Vacuum excavation, also known as potholing, is a method of exposing utilities using water and suction. Vermeer offers some tips on how to estimate the operating costs of running vacuum excavators.
Vacuum excavators uncover utilities using high-pressure water, but material the can’t merely be piled up near the hole and filled back in. The soil mixed with water is considered spoil, or slurry, and must be transported to disposal sites, which requires effort and costs not associated with uncovering utilities with an excavator or backhoe loader.
“To estimate potholing expenses, contractors need to have a general understanding of what utilities their crews will encounter near the proposed drill path,” says Adam Bates, product manager at Vermeer. “The number of holes and depths need to be considered, as well as the site’s proximity to water and a disposal site. Depending on the customer, getting that information isn’t always easy, which makes estimating a bit of a moving target.”
How much does vacuum excavation cost?
To get a rough estimate of operating costs for vacuum excavation, Bates recommends starting with a hole count. “Each hole will usually be about 1 foot in diameter, but depths can vary,” he says. “Depending on ground conditions and climate, crews should be able to determine the approximate depth of each utility. So, if they need to excavate to a depth of 5 feet on average, they are removing around 4 cubic feet of material for each hole. However, the volume of liquid being suctioned into the spoil tank also needs to be accounted for. Fluid volume can vary depending on the type of soil conditions, but crews can usually expect it to be a 1:1 ratio.”
The formula for estimating vacuum excavation costs
A 1-foot diameter hole at a depth of 5 feet = 3.9 cubic feet or 0.15 cubic yard. This is doubled to account for the volume of water used: 3.9 x 2 = 7.8 cubic feet 0.3 cubic yards. Now multiply that total by the number of holes to be excavated. For example, ten holes would produce 3 cubic yards 606 gallons of spoil. If your crew is running an 800-gallon vacuum excavator, you can vacuum excavate around 13 holes before needing to dump the spoils.
What variables affect excavation costs?
Calculating the volume of material collected through vacuum excavation is pretty straightforward, but other considerations may not be.
“Over-the-road drive times and disposal costs for vacuum excavators can be all over the board,” says Bates. “In urban areas, a round trip from the jobsite to disposal facility may take from 30 minutes up to two hours depending on the time of day. That additional time doesn’t just compound the labor costs for the potholing crew. It can also have an impact on the productivity of the drill crew working behind them. It’s certainly not uncommon for HDD crews to be shut down for hours at a time because they are waiting for a vac stuck in traffic.”
Bates also said many communities regulate where spoils and slurry can be disposed, which has reduced the number of facilities. “I’ve heard from contractors working in large cities that their crews often have to drive to a location outside of city limits, and they pay substantially more than they used to just a few years ago. It’s a real issue,” he says.
Transport weight of the truck and trailer vacs must also be considered. Bates recommends calculating the distance to disposal sites, researching dump costs, and studying DOT weight regulations during the bid process. “After a project is completed, contractors should compare the estimated operational cost with actual expenses,” he says. “Going through this process will help them dial things in for future projects. Also, in some instances, investing in a way to take some of the variability out of a project is a better approach.”
Vermeer product solutions
In recent years, Vermeer has introduced several sizes of reclaimers to allow horizontal directional drill (HDD) crews to recycle drilling fluids, which helps reduce the amount of slurry they will need to dispose of.
For drilling and potholing crews, Vermeer began selling the MUD Hub solidification system. With this system, contractors can establish a centralized dumpsite for vacs to feed the MUD Hub used liquids. A solidification agent is then added to the wet material to absorb the moisture and create stackable material that can be transported by a regular dump truck, and possibly be disposed of at a regular landfill or reused in a variety of applications.
The XR2 vacuum excavator has a self-leveling shaker deck that separates solids from the liquids. Used water is pumped into onboard holding tanks for later disposal, and the separated solid material can be offloaded to a truck or stacked on site.
“With the XR2, crews can bring up to 1,500 gallons of fresh water to the job and leave with a similar amount of used fluids,” says Bates. “This setup gives the operator maximized wand time, which helps them stay on the job longer.
Source: Vermeer Corp.