Laserfiche WebLink
Colorado Geological Survey <br />Table 6.1-I. Hydrogeologic units in the Denver Basin. <br /> Unit Saturated <br />Era System Series Stratieraphic Thickness . Physical Description Hydrogeologic <br />_ Thickness Hy droloA_ic Characteristics <br />_ <br /> Unit (feet) Unit (feet) <br /> Holocene Unconsolidated gravel, Unconfined, shallow aquifer; very permeable; yields as <br /> Quaternary <br />Pleistocene Alluvium 0-125 <br />sand, silt, and clay Alluvial aquifer 0-100 <br />high as 3,000 gpm <br /> <br />o <br />Oligocene Castle Rock <br />0-50 Fine to coarse arkosic sand <br />None <br />0 Exposed in cliffs; forms cap rock on buttes; well drained, <br /> <br />N Conglomerate stone and conglomerate does not yield water <br />o <br />C <br />Eocene Water table aquifer in shallow units, and confined at depth. <br /> <br />U Tertiary <br />d <br />l <br />ti <br />S <br />d <br />D <br />D <br />w <br />on Transmissivit ranges from 500-5,000 d/ft; storage <br /> Dawson stone an <br />cong <br />omera <br />c <br />an a <br />s <br /> Paleocene Formation <br />0-1,200 <br />with interbedded <br />sandstone <br />aquifer <br />0-400 <br />coefficients range from 0.002-0.009; specific yields vary <br /> <br />siltstone and shale I <br />from 15-25o; domestic water source and municipal supply <br /> for Castle Rock; may yield as much as 300 gpm <br /> <br /> Shale, silty claystone, and E Water table aquifer near outcrop area; generally confined; <br /> Denver interbedded sandstone; N Denver least permeable of Denver Basin aquifers; transmissivity <br /> <br />Formation 800-1,000 beds of lignite and carbona <br />aquifer 0-350 ranges from 250-2,000 gpolff; storage coefficient 0.002; <br /> ceous siltstone and shale specific yield 10-17%; domestic and municipal water <br /> common ?y source; yields up to 200 gpm <br /> Water table aquifer near outcrop area; generally con- <br /> <br />Arapahoe Sandstone, conglomeratic <br />Q Arapahoe fined; most permeable of Denver Basin aquifers; trans- <br /> Formation 400-700 sandstone, and interbedded <br />c 0--400 missiviry ranges from 500-5,000 gpd/ft; storage coeffi- <br /> shale and siltstone N aquifer cient 0.002-0.009; specific yield 10-25%; principal aquifer <br /> <br />o Cretaceous Upper m source for municipal water; yields up to 700 gpm <br /> <br />N Cretaceous <br /> Upper part shale, silty shale, y Laramie <br />v <br />E <br />Laramie siltstone, and interbedded fine > <br />e <br />confining <br />0-400 Shale is impermeable <br /> sandstone; bituminous coal w <br /> Formation 100-600 <br />seams common <br />p unit <br /> Lower part sandstone and Laramie Water table aquifer near outcrop area; generally confined; <br /> shale <br />Fox-Hills moderately permeable; transmissivity ranges from <br />ffi <br />i <br />t 0 <br />001 <br />ifi <br />1 <br />000 <br />7 <br />000 <br />d/ft' <br />t <br /> <br />aquifer 0-250 orage coe <br />c <br />en <br />. <br />; spec <br />, <br />- <br />, <br />gp <br />s <br />c <br /> Fox Hills <br />100-200 Sandstone and siltstone yield 15-20%; source for domestic and municipal water; <br /> Sandstone interbedded with shale <br />yields up to 350 gpm <br /> <br />Pierre Shale 4500- Shale, calcareous, silty, and Confining unit <br />S 0 Impermeable <br /> 7,000 dense. <br />Modified from Robson and Banta, 1995 <br />Arapahoe Fox Hills <br />Formation Laramie <br />For anon Sandstone <br />- PleneShale , <br />7000 m o"0 7000 <br /> C <br />A L N <br />Castle Rack Conglomerate ° <br />6000 <br />- ' 6000 <br /> -- r:?? ? c r .m„? 3 v <br /> <br /> <br />_ <br />- <br />Arapahoe <br />Laramie Fox Hills m <br />5000 ?? _- _ [ oF.,<< aflon Formation Formation Sandstone 16 <br />L7 5000 <br /> <br />4000 .' -"?__-' - ---- - <br /> <br />- <br />4000 <br /> Pierre Shale - - - <br /> - ° - I Shale <br />3000 3000 <br /> Venial exaggeration x 20 0 10 20 Mi Modified from Robson, 1967 <br />Figure 6.1-3. General geologic cross sections through the Denver Basin. Line of section is located in Figure 6.1-2. <br />LARIMER <br />Longmont <br />90ULDf, <br />a b.. 0['der ?, <br />0 <br />'it3IKSIN? <br />_ Ao,Atag. <br />v\ <br />A P A H 0 <br />w I fj a -L B E R <br />LL y° 0 Liman <br />Hugo <br />39' ?V... - ??.. 96• <br />?o <br />olorado •. <br />Springs <br />105• <br />LI NCoLN', <br />Fbano <br />i - <br />1c4° Modified from Denver Museum <br />EXPLANATION of Nature and Science, 1999 <br />Castle Rock Conglomerate Denver Formation Laramie Formation- <br />Fox Hills Sandstone <br />Dawson Formation Arapahoe Formation Pierre Shale <br />A-A' Line of section <br />Figure 6.1.2. Generalized Denver Basin bedrock geology. <br />The Denver Basin's asymmetrical bowl shape causes rock units <br />near the western edge to dip more steeply than rocks near the <br />eastern edge of the bas}n (Figure 6.1-3). The outcrop area of each <br />successively deeper aquifer becomes larger while maintaining the <br />basin's overall kidney shape. The center of the basin lies just west <br />of Parker, where the L4ramie-Fox Hills aquifer is approximately <br />3,000 feet deep. <br />Robson (1987) estimate that about 470 million acre-feet of water <br />are stored in the Denver Basin aquifer system. The actual amount <br />of recoverable water is significantly less due to physical and practi- <br />cal limitations. In 1985; as a part of the research done to support <br />Senate Bill 5, the Colorado Division of Water Resources (DWR) <br />estimated that approximately 300 million acre-feet of water was <br />potentially recoverable!