One of the spotlight features for this issue is vacuum excavation (vac ex). This non-destructive digging process allows an excavator visual access to the utilities buried within a dig area. Using high pressure air or water to remove surrounding soil, vac ex safeguards against hitting or damaging underground assets. Non-invasive, cost effective and accurate, it reduces the risk associated with excavation. An additional benefit is the minimal impact it has on the surface, reducing disruption to traffic flows and other activities.
We feel this topic is important to cover because, as our underground becomes increasingly congested, digging without accurate knowledge of a utility’s location becomes increasingly dangerous.
CGA considers the use of vac ex to be a Best Practice (5-32), reading, “Vacuum excavation, when used appropriately, is an efficient, safe, and effective alternative to hand digging within the designated underground facility tolerance zone. Use of equipment also follows state/provincial laws and/ or local ordinances.”; and lists it as one of the methods for consideration when digging within the tolerance zone (5-20).
Further, ASCE 38-02 SUE Standards (5.4.3) states that a typical task by the engineer leading to utility Quality Level A is to “Excavate test holes exposing the utility to be measured in such a manner that protects the integrity of the utility to be measured. Exposure is typically performed via minimally intrusive excavation. In some cases, data gathering during utility construction may eliminate the need for excavation of the utility, as it is already exposed.”
Horizontal Directional Drilling (HDD) is a great tool to use for installing new utilities as this installation method avoids damage to sidewalks, patios, landscaping, and other aboveground features. However, since there is no open trench, it is possible to intersect another underground line, creating a cross bore. When these cross bores involve a gas and a sewer line, natural gas can invade the sewer system, back up into a building, and cause an explosion. Vac ex virtually eliminates the potential for cross bores as strategically placed potholes allow the HDD driller to watch the bore head pass by utilities already in the ground.
Of course, vac ex doesn’t remove the responsibility of the excavator to respect the process and follow the six best practices for safe excavation. Contacting 811 is still required, but what vac ex does do, literally, is bring the hidden infrastructure into the light of day.