What is the status of groundwater with respect to chlorides?

Chloride concentrations in groundwater result from sea-water intrusion, as well as over-abstraction.

Chloride levels are measured against three separate threshold values, which were developed as part of the implementation process of the Water Framework Directive, and which take into consideration parameters related to sea-water intrusion, anthropogenic pollution and geology.

The threshold values are: 1,000 mg/l for mean sea level groundwater bodies, 500 mg/l for coastal groundwater bodies, and 210 mg/l for perched groundwater bodies.

These threshold values also take into consideration specific “use-requirements” (such as potable, irrigative, etc) as well as the natural background characteristics of each groundwater body.

In 2011 the highest average chloride concentration was recorded at Pwales coastal aquifer (2,995mg/l), which registered a 28.4 per cent increase since 2010.

The lowest average concentration was recorded at the Nadur perched aquifer (91mg/l), where the average concentration also increased since 2010.

During this period, six out of eight perched groundwater bodies exceeded the threshold value, one more than in the previous year.

The limit value for the coastal aquifers was exceeded in all groundwater bodies, while the limit value for the mean sea level aquifers was not exceeded in any of them, similar to 2010.

For more information see The Environment Report Indicators 2010-2011 at http://www.mepa.org.mt/teri2010-2011 .