What issue can flatter sewer line grades cause?

Flatter sewer line grades can lead to odor nuisances and increased maintenance expenses due to the potential for wastewater to stagnate in the pipes. When sewer lines are not sloped adequately, the flow of wastewater may slow down, resulting in solids settling out of the flow and accumulating in the pipes. This accumulation can cause blockages and lead to backups, which are not only unpleasant but can also pose health hazards and require costly emergency maintenance to resolve. Additionally, stagnant water may contribute to odors from the sewer system, affecting nearby homes and businesses.

The other options, while perhaps related to sewer systems, do not accurately describe the primary issues associated with flatter grades. Increased water pressure is not a typical consequence of flatter grades; faster water flow would actually be a benefit of steeper grades; reduced pipe diameter does not directly relate to the grade of the sewer line but rather to the design and construction of the system itself.