Vadose zone moisture measurement through steel casing evaluation

Meisner, J.E.

doi:10.2172/263959

Cited by 4 publications

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“…These wells were completed with a variety of casing configurations with variations in casing diameter, casing thickness, and multiple construction or completion casings such as telescoping casings. Neutron attenuation due to casing thickness cannot be easily quantified because of the distribution of the neutron cloud and its subsequent migration (Meisner, 1995;Engleman et al 1995;Meisner et al 1996 ). Owing to a factor of four difference in the scattering cross-section of thermal neutrons and iron (in steel casing), a neutron travelling from the formation towards the detector can undergo an elastic collision and be directed away from the detector.…”

Section: Effects Of Borehole Configurationmentioning

confidence: 99%

Calibration of a Neutron Hydroprobe for Moisture Measurements in Small-Diameter Steel-Cased Boreholes

Ward¹,

Wittman²

2009

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Acknowledgments I wish to thank Jim Fields of Washington River Protection Solutions and Curt Wittreich of CH2MHill Plateau Remediation Company, LLC for supporting this work as well as the staff at S.M. Stoller Corporation, who provided schematics of probe geometry and field calibration data and were always available to answer questions related to data collection and logging operations. Thanks to Rick McCain in particular for providing schematics on the hydroprobe construction and engaging in helpful discussions that helped to focus the model simulations.v Executive SummaryComputation of soil moisture content from thermalized neutron counts requires a calibration relationship, but none exists for 2-in. tubes installed at the Tank T-106 interim barrier. A number of calibration options are available for the neutron probe, including vendor and field calibration, but none of these methods were deemed appropriate for the configuration of interest. The objective of this work was to develop a calibration relation for converting neutron counts measured in 2-in. access tubes to volumetric soil water content, θ. The calibration method chosen for this study was a computational approach based on Monte Carlo techniques. The Monte Carlo N-Particle Transport Code (MCNP), developed by Los Alamos, was chosen to perform the theoretical analyses of neutron diffusion in air, the probe shield, and in the Hanford calibration models. Model calibration was performed using field measurements in the calibration models with 6-in. access tubes. ) generated mean 16-s counts of 2264 and 2887, respectively. The shield count, N s , typically used as a standard count to compute the count ratio (CR), was 6168. The best-fit model relating water content to neutron counts was an exponential model that was essentially equivalent to that currently being used for 6-in. steel-cased wells. The MCNP simulations successfully predicted N s for the neutron shield and counts N in the three calibration models for which data were collected in the field. However, predicted counts for air, N a , (mean 16-s count= 14) were about 65% lower than the measured counts (mean 16-s count =43). This discrepancy can be attributed to uncertainties in the configuration used for the air measurements. MCNPsimulated counts for the physical models were essentially equal to the measured counts with values of 2370, 1515, and 2840 for models E, F, and G, respectively. Successful prediction of the response in 6-in. casings in the three calibration models was motivation to predict the response in 2-in. access tubes.Simulations were performed for six of the seven calibration models as well as four virtual models with the entire set covering a moisture range of 0 to 0.40 m 3 m -3. Predicted counts for the calibration models with 2-in. access tubes were 40 to 50% higher than in the 6-in. tubes. Differences between the 2-in. and 6-in. tube are attributed to the differences in the measurement geometry. The best-fit model relating θ to CR is of the form . This is more consistent with the ob...

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Section: Effects Of Borehole Configurationmentioning

confidence: 99%

Calibration of a Neutron Hydroprobe for Moisture Measurements in Small-Diameter Steel-Cased Boreholes

Ward¹,

Wittman²

2009

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“…The models contain moisture contents (percent by volume) of 5%, 12%, and 20% and are constructed with casing configurations for both 6-and 8-in.-diameter casings. The calibration procedures are documented in Meisner (1995) and Meisner et al (1996). Casing thickness corrections applied to the log data are documented in Meisner et al (1996).…”

Section: Detector Calibrationsmentioning

confidence: 99%

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

Horton¹,

Randall²

2000

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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.

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“…The neutron moisture detector utilized for the fiscal year 1999 logging will have a current calibration certificate that documents current calibration according to the methods outlined in Meisner (1995) and Meisner et al (1996). Measurements for the moisture tool calibration are acquired in the moisture calibration tanks located at Neil F. Lampson Inc., Pasco, Washington.…”

Section: Detector Calibrationsmentioning

confidence: 99%

Monitoring Plan for Fiscal Year 1999 Borehole Logging at 200 East Area Specific Retention Facilities

Horton¹

1999

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Vadose zone moisture measurement through steel casing evaluation

Abstract: NfA IO. Eyltr/Bldg./F.cility: 18. 19. AumO,&d R.pnimt.th 0.U lor Rul* Org&mk." 21. DOE APPROVAL (i f required) 11 Approved C t r l. Yo. Ce(6mt Manaoer Om. I 1 Disapproved u/camnts

Cited by 4 publications

References 0 publications

Calibration of a Neutron Hydroprobe for Moisture Measurements in Small-Diameter Steel-Cased Boreholes

Calibration of a Neutron Hydroprobe for Moisture Measurements in Small-Diameter Steel-Cased Boreholes

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

Monitoring Plan for Fiscal Year 1999 Borehole Logging at 200 East Area Specific Retention Facilities

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