Laserfiche WebLink
The Denver Basin's early geologic studies, summarized by Romero (1976), have resulted <br />in an inconsistent naming of the principal bedrock aquifers. In the late 19th century, <br />geologists applied the names Denver and Arapahoe to strata that nearly coincide with <br />the current designations (Emmons et al., 1896). From the early 1900s to about the mid- <br />1970s, the three uppermost principal aquifers (Dawson, Denver, and Arapahoe) of the <br />Denver Basin were lumped into one unit and were referred to as the Dawson Arkose <br />with various subunits referred to by lithology, such as lower, middle, and upper <br />conglomerate of the Dawson. In the 1970s, an examination of geophysical logs indicated <br />that the three uppermost aquifers could be mapped as units closely corresponding to the <br />early stratigraphic nomenclature, and the upper three aquifers became known again as <br />the Denver, Dawson, and Arapahoe (DWR 1985b). These aquifers were mapped in the <br />late 1970s and early 1980s, with the results provided in a set of USGS reports (Robson et <br />al. 1981, Robson and Romero 1981a, Robson and Romero 1981b, Robson 1983, Robson <br />1987). <br />Of note is an area in the northwest corner of the Denver Basin region referred to by the <br />DWR as the Complex Area. This is a portion of the Denver Basin with extensive faulting <br />and vertical displacement in which geologic data should be viewed with some caution <br />due to the geologic complexity. Contours for the Laramie-Fox Hills and Arapahoe <br />Aquifer are not shown for this area. Information on the characteristics of the Laramie- <br />Fox Hills Aquifer in this Complex Area can be found in a report by Kendall Kittleson <br />(Kittleson, 2004). <br />1.2.2 Bedrock Data Processing and Screening <br />To create the structural top and bottom contours and the net sand thickness maps, it was <br />necessary to query data from the database for each aquifer surface, grid the data, <br />identify and exclude outliers, add control data, re-grid the data, and then use ground <br />surface and the T42.3 base of alluvium surface to refine the maps. Each of these <br />processing steps will be discussed in detail in the following sections. <br />Data for each aquifer surface were selected from the 2005 edition of HydroBase using <br />appropriate database queries. Due to the divided nature of the Dawson and Arapahoe <br />Aquifers and the current coding of picks in HydroBase for those aquifers, the database <br />has to be queried differently for them than for the Denver and Laramie-Fox Hills <br />Aquifers. <br />For the simpler case involving the Denver and Laramie-Fox Hills Aquifers, attribute <br />queries were run in the database to select the necessary picks for the various surfaces. <br />For example, to select picks representing the top of the Denver Aquifer, the "Aquifer" <br />field was set to 'Denver' and the picks were obtained from the "Glogtop" field of the <br />Geophlogs table. <br />The more complicated process required for the Dawson and Arapahoe Aquifers <br />involved a combination of attribute and spatial queries. As an example, the bottom of <br />the Upper Arapahoe Aquifer, which will be referred to as KAUB, is used below to <br />illustrate the complexity of the queries needed to select the appropriate picks. <br />SPDSS Phase 2 Task 42.2 TM -Final 5 <br />2/13/06 <br />