What is the status of groundwater with respect to chlorides?

New national quality standards for groundwater have been proposed as part of the implementation process of the Water Framework Directive for parameters related to sea-water intrusion, anthropogenic pollution and geology.

For chlorides, three separate threshold values have been established: 1000 mg/l for mean sea level groundwater bodes, 500 mg/l for coastal groundwater bodies, and 210 mg/l for perched groundwater bodies.

The development of these threshold values takes into consideration specific “use-requirements” (such as potable, irrigative, etc) as well as the natural background characteristics of each groundwater body. In 2009 the highest chloride concentration was recorded at Pwales coastal aquifer (2,430.7mg/l), which is almost five times more than the threshold value, while the lowest concentration was recorded atthe Mellieħa perched aquifer (143.4mg/l). At the same time, three out of eight perched groundwater bodies exceeded the threshold value, while the limit value for the coastal aquifer was exceeded by all groundwater bodies. The threshold value for the mean sea level aquifer was not exceeded.

For more information see The Environment Report Indicators 2009 at www.mepa.org.mt/teri2009.