Storing Co2 Under Ground

People are saying that it would be good to capture Co2 and place it deep under ground. This idea is a good thing to make the air cleaner and such but it would cost a boat load of money to maintain and start.  Almost 10 billion dollars would be the cost of putting it under ground. The method they would use would be to inject the Co2 into a brine and send that brine under ground. That is what would make up most of the expenses. The storage could also be used to  generate electricity potentially. I feel that this would really help the environment, even though maybe after a while it would have to much of a build up. For now it would be an awesome idea.