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The KAUB surface can also be thought of as the top of the confining layer that divides <br />the Arapahoe Aquifer in its northern half, as shown in Figure 3. However, not all picks <br />coded as KAUB in the database represent the top of the confining unit. KAUB picks in <br />the database can represent the top of the confining unit or the bottom of the entire <br />Arapahoe Aquifer in either the divided or undivided region. If one were to select all <br />KAUB picks from the database and use them to develop a contour map of the top of the <br />confining unit, the map would be spotted with bull's eye contours caused by the KAUB <br />picks that actually represent the bottom of the entire Arapahoe Aquifer. Therefore, the <br />process described below was followed to avoid selecting KAUB picks from the database <br />that do not represent the actual KAUB surface. <br />The HydroBase table containing the geophysical log picks was formatted by CDM from <br />a many record per geophysical log to a one record per geophysical log format. This new <br />table format allowed all picks for a unique log to be evaluated in one row, which <br />facilitated the ability to select picks. This new table format was then imported into <br />ArcMap to conduct spatial and attribute queries. The combination of the spatial and <br />attribute queries allowed the differentiation between geophysical log picks representing <br />the divided and undivided portions of each aquifer. For example, if a log in the divided <br />region of the Arapahoe Aquifer contained picks for the KAUB and the KALB (Lower <br />Arapahoe bottom, which is equal to the entire Arapahoe bottom) and KAUB equals <br />KALB, this indicates that the KAUB pick actually represents the Arapahoe bottom <br />surface. This combination of a spatial and attribute query allowed one to select the picks <br />representing the various aquifer surfaces. This process also helped to identify the picks <br />that were stored as duplicates in the database. In the example above, KAUB equals <br />KALB and, therefore, the KAUB pick is a duplicate pick. Detailed instructions for <br />querying the picks for each surface can be found in Appendix A. <br />After all picks had been queried for each aquifer surface, the picks were imported into <br />an automated gridding program to create the top and bottom contours and the net sand <br />thickness maps. Details on the gridding process can be found in Section 1.2.3. <br />Table 1 provides a summary, by aquifer surface, of the total number of picks that were <br />queried from HydroBase for the top, bottom, and net sand thickness of each aquifer, the <br />number of duplicate picks, the number of outlier (bull's eye) picks, and the total number <br />of HydroBase picks used for contouring, the number of control picks, and the final <br />number of picks that were used in the analysis and contouring. The identification of <br />outlier picks is discussed in Section 1.2.4. During the querying process, picks that did <br />not satisfy the query parameters were not extracted from HydroBase and are not <br />reflected in the counts in Table 1. In some cases (such as for the Denver Aquifer) there <br />are more picks reported for the bottom of the aquifer than for the top. This is because <br />near the aquifer's boundary, the top is an erosional surface and does not represent the <br />original top of the aquifer. In such cases the top is at or near ground surface and may be <br />missing the key marker beds that would have defined the top of the aquifer, as <br />interpreted by the DWR staff. <br />SPDSS Phase 2 Task 42.2 TM -Final 6 <br />2/13/06 <br />