What term is used to describe the undisturbed natural surface of the ground?

The correct term for the undisturbed natural surface of the ground is "Grade - Natural." This term refers to the original contour and elevation of the land prior to any construction, excavation, or grading activities that may alter the natural landscape. Understanding the concept of natural grade is crucial in disciplines such as grading, drainage, and stormwater management, as it serves as a reference point for assessing changes in land form and for planning effective drainage solutions.

In contrast, the term "Foundation" generally pertains to the underlying structure that supports a building or other construction and does not specifically describe the surface of the ground. "Finish Grade" refers to the final elevation of the soil after grading and preparation for landscaping or construction, which is a modification of the natural grade. "Filter strip" refers to an area of vegetation designed to remove pollutants from runoff water, contributing to stormwater management but not relating to the undisturbed ground surface. Understanding the distinction between these terms helps clarify the role of various elements in site preparation and stormwater management strategies.