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<br />
<br />Milos M. Novotny and William E. Sanford
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<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 H20 at STP.
<br />
<br /> Residence
<br /> Time TR EA
<br />Sample Aquifer [yr] rCl [cm2STP/g] X2
<br />DON-04 Arapahoe 8,000 9.8 3.9x10-3 3.14
<br />Pii-.J-02 Arapahoe >30,000 3.6 8.1 X 10-4 3.98
<br />PARK-01 Arapahoe 24,000 6.2 2 .6x1 0-3 0.38
<br />AUR-08 Arapahoe 22,000 3.9 4.2x10-3 1.98
<br />PARK-03 Denver 24,000 2.5 1Ax10-3 3.85
<br />AUR-07 Denver 23,000 7.8 1.9xlO-3 1.16
<br />
<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 />
<br />SUMMARY
<br />
<br />The use of environmental tracers, specifically l4C 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 l4C activ-
<br />ity has caused samples to appear 'old'.
<br />
<br />ACKNOWLEDGMENTS
<br />
<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 />
<br />The Rocky Mountain Association of Geologists
<br />
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