Sampling 101 – Pump or Bailer? - Part 1 of 3

As portable pumps for sampling ground water have become more and more common, beginners in the field of environmental sampling have asked for some guidelines for choosing between the portable pumps and the older methodology of bailers. This article is an attempt to describe types of bailers and portable, low-flow submersible pumps, the differences between them with regard to purging and sampling, and to give a cursory review of the advantages and disadvantages of each with respect to sample quality. Other sampling methods, not discussed in this article, are the hydropunch, suction and inertia pumps, and air-lift pumps.


BAILERS Bailers are hollow cylindrical tubes with a device on the top to lower or raise the bailer by a cord into a well, and a device, called a check valve, on the bottom to allow water to enter and to stay in the bailer while raising it from the well. They vary in length and diameter according to the well sampled and the volume desired, and in design according to the contaminant sampled. Water collected from a well may be poured into a separate sample container, such as a glass volatile organic analysis (VOA) container by releasing a valve on the bottom of the bailer (the check valve) into the sample container. Bailers come in a variety of either reusable or disposable design, and of various materials. Some of the advantages of bailers are low cost, portability, and ease of use. Bailers also have their disadvantages; they can be very time-consuming, if also used for purging the well; they are ineffective in large diameter or very deep wells; the depth of the sample point within the aquifer may be difficult to determine; freezing temperatures or very turbid well water may affect check valve operation; poor design may increase aeration or turbidity in the water sample, thus affecting sample quality; and the operator may be adversely exposed to contaminants. All bailers require technique and skill to operate effectively and efficiently – there is no substitute for skill in obtaining a good sample. Recent developments in bailer design include a larger ball in the check valve, the larger opening allowing the bailer to sink more quickly without causing more turbulence. Bailers may also use clear polyvinyl chloride (PVC), which is denser than polypropylene (PP); the additional density precludes the necessity of weighting the bailer.

Disposable bailers are designed to be used only once and disposed of after sampling. Modern disposable bailer designs, such as Ecobailer, Aqua Bailer or Clearwater Engineering, have incorporated dependable check valves and non-binding valve end designs. Disposal Teflon and PVC bailers are heavy enough to facilitate non-turbulent entry into the water column; however, PP is lighter, with a specific gravity less than water (it floats), and typically requires weighting to facilitate sinking. Advantages of disposable bailers are that they are reasonably inexpensive and available in bulk, and they are decontaminated and sealed in a clean room environment, virtually guaranteeing that the sample is free of contamination. Because they are only used once and disposed of, the sampler does not need to bring decontamination solutions or equipment into the field, saving time and additional expense during field operations.

Reusable bailers are meant to be, as the name implies, reused many times. Reusable bailers are typically made of stainless steel or Teflon, and are designed to withstand cracking and weakening where the bailer cord is attached. They and are made of strong, resistant material to help protect the check valve from scratches, which could cause the sample to be lost or compromised. They are also made sturdily, in order to be taken apart and cleaned. Reusable bailers are typically made of heavier materials, allowing them to sink more quickly into the well for efficient purging and sampling. Various reusable bailer manufacturers, such as Norwell, have online specification sheets available for comparison, which may be obtained through various equipment dealers or retailers, such as www.enviroequipment.com. Reusable bailers are cleaned and sealed before using to guarantee the sample is free from contamination; they must be cleaned and decontaminated after sampling and before reuse.

By Orrin Hall