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Work Plan for Refined Plume Definition and Management of Floating Product-7500 W 11th St., Tracy, CA, Page 43 will be ineffective in evacuating LNAPL from any significant distance around the point of extraction. These representative elementary volume effects are, of course, present at several scales. For example, at one scale, the representative elementary volume would have -- dimensions on the order of the distance between thin zones of permeable silt contained within a clay layer. On another scale, estimating the size of the representative elementary volume would involve consideration of the typical distance separating the substrata within �- the sequential system of clay and sandy materials that are present in the subsurface. Clearly, it is not, in practice, possible to accurately quantify the size of the representative elementary volume for any given geotechnical application. However, for the purposes of designing a floating product extraction system, it is readily apparent that, at the Navarra Site, the representative elementary volume has dimensions on the order of several feet. LNAPL extraction systems that are designed around small-diameter borings or similarly small-scale elements will not intersect a sufficient number of the zones of relatively high permeability that are contained within the mass of soil for the extraction system to operate effectively over lateral and vertical distances of that size. 9.3.3 Well Diameter Excavation Dimensions and Construction Method Considerations a In addition to the scale effects related to the heterogeneous nature of soil discussed above, there are also scale effects related to the hydraulics of flow to a well or other excavation. The effects of construction techniques on the performance of well in the context of its efficiency as an element of an LNAPL-removal system compared to the efficiency of an excavated trench or pit used for that purpose must also be considered. These hydraulic issues are discussed below. 9.3.3.1 Influence of Well or Excavation Size on Effectiveness of Extraction Systems When designing LNAPL extraction systems, it is useful to consider the effects of well diameter or, as applicable, excavation size on the ability of the system to capture contaminated liquids from a wide area within a plume of affected groundwater. The influence of well or excavation size on the effectiveness of extraction systems can be illustrated by consideration of the equilibrium well equation for extraction of groundwater from a well that penetrates completely through a confined aquifer (Slichter 1899, Turneaure and Russell 1901, Thiem 1906). That equation can be stated as: Q=(Kb [H-h])/(528 log R/r) Equation 2 Where: Q W well yield or pumping rate, in gpm K = hydraulic conductivity of the water-bearing formation, in gpd/fl H = static head measured from bottom of aquifer, in ft H w depth of water in the well while pumping, in ft. SJC