Volatile halogenated hydrocarbons (VHHs) exceed the limit of 1 µg/l at 3% of monitoring sites across Switzerland. In urban catchment areas, the concentrations of VHHs are above this value at almost 11% of the monitoring sites.
According to the Waters Protection Ordinance (WPO), groundwater should generally contain no persistent synthetic substances. For groundwater that is used for drinking water or is intended as such, there is also a limit value ('numerical requirement') of 1 microgram per litre (µg/l) for VHHs. In 2017, the concentrations of VHHs were above this limit at 3% of the NAQUA monitoring sites. VHHs were detected in the groundwater at 24% of all monitoring sites.
Tetrachloroethene and trichloroethene
The most commonly detected substances were tetrachloroethene and trichloroethene. The substance that exceeded the limit value of 1 µg/l most frequently was, by a considerable margin, tetrachlorethene. In total, at 12 monitoring sites (equivalent to 2%) the concentrations of tetrachloroethene were above this value.
Both chemicals have been used in large quantities as solvents and detergents in industry and commerce and entered the environment mainly in the 2nd half of the 20th century as a result of careless handling. This resulted in contaminated land at former operating sites and old landfill sites which is usually the cause of ground water pollution today. Both substances are highly persistent in groundwater.
Between 2007 and 2017, the number of monitoring sites where VHHs were detected in concentrations of more than 1 μg/l decreased from just below 5% to 3%. During this period, the number of VHHs detected in groundwater also decreased slightly.
The number of monitoring sites where trichloroethene and 1,1,1-trichloroethane have been detected has declined slightly over the past 15 years. In the case of tetrachloroethene, no clear trend is evident.
Last modification 12.05.2020