Is there a preference in low-flow sampling of using peristaltic pumps or bladder pumps?

The use of a peristaltic pump versus a bladder pump is really going to be dependent most specifically on depth first. A peristaltic pump has a theoretical lift limit of about 31 feet. The reality of it is this: most peristaltic pumps lift water a maximum of anywhere between 23 to 28 feet depending on the pump. So, if your water level is less than 20 feet from ground service and you anticipate any significant drawdown, a peristaltic pump might work from a standpoint of physical application. From there, you have to consider your parameters of interest. If you have a highly gas charged system and your parameters are gas sensitive, such as VOC or in the case of some metals, then a peristaltic pump may or may not be appropriate. For example, the latest U.S. EPA Region I guidance document on low flow purging and sampling specifically calls out peristaltic pumps as being limited for sampling certain parameters, same thing with the Florida DEP guidelines. Generally, both of these recommend not using peristaltic pumps for VOCs. But again, you need to go to the literature on those pumping devices to determine whether or not one is better than the other for your application. The advantage of a bladder pump is that, not only, can it work in depths below 30 feet, in fact it can work in depths greater than 1,000 feet, but it's also not limited by any specific parameters. Water pumps are acceptable devices for any and all parameters so they are more universally applicable, but peristaltic pumps can work in certain applications.