Groundwater research, for example for contamination, starts with sampling. Groundwater levels can vary greatly; sometimes the groundwater is situated a few centimetres below ground level, while in other places it can be tens of metres deep. The depth of the groundwater determines which pump or water sampler is required for sampling. In addition, the choice of a groundwater pump also depends strongly on the applicable sampling protocols and the target parameters in the research.
In this article we discuss the peristaltic pump, Gigant submersible and booster pumps, MP 1 submersible pump, ball valve pump and various sampling hoses.
For sampling at a groundwater level between 0 and approximately 8 metres deep (minus the ground level), the peristaltic pump is a suitable device. This groundwater pump is robust and designed to be used in various field conditions. The peristaltic pump sucks up the water using a flexible suction hose, in combination with a polyethylene delivery hose. The delivery height (suction height) is limited by the air pressure and the friction of the hose. That is why the peristaltic pump can be used at groundwater levels of up to approximately 8 metres at the most.
The great advantage of a peristaltic pump is that the sample only comes into contact with the inside of the hoses used. These pump hoses are replaced after each sampling, which minimises the chance of contamination of the sample.
When the peristaltic pump is not running, the flexible pump hose is completely compressed in the pump housing. As a result, the water remains in the hose and does not flow back.
If groundwater is located deeper than 8 metres, a peristaltic or suction pump is not powerful enough. At this depth, a pump is required that pushes the water upwards. Centrifugal pumps, also known as submersible pumps, are generally used for this purpose. A centrifugal pump is connected to a hose and an electrical cable and is placed below groundwater level in a monitoring well.
There are 2 types available:
The Gigant and booster pumps are small centrifugal submersible pumps. They fit in small sampling filters (from 37 mm), but also have a limited lifespan. One Gigant pump can push water 9 metres upwards, calculated from the groundwater level. The booster pumps can be used as amplifiers; by placing one, two or a maximum of three boosters directly above the Gigant pump, the delivery head can theoretically be increased to 18, 27 or a maximum of 36 metres. To do this, cut the hose and slide it under and on top of the connection nipple of the Booster pump.
For groundwater levels up to 11 metres deep, with a maximum of 2 pumps in series, the external pump connection of the hose pump can function as an energy source. This also allows the speed of the pumps to be controlled electronically. The pumps are not suitable for connecting in-line filters 0.45 micron directly. The low price makes these pumps suitable for single use, which also helps to prevent cross-contamination.
The MP 1 submersible pump is suitable for pumping and sampling wells with groundwater up to a maximum depth of 90 metres. This pump fits in wells with a diameter of 50 mm or more.
The pump motor, and therefore the flow rate, is controlled by a continuously adjustable frequency converter (230V), with which the pump flow rate can be regulated from 0 to 2 m3 per hour.
The actual flow rate at the selected frequency depends on the groundwater level; at high groundwater levels the pump flow rate is high, at very low groundwater levels the flow rate at the same selected frequency can be low. This makes the pump suitable for quickly pumping the well and for taking water samples at lower pumping speeds. The MP 1 submersible pump delivers a constant flow of non-aerated water.
A very simple pump with the push principle is the ball valve pump, with which you can pump water from a depth of up to 50 metres, depending on the materials and conditions. Contamination can easily be prevented by replacing the hose at each sampling event and cleaning the stainless steel ball valve pump.
A ball valve pump consists of a hose with a stainless steel non-return valve at the bottom, fitted with a ball seal. Once inserted under water, water enters the hose via the valve. When the hose is then given an up and down movement, by hand or via a lever, new water is sucked into the hose, while at the same time the water is pushed further upwards.
The applicability and flow rate are largely determined by the groundwater level, the diameter of the monitoring well, the diameter of the hose, the length of the hose and the stiffness of the hose.
However, this type of pump is lightweight, easy to use and quick to install. A point of attention is the location of the ball valve in the water column. The ball valve must move under water and not above the groundwater level. In that case, air would be mixed with the sample water. In addition, it is prescribed to install the pump above the filter section of the monitoring well instead of at the level of the filter, because this can otherwise provide cloudy water samples.
The peristaltic pump uses a flexible suction tube of approximately 30 cm in the pump housing. A silicone tube is usually used for this. LDPE tube is usually used as a feed tube, which is connected to the silicone tube and inserted into the well. Both tubes are relatively cheap and do not release any contaminants into the water sample. The tubes are periodically chemically tested for this. Sampling procedures stipulate that tubes must be replaced with each sampling to prevent as much contamination of the samples as possible.
The MP 1 submersible pump is supplied with an LDPE or PTFE tube. The LDPE tube is relatively cheap and therefore suitable for replacing after each sampling to prevent contamination. PTFE tubing is used, for example, in situations where it is assumed that the water is not contaminated and, taking into account cleaning procedures, it is intended to be used multiple times. Of course, PTFE is not recommended for use when PFOA is the target parameter.
