Information from www.dnr.state.wi.us/org/water/dwg/gw/dsk-3a.htm

Suction-lift Pumps = peristaltic pumps

Suction-lift pumps, especially surface centrifugal pumps, are considered unacceptable for collecting VOCs, dissolved metals, pH, Eh and other gas-sensitive or volatilizing substances or measurements. The vacuum applied on the sample during collection may cause degassing. Suction-lift pumps are considered acceptable for collecting major and minor ions that are not gas-sensitive (refer to Section 2.6.7). Peristaltic and surface centrifugal pumps are two common types of suction lift pumps. Of these two suction-lift pumps, the peristaltic pump is far less likely to adversely affect samples compared to surface centrifugal pumps.

As suction-lift implies, these pumps work by creating a vacuum or suction (in the sampling tube) that pulls groundwater to the surface. In theory, suction-lift pumps should be able to lift water up to 32 feet (9.7 meters); however, in practice, anywhere from 15 to 25 feet (4.6 to 7.6 meters) is the upper limit of their effectiveness. Pumping rates for suction-lift pumps typically range from 0.03 to 15 gallons per minute (gpm) or 0.1 to 57 liters per minute (L/min). Peristaltic pumps commonly have the lower pumping range (0 to 8 gpm or 0 to 30 L/min) while surface centrifugal pumps have pumping rates as high as 40 gpm (150 L/min).

Peristaltic Pumps

Barker and Dickhout (1988) conducted laboratory research to evaluate the loss of volatile organic analytes from groundwater charged with dissolved gasses such as methane and carbon dioxide. A positive displacement bladder pump (Well Wizard®, QED, Inc.), inertial-lift pump (WaTerra® pump) and peristaltic pump were employed in sampling methane-charged groundwater from a monitoring well for volatile aromatic hydrocarbons and CO2-charged water reservoir (i.e., an artificial laboratory well) spiked with known concentrations of volatile chlorinated hydrocarbons. In both the field and laboratory cases, the peristaltic pump provided samples with a significant negative bias (9 to 33 percent lower) relative to the bladder pump and inertial-lift pump methods.

Baerg et al., (1992) conducted laboratory research to evaluate the loss of volatile organic compounds (VOCs) caused by the sampling method used. Several devices (peristaltic pump, stainless and Teflon® bailers, VOA trap sampler, bladder pump, inertial-lift pump and double valve sampler) were used to collect samples for VOCs from a laboratory monitoring well. VOC analytical results for the peristaltic pump were 7 percent to 12 percent lower than the control VOC concentrations. The inertial-lift pump performed the worst with VOC results up to 34 percent less than the control.

Imbrigotta et al., (1988) conducted a field evaluation of seven sampling devices for purgeable organic compounds (POCs) in groundwater. One of the devices tested was a peristaltic pump outfitted with Teflon® tubing and a glass Erlenmeyer receiving flask for sample collection. It was pumped at 600 ml/min (0.6 L/min) or less. Of the seven devices tested, the peristaltic pump consistently recovered lower POC concentrations than the other devices and had the lowest precision of the four pumps tested (gear submersible, bladder, helical-rotor and peristaltic pumps); however, it had a greater precision than all three grab samplers tested (syringe, open bailer and point-source bailer).

Tai et al., (1988) found good recoveries of VOCs under lab conditions using a peristaltic pump outfitted with Teflon® tubing and used under low lift conditions - 5 feet in this case.

In general, the lower the lift, the lower the pumping rate, and using non-sorptive tubing such as Teflon® will minimize the effects a peristaltic pump may have on a sample.

Operation and Materials

Peristaltic pumps are very easy to use. The sample tubing is usually 1/4 inches in diameter and open at both ends. Some kinds of flexible tubing (e.g., silicone and Tygon®) can leach plasticizers and sorb organic compounds that may adversely affect sample quality.

Place the suction end of the tube into the well to the desired depth. Place the discharge end in the sample container. You can attach a transfer vessel, a filtering device chamber or an in-line filter directly to the pump's discharge tubing. This is the recommend filtering method. Rotating two or more rollers along the sample tubing causes a vacuum on the tubing, thus lifting the water out of the well. Decontamination usually consists of running a detergent or disinfectant through the sampling tube, followed by appropriate decontamination rinses.

Advantages of peristaltic pumps

Allows for easy, direct in-line filtration of samples.
Portable, easy to use and little operator training is required.
Readily available and relatively inexpensive.
Variable flow rates are possible.
Sample does not contact pump parts.
Durable and reliable.
Can be used in wells of any diameter.

Limitations of peristaltic pumps

Requires a power source.
Vacuum may cause volatilization and degassing in gas-sensitive or volatile samples.
Lift restriction of 25 feet (8 meters) or less.
Flexible sample tubing (e.g., silicone and tygon) may leach placticizers and adsorb or desorb organic compounds.
Field repair may be difficult.