Abstract: Apparatus for confirming the presence or absence of leaks in a liquid storage container, particularly in partially filled underground storage tanks, subjected to partial vacuum for the purpose of testing the tank for the presence of a leak in the area above the liquid using a hydrophone or microphone either positioned in or attached to the container to detect the sound produced by the ingress of fluid into the container as a result of the vacuum. The ingress of fluid is confirmed by recording and observing the vacuum pump on/off cycles that define a time period for the system to change from a high vacuum state at a first predetermined pressure toward a low vacuum state at a second predetermined pressure, with the pump operated to restore tank vacuum level at the end of each period back to the first predetermined pressure, such observed trends of the measured patterns in the on/off cycles for a leaking container being distinguishable from the on/off cycles for a non-leaking container.

Abstract: Method of confirming the presence or absence of leaks in a liquid storage container, particularly in partially filled underground storage tanks, subjected to partial vacuum for the purpose of testing the tank for the presence of a leak in the area above the liquid using a hydrophone or microphone either positioned in or attached to the container to detect the sound produced by the ingress of fluid into the container as a result of the vacuum. The ingress of fluid is confirmed by recording and observing the vacuum pump on/off cycles, the on/off cycles for a leaking container being distinguishable from the on/off cycles for a non-leaking container.