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District Ground water Development and Management Studies (Reappraisal survey) has been taken up in Tiruvallur district. The total target area is 3400sq.km and fully covered during AAP 2004-05. The area is normal and having 14 blocks. The study area lies between 13°00’00’’ to 13°35’00’’N latitudes and 79°20’00’’ and 80°17’30’’E longitudes with boundaries of Andhra Pradesh in north, Chennai and Kancheepuram districts in south Bay of Bengal in east and Vellore dist in west. A total no of 77 key wells have been established during premonsoon period and 220 no of wells inventoried. The previous survey has done in 1994-95 and notable decline of water level was observed. The area has sedimentary formations in east and hard rock formation in west. In sedimentary formation the top recent alluvium comprising sand and sandy clay is followed by hard sandstone of Gondwana formation. In hard rock area are comprising with crystalline formation of granitic gneisses and charnockite rocks with intrusive dykes of Archaean age. The depth of the dug well ranges from 4.83 to 19.35mbgl. The water level ranges from 3.52(Pulicate lake) to 14.50(Kadambattur)mbgl in premonsoon period, where as it was 3.25 to 11.45 in 1994-95 survey. In post monsoon period it ranges 2.64 to 13.20mbgl and in 94-95 survey it ranged 0.35 to 8.40mbgl. The depth of bore wells in sedimentary area ranges from 40 to 60 mbgl and static water level ranges from 10.50 to 19.00mbgl. In hard rocks area, the depth of bore wells ranges from 100 to 200m and static water level is 15 to 40m. The yields range from meager to 10 lps. The E.C ranges from 250 to 2300 micro siemens in normal area. Comparing with previous study in hard rock areas, most of Dug wells have been abandoned in Tiruttani taluk and more no of bore wells have been drilled due to decline of phreatic aquifers. The yield of bores is also decreased due to shortfall of rainfall. The artificial recharge structures have to be erected in Tiruttani taluk. The well fields may be categorized in 5 nos. between Korataliyar and Coovum rivers as Poondi, Tamaraipakkam, Kannigaiper, Panjetty having SW-NE trend and Minjur in NW-SE trend. These well fields contributes drinking water to Chennai Metro with an approximate pumping of 3000 m3 /day. The well fields in Minjur meets sea water intrusion threat and studied by various agencies.The interface of saline and fresh water is progressed further in west due to heavy pumping compared with previous study. It is advanced in village of Neidavayal, Kalpakkam, Velambakkam. EC ranges to 2000 to 8000 micro siemens. The blocks of Ellapuram, Minjur, Pallipattu, R.K.Pet, Tiruvallangadu, Tiruttani are over exploited, Kadambattur and poonamallee are critical, Gummidipoondi, Madhavaram, Poondi, Sholavaram, Tiruvallur are semi critical. The safe block is Villivakkam and it is Urban area of Chennai outskirts. The hydrological studies were carried out in Alukuli watershed of Poondi block and Sirugumi watershed of Pallipattu and Tiruttani block.
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