The plugging and abandonment (P&A) of a Class 1 Hazardous injection well (previously a Class II, oil and gas well) in California was dependent upon satisfying state and federal requirements, which included placement of cement plugs inside the casing and, if needed, in the annular space between the casing and the original drilled hole. Pressure which had built up inside the annular space between the tubing and casing during the ten year shut-in period was suspected to be caused by a very small casing leak. The concerns regarding the unconfirmed existence and unknown location of this suspected leak in the casing made the P&A Plan more complicated and potentially more expensive to account for all the possible scenarios that could occur. The U.S.E.P.A. required that the P&A Plan include locating the cause of the casing pressure and either remediating the leak or preventing any future harmful effects to the environment. Since a temperature tool would be utilized to establish External Mechanical Integrity in the well, it was decided that the same tool could possibly be used to locate the casing leak. The development of these "alternate" procedures were based upon the principles of the temperature tool's ease of operation, its sensitivity and resolution, and its reliability. The temperature tool was used to reflect a disturbance of fluids in the tubing/casing annulus that were previously stable. This paper discusses those procedures, the results and conclusions of that portion of the P&A operation, and the rig time cost savings from conventional methods.