Hydrologic Resources Management Program and Underground Test Area Project FY 2000 Progress Report Page: 25 of 156
PDF-FILE: 153 ; SIZE: 144.4 MBYTES pagesView a full description of this report.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
The 36C/Cl ratios measured for RNM-2S groundwaters collected in 1999 and 2000 are
1.64 x 10-10 and 1.62 x 100, respectively. These ratios are approximately two orders of
magnitude greater than observed at RNM-1, implying that 36C1 tended to move
conservatively with groundwater during pumping. It is notable that low level abundances
of the fission products 99Tc and 129I were also detected (by Accelerator Mass
Spectrometry) in the RNM-2S samples taken in 1999. As with 36C1, these species tend to
move as conservative anions in groundwater.
Uranium isotopes were analyzed for the RNM-2S sample collected in June 2000. The
data are similar to that of the RNM-1 sample taken the same year, and indicate natural
isotopic abundances.
UE-5n
Water samples were collected at UE-5n on 09 September 1999 at a depth of 222 m (730
ft) below the surface. Water was withdrawn using a Bennett pump with a pumping rate
of 1.9 L/min. The purge volume at the start of sampling was ~5300 L. Finnegan and
Thompson (2001) report tritium activities in the range of 1.32 x 105 to 1.48 x 105 pCi/L
for these samples. The 3He/4He ratio measured for UE-5n groundwater is more than two
orders of magnitude above atmospheric levels (R/Ra = 4.5 x 102) reflecting the in-growth
of 3He from tritium decay. Assuming a tritium activity of 1.32 x 105 pCi/L, the 3H-3He
age of the groundwater is calculated to be 9.5 years. This is significantly younger than
the ages measured at RNM-1 and RNM-2S, but approximately coincides with the first
appearance of tritium at UE-5n in 1989. This tends to support the idea that the source of
contamination in UE-5n originated from water that infiltrated from Cambric ditch. The
fact that UE-5n groundwater has a 8D-6180 pair that plots along the evaporation trend in
Figure 1 further strengthens this argument.
The 36C1/Cl ratio measured at UE-5n (6.10 x 10~0) is actually higher than the values
found in RNM-2S. This observation provides further evidence that 36C1 moves
conservatively with tritium in groundwater. Very low levels of 99Tc and 129I were also
observed in UE-5n groundwater (Table 1). Lastly, it is notable that the 14C concentration
in UE-5n is quite low (18.8 percent modem) given the amount of tritium present in the
water. In comparison, the 14C concentration at RNM-2S is 413 percent modern.
Assuming that UE-5n contains recycled water originating from RNM-2S, the difference
in 14C values at these two wells implies radiocarbon has been removed from solution. A
possible explanation is that the 14C (which is transported dominantly as HCO3-) was
removed by isotopic exchange with calcite during re-infiltration from Cambric ditch.
Calcite is a common trace mineral in the unsaturated alluvium at the Nevada Test Site,
and is known to readily exchange carbon isotopes with bicarbonate groundwaters.13
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Davisson, M. L.; Eaton, G. F.; Hakemi, N. L.; Hudson, G. B.; Hutcheon, I. D.; Lau, C. A. et al. Hydrologic Resources Management Program and Underground Test Area Project FY 2000 Progress Report, report, July 1, 2001; California. (https://digital.library.unt.edu/ark:/67531/metadc1411019/m1/25/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.