The ground water level at Calcutta airport has risen to six inches below the primary runway this monsoon, adding to safety concerns triggered by rubber deposits and patches of concrete peeling off the main tarmac. "One of the reasons for the surface becoming fragile is the rising water level under the runway. During monsoon, the condition is aggravated, and this is causing moisture accumulation on the runway,' a senior airport official said on Sunday. The water level has risen not because of excessive rain, though. "The drainage system around the airport is getting clogged. Monsoon water is flowing back instead of being drained out,' the official said. Three clogged canals