QL "D" is the most basic level of information for utility locations. It comes solely from existing utility records or verbal recollections. QL "D" provides an overall “feel” for the congestion of utilities and is useful primarily for project planning and route selection activities.
QL "C" involves surveying visible utility facilities (e.g., manholes, valve boxes, etc.) and correlating
this information with existing utility records (QL "D" information). Its usefulness, therefore, is primarily on projects where utilities are not prevalent, or are not too expensive to repair or relocate.
QL "B" involves the determinations of the existence and horizontal position of virtually all utilities within the project limits. This activity is called “designating”. Information provided by QL "B" can enable the accomplishment of preliminary engineering goals. Slight adjustments in design can produce substantial cost savings by eliminating utility relocations.
QL "A" also known as “locating”, is the highest level of accuracy presently available and involves the full use of the subsurface utility engineering services. It provides information for the precise plan and profile mapping of underground utilities through the nondestructive exposure of underground utilities, and also provides the type, size, condition, material and other characteristics of underground features.