Ward Valley An Examination of Seven Issues in Earth Sciences and Ecology (1995) / Chapter Skim
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6 SUBSURFACE MONITORING PROGRAM
6 SUBSURFACE MONITORING PROGRAM
Pages 151-168
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From page 151... ...
Performance monitoring of the unsaturated zone is critical because this is the primary bamer to radionuclide migration. The data provided by the proposed unsaturatedzone monitoring program will be critical in evaluating the performance of the Ward Valley facility and win be compared with the results of performance assessment models of the site.
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From page 152... ...
Monitoring ambient conditions distant from the engineered facility will provide background data and act as a control for comparison with monitoring data from the engineered facility. An additional reason for continuing site characterization studies is that, as our conceptual understanding evolves of how arid systems behave and our ability to measure and monitor hydraulic parameters improves, the resulting reliable data w'll reduce uncertainties and increase confidence that the site will perform
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From page 153... ...
PERFORMANCE MONITORING OF THE UNSATURATED ZONE The original unsaturated-zone monitoring plan in the license application was subsequently enhanced on the basis of recommendations from a select committee on this subject. Thirteen objectives for the proposed monitoring program were outlined and included the following: provide early detection of significant contaminants; monitor beneath, adjacent to, and above the waste; incorporate improved monitoring technology as it becomes available; avoid compromising the integrity of the disposal system; · provide acceptable accuracy and reproducibility.
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From page 154... ...
154 Cal o o C)
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From page 155... ...
evaluate the performance of the cover in minimizing infiltration. To meet these objectives, the monitoring will consist of: · measurement of vertical water-vapor flux Tom the land surface using flux chamber, porometer, or other equivalent method; · measurement of plant transpiration using flux chamber, porometer, or other equivalent method; · vegetation sampling and analysis for 3H and i4C radionuclides; · soil-gas sampling at I.5, 3.6, and 5 m semiannually and analysis of 3H, i4C, and 222Rn; · neutron logging to detect changes in water content and gamma-spectral logging to detect changes in radionuclide composition using access tubes installed to 5 m on a regular schedule and within 24 hr of precipitation events 22.5 cm.
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From page 156... ...
Committee Observations on Proposed Performance Monitoring of the Unsaturated Zone -Major IssuesThe committee concludes that the foregoing description of the monitoring program demonstrates that there are detailed plans to concluct performance monitoring
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From page 157... ...
In contrast to humid sites, arid sites have thick unsaturated zones and allow detailed monitoring of concentration gradients to evaluate movement of radionuclides. The committee strongly recommends developing investigation and action levels for performance monitoring in the unsaturated zone.
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From page 158... ...
Continual updates of performance assessment models at least every 5 yr would act as a check on the monitoring data and would lead to accurate post-closure performance assessments. / Extension of Site Characterization Database during Operational Monitoring and integration with Performance Assessment As was mentioned in Chapter 3, the I-yr monitoring data set collected prior to license application is inadequate to evaluate with a high degree of confidence subsurface flow in desert sites that are subjected to large interannual variations in rainfall.
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From page 159... ...
, and steel or some other longer lasting material should be used instead. Technology Development The proposed monitoring program includes a variety of technologies that provide multiple lines of evidence to evaluate performance of the facility.
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From page 160... ...
This monitoring of ambient conditions would act as a control site to provide background data against which monitoring data from the engineered facility can be compared. Important information on site characteristics that should be collected during operations includes representative data on subsurface temperatures and water potentials that more accurately reflect ambient conditions and would help to avoid problems with ambient air temperatures on data loggers, as were found during prelicense monitoring.
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From page 161... ...
Because many of the technologies proposed for the TCDU are not straightforward, research should be conducted to ensure that reliable data will be collected. SUMMARY AND CONCLUSIONS Monitoring in the Unsaturated Zone · With regard to the Wilshire group's comments concerning the absence of downgradient monitoring plans, it appears their concerns are not borne out by the administrative record.
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From page 162... ...
· Because performance data for engineered barriers in arid settings are limited, significant emphasis must be given to design and performance testing of the TCDU and the scope of the TCDU studies should be greatly expanded to include all aspects of site characterizations monitoring, and performance assessment. THE COMPLIANCE MONITORING PLAN FOR TIIE SATURATED ZONE The Wilshire Group Position The Wilshire group stated that in the license application, no plans were revealed for monitoring ground water downgradient from the site (Wilshire et al., 1993a)
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From page 163... ...
Detailed specific response actions that might be implemented if ground-water monitoring data exceed action levels are not presented by the applicant, although they do provide a listing of some of the types of actions that might be taken. These range Tom more dense spatial and temporal data collection to confirm and delineate the area of exceedance, to exhuming the waste and/or ground-water remediation.
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From page 164... ...
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From page 165... ...
The new monitoring wells will be screened in the upper 15 m of the saturated zone and the lower 3 m of the unsaturated zone. Wells u ill be sampled quarterly during the operational and post-closure period.
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From page 166... ...
These databases are more useful to recognize changes occurring in water chemistry over time caused by leach ate reaching the zone of uppermost saturation. Furthermore, they may detect changes in vertical fluid potential that could be related to local recharge.
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From page 167... ...
1993b. Description of earth science concerns regarding the Ward Valley low level radioactive waste site plan and evaluation.
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