On-Site Sewage Facilities (OSSF) – Installer I Practice Exam 2025 - Free Installer I Practice Questions and Study Guide

The maximum slope allowed for a trench during excavation is set to ensure the safety and stability of the trench walls, preventing collapses that could pose a risk to workers and equipment. A slope of 1 inch per 25 feet is considered the standard because it provides a gradual incline, allowing for adequate support of the trench walls while minimizing the potential for soil erosion or instability.

This specific ratio strikes a balance, ensuring that the trench provides sufficient access for installation and maintenance of on-site sewage facilities while adhering to safety regulations. The stability of the trench is crucial, especially in varying soil types which can influence how well the walls hold up under weight. Calculating the slope in this manner allows workers to determine the right depth and width for safe operations within a trench.

In contrast, steeper slopes, such as those indicated by the other options, do not comply with safety guidelines, as they increase the likelihood of soil shifting and collapsing into the working area, which can put workers at significant risk. Therefore, using a slope of 1 inch per 25 feet is not only compliant but also a best practice in the field of excavation for on-site sewage facilities.