Islands’ aquifers in a precarious state
The first line in the chapter on freshwaters in The Environment Report 2008 reads: “Malta’s groundwater resources are being overexploited due to widespread unauthorised abstraction, with resultant seawater intrusion.” It is beyond doubt that the...
The first line in the chapter on freshwaters in The Environment Report 2008 reads: “Malta’s groundwater resources are being overexploited due to widespread unauthorised abstraction, with resultant seawater intrusion.” It is beyond doubt that the islands’ aquifers are in a precarious state, quantitatively and qualitatively.
The costs are truly considerable but Malta’s circumstances make desalination inevitable. Our precious aquifers alone would never be enough to cope with water demand.
About 55 per cent of the water that reaches our homes and establishments is derived from reverse osmosis (RO) plants. These plants are expensive to run, consuming an estimated four per cent of total power generated by Enemalta, implying that the plants inevitably contribute to Malta’s carbon footprint.
The four per cent figure represents a marked improvement over higher power consumption rates in the past but the sustainability of the carbon footprint from Malta’s RO plants also needs to be assessed in the light of recent developments in EU emissions trading legislation. He who once said that in Malta water is as expensive as whisky was definitely on the right side of history.
As with all other subsurface water bodies, Malta’s aquifers rely on rainfall for recharge. This neither implies that all the rainfall ultimately ends up in aquifers nor that all the rainfall that reaches the aquifers is there to stay. Aquifers move under the influence of gravity and rock displacements and water seeps through the ground as subsurface discharge.
For Maltese aquifers, this loss amounts to about half the recharge water. Land use practices in recent decades, including the more than a 2,000-kilometre road network, have made matters worse as a result of a considerably diminished ability of the ground to absorb water and this to the detriment of the aquifers beneath.
Malta’s water distribution network also leaves much to be desired. The figures for 2007 show a huge difference between water production and billed water consumption, with about half the water produced either being consumed but not billed or simply leaking out of the system. One argument has it that, at least, system leakages, for which Water Services Corporation is ultimately responsible, serve to replenish the aquifers themselves. Our unintended recharge of the aquifers clearly comes at a cost! And, then, how does one invest in the amelioration of our roads to top-class European standards when what lies beneath is a more serious problem?
The qualitative status of Malta’s aquifers is a matter of concern. The islands’ small size coupled to the porous nature of the lower coralline and globigerina make the relatively high chloride levels in the mean sea level aquifer understandable. Chlorides in water are not usually considered a health hazard but the World Health Organisation assigns a drinking water quality standard for chlorides at 250 milligrammes per litre (mg/l), above which the substance would be detectable to taste. Readings taken in 2007 for chloride levels at Ta’ Kandja and Tal Ħlas WSC pumping stations, which tap Malta’s lower coralline aquifer, were found to be within the 1,400 – 1,750 mg/l and 1,050 – 1,400 mg/l brackets respectively, well above the 250 mg/l threshold.
Chloride levels are typically lower in the perched aquifer systems than in the mean sea level aquifer. The Tal Ħlas station is located at the centre of mainland Malta relatively far away from the coast and, yet chloride, levels are significantly high. Nothing could be more indicative that Malta’s mean sea level aquifer is subject to sustained over-abstraction.
Nitrate contamination is a more complex issue given a potential health hazard. The entire span of the Maltese islands is designated as a nitrate vulnerable zone under the provisions of Directive 91/676 as amended, the Nitrates Directive. Malta’s Nitrates Action Programme reports that 13 out of 15 groundwater systems are “heavily polluted by nitrates”.
EU legislation stipulates that nitrate levels in drinking water should not exceed a 50mg/l level. Nitrate levels at Tal Ħlas and Ta’ Kandja were both found to exceed this limit, the most severe case being that of Mġarr with nitrate levels exceeding 150mg/l.
The severity of the situation is best described through the data given for various sections of Malta’s aquifers as tabulated in the Nitrates Action Programme itself. Nitrate mean levels as alarmingly high as 137.3 mg/l in the Rabat-Dingli perched, 364.6 mg/l in the Pwales coastal, 335.4 mg/l in the Mellieħa coastal are recorded, together with 215.2 mg/l, 315.9 mg/l and 133.5mg/l in the Xagħra, Żebbuġ and Victoria-Kerċem perched systems in Gozo respectively.
The nitrate content of aquifers needs to be addressed by improved agricultural practice particularly in the use of fertiliser. WSC does a formidable job in ensuring the public supply of water is clean and up to the desired standard. The discussion about the water policy proposal for Malta launched in July 2010 continues.
sapulis@gmail.com
The author specialises in environmental management.