PNNL

Abstract

A critical unknown in long-term engineered barrier use is the post-fire hydrologic function where institutional controls are in-tact but there are no resources to implement maintenance activities such as re-planting. This objective of this study was to simulate wild fire on an engineered barrier at the Hanford Site and document the post-fire changes in barrier performance. Soil physical, chemical, and hydrologic conditions; plant floristics and density; and animal use were characterized pre- and post-burn. Fuel load on the surface ranged from 4.7 to 5.71 tons/acre. Fire was initiated by drip torch and measurements of flame height and temperature were made at nine locations on the barrier surface. Flame heights exceeded 30 ft and temperatures ranged from 250 oC at 1.5 cm below the surface to over 700 oC at 1 m above the surface. Soil organic matter, soil wettability, and hydraulic conductivity all decreased significantly relative to pre-fire conditions. Post-fire samples showed an increase in major soil nutrients, pH, and electrical conductivity measured in 1:1 extracts whereas organic matter decreased. Decreases in wettabilty and organic matter are indicative of conditions more conducive to runoff and soil loss. The results of this study will contribute to a better understanding of post-fire recovery in a post-institutional control environment. This should lead to enhanced stakeholder acceptance regarding the long-term efficacy of ET barriers. This study will also support improvements in the design of ET barriers and performance monitoring systems. Such improvements are needed to best meet the long-term commitment to the safe in-place isolation of waste for hundreds if not thousands of years.