Company Profile

Salvaging suction slurry

Following its introduction of hydro excavation to this country, the Southeys Group
has launched Sustainable Sand and Stone, a large plant in Auckland that recycles hydro excavation waste into clean, high-grade sand and aggregate. Article supplied.

Hydro excavation is a popular and precise method of trenching, particularly in urban areas where access can be difficult and where underground services could be damaged by heavy machinery. 

However, every year, thousands of tonnes of muddy slurry from hydro excavation is dumped into fill sites around the country to be stored, dried and used as fill for gullies on farmland.

The dumpsites are generally in rural areas, which means trucking the waste long distances leading to higher fuel and emissions costs. 

A normal 21 ton hydro excavation unit has a tare weight of around 12t, which leads to an inefficient tonne-per-kilometre transport cost both in fuel and emissions.

Because of the un-engineered nature of the fill, there are future land use limitations and, in many cases, an environmental impact caused by filling gullies and reducing the overall surface area of the land. 

The water from the slurry that doesn’t evaporate eventually finds its way into settling ponds to remove the silt before it can be reused for irrigation or potentially end up in waterways.

Southey’s innovative solution

The Southey’s management team of Rob Southey, Sheryl Lean, and Kevin Chapman, could see that the sustainability of this process was quickly becoming unfeasible, especially as central and local government contracts demand more and more environmental responsibility.

Rob Southey brought the first hydro excavation units to New Zealand in 2010 and has since designed, built and sold many to operators around the country and for his own fleet. 

“We’ve worked hard to get the weight of our excavation units down, to improve our truck tare and get a more efficient payload, but at the end of the day that gear has to be fit for purpose and last. Lighter units have shorter life expectancies, which is even worse for the environment.

To improve the environmental impact of Southey’s operations and even those of the industry, the team began investigating how to take the excavation waste and recover its usable components.

“Basically, we are now able to turn the waste slurry back into high-quality aggregates and water in the middle of Mangere, Auckland, which means a huge reduction in transport costs and CO2 emissions,” says Rob. “What’s more, our water use is neutral because we recycle it back into our hydro trucks for the next job.

“However, that is just the first half of the story … as it moves through our plant, the slurry is washed and separated, which leaves us with paving sand, coarse sand and drainage metal from 7mm up to 20mm plus.

“That clean, engineering-grade aggregate is ready to go straight back into construction. This reduces the demand on resources from seabed sand mining in places like the Kaipara Harbour and Pakiri Beach and from other quarrying activities. 

“In comparison, our extracted resource is a by-product of highly accurate excavation, of which over 90 percent can be reused in meaningful applications at a fraction of the  emissions … we’re pretty proud of what we’ve achieved and it’s just the beginning.”

From farms to recycling factory

To achieve its project the Southey’s team leveraged its international contacts and, after a global search of waste aggregate recycling plants, a choice of equipment supplier quickly became obvious, says Rob.

“There were companies processing street sweepings and extracting the aggregates in Europe and in other countries, so we started some conversations and got out and looked at a few operations.

“There are a real range of options out there, but we were looking for a partner that shared our values. Southey’s has always been about quality, if we’re buying something we want to know it’ll last and, if there are any issues, that we’re going to get the support we need fast.

The Southeys Group signed the deal in 2019 and since then has been on the Covid rollercoaster with delivery schedules pushed out due to delays in manufacturing, shipping and construction. 

“Six engineers were supposed to come to New Zealand for eight weeks to assemble the plant but because of border restrictions, a NZ-based team had to build the entire plant off the plans, which took six months,” says Rob. “Then there were inevitable teething problems of a new venture. 

“We’ve learnt a lot and we think our supplier, which still monitors and supports the plant from its homebase, has too. There were a few sleepless nights but, under the circumstances, it couldn’t have gone much better and the outcome is exactly what we’d hoped for.”

Quality management

When it comes to hydro excavation waste recycling not all processes are equal and the quality of the outputs was an uncompromising goal for Sustainable Sand and Stone.

“We didn’t just want to separate dirt and water; that is relatively straightforward,” says Rob. “To us sustainable recycling is extracting as much as we can from the inputs and producing consistent quality-controlled product. 

“Our plant uses a range of process steps – each with dedicated technical instrumentation and automated process control running through a plant-wide PLC (Programmable Logic Controller). That plus some patented technology and an in-house quality control lab, results in a range of extremely clean and precisely sized products.”

Future focused

It’s early days for the operation, which has only been fully operational for two months, and the group has big plans. 

“We’re just at the point now where we are starting to redirect all of our own local excavation slurry into the plant to support our Scope One emissions goals, but pretty soon we think we’ll have capacity to start taking waste from others too,” says Rob.

“On the other side of the equation, we are having conversations with civil contractors, landscape suppliers and the broader construction industry about clean, low emission, recycled aggregate supply.”

The materials are supplied at around existing market prices, but Rob says with sustainability expectations, especially around emissions for larger projects, they help contractors meet those  emission reduction targets.

“Depending on how you slice it, we’ve basically eliminated CO2 from the resource extraction. That has to be compelling.”

Looking forward, Sustainable Sand and Stone has goals beyond hydro excavation waste. 

“The new plant has the potential to deal with a broad range of aggregate-based waste,” says Rob.

“We’re looking at the ability to process everything from substrates containing asbestos, hydrocarbons and other contaminants. It has been a big investment but we’re bloody excited about its future!”

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