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).
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withdrawn.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
, 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.