All purging equipment that has been or will be in contact with ground water should be

decontaminated prior to use. Decontamination procedures outlined in Section 7.3.4 are

generally adequate. If the purged water or the decontamination water is contaminated (e.g.,

based on analytical results), the water should be stored in appropriate containers until

analytical results are available, at which time proper arrangements for disposal or treatment

should be made (i.e., contaminated purge water may be a hazardous waste).

7.3

Ground Water Sampling Equipment Selection and Use

There are three broad categories of ground water sampling devices: 1) grab samplers,

2) positive displacement (submersible) pumps, and 3) suction lift pumps (Pohlmann and Hess,

1988; Herzog et al., 1991). Gas contact pumps also are available but are not recommended

for ground water purging or sampling applications (Pohlmann and Hess, 1988). Table 12 is a

useful guide for selecting devices for sampling. The Agency prefers that all sampling

equipment be dedicated to a particular well. To encourage innovation, the Agency may allow

the use of other devices that are not specifically mentioned above if the owner/operator

demonstrates to the Agency's satisfaction (or to the authorized state's satisfaction) that the

device will yield representative ground water samples.

The following recommendations apply to the selection of sampling equipment:

Sampling equipment should be chosen based on the analytes of interest and the

characteristics and depth of the saturated zone from which the sample is

withdrawn. For example, the choice of sampling equipment should reflect

consideration of the potential for LNAPLs and DNAPLs (Section 7.2.3).

Sampling equipment should be constructed of inert material. Sample collection

equipment should not alter analyte concentrations, cause loss of analytes via

sorption, or cause gain of analytes via desorption, degradation, or corrosion.

Sampling equipment should be designed such that Viton

, Tygon

, silicone, or

neoprene components do not come into contact with the ground water sample.

These materials have been demonstrated to cause sorptive losses of

contaminants (Barcelona et al., 1983; Barcelona et al., 1985b; Barcelona et al.,

1988b; Barcelona et al., 1990). Barcelona (1988b) suggests that sorption of

volatile organic compounds on silicone, polyethylene, and PVC tubing may

result in gross errors when determining concentrations of trace organics in

ground water samples. Barcelona (1985b) discourages the use of PVC

sampling equipment when sampling for organic contaminants.

Sampling equipment should cause minimal sample agitation and should be

selected to reduce/eliminate sample contact with the atmosphere during sample

transfer. Sampling equipment should not allow volatilization or aeration of

samples to the extent that analyte concentrations are altered.

November 1992

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