 The quality of ground water is poor compared to the northern shores of Tamil Nadu due to the presence of marine and semi @-@ marine origin in sediments . The images from the satellite IRS 1A shows Thiruthuraipoondi was a coastal town ( which is an inland in modern times ) and the sea has regressed up to Vedaranyam in modern times . The analysis of backwaters from 1932 to 1992 indicates considerable enlargement in the region and occurrence of number of <unk> . 
