GROUNDWATER MINING IN THE TRIPOLI AREA, LEBANON

The Koura-Zgharta Miocene Limestone aquifer is the principal source of water that supplies Tripoli, the second largest city in Lebanon, and the surrounding towns. The aquifer is confined and highly fractured and karstified in places. Its thickness ranges between 100 and 200 meters. The aquifer consists of reefal limestone, marly limestone, limestone, and horizons of marl and sandy marl. Depending on the nature of lithology, intensity of fracturing, and solution activity, values of the transmissivity vary from 5 to 5460 m2/day with a geometric mean of 55 m2/day.

The increasing population in the study area, about 165 Km2, has placed an ever- increasing demand for groundwater. The civil war that extended over 15 years (1975-1990) in Lebanon significantly strained the groundwater resources in the study area, and the country in general, as the rapid increase in the population was not accompanied by proper development of the surface-water resources. The latter was practically nonexistent mainly due to the difficulty of constructing dams during the war years. This situation has resulted in over-pumping of the aquifer.

Major sources of recharge to the aquifer are precipitation and seepage from rivers. Recharge from precipitation was calculated by dividing the study area into 13 hydrologic units. Recharge in each unit was obtained as the difference between the volume of precipitation and that of actual evapotranspiration. Recharge from precipitation is estimated at 42 million m3/year, and recharge from rivers at 29 million m3/year. Thus, the total annual recharge to the aquifer is 71 million m3. The main sources of discharge from the aquifer are natural outflow to the Mediterranean Sea and withdrawal of groundwater from pumping wells. Outflow to the sea is 60.9 million m3/year, and discharge by pumping wells is 13.9 million m3/year. The total discharge from the aquifer is, therefore, 74.8 million m3/year.

Comparing the total recharge and discharge values shows that groundwater in the aquifer is currently being mined at an annual rate of 3.8 million m3. In addition to the permanent loss of groundwater from storage, mining of groundwater makes the aquifer in Tripoli area vulnerable to land subsidence and contamination by seawater intrusion. The aquifer in the Tripoli area is already polluted with wastewater.