Paschke, S.S. Oliver, N.B. 2020 vector digital data U.S. Geological Survey Data Release unknown Denver, CO U.S. Geological Survey https://doi.org/10.5066/P9CHGG0V Paschke, S.S., editor 2011 publication U.S. Geological Survey Professional Paper PP 1770 Reston, VA U.S. Geological Survey 274 p. https://doi.org/10.3133/pp1770 This line dataset (PP1770_alt_base_LKA_con.shp) consists of contours of equal base altitude, in feet, for the lower Arapahoe aquifer of the Denver Basin aquifer system, Colorado. A point dataset was generated in ArcGIS 9.2 (Environmental Systems Research Institute, Inc., 1999-2004) from the Colorado Division of Water Resources Denver Basin geophysical log database (Brian Ahrens, Colorado Division of Water Resources, written commun., 2003), and the point data were contoured using either an ordinary kriging method or an inverse-distance weighted method available in ArcGIS, depending on which method resulted in the least error. This resulting dataset was then used to define the base altitude of the Arapahoe confining unit (model layer 9) in a MODFLOW-2000, three-dimensional groundwater-flow model of the Denver Basin (Paschke, 2011). See the "Supplemental Information" section of this metadata for more detailed descriptions of the datasets, their application, and references. These datasets were used as the basis for preparing contours of equal base altitude for the bedrock aquifers and confining units, which were then used to define the base altitude of the bedrock aquifers in a MODFLOW-2000, three-dimensional groundwater-flow model of the Denver Basin aquifer system (Paschke, 2011). The Denver Basin aquifer system is composed of Tertiary and Cretaceous sandstone bedrock aquifers that occur in the uppermost layers of the structural Denver Basin above the Cretaceous Pierre Shale confining layer. Colorado State legislation administrating the Denver Basin recognizes and defines four primary bedrock aquifers, two of which are subdivided into upper and lower units (Romero, 1976; Robson, 1987; Graham and VanSlyke, 2004). From oldest to youngest (bottom to top), the four primary units are the Laramie-Fox Hills aquifer, the Arapahoe aquifer, the Denver aquifer, and the Dawson aquifer. In parts of the basin, confining units further divide the Arapahoe and Dawson aquifers into upper and lower units. Thus, the six Denver Basin bedrock aquifers and five intervening confining units used to develop geologic layers for the groundwater flow model are, from oldest to youngest, the Laramie-Fox Hills aquifer (KLF), Laramie confining unit (KLC), lower Arapahoe aquifer (LKA), Arapahoe confining unit (KAC), upper Arapahoe aquifer (UKA), Denver lower confining unit (TKDLC), Denver aquifer (TKD), Denver upperconfining unit (TKDUC), lower Dawson aquifer (LTDW), Dawson confining unit (TDWC), and upper Dawson aquifer (UTKD). The synclinal structure of the Denver Basin causes the bedrock aquifer units to crop out in a ring pattern where the oldest rocks of the Laramie-Fox Hills aquifer crop out around the outer margins of the basin and the youngest rocks of the Dawson aquifer crop out in the center of the basin. Confined groundwater conditions generally are found in the bedrock aquifers where they are overlain by younger units, and unconfined groundwater conditions are generally found in outcrop areas. The hydrogeologic framework for the Denver Basin groundwater model consists of GIS data sets, which define the lateral extent and base altitude of each aquifer and confining unit represented in the model. For the aquifer units, maps of silt-plus-sand thickness also were developed and used as multipliers for hydraulic conductivity and specific yield in the groundwater flow model. This study modified maps showing the extent of aquifers and confining units published by the CDWR (VanSlyke and others, 1988a, 1988b, 1988c, 1988d) along the western basin margin to include geologic contacts mapped by Robson and others (1998), and the results defined the extent of active cells for each model layer. Topographic altitude data for land surface and streamflow routing were derived from the 30-meter-resolution National Elevation Dataset (NED) (U.S. Geological Survey, 1999). Maps of the altitude of the base of the bedrock aquifers and confining units and the silt-plus-sand thickness were generated in ArcGIS 9.2 (Environmental Systems Research Institute, Inc., 1999-2004) from the CDWR Denver Basin geophysical log database (Brian Ahrens, Colorado Division of Water Resources, written commun., 2003) using ordinary kriging and inverse-distance weighed (IDW) methods, depending on which method resulted in the least error. The CDWR geophysical-log database contains top and bottom elevations for each of the six bedrock aquifers (geophysical log "picks") for about 4,400 geophysical logs. The geophysical log picks were processed into ArcGIS point-data shapefiles representing the base altitude for each of the six bedrock aquifers and five confining units, and the altitude data points were contoured in ArcGIS. Contouring methods and model-fitting parameters are presented in Table A1 of Paschke (2011). The resulting point data and vector contour maps are listed in Table A2 of Paschke (2011) and are published herein as GIS datasets. The datasets are updated versions of the base-altitude maps published by the CDWR (VanSlyke and others, 1988a, 1988b, 1988c, 1988d), and interpretations of the data are discussed in the "Hydrogeologic Framework" section of Professional Paper 1770 Chapter A (Paschke, 2011). For many logs in the CDWR geophysical-log database, a silt-plus-sand thickness value was recorded for each bedrock aquifer. These silt-plus-sand-thickness values also were processed into ArcGIS point-data shapefiles, and the data points were contoured using either an ordinary kriging method or an IDW method available in ArcGIS, depending on which method resulted in the least error. The resulting point data and vector contour maps are published herein as GIS datasets and represent updated versions of the silt-plus-sand maps published by the CDWR (VanSlyke and others, 1988a, 1988b, 1988c, 1988d). Percent silt-plus-sand-thickness values were calculated from the silt-plus-sand-thickness point data for each of the six bedrock aquifers as the silt-plus-sand thickness divided by the total layer thickness, and the percent silt-plus-sand-thickness values were contoured using an IDW method available in ArcGIS. Averaged percent silt-plus-sand values for each model grid cell were used as multiplier arrays for hydraulic-conductivity and specific-yield values in the groundwater flow model as described in the "Hydrogeologic-Unit Properties" section of Professional Paper 1770 Chapter C (Paschke, 2011). References: Graham, Glenn, and VanSlyke, George, 2004, Development of the regulatory framework for Denver Basin aquifers: The Mountain Geologist, v. 41, no. 4, p. 153-160. Paschke, S.S., ed., 2011, Groundwater Availability of the Denver Basin aquifer system, Colorado, U.S. Geological Survey Professional Paper 1770, 274 p. Robson, S.G., 1987, Bedrock aquifers in the Denver Basin, Colorado-A quantitative water-resources appraisal: U.S. Geological Survey Professional Paper 1257, 73 p. Robson, S.G., Van Slyke, G., and Graham, G., 1998, Structure, outcrop, and subcrop of the bedrock aquifers along the western margin of the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA-742, scale 1:50,000, 5 sheets. Romero, J.C., 1976, Ground-water resources of the bedrock aquifers of the Denver Basin: Colorado Division of Water Resources Report, 109 p. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988a, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Dawson aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 1 (DBA-1), 3 plates. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988b, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Denver aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 2 (DBA-2), 3 plates. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988c, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Arapahoe aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 3 (DBA-3), 3 plates. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988d, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Laramie-Fox Hills aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 4 (DBA-4), 3 plates. 2011 publication date Complete None planned -105.2349 -103.9221 40.1529 38.7505 ISO 19115 Topic Category inlandWaters None inland waters groundwater lower Arapahoe aquifer base-altitude contours Denver Basin aquifer system None Denver Basin Colorado None Cretaceous None 1988-2003 None. Please see “Distribution Info” for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Suzanne Paschke U.S. Geological Survey, ROCKY MOUNTAIN REGION Supervisory Hydrologist mailing address

Mail Stop 415, W 6th Ave Kipling St

Lakewood CO 80225 US 303-236-6904 303-236-4912 spaschke@usgs.gov withheld Shapefile of contours for the base altitude of the lower Arapahoe aquifer (LKA). ESRI Shapefile FGDC Unclassified None Version 6.2 (Build 9200) ; Esri ArcGIS 10.7.0.10450 All attempts were made to compare 100 percent of the digital attribute data to the original source database. Verification was done by visual and manual comparison, combined with on-screen review of the source with hard copy plots. In addition, Access queries were run to identify duplicate data. Errors resulting from the quality of the source map, the automation process and the scale resolution can affect the accuracy of the data. feet Verification was done by visual and maual comparison, combined with on-screen review of the source with copy plots. In addition, Access queries were run to identify duplicate data. Errors resultingfrom the quality of the source map, the automation process and the scale resolution can affect the accuracy of the data. No tests for topological consistency were made, however, all base-altitude contour datasets were derived using standard GIS interpolation methods (ordinary kriging) from a single source dataset. Point features are from digital data from Colorado Division of Water Resources and are complete for Denver Basin. This dataset is derived from a geophysical-log database developed by the Colorado State Engineer's office, Colorado Division of Water Resources. Source information for the database comes from paper files which were hand entered into a computer database. Potential well placement errors may be present where location information was inaccurate, unknown or incorrectly entered by automation processes. Contours derived from such data inherit the accuracy of the original well locations. Wells in the original Access database had locations recorded either as a Public Land Survey System (PLSS) description or as coordinates in the Universal Transverse Mercator (UTM) projection system, Zone 13 North. If they were available, the UTM coordinates were used for the well location. Well locations for which only a PLSS description was available are accurate to the quarter-quarter section in all but a few instances. Wells in this GIS dataset having only a PLSS location were located at the centroid of the quarter-quarter section described in the Access database. Vertical accuracy of the interpretation from geophysical logs of the altitude of the base of the unit is assumed to be good, but variable. Vertical accuracy cannot be assumed to exceed National Map Accuracy Standards for the scale each map is plotted. The vertical accuracy standard requires that the elevation of 90 percent of all points tested must be correct within half of the contour interval. On a map with a contour interval of 10 feet, the map must correctly show 90 percent of all points tested within 5 feet (1.5 meters) of the actual elevation. Vertical datum is the National Geodetic Vertical Datum of 1929 (NGVD 29). VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A. 1988 Denver Basin Atlas no. 3 (DBA-3) vector digital data Denver Basin Atlas DBA-3 Denver, CO Colorado Division of Water Resources 200 None 1988 publication date VanSlyke and others, 1988 Boundary for extent of aquifer or confining unit Colorado Division of Water Resources, Colorado State Engineers Office 2003 Access database database was obtained from Brian Ahrens, written communication, 2003. CD-ROM 2003 publication date Colorado Division of Water Resources, 2003 The original database was in the form of a compact disk. The CD contains aquifer descriptions and interpretive data from geophysical logs for wells in the Denver Basin aquifer system. The format of the database is Microsoft Access. An Access database 'Den_Bas_Logs_2000.mdb' was provided to the U.S. Geological Survey by Colorado Division of Water Resources (Brian Ahrens, Colorado Division of Water Resources, written communication, 2003). The database contained geophysical log 'picks' for the tops and bottoms of aquifers and confining units in the Denver Basin. The database was queried, and the geophysical log picks were processed into point shapefiles, each of which represents the base altitude for six bedrock aquifers and five confining units in the Denver Basin aquifer system. Well location information provided in the original database was either in the form of a Public Land Survey System description or as a coordinate in Universal Transverse Mercator Zone 13 North. The dataset was projected into the Colorado State Plane Central Coordinate System (Lambert Conformal Conic, in feet), North American Datum of 1983. Usable wells were distinguished from wells with anomalous data or locations. Examples of such anomalies included wells missing top or base altitudes for units, negative elevation data, wells located outside the horizontal extent of the aquifer or confining layer, and wells with top or bottom values that were inconsistent with surrounding well values. Anomalous wells were not used for contouring or for subsequent data processing. withheld withheld 2006 U.S. Geological Survey Suzanne S. Paschke Hydrologist mailing

Denver Federal Center MS415 PO Box 25046

Lakewood CO 80225 US (303) 236-6904 (303) 236-4912 spaschke@usgs.gov A surface was interpolated from the data points for the base of the lower Arapahoe aquifer (PP_1770_alt_base_LKA_point.shp) using an ordinary kriging method. After this raster surface was made, 100-ft contours of the base of this unit were developed for the surface using the ArcToolbox contour tool. 20060101 U.S. Geological Survey Suzanne S. Paschke Hydrologist mailing

Denver Federal Center MS415 PO Box 25046

Lakewood CO 80225 US (303) 236-6904 (303) 236-4912 spaschke@usgs.gov Vector Simple FALSE 0 FALSE FALSE coordinate pair 0.6096 0.6096 meters North_American_Datum_1983 GRS_1980 6378137.0 298.257222101 PP1770_alt_base_LKA_con Shapefile of contours for the base altitude of the lower Arapahoe aquifer (LKA). Producer defined Feature Class 0 Value Contour interval in feet Producer defined contour interval, in feet. Vertical datum is the National Geodetic Vertical Datum of 1929 (NGVD 29). Value Double 19 0 0 Shape Feature geometry. Esri Coordinates defining the features. Shape Geometry 0 0 0 FID Internal feature number. Esri Sequential unique whole numbers that are automatically generated. FID OID 4 0 0 Contours in this dataset were developed the Colorado State Engineers Office Access geophysical-log database. The database contains well location information and the top and bottom elevation of the unit based on interpretation of geophysical well logs. Attributes in this contour dataset include a unique identifier field (Classes) for each contour interval and a Value field that contains the contour interval derived from the Access database, in feet. None. U.S. Geological Survey GS ScienceBase mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ESRI Shapefile ArcGIS v. 10.1 ESRI Shapefile Shapefile of contours for the base altitude of the lower Arapahoe aquifer (LKA). Winzip https://doi.org/10.5066/P9CHGG0V None. This dataset is provided by the U.S. Geological Survey as a public service. 20201209 Suzanne Paschke U.S. Geological Survey, ROCKY MOUNTAIN REGION Supervisory Hydrologist mailing address

Mail Stop 415, W 6th Ave Kipling St

Lakewood CO 80225 US 303-236-6904 303-236-4912 spaschke@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998 local time Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The use of firm, trade, or brand names in this report is for identification purposes only and does not constitute endorsement by the USGS. FGDC Unclassified None Suzanne Paschke U.S. Geological Survey, ROCKY MOUNTAIN REGION Supervisory Hydrologist 303-236-6904 303-236-4912 Mail Stop 415, W 6th Ave Kipling St Lakewood CO 80225 US spaschke@usgs.gov 20201209 ArcGIS Metadata 1.0 GS ScienceBase U.S. Geological Survey 1-888-275-8747 Denver Federal Center, Building 810, Mail Stop 302 Denver CO 80225 US sciencebase@usgs.gov None. This dataset is provided by the U.S. Geological Survey as a public service. ESRI Shapefile ArcGIS v. 10.1 ESRI Shapefile Winzip Shapefile of contours for the base altitude of the lower Arapahoe aquifer (LKA). https://doi.org/10.5066/P9CHGG0V https://doi.org/10.5066/P9CHGG0V 0.000 Shapefile Base-altitude contours for the lower Arapahoe aquifer of the Denver Basin aquifer system, Colorado 2020 Paschke, S.S. Oliver, N.B. U.S. Geological Survey Denver, CO vector digital data U.S. Geological Survey Data Release unknown Groundwater Availability of the Denver Basin Aquifer System, Colorado This line dataset (PP1770_alt_base_LKA_con.shp) consists of contours of equal base altitude, in feet, for the lower Arapahoe aquifer of the Denver Basin aquifer system, Colorado. A point dataset was generated in ArcGIS 9.2 (Environmental Systems Research Institute, Inc., 1999-2004) from the Colorado Division of Water Resources Denver Basin geophysical log database (Brian Ahrens, Colorado Division of Water Resources, written commun., 2003), and the point data were contoured using either an ordinary kriging method or an inverse-distance weighted method available in ArcGIS, depending on which method resulted in the least error. This resulting dataset was then used to define the base altitude of the Arapahoe confining unit (model layer 9) in a MODFLOW-2000, three-dimensional groundwater-flow model of the Denver Basin (Paschke, 2011). See the "Supplemental Information" section of this metadata for more detailed descriptions of the datasets, their application, and references. These datasets were used as the basis for preparing contours of equal base altitude for the bedrock aquifers and confining units, which were then used to define the base altitude of the bedrock aquifers in a MODFLOW-2000, three-dimensional groundwater-flow model of the Denver Basin aquifer system (Paschke, 2011). Suzanne Paschke U.S. Geological Survey, ROCKY MOUNTAIN REGION Supervisory Hydrologist 303-236-6904 303-236-4912 Mail Stop 415, W 6th Ave Kipling St Lakewood CO 80225 US spaschke@usgs.gov withheld Shapefile of contours for the base altitude of the lower Arapahoe aquifer (LKA). ESRI Shapefile Denver Basin Colorado Cretaceous 1988-2003 inlandWaters ISO 19115 Topic Category inland waters groundwater lower Arapahoe aquifer base-altitude contours Denver Basin aquifer system inlandWaters inland waters groundwater lower Arapahoe aquifer base-altitude contours Denver Basin aquifer system Denver Basin Colorado Cretaceous 1988-2003 None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. None. Please see “Distribution Info” for details. FGDC None Groundwater Availability of the Denver Basin Aquifer System, Colorado 2011 Paschke, S.S., editor U.S. Geological Survey Reston, VA publication U.S. Geological Survey Professional Paper PP 1770 274 p. https://doi.org/10.3133/pp1770 Version 6.2 (Build 9200) ; Esri ArcGIS 10.7.0.10450 true -105.2349 -103.9221 40.1529 38.7505 publication date 2011 The Denver Basin aquifer system is composed of Tertiary and Cretaceous sandstone bedrock aquifers that occur in the uppermost layers of the structural Denver Basin above the Cretaceous Pierre Shale confining layer. Colorado State legislation administrating the Denver Basin recognizes and defines four primary bedrock aquifers, two of which are subdivided into upper and lower units (Romero, 1976; Robson, 1987; Graham and VanSlyke, 2004). From oldest to youngest (bottom to top), the four primary units are the Laramie-Fox Hills aquifer, the Arapahoe aquifer, the Denver aquifer, and the Dawson aquifer. In parts of the basin, confining units further divide the Arapahoe and Dawson aquifers into upper and lower units. Thus, the six Denver Basin bedrock aquifers and five intervening confining units used to develop geologic layers for the groundwater flow model are, from oldest to youngest, the Laramie-Fox Hills aquifer (KLF), Laramie confining unit (KLC), lower Arapahoe aquifer (LKA), Arapahoe confining unit (KAC), upper Arapahoe aquifer (UKA), Denver lower confining unit (TKDLC), Denver aquifer (TKD), Denver upperconfining unit (TKDUC), lower Dawson aquifer (LTDW), Dawson confining unit (TDWC), and upper Dawson aquifer (UTKD). The synclinal structure of the Denver Basin causes the bedrock aquifer units to crop out in a ring pattern where the oldest rocks of the Laramie-Fox Hills aquifer crop out around the outer margins of the basin and the youngest rocks of the Dawson aquifer crop out in the center of the basin. Confined groundwater conditions generally are found in the bedrock aquifers where they are overlain by younger units, and unconfined groundwater conditions are generally found in outcrop areas. The hydrogeologic framework for the Denver Basin groundwater model consists of GIS data sets, which define the lateral extent and base altitude of each aquifer and confining unit represented in the model. For the aquifer units, maps of silt-plus-sand thickness also were developed and used as multipliers for hydraulic conductivity and specific yield in the groundwater flow model. This study modified maps showing the extent of aquifers and confining units published by the CDWR (VanSlyke and others, 1988a, 1988b, 1988c, 1988d) along the western basin margin to include geologic contacts mapped by Robson and others (1998), and the results defined the extent of active cells for each model layer. Topographic altitude data for land surface and streamflow routing were derived from the 30-meter-resolution National Elevation Dataset (NED) (U.S. Geological Survey, 1999). Maps of the altitude of the base of the bedrock aquifers and confining units and the silt-plus-sand thickness were generated in ArcGIS 9.2 (Environmental Systems Research Institute, Inc., 1999-2004) from the CDWR Denver Basin geophysical log database (Brian Ahrens, Colorado Division of Water Resources, written commun., 2003) using ordinary kriging and inverse-distance weighed (IDW) methods, depending on which method resulted in the least error. The CDWR geophysical-log database contains top and bottom elevations for each of the six bedrock aquifers (geophysical log "picks") for about 4,400 geophysical logs. The geophysical log picks were processed into ArcGIS point-data shapefiles representing the base altitude for each of the six bedrock aquifers and five confining units, and the altitude data points were contoured in ArcGIS. Contouring methods and model-fitting parameters are presented in Table A1 of Paschke (2011). The resulting point data and vector contour maps are listed in Table A2 of Paschke (2011) and are published herein as GIS datasets. The datasets are updated versions of the base-altitude maps published by the CDWR (VanSlyke and others, 1988a, 1988b, 1988c, 1988d), and interpretations of the data are discussed in the "Hydrogeologic Framework" section of Professional Paper 1770 Chapter A (Paschke, 2011). For many logs in the CDWR geophysical-log database, a silt-plus-sand thickness value was recorded for each bedrock aquifer. These silt-plus-sand-thickness values also were processed into ArcGIS point-data shapefiles, and the data points were contoured using either an ordinary kriging method or an IDW method available in ArcGIS, depending on which method resulted in the least error. The resulting point data and vector contour maps are published herein as GIS datasets and represent updated versions of the silt-plus-sand maps published by the CDWR (VanSlyke and others, 1988a, 1988b, 1988c, 1988d). Percent silt-plus-sand-thickness values were calculated from the silt-plus-sand-thickness point data for each of the six bedrock aquifers as the silt-plus-sand thickness divided by the total layer thickness, and the percent silt-plus-sand-thickness values were contoured using an IDW method available in ArcGIS. Averaged percent silt-plus-sand values for each model grid cell were used as multiplier arrays for hydraulic-conductivity and specific-yield values in the groundwater flow model as described in the "Hydrogeologic-Unit Properties" section of Professional Paper 1770 Chapter C (Paschke, 2011). References: Graham, Glenn, and VanSlyke, George, 2004, Development of the regulatory framework for Denver Basin aquifers: The Mountain Geologist, v. 41, no. 4, p. 153-160. Paschke, S.S., ed., 2011, Groundwater Availability of the Denver Basin aquifer system, Colorado, U.S. Geological Survey Professional Paper 1770, 274 p. Robson, S.G., 1987, Bedrock aquifers in the Denver Basin, Colorado-A quantitative water-resources appraisal: U.S. Geological Survey Professional Paper 1257, 73 p. Robson, S.G., Van Slyke, G., and Graham, G., 1998, Structure, outcrop, and subcrop of the bedrock aquifers along the western margin of the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA-742, scale 1:50,000, 5 sheets. Romero, J.C., 1976, Ground-water resources of the bedrock aquifers of the Denver Basin: Colorado Division of Water Resources Report, 109 p. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988a, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Dawson aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 1 (DBA-1), 3 plates. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988b, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Denver aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 2 (DBA-2), 3 plates. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988c, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Arapahoe aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 3 (DBA-3), 3 plates. VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 1988d, Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Laramie-Fox Hills aquifer, Denver Basin, Colorado: Colorado Division of Water Resources, Denver Basin Atlas no. 4 (DBA-4), 3 plates. 1 -105.234907 -103.922121 40.152888 38.750518 Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The use of firm, trade, or brand names in this report is for identification purposes only and does not constitute endorsement by the USGS. FGDC None All attempts were made to compare 100 percent of the digital attribute data to the original source database. Verification was done by visual and manual comparison, combined with on-screen review of the source with hard copy plots. In addition, Access queries were run to identify duplicate data. Errors resulting from the quality of the source map, the automation process and the scale resolution can affect the accuracy of the data. Verification was done by visual and maual comparison, combined with on-screen review of the source with copy plots. In addition, Access queries were run to identify duplicate data. Errors resultingfrom the quality of the source map, the automation process and the scale resolution can affect the accuracy of the data. feet No tests for topological consistency were made, however, all base-altitude contour datasets were derived using standard GIS interpolation methods (ordinary kriging) from a single source dataset. Point features are from digital data from Colorado Division of Water Resources and are complete for Denver Basin. This dataset is derived from a geophysical-log database developed by the Colorado State Engineer's office, Colorado Division of Water Resources. Source information for the database comes from paper files which were hand entered into a computer database. Potential well placement errors may be present where location information was inaccurate, unknown or incorrectly entered by automation processes. Contours derived from such data inherit the accuracy of the original well locations. Wells in the original Access database had locations recorded either as a Public Land Survey System (PLSS) description or as coordinates in the Universal Transverse Mercator (UTM) projection system, Zone 13 North. If they were available, the UTM coordinates were used for the well location. Well locations for which only a PLSS description was available are accurate to the quarter-quarter section in all but a few instances. Wells in this GIS dataset having only a PLSS location were located at the centroid of the quarter-quarter section described in the Access database. Vertical accuracy of the interpretation from geophysical logs of the altitude of the base of the unit is assumed to be good, but variable. Vertical accuracy cannot be assumed to exceed National Map Accuracy Standards for the scale each map is plotted. The vertical accuracy standard requires that the elevation of 90 percent of all points tested must be correct within half of the contour interval. On a map with a contour interval of 10 feet, the map must correctly show 90 percent of all points tested within 5 feet (1.5 meters) of the actual elevation. Vertical datum is the National Geodetic Vertical Datum of 1929 (NGVD 29). An Access database 'Den_Bas_Logs_2000.mdb' was provided to the U.S. Geological Survey by Colorado Division of Water Resources (Brian Ahrens, Colorado Division of Water Resources, written communication, 2003). The database contained geophysical log 'picks' for the tops and bottoms of aquifers and confining units in the Denver Basin. The database was queried, and the geophysical log picks were processed into point shapefiles, each of which represents the base altitude for six bedrock aquifers and five confining units in the Denver Basin aquifer system. Well location information provided in the original database was either in the form of a Public Land Survey System description or as a coordinate in Universal Transverse Mercator Zone 13 North. The dataset was projected into the Colorado State Plane Central Coordinate System (Lambert Conformal Conic, in feet), North American Datum of 1983. Usable wells were distinguished from wells with anomalous data or locations. Examples of such anomalies included wells missing top or base altitudes for units, negative elevation data, wells located outside the horizontal extent of the aquifer or confining layer, and wells with top or bottom values that were inconsistent with surrounding well values. Anomalous wells were not used for contouring or for subsequent data processing. 2006 Suzanne S. Paschke U.S. Geological Survey Hydrologist (303) 236-6904 (303) 236-4912 Denver Federal Center MS415 PO Box 25046 Lakewood CO 80225 US spaschke@usgs.gov Colorado Division of Water Resources, 2003 VanSlyke and others, 1988 A surface was interpolated from the data points for the base of the lower Arapahoe aquifer (PP_1770_alt_base_LKA_point.shp) using an ordinary kriging method. After this raster surface was made, 100-ft contours of the base of this unit were developed for the surface using the ArcToolbox contour tool. 2006-01-01 Suzanne S. Paschke U.S. Geological Survey Hydrologist (303) 236-6904 (303) 236-4912 Denver Federal Center MS415 PO Box 25046 Lakewood CO 80225 US spaschke@usgs.gov Boundary for extent of aquifer or confining unit 200 Geologic structure, sandstone/siltstone isolith, and location of non-tributary ground water for the Arapahoe aquifer, Denver Basin, Colorado VanSlyke and others, 1988 1988 Denver Basin Atlas no. 3 (DBA-3) VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A. Colorado Division of Water Resources Denver, CO vector digital data Denver Basin Atlas DBA-3 publication date 1988 The original database was in the form of a compact disk. The CD contains aquifer descriptions and interpretive data from geophysical logs for wells in the Denver Basin aquifer system. The format of the database is Microsoft Access. CDROM Geophysical-Log Database Colorado Division of Water Resources, 2003 2003 Colorado Division of Water Resources, Colorado State Engineers Office Access database database was obtained from Brian Ahrens, written communication, 2003. publication date 2003 0 1.0 PP1770_alt_base_LKA_con 002 3075590.962218 3441164.306719 1337790.789450 1844952.216112 1 0.000 Projected GCS_North_American_1983 Linear Unit: Foot_US (0.304801) NAD_1983_StatePlane_Colorado_Central_FIPS_0502_Feet <ProjectedCoordinateSystem xsi:type='typens:ProjectedCoordinateSystem' xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:typens='http://www.esri.com/schemas/ArcGIS/3.2.0'><WKT>PROJCS[&quot;NAD_1983_StatePlane_Colorado_Central_FIPS_0502_Feet&quot;,GEOGCS[&quot;GCS_North_American_1983&quot;,DATUM[&quot;D_North_American_1983&quot;,SPHEROID[&quot;GRS_1980&quot;,6378137.0,298.257222101]],PRIMEM[&quot;Greenwich&quot;,0.0],UNIT[&quot;Degree&quot;,0.0174532925199433]],PROJECTION[&quot;Lambert_Conformal_Conic&quot;],PARAMETER[&quot;False_Easting&quot;,3000000.000316083],PARAMETER[&quot;False_Northing&quot;,999999.999996],PARAMETER[&quot;Central_Meridian&quot;,-105.5],PARAMETER[&quot;Standard_Parallel_1&quot;,38.45],PARAMETER[&quot;Standard_Parallel_2&quot;,39.75],PARAMETER[&quot;Latitude_Of_Origin&quot;,37.83333333333334],UNIT[&quot;Foot_US&quot;,0.3048006096012192],AUTHORITY[&quot;EPSG&quot;,2232]]</WKT><XOrigin>-118767900</XOrigin><YOrigin>-94525500</YOrigin><XYScale>36985113.707064793</XYScale><ZOrigin>-100000</ZOrigin><ZScale>10000</ZScale><MOrigin>-100000</MOrigin><MScale>10000</MScale><XYTolerance>0.0032808333333333331</XYTolerance><ZTolerance>0.001</ZTolerance><MTolerance>0.001</MTolerance><HighPrecision>true</HighPrecision><WKID>102654</WKID><LatestWKID>2232</LatestWKID></ProjectedCoordinateSystem> 20240513 15353700 20240513 15353700 20240528 22165400 FALSE dataset EPSG 5.3(9.0.0)