The final quality level to discuss is also the one that provides the most certainty. Quality Level A (QLA) is achieved when the utility is exposed and can be seen and measured in the field. The location is then surveyed so that an accurate understanding of its horizontal and vertical location can be found.
While the standard does not state how excavation is to take place it is very common for non-destructive vacuum excavation methods to be used. There are typically two types of vacuum excavation, hydro-vac and dry-vac. Both methods are suitable, and both have their pros and cons. Prior to excavating there may be a need to core or cut asphalt or concrete. Following excavation, it is important to adequately backfill the holes so that there is no damage to utilities and that there is no settlement that could compromise the area.
One of the key updates to the ASCE 38 standard is survey tolerance for QLA. The 38-02 standard requires measurements within 15mm in the vertical dimension. The new 38-21 will relax those standards to within 30mm in the vertical dimension. This was done as a realization that the standard methods used to survey QLA test holes are more easily capable of achieving the 30mm tolerance. This tight tolerance also makes it very important to use the correct overall control as well as localized project control when tying in test hole locations.
Documenting QLA test holes is very critical. In addition to surveying the location for inclusion on the drawing, other data is also collected and recorded on test hole data sheets. Key information like Utility type, material, depth of asphalt, and surface elevations are all recorded and included in the overall SUE report for the project. Photos of the test holes are also important for documenting the information before the holes are backfilled.
Quality Level A test holes are the most expensive data to achieve and therefore should be used very strategically at critical locations. As SUE providers we can help to choose those locations to ensure that critical information is collected as cost effectively as possible.