Hazardous contaminants buried within vadose zones can accumulate in soil gas. The concentrations and spatial extent of these contaminants are measured to evaluate potential transport to groundwater for public risk evaluation. Tritium is an important contaminant found and monitored for in vadose zones across numerous sites within the US nuclear weapons complex, including Los Alamos National Laboratory. The extraction, collection, and laboratory analysis of tritium from subterranean soil gas presents numerous technical challenges that have not been fully studied. Particularly, the lack of moisture in the soil gas in the vadose zone makes it difficult to obtain enough sample (e.g., > 5 g) to provide for the required measurement sensitivity, and often, only small amounts of moisture can be collected. Further, although silica gel has high affinity for water vapor and is prebaked prior to sampling, there is still sufficient residual moisture in the prebaked gel to dilute the relatively small amount of sampled moisture; thereby, significantly lowering the "true" tritium concentration in the soil gas. This paper provides an evaluation of the magnitude of the bias from dilution, provides methods to correct past measurements by applying a correction factor (CF), and evaluates the uncertainty of the CF values. For this, 10,000 Monte Carlo calculations were performed, and distribution parameters of CF values were determined and evaluated. The mean and standard deviation of the distribution of CF values were 1.53 ± 0.36, and the minimum, median, and maximum values were 1.14, 1.43, and 5.27, respectively.

Remarks: The pressure transducer was installed above the pump at an elevation of 6776.83 ft until April 30, 2007, when the pump was removed from the well. Transducer data before April 30, 2007, do not represent water level elevations below 6776.83 ft. The screen bottom elevation is 6773.2 ft.

Remarks: Alluvial well CDBO-6 has a bladder pump installed in a 2-in. casing. The pressure transducer sensor elevation is 6776.83 ft. The transducer may not be installed any lower due to interference with the pump. The screen bottom elevation is 6773.2 ft. The groundwater elevation may at times be above the screen bottom, but below the transducer sensor.

No abstract

We report air-monitoring measurements of the fission products released from the Fukushima-Daiichi nuclear-power-plant accident in 2011. Clear gamma-spectrometry peaks were observed from Cs-134, Cs-136, Cs-137, I-131, I132, Te-132, and Te-129m. These data, together with measurements of other radionuclides, are adequate for an assessment and assure us that radionuclides from Fukushima Daiichi did not present a threat to human health at or near Los Alamos. The data demonstrate the capabilities of the Los Alamos air-monitoring systems.