Evapotranspiration Landfill Cover Design: Characterization and Soil Environment

Abstract

Physical and chemical soil properties including soil particle size distribution, texture, soil water retention characteristics, hydraulic conductivity, and soil productivity influence potential evapotranspiration (ET) cover performance. Borrow source characterization is necessary to define the spatial variability of soil properties, the location(s) of suitable material, and a method to select material during excavation. Understanding the soil environment of a borrow source provides insight for site characterization including soil sampling design and data interpretation. The methods for soil characterization at three sites in the United States are discussed. Soil near Colorado Springs, Colorado developed predominantly from aeolian (loess) deposits and had distinct soil horizons with relatively uniform soil properties. The site soil sampling plan and data interpretation considered soil morphology and was based on collection of discrete soil samples from each soil horizon. Soil near Golden, Colorado developed from fluvial deposits. Horizons from soil forming factors were not present due to prior soil removal (quarry operation) and soils were spatially variable throughout the profile with interbedded fine and coarse-grained horizontal layers. A statistical approach was used to collect soil samples from this fluvial deposit. Composite soil samples were obtained from the vertical face of excavated pits that were randomly selected. Soil characterization was based on analysis of duplicate samples, composite samples that included fine-grained clay clods, and composite samples from which clay clods were removed by sieving. This evaluation was conducted to assess the potential variability of soil properties that impact ET cover performance. Soils for a site near Arlington, Oregon were located in facility stockpiles. Characterization of stockpiles is problematic, particularly if materials are not segregated by soil type. Soil characterization considered the potential variability of site soil types that were excavated for stockpiles.