When a grade conflict exists between a water main and a sewer main, which of the following is the best solution?

When a grade conflict exists between a water main and a sewer main, having the water main adjusted while maintaining the grade on the sewer main is considered the best solution because it preserves the integrity and function of both systems. Water mains must be placed above sewer mains to prevent any potential contamination of the water supply. By adjusting the water main to ensure it is at a greater elevation than the sewer, the likelihood of cross-contamination and health risks is minimized.

This approach also ensures that both systems operate efficiently without the complications associated with pumping or siphoning. It avoids the complications of having to deal with gravity drainage issues that may arise from adjusting the sewer main instead. Furthermore, this method aligns with civil engineering standards and best practices, which prioritize the protection of potable water sources and the structural safety of the sewer systems.

The other solutions involve more complex configurations that could introduce risks or additional maintenance complications, such as potential blockages or the need for constant monitoring of pump stations or siphonal flow, which complicates routine operations and increases overall system vulnerability.