Vacuum excavation remains a leading method deployed by construction and utility crews for project digging in a variety of applications. Leveraging the kinetic energy from a high-velocity stream of air or water, vacuum excavation operators have the unique ability to break up ground soil and then remove it through a powerful suction hose to reuse as backfill or transport for disposal. 

Given the many advantages associated with this process, it has become particularly effective for exposing buried infrastructure in a safer, smarter and more efficient manner than more conventional means and hand tools. That’s why today’s construction and utility teams often opt for this technology in the interest of mitigating safety, damage and compliance risk, as well as limiting environmental impact, optimizing project plans and maximizing profitability.

Because vacuum excavation can be utilized via an air-based or water-based approach, it’s important for teams to choose the method that best suits the parameters of each project. Air vacuum and hydro vacuum excavation feature different pros and cons that should be considered in the context of individual jobs. Following is an informative breakdown to help explain when and why each form of vacuum excavation should be deployed for the best possible outcomes.  

Air Vacuum Excavation

Until recently, air was the most commonly used form of vacuum excavation, and there continues to be a major swath of projects for which this approach is ideal. Otherwise referred to as airvac, pneumatic or air-knife excavation, this method uses compressed air as a source of energy to penetrate the ground soil, expand porous materials and blow the particles apart so they can be siphoned through the vacuum. 

Pros of Air Vacuum Excavation 

• Compressors can generate a limitless supply of air for vacuum excavation, so air is a much less limited resource than water. Airvac can be especially helpful at sites where there’s not easy access to a water source. With an infinite supply of the air pressure needed to dig, there’s no concern over having to “refill” during the excavation process.
• Air vacuum excavation generally operates under lower conditions of pressure and force, so it could be a more fitting option for fragile utilities or those incapable of withstanding direct contact from highly pressurized streams of water. As air is a gas, it will compress and flow around a utility without damaging or abrading the surface. 
• The vacuumed spoils from an airvac project can typically be reused for backfill. Many utility applications are leveraging this option more frequently than before, given the routine sequence of exposing the lines, performing the work and then putting the ground materials back in place.
• When backfilling is not possible or warranted, these dry spoils are easily disposed of. Since the soil is not wet and heavy, it is less expensive to transport or dump.
• The units or equipment required for air vacuum excavation are usually smaller, lighter, more portable and more economical. Because of this, airvac can generally be managed with reduced manpower, trucks and equipment, and it has been known to suit smaller work crews.
• Air is a nonconductive resource, supporting even greater safety mitigation for projects that involve live utilities and electrical risks. Its nonconductive nature makes it less of a hazard to the work crew managing the job. 
• Air vacuum excavation might also be the safer option when there’s risk of chemical reaction with ground materials. 
• Because of the less forceful impact of air flow versus water flow—as well as the ability to backfill easily—air vacuum excavation helps minimize environmental impact. It doesn’t have the potential to damage trees or roadbases. 

Cons of Air Vacuum Excavation

• Because there’s less force and power associated with the airvac process, it’s not as suitable for projects involving very cold, hard or dense ground materials. And the more compact the soil, the more operator effort will be required to perform the airvac excavation. 
• The deeper you have to dig, the greater the probability of reaching colder, harder and wetter subsurfaces, which can render air excavation ineffective. As such, airvac may not be practical for jobs that require digging to deeper subsurface locations. 
• Another byproduct of reduced force is the reduced speed with which air vacuum excavation can be managed. Therefore, this method could involve a longer draw on project time. 
• Given the nature of the compressive action involved in airvac efforts, it has the potential to “sandblast,” or produce a dust cloud in very dry conditions—an outcome that could be detrimental to the immediate environment surrounding the excavation. 

Hydro Vacuum Excavation

With the advent of less expensive water systems, hydro vacuum excavation has become more prevalent. In fact, some airvac trucks now come equipped with a water tank and water heater allowing for hydro excavation in difficult conditions. Hydro excavation—also known as hydrovac, hydro trenching or soft digging—uses highly pressurized, heated streams of water to break up the soil before it’s suctioned out and stored in nearby debris tanks or trucks for transport. 

Pros of Hydro Vacuum Excavation

• A primary benefit of hydro vacuum excavation is the relative ease and speed of excavating. It produces a higher density of water, making it extremely powerful and efficient. 
• Hydro excavation is often the most ideal option for large-scale projects, mostly because it has proven to be a faster and more economical method. It is usually the more efficient way to move ground material, providing construction operators with the means to dig deeper into the ground—with both greater precision and higher levels of equipment capacity.
• The pressurized water stream created via hydro vacuum excavation equipment enables crews to penetrate and pulverize virtually all types of soil. For projects that involve more compact or tougher soil conditions, like clay or rocky earth, hydro excavation is best. 
• If you’re dealing with low-temperature ground materials like frozen soil, water is a more formidable approach because it is more effective in terms of breaking up the area. It can even be heated to more easily handle these conditions. That’s why it’s often applied in colder climates and during winter seasons in northern locations.
• Because water is a natural lubricant, it is less harsh on excavation equipment, thereby minimizing wear and tear on the vacuum machinery. It also helps to control static electricity.
• With hydrovac methods, you’re able to avoid the potential sandblasting that can sometimes occur with air vacuum excavation, particularly in dry conditions. 
• The equipment employed for hydro vacuum excavation is immensely more advanced than traditional options, which equates to safer projects requiring less manual labor and overall risk of injury or death.

Cons of Hydro Vacuum Excavation

• Hydro excavation is limited to the supply of water in the systems holding tank, which can become a particularly important challenge when there is a significant distance between the work site and the nearest applicable source of water. When the tank’s supply is exhausted, the unit must be refilled before excavation can continue. 
• Hydrovac units require larger trucks or trailers of sufficient capacity to handle the volume and weight of water. These units usually have a tank for “clean” water and another in which to store the slurry.
• Water is highly conductive of electricity, which introduces a safety consideration when working near buried electric infrastructure.
• The wet soil suctioned from hydrovac methods may not be suitable as backfill once a utility has been exposed, thereby necessitating the procurement of dry fill by the excavator. 
• There’s also an added expense of having to transport heavy vacuumed materials to a disposal site, as well as a high price for dumping fees. With hydrovac, you must factor in state and local weight restrictions depending on your transport needs.
• Hydro excavation trucks require distinct care in terms of being winterized, so this is an additional cost and management factor to keep in mind. And because working with water can be difficult in cold or freezing conditions, environmentally friendly antifreeze solutions may be required. 

The Choice Between Airvac & Hydrovac

Understanding the distinctions between these two forms of vacuum excavation is critical to planning your approach for any construction or utility project requiring this method of excavation.

Even as the benefits gleaned from using this technology become more apparent, there’s still much to be considered in the way of selecting the best deployment method.

Comprehending the differences described here is one of the first fundamental steps to planning a successful, safe and cost-effective project. That’s why it’s best to partner with an experienced vacuum excavation partner who can make an expert recommendation and carry out the work in the best way possible.

Download our latest whitepaper before you begin your next excavation project: Vacuum Excavation: The Future Of Digging.