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Guide for Characterization of Sites Contaminated with Energetic Materials
37
APPENDIX E: SAMPLE CONSERVATION: MAXIMUM HOLDING
TIMES
Soil/Sediment Samples
For soil samples, Method 8330 specifies a maximum pre-extraction holding
time (MHT) of 7 days in the dark at 4C for nitramines and nitroaromatics.
However, studies have shown that nitramines are stable over an eight-week
period when held at 4C in the dark, and that nitroaromatics were stable for the
same period when frozen (Grant et al. 1993a, Jenkins et al. 1994). Therefore, if
agreed upon by the parties involved, soil samples can be held beyond 7 days; if
stored in the dark and frozen, for an additional 7 weeks prior to extraction.
Water Samples
For water samples, Method 8330 specifies a maximum pre-extraction holding
time (MHT) of 7 days in the dark at 4C for nitramines and nitroaromatics.
Studies have evaluated the pre-extraction holding times for nitroaromatic and
nitramine explosives (Maskarinec et al. 1991, Grant et al. 1993b) and the preser-
vation of water samples (Jenkins et al. 1995b). The first two studies demonstrated
that an MHT of 50 days could be used for both nitramines and nitroaromatics in
many types of water samples when refrigerated at 4C. However, water with
active microbial populations (such as surface water) showed significant losses of
TNB and TNT within a day or two when refrigerated at 4C. The preservation
study concluded that the MHT for water samples containing nitroaromatics such
as TNT, TNB, and tetryl can be extended to at least 28 days by acidification to
pH 2 using NaHSO4 (e.g., 1.2 g/L). Furthermore, the acidification did not affect
the stability of nitramines that were already stable over a period of 50 days, with
or without preservation. Therefore, all water samples should be acidified to pH 2
(or less) soon after collection. Once acidified, they should be stored in the dark at
4C. Under these conditions, water samples can be held beyond 7 days, if agreed
upon by the parties involved, for an additional 21 days prior to extraction.
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