Only a fool would make a claim that, in a side by side single hole dig comparison, air excavation would be faster than hydro excavation. Water will always cut faster and help dig faster. However, if we step back a moment and examine all the time factors involved with a given project, we can begin to understand that there are definitely times when digging with air might be a better or faster alternative. Let us take a look at a few of the factors that might determine when it would be best to use air or water for an excavation project.
At the start of the day (or end of previous day) a hydro excavator unit must be filled up with water. The refill process can take even longer if water is not available nearby, instead leaving an operator to drive far distances to fill up.
Larger hydro excavation units hold around 1300 gallons of water, whereas smaller units can have as little as 350 gallons. So even with the larger water tanks, you likely get between 3-5 hours of hydro dig time before you run out of water. Now comes the big challenge; how far away is a water source to your job site? If you are lucky, your daily fill source is close by. If not, a lot of time can be spent traveling back and forth to get water for a hydro excavation job.
Meanwhile, air excavation units rarely need water and almost always go the entire day (sometimes a week) without needing to be refilled. It is nice to have some on board water when challenged with a difficult dig spot, but is not always necessary. If your water source is close by, this would be a non-factor. However, if you are driving a distance to reach a water source, it could point towards air excavation being a better alternative.
Similar to the water source location, added travel to dump your debris tank can be a long and costly non-value added process for hydro excavation. Debris from hydro excavation can rarely be used as back fill because of its slurry form and therefore must be dumped at a different location. Air excavation debris is dry, can be used as backfill and dumped directly back into the same hole. Again, if your debris dump location is close, this could be a non-factor. If your dump location is a time long consuming travel distance away, air excavation may prove to be the better alternative.
Understanding the scope of the project is an important factor in determining whether to dig with air or water. When do you get paid? Is it after the hole is dug and fenced off? Is it after the hole is dug, utilities exposed, repaired, documented and the hole returned to its original condition? As discussed previously, debris from air excavation can be immediately used for back fill, while hydro excavation may require extra time and costs to haul back fill material to the job site to back fill holes.
Let us go back to one of the original statements . . . “Water will always cut faster and help dig faster”. If you have a very large area (or several large areas) to dig, water will drive faster results. Digging faster, as well as large debris tanks commonly found on hydro excavation units, will help negate or reduce some of the above previous hydro excavator pitfalls such as travel time to dump sites and to water sources when excavating larger areas.
Hydro Excavation is generally preferred over digging with air when it comes to cold weather applications.
We reviewed several time factors involved with common soft dig projects, and one could argue there are many more. Each project can be unique, so what is the better method, air or water? If you have a large area to excavate, can dump on-site, have a close water source, and do not have to back fill then hydro excavation is your obvious choice. If you are digging small test holes, need to back fill when complete, and do not have a local spot to dump or fill with water, then using air excavation would likely be a better alternative.
You can read additional comparisons, as well as operator testimonials, between air and hydro excavation at Dig Different Magazine. Dig Different has also featured the RAMVAC AX-4000 Air Excavation Truck on their website.
Chris Falk is currently the Air Excavation Product Manager for RAMVAC Vacuum Excavators by Sewer Equipment. His knowledge and expertise on this subject comes from spending many years in the field working next to contractors from a number of industries on job sites utilizing excavation equipment in many different applications, both hydro and air. Chris has been an employee at Sewer Equipment for 14 years, spending 6 years focusing on hydro excavation equipment and 4 years with the addition of air excavators. For follow-up questions and comments, Chris can be reached at email@example.com