EDI Uses Various Approaches to Get the Task Done
How do you extract 2 litres of groundwater from a monitoring well that’s only 4 to 10 centimetres wide and over 100 metres deep? This is one of the challenges faced by Hanna Donaldson, a senior biologist and Strategic Initiatives Director at EDI, and her water monitoring team.
Industrial clients, such as our mining clients, are often required to monitor the quality of groundwater at their sites. “We have learnt that you have to find the right tool for the job,” explains Hanna. “Peristaltic pumps are traditionally used to collect water samples from shallow wells of 25 m or less, but that wasn’t going to work for some of the deeper wells we needed to sample. In British Columbia, the Ministry of Environment and Climate Change Strategy requires quite low turbidity in a sample, which can also be a challenge.” Hanna and her team have used two different types of equipment for collecting groundwater from deep monitoring wells: a low flow bladder pump and a HydraSleeveTM.
Low flow bladder pumps are effective at retrieving water, but they can be time consuming at greater depths. This type of system involves lowering a bladder pump to the required depth in a well and then allowing it to fill with water. When compressed gas is sent down a drive line, the bladder constricts and pushes the water up into a sample line. A check valve prevents water from flowing back down to the pump. When compressed gas is withheld, the bladder refills with water. The pressure and release cycles are repeated, providing a flow of water up the sample line. The bladder pump system requires on-site monitoring for the entire length of time required to collect a sample and only one or two samples can be collected in a day. The process can be sped up depending on the type of compressed gas used within the system, but it may still take several hours to purge the well and retrieve a complete sample.
For wells that have greater depths and the amount of sampling time is a consideration, EDI uses a HydraSleeve, which is a specially designed, compressed plastic bag with a top collar and weighted bottom. The sleeve is lowered into a well to the depth of the well screen and left in place for 24 hours to equilibrate within the monitoring well. Team members can leave the site and travel to other wells to set up additional HydraSleeves. Upon retrieval, the sample is collected as the sleeve is pulled to the surface. Retrival and bottling takes between 5 to 15 minutes per sample, depending on well depth, so the number of samples collected per day is mainly limited by how close the wells are to each other. The HydraSleeve involves less equipment than a low flow bladder pump, which is beneficial for sampling at remote locations with limited access. Collecting duplicate samples can, however, be a challenge depending on required sample volumes.
Since both deep well sampling systems have their advantages and draw backs, EDI works with clients to devise practical solutions for monitoring requirements. To read more about EDI’s innovative approaches to monitoring, click HERE. To learn more about the services EDI provides, click HERE.