New permeameters for in-situ characterization of unsaturated heterogeneous permeability. 1998 annual progress report

摘要

Thick unsaturated zones underlie many Department of Energy (DOE) landfills, industrial areas, and waste storage sites in the western US and are the primary pathway for contaminants to migrate into underlying aquifers. The spatial variability of unsaturated hydraulic properties in these heterogeneous geologic materials directly influences the movement of water and non-aqueous phase liquids (NAPL''s). Poor characterization of heterogeneity may lead to ineffective remedial designs and increased risk, requiring subsequent additional remedial actions at increased cost and time. Remedial design can be improved using probabilistic risk-based decision analysis, which requires a large number of hydraulic property observations. Laboratory methods for estimating the unsaturated permeability are expensive, time-consuming, and may not yield results representative of heterogeneous field conditions. Simple and rapid field methods for estimating in-situ unsaturated permeability are appealing and potentially cost-effective. The primary objective of the EMSP research is to design, develop, and test new permeameters for use in spatial variability studies. The authors have established a series of permeameter design criteria, including: (1) measurements should be relatively rapid, (2) the total cost per data point should be low, (3) results would accurately reflect the variation of unsaturated hydraulic properties between sampled locations, (4) the volume sampled (measurement support) would be small, and (5) useful range would be relevant to the range of soil moisture conditions encountered at DOE sites. This report summarizes work after year two of a 3- year project. They report their activities to date related to development and testing of techniques for inverting permeameter data, development of numerical tools for data inversion, error evaluation for permeameter design, and permeameter component design.'