What problem is likely caused by flatter sewer line grades?

Flatter sewer line grades can lead to a phenomenon known as "sewer stagnation," where wastewater does not flow efficiently through the pipes. When the gradient of the sewer line is too gentle, gravity isn’t enough to keep the flow moving at an adequate speed. This can result in the accumulation of waste materials and a buildup of solids within the sewer line.

As solids settle inside the pipes, they can create blockages, which contribute to unpleasant odors and increased maintenance requirements to clear out these clogging materials. Additionally, the stagnation can foster the growth of bacteria, leading to further odor issues. Regular maintenance becomes necessary to address these problems, thus increasing overall maintenance expenses.

In contrast, increased pressure and flow are typically observed with steeper grades, while reduced risk of flooding or excessive chemical reactions are not directly linked with the grading of sewer lines in this context.