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Milos M. Novotny and William E. Sanford
<br />Table 4.
<br />Carbon -14 residence times and results of recharge temperature model for groundwater samples of the Denver Basin, Colorado;
<br />objective function of noble gas model (x2); excess air component (EA) reported as cm2 gas per gram H2O at STR
<br />locally in the aquifers, movement of younger Holocene
<br />groundwater through the complex architecture of the allu-
<br />vial sediments comprising the aquifers may occur, espe-
<br />cially in areas with significant drawdown such as Parker
<br />and Aurora.
<br />SUMMARY
<br />The use of environmental tracers, specifically 14C and
<br />noble gases, benefits the characterization of groundwater
<br />flow in the Denver Basin, especially as a calibration para-
<br />meter for a revised groundwater model. The results can be
<br />loosely viewed as maximum residence times of those
<br />groundwater samples. Recharge temperatures are directly
<br />related to residence times, with the younger waters being
<br />recharged at warmer temperatures than the older waters,
<br />consistent with the older water being recharged during the
<br />last glaciation. The relationship of estimated recharge tem-
<br />peratures and residence times to climate record suggests
<br />there may be a significant component of Holocene
<br />groundwater in some samples or that dilution of 14C activ-
<br />ity has caused samples to appear `old'.
<br />ACKNOWLEDGMENTS
<br />The authors acknowledge all who provided assistance
<br />in this work, especially Dr. Robert Raynolds who was able
<br />to provide research support through the Denver Museum
<br />of Nature & Science, and Dr. Andrew Manning of the
<br />United States Geological Survey who was generous in
<br />sharing knowledge regarding noble gas modeling. Grati-
<br />tude is also extended to the municipalities of Parker,
<br />Aurora, The Pinery and Donala; the Colorado Water Con-
<br />servation Board; Colorado Division of Water Resources;
<br />and the Cherry Creek Valley Water Authority.
<br />The Rocky Mountain Association of Geologists 166
<br />REFERENCES
<br />Aeschbach - Hertig, W., F. Peeters, U. Beyerle, and R. Kipfer, 1999,
<br />Interpretation of dissolved atmospheric noble gases: Water
<br />Resources Research, v. 35, p. 2779 -2792.
<br />Aeschbach - Hertig, W., F. Peeters, U. Beyerle, and R. Kipfer, 2000,
<br />Palaeotemperature reconstruction from noble gases in ground
<br />water taking into account equilibration with entrapped air:
<br />Nature, v. 405, p. 1040 -1044.
<br />Clark, I. D., and P. Fritz, 1997, Environmental isotopes in hydro -
<br />geology: Ottawa, Canada, Lewis Publishers, 328 p.
<br />Clark, J. F., M. L. Davisson, G. B. Hudson, and P. A. Macfarlane,
<br />1998, Noble gases, stable isotopes and radiocarbon as tracers
<br />of flow in the Dakota aquifer, Colorado and Kansas: Journal of
<br />Hydrology, v. 211, p. 151 -167.
<br />Crifasi, R. R., 1992, Alluvial architecture of Laramide orogenic sed-
<br />iments: Denver Basin, Colorado: The Mountain Geologist, v.
<br />29, p. 19 -27.
<br />Custodio, E., 2002, Aquifer overexploitation: what does it mean ?:
<br />Hydrogeology Journal, v. 10, p. 254 -277.
<br />Hansen, W. R., J. Chronic, and J. Matelock, 1978, Climatography
<br />of the Front Range urban corridor and vicinity, Colorado,
<br />Washington, D.C., USGS, p. 59.
<br />Manning, A. H., and D. K. Solomon, 2003, Using noble gases to
<br />investigate mountain -front recharge: Journal of Hydrology, v.
<br />275, p. 194 -207.
<br />Manning, A. H., D. K. Solomom, and A. L. Sheldon, 2003, Appli-
<br />cations of a total dissolved gas pressure probe in groundwater
<br />Studies: Groundwater, v. 41, p. 440 -448.
<br />Muhs, D. R., J. N. Aleinikoff, T. W. Stafford Jr., R. Kihl, J. Been, S.
<br />A. Mahan, and S. Cowherd, 1999, Late Quaternary loess in
<br />northeastern Colorado: Part I - Age and paleoclimatic signifi-
<br />cance: GSA Bulletin, v. 111, p. 1861 -1875.
<br />National Oceanic and Atmospheric Administration, 2002, mean
<br />annual temperature, Colorado Springs, 1948 -2001,
<br /><http: / /www.noaa.gov /pub /climate /cosann.htm> Accessed
<br />July 2002.
<br />Novotny, M. M., 2004, A preliminary study of dissolved noble
<br />gases and carbon -14 in groundwater of the principal bedrock
<br />aquifers, Denver Basin, Colorado, Master's thesis, Colorado
<br />State University, Fort Collins, 105 p.
<br />Residence
<br />Time
<br />TR
<br />EA
<br />Sample
<br />Aquifer
<br />[yr]
<br />1,C]
<br />[cm2STP /g]
<br />x2
<br />DON -04
<br />Arapahoe
<br />81000
<br />9.8
<br />3.9x10-3
<br />3.14
<br />PIN -02
<br />Arapahoe
<br />>30,000
<br />3.6
<br />8.1 x10-4
<br />3.98
<br />PARK -01
<br />Arapahoe
<br />24,000
<br />6.2
<br />2.6x10-3
<br />0.38
<br />AU R -08
<br />Arapahoe
<br />22,000
<br />3.9
<br />4.2x10-3
<br />1.98
<br />PARK -03
<br />Denver
<br />24,000
<br />2.5
<br />1.4x10-3
<br />3.85
<br />AU R -07
<br />Denver
<br />23,000
<br />7.8
<br />1.9x10-3
<br />1.16
<br />locally in the aquifers, movement of younger Holocene
<br />groundwater through the complex architecture of the allu-
<br />vial sediments comprising the aquifers may occur, espe-
<br />cially in areas with significant drawdown such as Parker
<br />and Aurora.
<br />SUMMARY
<br />The use of environmental tracers, specifically 14C and
<br />noble gases, benefits the characterization of groundwater
<br />flow in the Denver Basin, especially as a calibration para-
<br />meter for a revised groundwater model. The results can be
<br />loosely viewed as maximum residence times of those
<br />groundwater samples. Recharge temperatures are directly
<br />related to residence times, with the younger waters being
<br />recharged at warmer temperatures than the older waters,
<br />consistent with the older water being recharged during the
<br />last glaciation. The relationship of estimated recharge tem-
<br />peratures and residence times to climate record suggests
<br />there may be a significant component of Holocene
<br />groundwater in some samples or that dilution of 14C activ-
<br />ity has caused samples to appear `old'.
<br />ACKNOWLEDGMENTS
<br />The authors acknowledge all who provided assistance
<br />in this work, especially Dr. Robert Raynolds who was able
<br />to provide research support through the Denver Museum
<br />of Nature & Science, and Dr. Andrew Manning of the
<br />United States Geological Survey who was generous in
<br />sharing knowledge regarding noble gas modeling. Grati-
<br />tude is also extended to the municipalities of Parker,
<br />Aurora, The Pinery and Donala; the Colorado Water Con-
<br />servation Board; Colorado Division of Water Resources;
<br />and the Cherry Creek Valley Water Authority.
<br />The Rocky Mountain Association of Geologists 166
<br />REFERENCES
<br />Aeschbach - Hertig, W., F. Peeters, U. Beyerle, and R. Kipfer, 1999,
<br />Interpretation of dissolved atmospheric noble gases: Water
<br />Resources Research, v. 35, p. 2779 -2792.
<br />Aeschbach - Hertig, W., F. Peeters, U. Beyerle, and R. Kipfer, 2000,
<br />Palaeotemperature reconstruction from noble gases in ground
<br />water taking into account equilibration with entrapped air:
<br />Nature, v. 405, p. 1040 -1044.
<br />Clark, I. D., and P. Fritz, 1997, Environmental isotopes in hydro -
<br />geology: Ottawa, Canada, Lewis Publishers, 328 p.
<br />Clark, J. F., M. L. Davisson, G. B. Hudson, and P. A. Macfarlane,
<br />1998, Noble gases, stable isotopes and radiocarbon as tracers
<br />of flow in the Dakota aquifer, Colorado and Kansas: Journal of
<br />Hydrology, v. 211, p. 151 -167.
<br />Crifasi, R. R., 1992, Alluvial architecture of Laramide orogenic sed-
<br />iments: Denver Basin, Colorado: The Mountain Geologist, v.
<br />29, p. 19 -27.
<br />Custodio, E., 2002, Aquifer overexploitation: what does it mean ?:
<br />Hydrogeology Journal, v. 10, p. 254 -277.
<br />Hansen, W. R., J. Chronic, and J. Matelock, 1978, Climatography
<br />of the Front Range urban corridor and vicinity, Colorado,
<br />Washington, D.C., USGS, p. 59.
<br />Manning, A. H., and D. K. Solomon, 2003, Using noble gases to
<br />investigate mountain -front recharge: Journal of Hydrology, v.
<br />275, p. 194 -207.
<br />Manning, A. H., D. K. Solomom, and A. L. Sheldon, 2003, Appli-
<br />cations of a total dissolved gas pressure probe in groundwater
<br />Studies: Groundwater, v. 41, p. 440 -448.
<br />Muhs, D. R., J. N. Aleinikoff, T. W. Stafford Jr., R. Kihl, J. Been, S.
<br />A. Mahan, and S. Cowherd, 1999, Late Quaternary loess in
<br />northeastern Colorado: Part I - Age and paleoclimatic signifi-
<br />cance: GSA Bulletin, v. 111, p. 1861 -1875.
<br />National Oceanic and Atmospheric Administration, 2002, mean
<br />annual temperature, Colorado Springs, 1948 -2001,
<br /><http: / /www.noaa.gov /pub /climate /cosann.htm> Accessed
<br />July 2002.
<br />Novotny, M. M., 2004, A preliminary study of dissolved noble
<br />gases and carbon -14 in groundwater of the principal bedrock
<br />aquifers, Denver Basin, Colorado, Master's thesis, Colorado
<br />State University, Fort Collins, 105 p.
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