Which of the following is NOT an option for managing risk of root interference with sewer lines?

The option related to planting trees with aggressive root systems near sewer lines is not an effective strategy for managing the risk of root interference. In fact, planting such trees would likely exacerbate the problem. Aggressive root systems can invade sewer lines, causing blockages, pipeline damage, and expensive repairs.

The other options provide methods to mitigate existing root interference or to prevent future issues. Mechanical removal of roots helps alleviate blockages without introducing harmful substances into the environment. Killing roots with chemicals might be used as a last resort to clear roots from sewer lines, although this can have significant environmental impacts and may not be a sustainable long-term solution. Restoring the integrity of the pipe with liquid sealants can provide a means to prevent further infiltration by roots and help maintain the pipes' functionality. Overall, option C stands out because it directly contributes to the very problem that needs managing, highlighting the importance of strategic planning in urban forestry and infrastructure management.