Which method involves sensors detecting petroleum product in the soil?

Vapor monitoring is a method that specifically involves the use of sensors to detect petroleum vapors in the soil and the surrounding environment. These sensors can identify the presence of hydrocarbon vapors that can escape from underground storage tanks due to leaks or breaches in the tank's integrity. The focus on vapor detection is essential because it allows for early detection of problems that could indicate a leaking tank, thus enabling timely remediation efforts to prevent soil and groundwater contamination.

While other methods listed have their own roles in monitoring for potential leaks from underground storage tanks, they do not specifically focus on the detection of vaporized petroleum products in the soil. Groundwater monitoring, for example, primarily involves assessing the quality and contaminants present in groundwater. Leak detection monitoring generally refers to methods that may involve fluid detection in various ways, but not specifically limited to vapor sensors. Soil sampling involves physically taking soil from the site to test for contaminants but does not utilize sensors to continuously detect vapors. The specificity of vapor monitoring to detect petroleum vapors makes it the correct answer in this context.