Hydrovac slurry has been a contentious issue in Alberta’s oilfield and construction industry for several years.
Hydrovac waste – or slurry – is what’s left when a hydrovac uses high-pressure water to dig through soil and clay. It’s basically thick mud, composed of around 60% water and 40% solids.
Hydrovac slurry has become a hot topic because of confusion caused by constantly changing regulations. With a massive increase in the amount of hydrovac trucks being contracted by utility and construction companies, there has also been an increase in illegal dumping.
There are two major problems. The first is that daylighting holes are generally deep and narrow, which means different layers of soil and clay are mixed together. The resulting slurry isn’t topsoil; it’s a mix of soil and clay that isn’t good for much of anything, especially dumping onto agricultural farmland.
The second problem is that work areas that tend to have a lot of hydrovac work, such as new pipelines, also tend to serve as conduits for contamination to travel on the tires of trucks and through water runoff. These contaminants often end up along farmer’s fields and in watersheds.
On top of that, hydrovac slurry is too wet to be put into landfills and too thick to be dumped into sewers.
Dealing with hydrovac slurry
So, how should it be dealt with?
First of all, make sure you’re up to date on provincial and local bylaws. Read through material by Alberta Environment and Parks and contact them if your situation is unclear.
Next, before you begin digging, make sure your truck container and the water you’re using are clean and won’t introduce any contaminants.
Inspect the site and ensure there aren’t any contaminants in the worksite. Scan the site for evidence of spills or hydrocarbons. If the ground is oily or smelly, you’ll probably need to take it to a proper waste treatment centre. If the site has a history that suggests that it’s probably contaminated, it probably needs to be tested.
If you’re digging through topsoil such as in a farmer’s field or somewhere there’s grass, the topsoil should be hand-dug and set aside for later remediation.
Now that you’ve ensured the site isn’t contaminated and you’ve saved any topsoil that’s been displaced, you can go ahead and excavate. Either you’ll find your underground infrastructure and finish up or your hydrovac unit’s tank will fill up beforehand. What are your options?
Ideally, the landowner has their own properly dug and lined storage pond where the slurry can separate. This is definitely the preferred option as it saves you from having to drive across town to some disposal site.
Another option is to spread the slurry on the original dig site to dry out and then incorporate it as a fill material (such as grading a road, or backfilling). The slurry has to be contaminant-free and you can’t dump it on agricultural land.
If dumping on site isn’t an option, that’s where things get tricky.
Around Edmonton, dump sites tend to come and go. Many have been shut down, leaving only a few which can result in much longer turn-around times, especially during rush hour.
Finally, your slurry must be classified before leaving the work site. Then it can be driven to an approved hydrovac waste facility. Contaminated slurry must be taken to an appropriate hazardous waste management facility such as Tervita. Being caught dumping illegally can result in massive fines.