The Australian Water Quality Centre’ Field Services Team has recently acquired a low flow bladder pump and controller to improve its capabilities for groundwater sampling.
For many years the Field Services Team used a submersible pump which transferred water to the surface at a continuous discharge rate. This type of pump was designed to discharge fixed volumes of water drawing at very high rates. The technique, while very useful for bores that require large volumes of water to be purged prior to sample collection, for most environmental based sampling this high flow rate can create a few problems:
- Increasing the turbidity of the water;
- Agitated water mixing with air can cause error in analytical results;
- Abrasive materials present in turbid water can damage to the pumps soft moving parts;
- Non-mobile constituent can become mobile triggering a misrepresentation of the quality of mobile groundwater;
- Increasing the stress applied to the bore.
All these problems are addressed with the new bladder pump which collects samples through a low flow purge technique (micro-purge). This allows samples to be collected at a discharge rate less than the recharge capacity of the well (Figure 1), therefore targeting a certain zone within the aquifer without agitating the water. The new bladder pump can collect samples at a minimum flow rate of 0.1L/min. This type of sample collection ensures a reliable representation of the mobile constituents while also reducing the volume of water being purged from the bore.
Figure 1: Maz Ghamrawi collecting a groundwater sample. Prior to sample collection water quality is monitored using YSI probe within a flow cell recording Conductivity, pH, Temperature, and Dissolved Oxygen. The readings are recorded every three minutes until three consecutive readings show the parameters have stabilised.