Measuring Successful Rehabilitation

In the past several years, a growing number of communities have reported successful sewer rehabilitation projects -projects where more than 50% of the I/I was removed from the sewers. Successfully removing I/I is a problem facing thousands of sewer agencies, worldwide, yet very few have succeeded. Recent successes, particularly in Nashville, TN and Sydney Australia have sparked interest in fixing leaky sewers as a viable alternative to regaining sewer capacity or treatment plant capacity. Clermont County, Ohio and Nashville, Tennessee have gone so far as to bid rehabilitation projects with incentive payments attached to the amount of I/I actually removed from the sewer system. But how do we measure the amount of I/I actually removed? How do we know when we have enough data? How do we attach bonus or penalty payments?