Assessment of Tritium Activities in Bailed versus Pumped Samples from Wells at the Nevada National Security Site

Technical Report · Thu Nov 01 00:00:00 EDT 2018

DOI:https://doi.org/10.2172/1483945· OSTI ID:1483945

Hershey, Ronald L. ^[1]

---

1. Nevada System of Higher Education, Reno, NV (United States). Desert Research Institute (DRI)

The Underground Test Area (UGTA) Activity uses a variety of methods to collect groundwater samples to identify radionuclide migration from underground nuclear tests. These include depth-discrete bailing, pumping with low-volume rod pumps, and pumping with electrical submersible pumps. The Nevada National Security Site (NNSS) Integrated Groundwater Sampling Plan specifies that when sampling with a pump, a minimum of three effective well volumes are withdrawn and then samples are collected after water-quality parameters have stabilized. In locations where pumping is not feasible, depth-discrete bailing is used and purging prior to sampling is usually not required. A recent study evaluated three sampling technologies and recommended that historical tritium results be evaluated where both pumped and bailed samples are available to identify preferred sampling protocols for the collection of tritium samples. The tritium (³H) activities were obtained from the UGTA chemistry data base. Wells were identified with known ³H activities above method detection limits, and then evaluated if both bailed and pumped samples had been collected. Twenty two wells and piezometers with bailed samples, pumped samples, and ³H activities above background were identified for further consideration. The conclusions from this analysis are: Bailed samples collected for ³H analysis near the water surface in a well are lower in ³H activity than bailed samples from within screened intervals and pumped samples. Depth-discrete bailed samples from within the screened intervals are generally in good agreement with pumped samples from developed wells and piezometers. Depth-discrete bailed samples from undeveloped wells and piezometers are in good agreement with the first pumped samples. However, the next pumped samples increased in ³H activity, resulting in a greater percent difference between the undeveloped bailed samples and later pumped samples. Continuous pumping over extended periods removing large purge volumes from wells can perturbate the surrounding groundwater system for long periods of time. These perturbations can cause large changes in ³H activities in the aquifer near the well because of the mixing of groundwater with variable ³H activities. Recommendations include: Bailed samples for ³H should not be collected near the water surface in the well. Bailed samples should be collected from within the well screen. Logs of temperature, chemistry, and thermal flow should be evaluated to identify optimal depths within the well screen to collect depth-discrete bailer samples. Purging of large volumes of water from the well over extended periods of time should be avoided when collecting ³H samples. Sufficient time should be allowed after pumping large volumes of water from the well (e.g., after well development) for the surrounding aquifer and ³H activities to return to ambient conditions

• Research Organization: Nevada Univ., Reno, NV (United States). Desert Research Institute; Nevada System of Higher Education, Reno, NV (United States). Desert Research Institute (DRI)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Environmental Management Nevada Program, Las Vegas, NV (United States)
• DOE Contract Number: NA0003590; NA0000939
• OSTI ID: 1483945
• Report Number(s): DOE/NV/0003590-28; 45285; DOE/NV/0003590-28; TRN: US1902683
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Underground Test Are
UGTA
groundwater samples
radionuclide migration
depth-discrete bailing
pumping
low-volume rod pumps
electrical submersible pumps
NNSS
sampling
water quality parameters
purging
tritium
sampling protocols
piezometers
perturbate
aquifer
temperature
thermal flow
chemistry
optimal depths
ambient conditions