Saldanha in the Western Cape of South Africa is a small port town on the northern shore of Saldanha Bay. The bay is a naturally sheltered harbor, making it ideal for exporting iron ore on massive ships. It serves the region’s base metal mines and a heavy minerals smelter and is also the location of a large crude oil storage facility. In addition, the town is home to over 20,000 residents who follow their trade based on the economic drivers in the area, including shipping companies, industrial production plants, and the railway line. As such, it is important that the water resources in the area, including groundwater, be monitored and protected from contamination.
GEOSS needed equipment that could handle sampling for potential VOCs (volatile organic compounds) VPHs (volatile petroleum hydrocarbons) and general chemistry at potentially contaminated locations. They also required a sampling solution that could be used in narrow diameter boreholes.
Based on their criteria, GEOSS selected a Solinst 1″ diameter Model 407 Bladder Pump. Solinst Bladder Pumps allow low flow purging and sampling – ideal when monitoring for VOCs. Low flow sampling involves extracting groundwater at rates comparable to ambient groundwater flow so that the drawdown of the water level is minimized, and the mixing of stagnant water with water from the screened intake area in a well is reduced, overall, providing a representative sample.
When a Bladder Pump is installed down a well (or borehole), water rises inside the bladder and sample tubing to static level. Compressed gas is applied to the pump via the drive tubing using a Control Unit. Pressure causes the bladder to compress and closes the bottom check valve, forcing water from the bladder into the sample tubing. Pressure is released from the Bladder Pump during a vent cycle. The bladder opens as water refills the pump, while the top check valve prevents sample water from falling back into the bladder. Cycling the drive and vent provides water flow.
Currently, GEOSS use a 1″ diameter Solinst Bladder Pump that they transport from site to site to sample groundwater. Between each sampling event, the Bladder Pump is decontaminated to prevent cross-contamination between wells. There are often over 30 samples to be collected each week, so efficient and proper decontamination is a crucial element to all sampling campaigns. They are using a portable setup that includes the Solinst Model 464 Electronic Pump Control Unit to regulate the vent/drive cycles, and a nitrogen cylinder for the gas source.
A Solinst Model 122 Interface Meter is also used in the project to measure water level and to detect any free phase in the groundwater. Michael Holloway, of GEOSS, said, “The equipment is used for the sampling and low flow purging of narrow diameter sampling boreholes. As hydrogeologists, we purge the borehole first before collecting a representative sample of the groundwater and not particularly water that has been standing stagnant inside the borehole.”
The purpose of the groundwater-sampling program is to detect any contamination in the region’s aquifers, as well as to track the movement and spatial distribution of any contaminant plumes that are found. Simple and robust groundwater sampling equipment that can easily be carried short distances to out-of-reach areas. It is noted, “The Bladder Pump is versatile and can be used across a few sites within the project where a vehicle can’t get to… it’s easy enough to carry the entire Bladder Pump setup and then continue the fieldwork without wasting too much time.”
Overall, the advantages to using a Solinst Bladder Pump are:
When selecting a groundwater sampler, there are some key factors to consider. The physical attributes of the well: diameter, calculated purge volumes, depth to water and sampling intervals, and the accessibly to the well for transporting sampling equipment. The well hydraulics, for recharge and recovery, turbidity, etc. must also be taken into account. The aim is to collect a high quality groundwater sample as efficiently and economically as possible. Bladder pumps are EPA approved for low flow sampling and groundwater collection for Volatile Organic Compound (VOC) analysis.
