SPDSS_Task43-2_Phase2_DenverBasinRegionAquiferProperty

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needing to be calculated from the information provided. In addition, a majority of the aquifer property data was derived from specific capacity data. To create a consistent basis for evaluating and presenting the data, the aquifer T or K data were converted to consistent units of feet for length and day for time. This section describes the methods used to obtain an internally consistent aquifer property data set. One of the important aspects of processing the data is determining the aquifer to which a given data value should be assigned. An understanding of the basic framework and nomenclature of the Denver Basin aquifers is helpful in understanding this task. 1.2.1 Denver Basin Bedrock Aquifer Nomenclature The current designation of the Denver Basin bedrock aquifers was established in 1985 during the promulgation of the Denver Basin Rules, 2 CCR 402-6 (DWR 1985a). The four principal aquifers of the Denver Basin are from top to bottom, the Dawson, the Denver, the Arapahoe, and the Laramie-Fox Hills. The Dawson and Arapahoe Aquifers are further subdivided into upper and lower units over portions of their respective extents, resulting in a total of six bedrock aquifers in the Denver Basin. Each aquifer is generally defined by the presence of relatively thick sand rich layers underlain by a layer of shale or mudstone, which acts as a confining layer for the next aquifer below. These layers can be correlated from geophysical logs over large areas. The divided areal extents (footprints) for the Dawson and Arapahoe Aquifers define the extent of the confining units which divide the respective aquifers into upper and lower units. These footprints approximate the aquifer footprints defined in the SB-5 Denver Basin Atlas plates (DWR 1985a). Early geologic studies of the Denver Basin, summarized by Romero (1976), led to an inconsistent naming of the principal bedrock aquifers. In the late 19th century, geologists applied the names Denver and Arapahoe to strata that nearly coincide with the current designations (Emmons et al., 1896). From the early 1900s to about the mid 1970s, the three uppermost principal aquifers of the Denver Basin were lumped into one unit and were referred to as the "Dawson Arkose," with various subunits referred to by lithology such as "lower-," "middle-" and "upper conglomerates" of the Dawson. In the 1970s, an examination of geophysical logs indicated the three uppermost aquifers could be mapped as units closely corresponding to the early stratigraphic nomenclature, and the upper three aquifers became known again as the Dawson, Denver, and Arapahoe (DWR, 1985b). These aquifers were mapped in the late 1970s and early 1980s, with the results provided in a set of USGS reports (Robson et al. 1981, Robson and Romero 1981a, Robson and Romero 1981b, Robson 1983, Robson 1987, and Robson 1996). In 1985 the Denver Basin Rules were established, which divided portions of the Dawson and Arapahoe Aquifers into upper and lower units. For administrative purposes, in the Denver Basin Rules, the undivided portions of the Dawson and Arapahoe were assigned to the Upper Dawson and Upper Arapahoe Aquifers, respectively. However, for the purposes of the SPDSS study, a physical definition for the Dawson and Arapahoe Aquifers was used where data from the undivided portions of these aquifers were assigned to the lower unit of the respective aquifer. This was done so the data from the SPDSS Phase 2 Task 43.2 TM -Final 8 2/ 13/ 2006