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Title: Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier

Abstract

Surface barrier technology is used to isolate radioactive waste and to reduce or eliminate recharge water to the waste zone for 1000 years or longer. However, the design and evaluation of such a barrier is challenging because of the extremely long design life. The Prototype Hanford Barrier (PHB) was designed as a 1000-year barrier with pre-determined design and performance objectives and demonstrated in field from 1994 to present. The barrier was tested to evaluate surface-barrier design and performance at the field scale under conditions of enhanced and natural precipitation and of no vegetation. The monitoring data demonstrate that the barrier satisfied nearly all key objectives. The PHB far exceeded the Resource Conservation and Recovery Act criteria, functioned in Hanford’s semiarid climate, limited drainage to well below the 0.5 mm yr-1 performance criterion, limited runoff, and minimized erosion. Given the two-decade record of successful performance and consideration of all the processes and mechanisms that could degrade the stability and hydrology in the future, the results suggest the PHB is very likely to perform for its 1000-year design life. This conclusion is based on two assumptions: (1) the exposed subgrade receives protection against erosion and (2) institutional controls prevent inadvertent human activitymore » at the barrier. The PHB design can serve as the base for site-specific barriers over waste sites containing underground nuclear waste, uranium mine tailings, and hazardous mine waste.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1339808
Report Number(s):
PNNL-SA-121353
Journal ID: ISSN 0301-4797; 830403000
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Environmental Management; Journal Volume: 187
Country of Publication:
United States
Language:
English
Subject:
Surface Cover; Nuclear Waste; Infiltration Control; Waste Isolation

Citation Formats

Zhang, Zhuanfang Fred, Strickland, Christopher E., and Link, Steven O. Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier. United States: N. p., 2017. Web. doi:10.1016/j.jenvman.2016.11.007.
Zhang, Zhuanfang Fred, Strickland, Christopher E., & Link, Steven O. Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier. United States. doi:10.1016/j.jenvman.2016.11.007.
Zhang, Zhuanfang Fred, Strickland, Christopher E., and Link, Steven O. Wed . "Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier". United States. doi:10.1016/j.jenvman.2016.11.007.
@article{osti_1339808,
title = {Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier},
author = {Zhang, Zhuanfang Fred and Strickland, Christopher E. and Link, Steven O.},
abstractNote = {Surface barrier technology is used to isolate radioactive waste and to reduce or eliminate recharge water to the waste zone for 1000 years or longer. However, the design and evaluation of such a barrier is challenging because of the extremely long design life. The Prototype Hanford Barrier (PHB) was designed as a 1000-year barrier with pre-determined design and performance objectives and demonstrated in field from 1994 to present. The barrier was tested to evaluate surface-barrier design and performance at the field scale under conditions of enhanced and natural precipitation and of no vegetation. The monitoring data demonstrate that the barrier satisfied nearly all key objectives. The PHB far exceeded the Resource Conservation and Recovery Act criteria, functioned in Hanford’s semiarid climate, limited drainage to well below the 0.5 mm yr-1 performance criterion, limited runoff, and minimized erosion. Given the two-decade record of successful performance and consideration of all the processes and mechanisms that could degrade the stability and hydrology in the future, the results suggest the PHB is very likely to perform for its 1000-year design life. This conclusion is based on two assumptions: (1) the exposed subgrade receives protection against erosion and (2) institutional controls prevent inadvertent human activity at the barrier. The PHB design can serve as the base for site-specific barriers over waste sites containing underground nuclear waste, uranium mine tailings, and hazardous mine waste.},
doi = {10.1016/j.jenvman.2016.11.007},
journal = {Journal of Environmental Management},
number = ,
volume = 187,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • A surface barrier (or cover) is a commonly used technology for subsurface remediation. A key function of the barrier is to reduce or eliminate the movement of meteoric precipitation into the underlying waste zone, where it could mobilize and transport contaminants. Surface barriers are expected to perform for centuries to millennia, yet there are very few examples of performance for periods longer than a decade. The Prototype Hanford Barrier was constructed in 1994 over an existing waste site to demonstrate its long-term performance for a design period of 1000 years. This barrier is a field-scale evapotranspiration-capillary (ETC) barrier. In thismore » design, the storage layer consists of 2-m-thick silt loam. The 19-year monitoring results show that the store-and-release mechanism for the ETC barrier worked efficiently as the storage layer was recharged in the winter season (November to March) and the stored water was released to the atmosphere in the summer season (April to October) via soil evaporation and plant transpiration. The capillary break functioned normally in improving the storage capacity and minimizing drainage. The maximum drainage observed through the ET barrier at any of the monitoring stations was only 0.178 mm yr-1 (under an enhanced precipitation condition), which is less than the design criterion. A very small amount (2.0 mm yr-1 on average) of runoff was observed during the 19-year monitoring period. The observed storage capacity of the storage layer was considerably (39%) larger than the estimated value based on the method of equilibrium of water pressure. After a controlled fire in 2008, the newly grown vegetation (primarily shallow-rooted grasses) could still release the stored water and summer precipitation to the atmosphere via transpiration. The findings are useful for predicting water storage and ET under different precipitation conditions and for the design of future barriers.« less
  • Highlights: Black-Right-Pointing-Pointer All ET covers produced rates of percolation less than 32 cm yr{sup -1}, the maximum allowable rate by the Ohio EPA. Black-Right-Pointing-Pointer Dredged sediment provided sufficient water storage and promoted growth by native plant species. Black-Right-Pointing-Pointer Native plant mixtures attained acceptable rates of evapotranspiration throughout the growing season. - Abstract: Evapotranspiration (ET) covers have gained interest as an alternative to conventional covers for the closure of municipal solid waste (MSW) landfills because they are less costly to construct and are expected to have a longer service life. Whereas ET covers have gained acceptance in arid and semi-arid regionsmore » (defined by a precipitation (P) to potential evapotranspiration (PET) ratio less than 0.75) by meeting performance standards (e.g. rate of percolation), it remains unclear whether they are suitable for humid regions (P:PET greater than 0.75). The goal of this project is to extend their application to northwest Ohio (P:PET equals 1.29) by designing covers that produce a rate of percolation less than 32 cm yr{sup -1}, the maximum acceptable rate by the Ohio Environmental Protection Agency (OEPA). Test ET covers were constructed in drainage lysimeters (1.52 m diameter, 1.52 m depth) using dredged sediment amended with organic material and consisted of immature (I, plants seeded onto soil) or mature (M, plants transferred from a restored tall-grass prairie) plant mixtures. The water balance for the ET covers was monitored from June 2009 to June 2011, which included measured precipitation and percolation, and estimated soil water storage and evapotranspiration. Precipitation was applied at a rate of 94 cm yr{sup -1} in the first year and at rate of 69 cm yr{sup -1} in the second year. During the first year, covers with the M plant mixture produced noticeably less percolation (4 cm) than covers with the I plant mixture (17 cm). However, during the second year, covers with the M plant mixture produced considerably more percolation (10 cm) than covers with the I plant mixture (3 cm). This is likely due to a decrease in the aboveground biomass for the M plant mixture from year 1 (1008 g m{sup -2}) to year 2 (794 g m{sup -2}) and an increase for the I plant mixture from year 1 (644 g m{sup -2}) to year 2 (1314 g m{sup -2}). Over the 2-year period, the mean annual rates of percolation for the covers with the M and I plant mixtures were 7 and 8 cm yr{sup -1}, which are below the OEPA standard. The results suggest the application of ET covers be extended to northwest Ohio and other humid regions.« less
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