. For this purpose, river water from the nearby Rhine is added to the groundwater. After pre-treatment in a sand filter, the Rhine water is allowed to percolate through ditches and ponds. While passing through the ground, the micro-organisms are filtered out and trace substances are dissipated. Then the mixture of groundwater and infiltrated river water is brought back up to the surface again via thirty drinking water springs.

“The safety of the drinking water in Hardwald depends to a large extent on the artificial infiltration of Rhine water”, says Urs von Gunten, summing up the situation. Some two kilometres in length, the protective groundwater “hill” or barrier that is formed in this way constitutes a hydraulic boundary and prevents pollutants from the surrounding regions from being carried into the Hardwald. The experts are developing a groundwater model to improve the water management in this geologically complex region, with its rock and granular soil aquifer and numerous industrial groundwater extraction points. “We are examining how much river water should be infiltrated and which springs are best suited for obtaining the drinking water”, says Adrian Auckenthaler. “Generally we have found that the springs at the outlying western region are less well protected than those in the middle.”

New pollutants find their way into Hardwald via the Rhine water infiltration into the groundwater barrier. “The Rhine in Basel conducts 70 % of the water out of Switzerland, which also means about 70 % of the purified waste water”, the experts write in their report. This means that the Rhine water also contains many critical trace substances. From the engineers’ standpoint, the creation of the “water barrier” is not an ideal solution, Urs von Gunten concedes: “With this method one has to infiltrate almost twice the quantity of water.” So the experts are also investigating whether it would be better to treat the Rhine water directly. Urs von Gunten: “The infiltration has various positive effects, as the measurements have shown. Of some 130 trace substances that were detected in the Rhine, only about 50 are left after passing through the ground. And while Rhine water contains about two milligrams of organic material per litre, after the infiltration it is just half a milligram per litre. Moreover the infiltration serves to balance out the seasonal variations in temperature.”

“Since December 2013 an activated carbon filter has been used in the Hardwald”, says Adrian Auckenthaler. The filter is very good at retaining most of the remaining unwanted substances – but not all of them. “In the event of accidents or illicit passing of effluent into the surface water in the catchment area of the Rhine, increased concentrations of trace substances can occur in the river”, the experts add in their report, and cite examples involving polyfluorinated tensides or the inflow of biocides from the Leibstadt nuclear power plant. Now during the joint project they are clarifying how the water can be treated even more thoroughly in the most efficient manner.

From the lab to the working world

“We are testing a two-stage procedure – a combination of activated carbon with additional oxidation”, says Urs von Gunten. While the activated carbon filters out substances from the water, the oxidation converts the harmful trace substances. One traditional method makes use of the oxidising power of ozone. But this can lead to the formation of bromate as a side-product from bromide, which is classed as potentially carcinogenic. “By using a newly developed ozone-based technique, it is possible to suppress the unwanted formation of bromate while retaining the same elimination of trace substances”, the drinking water expert explains. It is hoped that a pilot plant, which was installed next to the activated carbon filter in Hardwald, will demonstrate that the new method of additional oxidation will work just as well on a large scale as it does in the laboratory. “Things are looking very promising so far”, Urs von Gunten concludes.

Promote regional cooperation

In Switzerland there are more than 3,000 water supplies, in Basel-Country there are 95, more than the number of communes (local administrative regions). It is precisely the small water supply utilities that have difficulty in managing their tasks and challenges by themselves. “So the Canton is endeavouring to secure  a stronger collaboration between the water supply facilities”, Adrian Auckenthaler points out. In the social sciences sub-project run by researchers of Eawag and the University of Bern the goals and challenges are being studied from the standpoint of the actors, and their preferred modes of cooperation are identified. The aim is to answer the question, which organisation structures can best be used to manage the challenges, and what re-organisation measures are needed to achieve the political goals.

In general the stakeholders want to work together more closely. They also confirm how the Canton plays an active role in advising the water supply utilities. “This is good to hear”, says Adrian Auckenthaler, “because after all in future the constant pressure of demand imposed on the remaining groundwater protection areas will necessarily lead to the halting of extraction from the endangered drinking-water springs, and this in turn will make the regional cooperation necessary.”

Stimulus for the water supplies

The results of the project should benefit the whole of Switzerland. For with its hilly agricultural areas and the heavily industrialised urban region, Basel-Country is like a little replica of Switzerland, says Urs von Gunten. “In the field of water supply, the various different resources form a kind of ‘Swiss Miniature’,” referring to the model village. “This means that basic principles can be derived from this example, which can be applied effectively to other systems. This is why this project is so valuable.”