Rapid investigations to assess impacts of aquifer recharge - Tumkur district (Karnataka) - A report by ACWADAM and BIRD-K

The principle objectives of the study were:

•  Impact analysis of aquifer recharge through borewells done by BIRD-K in Pavagada and Sira Clusters
• Suggest new sites for aquifer recharge through borewells in Bagepalli cluster.

The methodology used a background study of the area through images from Google Earth. A detailed geological fieldwork in the area was carried out. Various structural and hydrogeological measurements were made to map out the aquifer systems within the area. Water levels in borewells and dug wells were measured. The study area included seven watersheds and falls in two clusters namely Pavagada and Sira. Both these clusters are located in the Tumkur district of Karnataka.

The report makes some recommendations for recharge augmentation and fluoride mitigation:

• A hydrogeological survey should be done before selecting the site for borewell recharge.
• Mapping of structural features in the area such as fracture zones, dykes etc, is important.
• The depth of the recharge borewell should not be considered the same for all areas. The depth needs to be decided after gaining some information about the geology and the nature of aquifers.
• The shallow unconfined aquifer should be completely cased out in the recharge borewell to avoid any leakage between different aquifers and also to prevent entering of fluoride from the shallow aquifer.
• If a geological log is made during the time of drilling a borewell, it would be helpful in interpreting the subsurface geology.
• In terms for impact assessment of the borewell recharge, it is important to measure the water levels in the surrounding borewells. The water levels should be taken accurately with a measuring tape.
• The surface elevation at the borewell is also to be noted.
• Periodic rainfall data of the area should be regularly collected.
• Mica (Biotite) rich granite/gneiss should not be used as a filter media in the recharge borewell. It might act as the source of fluoride in groundwater over the next years.
• Two areas near Bagepalli can be recommended for borewell recharge namely,  Boorgamadgu and Lagumudhapalli