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Guide for Characterization of Sites Contaminated with Energetic Materials
33
tive. Typically, three well volumes should be removed before sampling. This
volume may or may not be exceeded when using the low-flow procedure that
requires that stabilization parameters be used to judge if a sufficient amount of
water has been purged from the well. The water retrieved from the purging of the
well should be stored until analysis reveals the presence or absence of explosive
contaminants. Uncontaminated water can be disposed of directly on the site, but
contaminated groundwater should be treated by passing it through an activated
charcoal filter prior to disposal.
The low-flow procedure for groundwater sampling requires that groundwater
be purged from the well using a pump until specific parameters are stabilized.
Moreover, while purging groundwater the flow rate should be controlled so as to
limit a water-level draw down. When the sampling depth is less than 25 ft (7.6
m), a suction lift pump can be used; a submersible pump is recommended for
greater depths. The stabilization parameters include temperature, conductivity,
pH, turbidity, redox potential, and dissolved oxygen levels. Measurements are
taken at time intervals (3 to 5 min) or after successive half-well volumes. When
three or more of the parameters have stabilized (agree within 10% of each other
for three consecutive measurements), sufficient water has been purged from the
well and a groundwater sample can be taken. The positioning of the sample inlet
(collection point), water quality stabilization parameters, and flow rate should be
recorded for each sampling event. Moreover, the sampling team should strive to
match each of these parameters during all subsequent sampling events. For
monitoring wells where parameter stabilization cannot be obtained, no more than
five well volumes should be purged prior to sampling.
A minimum volume of 2 L water should be collected from each well and
poured into two 1-L amber glass containers. Groundwater samples should be
collected first from the wells expected to be the least contaminated to minimize
any cross-contamination when disposable or dedicated equipment is not used.
Since concentrations are unknown during the initial stages of a surveillance
program, only disposable or dedicated equipment should be used. When a bailer
or pump is reused for sampling, it should be decontaminated by rinsing it three
times with acetone and three times with distilled water between each well, and a
rinsate blank should be taken.
Samples suspected of being contaminated by TNT or TNT derivatives should
be stabilized by adding sodium bisulphate (e.g., 1.5 g/L), acidifying the aqueous
solution to pH 2 (Jenkins et al. 1995b). If samples are to be preconcentrated using
the salting-out solvent extraction method, they must be first neutralized prior to
extraction, or incomplete recovery of the amino compounds will result. If precon-
centration is to be achieved using solid-phase extraction, neutralization is not
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