UC Berkeley

The emergence of soil morphology has long been under emphasized in the planning and maintenance of engineered soils for waste containment. Recent studies report that soil change induced alterations to waste cover engineering properties, including hydraulic conductivity, can occur in as little as five-years post construction. With mandated waste cover performance lifetimes of hundreds to thousands of years, an understanding of long-term change can directly increase human and environmental health at a reduced cost. This manuscript explores how engineered soils for waste containment change through space and time and documents how such natural changes impact as-built engineered performance. Special emphasis is placed on cover systems in the Uranium Mill Tailings Radiation Control Act of 1978 (UMTRCA) portfolio managed by the United States Department of Energy, Office of Legacy Management (DOE-LM). Four sites were studied that represent engineering, climatic, and management conditions commonly found across the portfolio. Herein, we use 30-years of archived inspection reports to explore how setting, engineering design, and management influence rates and patterns of change; position engineered soils within a factorial framework of soil formation; discuss dominant pedogenic processes occurring in engineered soils over decadal time frames from field investigation and a literature review; and use a soil morphological development index to compare the soil morphology of in-service covers, and natural analogs, to measured hydraulic conductivity and radon diffusion coefficients to explore long-term rates of change.