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December 15, 1993 -3- 933-2713 <br /> as a pygmy or standard flow meter or using a dedicated device such as a flume. Based on <br /> past experience at the site, a pygmy or standard flow meter provides reliable determinations <br /> of surface water flow. However, installation of a flume or weir will be conducted if the <br /> hand-held devices do not provide the necessary accuracy needed for a project of this type. <br /> Geophysical Characterization <br /> Determination of groundwater flow within creek channel sediments is critical to conjunctive <br /> flow determinations. It is therefore necessary to develop a reliable cross-sectional profile <br /> of the creek sediments in order to determine the area through which groundwater is flowing <br /> (shown as "A" in equation 1 above). Geophysical techniques have proven to be a useful tool <br /> in determining cross-sectional profiles of creek sediments, particularly when a significant <br /> contrast exists between the creek sediments and the underlying bedrock, in terms of degree <br /> of consolidation. Based on existing data, the Cement Creek area should offer a sufficient <br /> contrast for geophysical purposes. Based on exposures and previous geologic data, the <br /> Cement Creek sediments are composed primarily of sands and gravels. These sediments <br /> overly volcanic bedrock. The contrast between the sands and gravels and the underlying <br /> bedrock should provide reliable estimates of the changes in depth of the creek sediments at <br /> selected cross-sectional locations. <br /> Two cross-sectional profiles are proposed to be evaluated using geophysical techniques. <br /> Tentative locations of the profiles are shown on Figure 2. Anticipated maximum depth to <br /> bedrock along the profiles is approximately 30 feet. Given the anticipated depth to bedrock, <br /> refraction techniques are proposed. Refraction techniques are generally useful for <br /> determining depth to the water table and depth to bedrock, both of which will be valuable <br /> for subsequent borehole drilling and piezometer installation activities. The following sections <br /> discuss the rationale for evaluating two cross-sectional profiles. <br /> Borehole Drilling <br /> After completion of the geophysical task, including data analysis to develop cross-sectional <br /> profiles at the two locations across Cement Creek, borehole drilling will be conducted to <br /> confirm the creek sediment thickness at selected locations. The boreholes will also be used <br /> to verify the depth to groundwater in the sediments. Two boreholes are proposed to be <br /> drilled along each of the two geophysical profile locations. One borehole is proposed to be <br /> drilled on each side of the Cement Creek surface water, if possible. During drilling, <br /> continuous sampling of the creek sediments is proposed to allow visual characterization of <br /> the materials and to develop a vertical profile of the sediments. In addition, samples will <br /> be collected to allow subsequent laboratory testing, as described in a following section of this <br /> proposal. A further benefit of borehole drilling will be to verify the groundwater table <br /> elevation within the creek sediments, which in turn will assist in defining the area through <br /> which groundwater flow is occurring ("A" in equation 1). <br /> Figure 2 illustrates the proposed borehole drilling locations. <br />