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^ Approximately 1 percent of the picks in HydroBase appear to be outliers based <br />on comparison with surrounding picks and based on the appearance of bull's-eye <br />contours. <br />^ Many layers appeared to exhibit negative and/or anomalous thicknesses after <br />the initial rounds of gridding. It was necessary to add estimated control picks to <br />constrain the grids and better approximate the thicknesses. <br />^ It was necessary to add estimated control picks of 10 feet in net sand thickness to <br />the perimeter of each aquifer to help constrain the net sands to pinch out near the <br />aquifer's perimeter. <br />5.0 Recommendations <br />The following are recommendations based on the Task 42.2 data analysis, which fulfills <br />the second objective of this task: <br />^ The DWR may want to consider removing duplicate picks from the configuration <br />data in HydroBase to facilitate identifying which picks represent each surface. <br />The DWR should consider reassessing the aquifer nomenclature for the picks <br />representing the various regions of the Dawson and Arapahoe Aquifers to <br />facilitate identifying which picks represent each surface. Recommended changes <br />are for all picks for the top of the entire Arapahoe Aquifer to be coded Arapahoe <br />top, all picks representing the top of the confining unit to be coded Upper <br />Arapahoe bottom, all picks representing the bottom of the confining unit to be <br />coded Lower Arapahoe top, and all picks representing the bottom of the entire <br />Arapahoe Aquifer to be coded Arapahoe bottom. The same approach is <br />recommended for the Dawson Aquifer. If these changes were made then only <br />attribute queries would be required to select the desired picks. This would <br />eliminate the need to perform spatial queries to select the desired picks. <br />Picks identified as outliers in Appendix B should be evaluated against the <br />original geophysical logs and either be corrected or flagged in HydroBase. A <br />database structure is being developed under Task 50 of the SPDSS that will <br />identify and track HydroBase outliers. <br />^ Prior to developing a groundwater flow model, the ground surface should be <br />considered for use in further defining the top of Dawson surface in areas where <br />the top of the Dawson Aquifer is not covered by the Castle Rock conglomerate or <br />unconsolidated valley-fill deposits. <br />^ When modeling the bedrock aquifers the confining layers between the bedrock <br />aquifers should be explicitly modeled because they have significant thickness, <br />store significant quantities of water and may factor into inter-aquifer flow. <br />SPDSS Phase 2 Task 42.2 TM -Final 22 <br />2/13/06 <br />