QUESTION
Suggestions needed on blasting a borewell in Bangalore, Karnataka

Dear Experts, I am constructing a duplex house in KR Puram area, Bangalore, for myself in which a borewell is dug for 900ft, after consulting with a local geologist. Since there is a house adjacent to my plot and when the neighbour complained about more dust coming out during digging, water was put inside the driller while digging the borewell. Though we found the soil was wet while digging, we could not ascertain the presence of water source. After digging 900ft, we waited for 30 mins and applied high pressure using the driller. Then some amount of water came out. The person who drilled the borewell told yield could be 1/2inch. After 3 weeks of digging, we used a nylon rope tied with a small container to check the depth of water and found to be at 150ft. Later we installed 4HP Texmo motor - 3phase, 12.5 guage HDPE pipes upto 850ft. For the first 2 days, water was pumped out for 1hour with no problem. Problem: On the third day, water came only for 15mins and later bubbles appeared. On the fourth day, water came only for 5mins further only bubbles are being observed. Everyone is suspecting the presence of rich water source. The driller is suggesting to go for a blast after checking the water source with a camera. My queries: 1> What are your suggestions given the current situation? 2> If blast is necessary, what precautions should be taken before/during/after blasting? There is a 3-storied building adjacent to the borewell location. 3> Current phase of construction of house: Pillars laid & completed brick work of ground floor till lintel level. Should blasting be done before putting the roof of the ground floor or doesn't it matter? 4> What are your recommendations for the motor power, pipes to be used for this borewell? Please treat this as urgent and kindly send your invaluable suggestions at the earliest. Thanks in advance, Best Regards, Raghu.

by
5 January 2010