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Table 3: Screened Aquifer Property Tests -Denver Basin Bedrock Aquifers <br /> <br />Reason for Exclusion <br />Pumping Test Specific <br />Ca aci <br />Lab <br />Duplicate Test 9 19 0 <br />Lab Sample from Impermeable Unit 0 0 13 <br />ell Completed in Multiple Aquifers 29 0 0 <br />Outside Mapped Aquifer Extent 0 13 0 <br />Insufficient Information to Estimate b 0 10 0 <br />ell Depth < 100 Ft. 0 16 0 <br />Total 38 58 13 <br />Lab data from clay and shale dominated core samples, collected from either confining <br />units between aquifers or from impermeable units within an aquifer were removed to <br />avoid biasing the aquifer hydraulic conductivity values. This includes samples reported <br />in Barkmann and Eddington (2001), Major (1983) and CDM (2004a). Most of these <br />samples were collected to determine the K value of low permeability materials present <br />between the aquifers. In future groundwater modeling, the results of low permeability <br />material lab samples will be useful in assigning K values to the confining layers and also <br />in determining the anisotropy value within a given formation. Lab samples from <br />sources that did not explicitly specify the aquifer materials tested, such as McConaghy et <br />al. (1964), were retained in the data set for analysis. However, this could bias the results <br />presented in Section 3 if these samples were also collected from low-permeability parts <br />of the aquifer. <br />1.2.3 Estimation of Transmissivity from Specific Capacity Tests <br />A large percentage of the SPDSS Denver Basin bedrock aquifer property data have been <br />derived from aquifer specific capacity tests obtained, compiled, and reported during <br />SPDSS Phases 1 and 2 under Tasks 43 and 37, respectively (CDM 2004a, CDM 2005). <br />This category of data required more analysis and processing than other categories of <br />data, as described in this section. <br />Specific capacity tests can be used to estimate aquifer transmissivity (Fetter 2001, Razak <br />and Huntley 1991, Robson 1983, Drisco111986). Determination of aquifer transmissivity <br />from specific capacity tests is typically performed by developing an empirical <br />relationship between transmissivity values obtained from aquifer pumping tests and the <br />corresponding specific capacity data obtained at the time of the aquifer test. The <br />relationship is then applied to estimate a transmissivity value at a given well that does <br />not have an aquifer test but does have a specific capacity test. For confined aquifers, <br />such as the Denver Basin bedrock aquifers, transmissivity can also be estimated from <br />specific capacity by using a modification of the Theis equation, as presented by Jacob <br />(Fetter 2001, Drisco111986) and shown below. The Theis equation was developed for <br />confined aquifers and therefore appropriate for use as the basis in this application. An <br />SPDSS Phase 2 Task 43.2 TM -Final 11 <br />2/ 13/ 2006 <br />