Title: Evaluating the long-term hydrology of an evapotranspiration-capillary barrier with a 1000 year design life

Abstract

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 this 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 thanmore » 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

Authors:

Zhang, Z. Fred ^[1]

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Publication Date:

Fri Jun 03 00:00:00 EDT 2016

Research Org.:

Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1298394

Report Number(s):

PNNL-SA-113332
Journal ID: ISSN 0043-1397; 830403000

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Water Resources Research

Additional Journal Information:

Journal Volume: 52; Journal Issue: 6; Journal ID: ISSN 0043-1397

Publisher:

American Geophysical Union (AGU)

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; Surface Cover; Storage Capacity; Water Balance; Capillary Break; Water Diver; Fire