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Memorandum to Gordon McCurry <br />January 25, 2006 <br />Page 2 <br />Task 42.3 Aquifer Configuration and Task 43.3 Aquifer Properties TM's for the South Platte <br />Alluvium <br />With regard to the TM's for Task 42.3 Aquifer Property and Task 43.3 Aquifer Configuration, our <br />only comments are that they both are well done and that the approaches used are reasonable. The <br />large water level declines and rises adjacent to one another in the Black Squirrel Aquifer are curious. <br />Our guess is that they reflect pumping effects. We suggest another look at the interpretation in that <br />area. The conclusions of both TM's are reasonable and we agree with their recommendations. <br />Task 43.2 Denver Basin Aquifer Property TM <br />Generally, we agree with the approach used in this TM. We are concerned about section 1.2.4 <br />Conversion of Transmissivity Data to Hydraulic Conductivity Values. Hydraulic conductivity was <br />estimated by dividing the transmissivity by the "net sand" thickness as determined (we think) by <br />DWR. Our belief is that DWR determines net sand plus silt. This needs to be clarified. If we are <br />correct, the hydraulic conductivity estimated is not representative of the sand zones, the silt zones, or <br />the aquifers themselves. Furthermore, the method of estimating hydraulic conductivity for wells that <br />partially penetrate the aquifer is potentially flawed because it assumes an even distribution of sand <br />and silt throughout the aquifer thickness. This may not be the case. <br />We agree with the conclusions except #6 and #8. Conclusion #6 is not supported by the analysis and <br />is likely incorrect. It should be deleted or properly supported. Conclusion #8 is simply untrue. The <br />hydraulic conductivity data are of little value in regional planning and they certainly do not represent <br />the entire aquifer as noted in Section 3.1 on page 18 and they should not be used for ground water <br />modeling. <br />We generally agree with the recommendations; however, we believe that #1 and #6 are unrealistic <br />because of the high cost of pumping tests ($5,000 to $20,000). <br />Task 44.2 Denver Basin Water Level TM <br />Generally, we feel that this analysis is overly conservative. By that we mean the interpretation is too <br />restricted to the immediate area surrounding the data. In light of this opinion, we feel that conclusion <br />#2 overstates the situation. We suggest deleting the words "alluvial and" from conclusion #3 <br />because we feel that Central is a significant source of alluvial water level data measurements. <br />We suggest conclusion #6 be revised. It over generalizes the water trend changes. Based upon <br />Figures 19-21, the number of water level rises is about equal to the declines away from the major <br />pumping centers. This observation may suggest that declines may be limited to only the areas <br />surrounding the pumping centers. We agree with the recommendations. <br />Task 44.3 South Platte Alluvium Water Level TM <br />Our only comment is that this TM is well done and the approach is reasonable. The conclusions are <br />reasonable and we agree with the recommendations. <br />\\File-server\SUPPORT1Documents\064UvIemo McCurry Camp Dresser McKee_1-25-06.doc <br />LEONARD RICE ENGINEERS, INC. <br />