Hydro excavation waste slurries should no longer be a worry

Hydro excavation slurry
Hydro excavation slurry is typically made up of 60% water and 40% solids and can be difficult and expensive to deal with and dispose of.

By Ryan O’Loan

Across North America and the rest of the world, we are seeing rapid redevelopment and rebuilding in urbanized areas. This often makes sense economically and environmentally, but the process also brings specific challenges. One of these is how to excavate sites safely and cost-effectively.

Hydro excavation, also known as daylighting, trenchless digging, and non-destructive digging, removes or moves soil and heavy debris with pressurized water, and is popular because of its reliability and accuracy. However, the process results in slurry, made up of 60% water and 40% solids.

This type of byproduct is difficult and expensive to deal with, especially if the intention is to dump it at a landfill site, due to its solid/liquid state and weight. The alternative is for hydro excavation slurry to be treated as liquid waste and be disposed of at liquid waste facilities.
This is also a high-cost exercise. Increasingly, strict legislation adds another layer of complexity, and potential cost. An additional concern is that these wastes are highly unpredictable, so the contractor never knows quite what material they’ll be dealing with, which makes preparations difficult.

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Wasting time driving to rural dumping locations

Whether treated as dry or wet waste, hydrovac trucks usually have to drive some distance to find legal disposal sites. This is time-consuming and costly to any business. Using expensive commodities like sawdust to solidify the hydrovac waste adds to the cost, as does the increased weight of the material being disposed of. This approach is inefficient and unsustainable.

Instead of these long drives, systems can now be set up much closer to where the excavation is taking place, even in urban locations. These systems can receive the slurry directly from trucks and can cope with the varied nature of the material, producing clean, compliant, recycled outputs such as sand, stone and clay.

They can even treat the water to a reusable state. This removes a lot of risk that waste handlers are exposed to. It also means operators can offload trucks quickly and return promptly to the dig site, maximizing the efficiency of the company’s most valuable asset, the hydrovac truck.

Recovered water can also be reused to fill outgoing trucks with industry-compliant recycled water. Beyond this, if heavily contaminated, the hydrovac waste can be further processed to remove heavy metals and hydrocarbons from the wastewater stream. This enables a wider range of more difficult (and therefore potentially more lucrative) waste streams to be processed.

Processing the waste on site is viable, practical, and cost-effective. It removes the risk of having to transport possibly toxic substances to waste disposal companies. This prevents possible leaks or accidents during transport, which are always a danger.

Dumping in rural locations is too costly

In addition to the time wasted and travel costs associated with driving to rural sites, landfill costs are an unnecessary and increasing burden on businesses looking to dispose of the byproducts of excavation.

Not only can operators reduce the costs of dumping, extracting and recycling material in the slurry, but they can also resell some material, such as recycled sand. It may even be possible to sell the sand back to the site being excavated. Using the right treatment system means operators can create new revenue streams from something that previously cost money to dispose of.

Such systems can require a large capital outlay, but many companies offer finance options to make them affordable. With the best systems proven to divert 85% of material from landfill, there is significant potential for return on investment.

Meeting stricter legislative requirements

With changing legislation, such as the Canadian Council of Ministers of the Environment’s Canada-wide Approach for the Management of Wastewater Biosolids, contractors continue to face challenges and hurdles when it comes to disposing of waste from their projects.

There is also increasing political will to close landfill sites due to their potential environmental costs.

Taking control of disposal options by reducing or eliminating dumping and recycling in-house instead, means rural dumpsites being shut down will not be a threat to running a successful enterprise. It also means the elimination of legal and environmental risks associated with current disposal methods.

Everyone involved in hydrovac excavation can identify the need to reduce waste slurry previously sent to landfill and the importance of recovering aggregates and water where possible. Processing slurry should not be seen as a distraction from excavation, but a crucial part of the process.

Case study

Ontario-based Da-Lee Environmental Services offers a range of waste classification services, including treatment, disposal, transportation and handling of hazardous and non-hazardous waste around southern Ontario from Toronto to the U.S. border. Prior to investing in new equipment, the company handled a range of solid liquid wastes by adding sawdust to solidify the materials sufficiently to allow them to be taken by truck to landfill. While this remains a responsible way to process these wastes, there were a number of efficiency issues that it wanted to improve upon.

Sawdust was an expensive commodity and represented a considerable annual overhead, not just in its purchase, but the logistics of purchasing and handling on-site. By adding sawdust, the material was solidified but not dewatered. This meant that the weight of the water was still going to landfill (an unnecessary extra expense) instead of being removed and processed through their on-site liquid waste treatment centre. The cost of taking these materials to landfill was considerable, both in terms of the cost per ton gate fee and the carbon footprint impact of the entire operation.

This led to the search for a more sustainable approach, one that decreased the weight of the waste going to landfill, the logistical burden on the team, and the impact on the environment. With an increasing demand for their services, Da-Lee needed a highly-efficient process that reduced both disposal and transport costs in order to maintain the level of service their customers were used to.

Da-Lee invested in CDEnviro equipment to reduce disposal and transport costs. The CDEnviro G:MAX was installed at the Stoney Creek site in 2018 to treat storm drain material, wastes from gullies, culverts and gross pollutant traps, hydro excavation waste and a range of other materials. The system employs wet processing techniques, specifically designed to treat and dewater the waste streams, extracting sand and oversize components in the process, and leaving the residual water easier to treat.

Recovered sand output products can be diverted from landfill and can be reused in a number of low-grade construction applications, such as pipe bedding, road fill and landscaping. The remaining dewatered material is easy to both dispose of and handle. With increased efficiency, Da-Lee is able to accept more contracts than before.

David Rogers, CEO at Da-Lee Group, said: “The G:MAX has helped us dewater many of our solid/liquid waste streams in a more efficient way than we were previously. From cost savings to a more streamlined process on-site, this has made a big impact across the business.”

Ryan O’Loan is with CDEnviro. Email: roloan@cdenviro.com

Read the full article in ES&E Magazine’s August/September 2020 issue:

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