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.�. Work Plan for Reflned Plume Defnition and Management of Floating Product-7500 W 11th St,, Tracy, CA. Page 42
<br /> sand zones, that the large mass includes more inclusions of such permeable zones that are
<br /> interconnected, or that it includes a singular continuous zone of high permeability materials
<br /> at a large scale.
<br /> In any specific soil mass, its measured hydraulic conductivity continues to increase until such
<br /> time as sufficient volume of soil has been included in the tested volume to incorporate
<br /> sufficient of the imbedded materials and features of the mass that have an influence on its
<br /> hydraulic conductivity at the mass scale. An understanding that such increases in measured
<br /> conductivity occur at the volume of the soil being considered increases can be understood
<br /> intuitively by geotechnical practitioners familiar with sedimentary deposition and other types
<br /> of soil and rock formation. However, if the geology is highly complex, it can be easily
<br /> envisioned that the hydraulic conductivity of the soil mass will continue to fall indefinitely as
<br /> the volume of geological materials considered increases. However, for any given engineering
<br /> design problem, such as the design of a floating product extraction system, there comes a
<br /> point where the increase in permeability with increasing size of the soil mass is relatively
<br /> small compared to the volume that will influence the performance of the engineering design.
<br /> When that point is reached, the scale of the soil mass being considered has reached the
<br /> representative elementary volume. As can be deduced from the discussion above, the size of
<br /> the representative elementary volume will depend on the synthetic interaction between the
<br /> scalar properties of the geologic medium and the technical requirements for the design of the
<br /> engineered system.
<br /> The concept of representative elementary volume and its importance to the accurate
<br /> measurement of the properties of earth materials and the design of geotechnical engineering
<br /> "Mao systems has been well understood in geotechnical engineering practice for at least half a
<br /> century (Harr 1962, Sedergren 1967, Rowe 1968, Watkins 1969, Baer 1972, Duncan, et al
<br /> 1972, Witherspoon, et al 1979, Freeze and Cherry 1979, Heuz6 1980, Watkins 1981,
<br /> Witherspoon, et al 1981, Watkins, et al 1983). Unfortunately, despite its importance,
<br /> particularly as it applies to groundwater flow, it appears only to have been recognized by
<br /> earth science practitioners from other disciplinary backgrounds in relatively recent times
<br /> (Hall, et al 1984, Domenico and Schwartz 1990, Fetter 1993, Girard and Edelman 1994,
<br /> Hanzlik 1998). However, its importance to proper evaluation of the hydraulic properties of
<br /> soil and rock masses and their relationship to engineered systems installed in the subsurface
<br /> �- is today fully embraced by experienced hydrogeologists as well as by geotechnical engineers
<br /> and is now incorporated into site characterization and groundwater regime modeling (e.g.,
<br /> see Min 2002) as a standard of professional practice.
<br /> As applied to the design of a floating product removal system at the Navarra Site,
<br /> consideration of parameters that are related to the site-specific representative elementary
<br /> volume can be understood intuitively. The geologic strata at the depth of the water table are
<br /> clastic alluvial deposits composed of sand$, silty clays and clays, which, when they were laid
<br /> down, included thin beds and zone of varying permeability (e.g., thin, high permeability silt
<br /> r layers included within strata that are otherwise formed from clays of relatively low
<br /> permeability). Obviously, if an engineered floating product removal system or any of its
<br /> subsurface elements is of a scale smaller than the typical spacing between such permeable
<br /> zones, it will be significantly less probable that it will intersect such zones and, if it does not,
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