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The most comprehensive data source available, Robson (1983), does not <br />differentiate data between the divided portions of the Upper and Lower <br />Arapahoe and Dawson Aquifers. However, the data for each of these aquifers <br />from the various data sources does not appear to differ appreciably between the <br />upper and lower units of each aquifer. Therefore the Robson (1983) data can be <br />included in the data sets for both aquifers; this will expand the data that can be <br />used in development of a groundwater model for the bedrock aquifers. <br />Transmissivity and hydraulic conductivity point data derived from specific <br />capacity tests provide a reasonable estimate of the aquifer hydraulic properties <br />where aquifer pumping test derived data are unavailable. However, the specific <br />capacity-based results can have potential inaccuracies due to well inefficiencies, <br />incorrect data entry into the original well construction forms, and inaccuracies <br />associated with the conversion of specific capacity to T and then to K. <br />The use of specific capacity data to supplement aquifer test derived K data <br />appears to be appropriate for all Denver Basin bedrock aquifers except for the <br />Upper Dawson Aquifer. In the Upper Dawson Aquifer there is limited <br />information on aquifer thickness, which is used to compute K from T, and the <br />methodology used to calculate T may be less applicable due to the unconfined to <br />semi-confined conditions that exist over portions of this aquifer. <br />• Due to the relatively small volume of aquifer material tested and the <br />heterogeneity of the Denver Basin aquifers, lab-based K values should be <br />considered the lowest confidence source of data when compared to aquifer <br />pumping or specific capacity tests. <br />Specific yield data is useful for determining how much water can be drained <br />from the Denver Basin Region bedrock aquifers where they have become <br />unconfined, and is a reasonable parameter for estimating the total volume of <br />water contained in the bedrock aquifers. In addition, aquifer storativity data are <br />appropriate for determining the volume of water available from confined <br />portions of these aquifers. <br />The median specific yield values obtained by the SPDSS differ from the SB-5 <br />values by a range of -25% less (Lower Dawson Aquifer) to 40% more (Laramie- <br />Fox Hills Aquifer). Though these differences seem to be large, they are based on <br />a limited data set. The geographic distribution of the data are very uneven and <br />the data were not segregated by lithology prior to summarizing them statistically <br />and comparing them against the SPDSS specific yield values. <br />• The aquifer hydraulic conductivity data presented in this TM serves as a <br />reasonable basis for regional scale water resources planning and groundwater <br />modeling. However, additional data processing is needed to convert K values <br />presented in this TM to those that are representative of total aquifer thicknesses. <br />SPDSS Phase 2 Task 43.2 TM -Final 26 <br />2/ 13/ 2006 <br />