To ensure a spray-on liner for an oil containment pit will not leak, it is filled to one-half the maximum depth with water and monitored for how many hours?

The correct answer is based on the standard practice for testing the integrity of a spray-on liner used in oil containment pits. When the liner is filled to half its maximum depth with water, monitoring it for a full 24 hours is essential to ensure that there are no leaks or compromises in the liner's integrity.

This extended monitoring period allows for thorough assessment, as fluctuations in temperature and other environmental factors could cause minor leaks to develop over time. The 24-hour timeframe provides a realistic indication of the liner's performance under conditions that mimic those it will endure when operational, ensuring that any potential issues are identified well in advance of putting the system into service.

In contrast, the shorter timeframes associated with the other options would not allow as comprehensive an evaluation, potentially leading to undetected weaknesses in the liner. This makes the 24-hour monitoring period the most reliable choice for ensuring the containment system's effectiveness and environmental safety.