A type of close interval survey that measures the potential between a structure and the ground surface after the cathodic protection system current has been turned off and the structure to soil potential has stabilized is called a(n) __________.

The correct term for a type of close interval survey that measures the potential between a structure and the ground surface after the cathodic protection system current has been turned off is the depolarized "off" survey. This method is important because it allows for the measurement of the potential that reflects the unaltered condition of the metal structure without the influence of cathodic protection current.

By turning off the cathodic protection system, the structure is allowed to 'depolarize', which means that any interference from the protective current is eliminated and the true electrochemical potential between the cathodic structure and the surrounding soil can be assessed. This provides critical data on the corrosion risk for the pipeline or structure.

Understanding this potential is essential for evaluating the effectiveness of the cathodic protection system and identifying any need for adjustments to ensure integrity and longevity. The ability to identify whether corrosion activities are likely taking place in the absence of protective measures guides maintenance and operational decisions.

Other options describe different types of surveys or methods. A native survey typically assesses the potential without any applied current and does not consider the off-state stabilization. An "on" survey characterizes the potential while the cathodic protection system is actively functioning, and thus does not provide