The mountainous Tirap district of Arunachal Pradesh has a geographical area of 2362 sq k.m. The district is located within N. Latitudes 26˚38΄ to 27˚47΄ and E. Longitude 95˚40΄. The study area is located within N. Latitudes 26˚57΄8.2584” to 27˚15΄51.90” and E. Longitude 95˚11΄31.35” to 95˚38΄15.32”. The district is having a mappable area of 125 sq.km. Tirap district was one of the oldest district of Arunachal Pradesh which was formed during the British time. Later on, the erstwhile Tirap district was bifurcated to form Changlang district in the year 1987. The district is predominantly hilly and the altitude varies from 500 metres above sea level to 4615 metres above sea level in the north eastern part of the district. Main rivers are Tirap, Tissa, Tissing and Chatju. The district is covered by alluvium deposited by the river Brahmaputra and its tributaries. The Tertiary and Quaternary sediments of the Naga-Patkoi belt extend north-eastward in Changlang and Tirap districts of south-eastern Arunachal Pradesh. The entire study area is covered by regular monitoring of 03 nos. of GWMS and another 08 wells have been established. All the water level data were collected and the wells are monitored periodically. CGWB has constructed 02 nos of exploratory wells and 01 observatory well in this area earlier and during current annual action plan (2022-2023), no exploration well has been constructed. Major aquifer of district is older alluvium. The aquifer of the district broadly can be divided into two groups. Shallow aquifer depth limit is 50m and below which deeper aquifer exists.