Results of 1999 Spectral Gamma-Ray and Neutron Moisture Monitoring of Boreholes at Specific Retention Facilities in 200 East Area, Hanford Site, Washington

Abstract

Twenty-eight wells and boreholes in the 200 East Are% Hanford Site, Washington were monitored in 1999. The monitored facilities were past-practice liquid waste disposal facilities and consisted of six cribs and nineteen "specific reterition" cribs and trenches. Monitoring consisted of spectral gamma-ray and neutron moisture logging. All data are included in Appendix B. '5U '8U and 154Eu were identified on speclral gamma logs from boreholes The isotopes 137Cs, '°Co, , , monitoring the PUREX specific retention facilities; the isotopes 137CS, '°Co, *%b, and *54Euwere identified on the logs from boreholes at the BC Controlled Area cribs and trenches; and *37CS, '°Co, and *25Sbwere, identified on the logs from boreholes at the BX specific retention trenches. Three boreholes in the BC Controlled Area and one at the BX trenches had previous spectral gamma logs available for comparison with 1999 logs. Two of those logs showed that changes in the subsurface distribution of *37CS and/or '°Co had occurred since 1992. Although the changes are not grea$ they do point to continued movement of contaminants in the vadose zone. The logs obtained in 1999 create a larger baseline for comparison with fiture logs. Numerous historical gross gamma logs exist from most of the boreholes logged. Qualitative comparison of those logs with the 1999 logs show many substantial changes, most of which reflect the decay of deeper short-lived isotopes, such as l'!Ru and l%b, and the much slower decay of shallower and longerlived isotopes such as *37CS. The radionuclides *37CS and '°Co have moved in two borehoIes since 1992. Given the amount of movement and the half-lives of the isotopes, it is expected that they will decay to insignificant amounts before reaching groundwater. However, gamma ray logging cannot detect many of the contaminants of interest such as 99Tc,N03, or 12~,all of which can be highly mobile in the vadose zone an~for the radionuclides, have long half-lives.

THE BC CRIBS & TRENCHES GEOPHYSICAL CHARACTERIZATION PROJECT ONE STEP FORWARD IN HANFORDS CLEANUP PROCESS

“…A mass calculation was then applied to the plume, which assumed that all of the nitrate was in the pore fluid and an average volumetric water content of 0.085 cm3 ~r n -~. The water content was derived from the top 60 meters of the gravimetric water content from C4191 cores multiplied by a bulk density of 1.6 g ~r n -~ The total mass of nitrate calculated at the BC Crib was 2 Volume estimates of the resistivity plume showed that an isop@ between 163 ohm-metm and…”

Interpretation of large‐scale, long‐term electrical geophysical monitoring guided by a process simulation

“…Radiological and inorganic liquid waste was directly disposed into subsurface infiltration galleries, including 20 unlined cribs and six concrete‐lined trenches (DOE/RL, 2008), because it was hypothesized that contaminants discharged to the subsurface could be selectively retained through ion exchange, with radioactivity decaying over time (Gee et al., 2007). Several borehole geophysical studies (Brodeur et al., 1993; Fecht et al., 1977; Horton & Randall, 2000) and geologic, geochemical, and hydraulic measurements (Serne et al., 2009) were conducted to assess that contaminants had not reached groundwater. They found that there was ongoing but limited vertical migration to approximately 70 m below ground surface but concluded that contaminants did not reach the water table, reported at a depth of 104 m (Benecke et al., 2006).…”