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Value Analysis of Vacuum Excavation - Picking the right size equipment

Extensive vacuum excavation programs are becoming the norm for large utilities across the country. Vacuum excavation is known to be the safest method for excavation in terms of human health and safety and the protection of infrastructure. As a result, the demand for vacuum excavation services and equipment has grown faster than the available pool of experienced operators and management personnel. Manufacturers can build equipment faster than service providers can man it with experienced operators. In many cases, those running the service operations don’t have the field experience to properly train crews or provide value engineered solutions to the end user.   

Productivity

Hourly based contracts need to have a basis for productivity. The two main components of productivity are crews and equipment.

Crews

Not all operators achieve the same productivity levels. One operator may excel at a task where another may fail, others may not have the same level of safety-oriented enthusiasm to create a baseline of production. Many factors make it difficult to quantify crew productivity but field experience does make it possible. 

Equipment 

Vacuum excavation equipment should be thought of as a tool in the toolbox. The right tool should be selected for the scope of the task order. The two main concerns here are having under-productive equipment or  over-productive equipment. Just like a carpenter does not use a sledgehammer to tap in finishing nails, a railroad worker would not use a trim and finish hammer to drive in railroad spikes.

Under-Productive Equipment Example:

The ABC utility company has a task order of 10 or more potholes in a congested transportation corridor. The contractor dispatches a small-sized unit to complete the task. The unit dispatched has set limits on capabilities including:

  • Spoil capacity – how much dirt fits into the unit
  • Water capacity – if using water and not air
  • Vacuum power – depth and strength to suck up rocks, cobble and other obstructions

Dispatching under-sized equipment greatly extends the time it takes to complete the job. The vacuum power of the unit slows down each hole marginally and the under-sized debris tank causes the crew to leave the work site several times to dump spoils and get more water. The ripple effect is even greater when traffic control costs increase, and you factor in the lost time of The ABC utility company’s field personnel.

While $180 per hour may look like a good price, the entire project might have taken 25% to 30% longer to complete and the actual cost would be much higher.

Solution – Use a Bigger Truck

Equipment Truck Cost Per Hour Traffic Control Per Hour Hours to Complete Total Cost
Small Truck $180 $50 12 $2,760.00
Large Truck $235 $50 8 $2,280.00

* Increase in time accounts for slightly slower digging, fetching water and dumping more frequently. Rates listed are for comparison purposes only and not based on actual quotes.

The result of using a larger truck saves 17 percent!

Over-Productive Equipment Example:

The ABC utility company has a task order of 3 potholes for dry utilities in a congested transportation corridor. The contractor dispatches a large-sized unit to complete the task. The unit is more than capable of completing the task – remember the capabilities:

  • Spoil Capacity – how much dirt can fit into the unit.
  • Water Capacity – if using water and not air.
  • Vacuum Power – depth and strength to suck up rocks, cobble and other obstructions.

* Spoil and water capacity are negated in this scenario.

The client has been conditioned to believe that bigger is better. But, this is where the $180 per hour small truck is ideal.

Solution – Use a Smaller Truck

Truck Cost Per Hour Traffic Control Per Hour Hours to Complete Total Cost
$180 $50 2 $460.00
$235 $50 2 $570.00

* Since it’s a small task order, dumping time and fetching water is not factored in.

The result of using a smaller truck saves The ABC utility company 23 percent. Further savings can be captured depending on ground conditions if Air Vacuum Excavation can be utilized.

Air Versus Water

Many will say that vacuum excavation with water is much faster than air while others say air is more cost effective than water.

When air or water use is a choice not regulated by the permitting agency, a few conditions must be considered to provide the best value.

  • Is there a specific task where air or water seems to provide a better result for The ABC utility company’s field personnel – such as pole holes or pole anchors?
  • Do the ground conditions allow for the same type of productivity?
  • Does the cost of bringing in backfill outweigh any potential productivity slowdown in the digging, if air is used?
  • Would using the native soil removed with air excavation be less expensive than importing backfill?
  • Is there an infrastructure concern where water would be disastrous?
  • Is there an environmental concern where airborne particles would be a health and safety concern?
  • Is there an environmental concern where water being introduced to the soil would cause a contamination plume to expand?

Solutions

A good vacuum excavation contractor has equipment in three size categories to match the tools with the task order.

  • Small capacity units that are either pulled or truck mounted for small task orders.
  • Medium sized equipment that can either dig with air or water and capable of holding spoils for 10 standard potholes.
  • Large 12 cubic yard debris sized equipment with powerful blowers for the toughest and most demanding excavation requirements.
  • Vacuums that can excavate with either air or water.