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<br />GR01....nwA11-:R RES/l1FSCE n\/E. ,-t\O RI'OHRCE n~IIPHUTl"RE E\TIIH11--S OF 11110 DEWEl< ASD .4RAP.-tilOf AQf1H.kl, DE..\l"f.R 8.4..\"/.\, COWR.'iDO
<br />
<br />Rl"Cha~e Temperature
<br />
<br />Tht' tCffipt'r.lturt" of rcchaT'Ring groundwatt"r, :10 approxi-
<br />mation of mean-annual air tempt'r.uure, can he estimJ.t...d
<br />from con("t"ntrJ,tion:-. of atmo~pheric nook 1l:1St".;. diS-.'iol\"(~d
<br />in groundw:Ul;'f using lht" general lempt'"ratllR"~as soluhil-
<br />ity rd:ltionship, Henry's Liw (e.g., ~tute el al., 1992;
<br />At"Sl.:hhadl-Henig t"1 aI., 1999). TIll' concentr.ltIons of int'rt
<br />Ra~s in gmundwater rt"sull from thl.:' lempt"r,llure- and
<br />pressure (de\';Hion)- ut:pcndent equihhration of w:Uer with
<br />the atmosphere, plus IhlO" addition of eXct's.'i air arising
<br />from dissolution of entr.Jined air huhhks h<:low the walef
<br />tahle (~tu!e and Schlosser, 200m, TIll.' excess air may be
<br />fr:Il..'1ionah."d due to partial dissolution or r""-t.'quilihr::uion of
<br />th.... gas (At'schhach-Hertig ...'1 :11.. 1999),
<br />\'ari:lIion in pak"Olempt'"ratllfes t'stim:ued from conn:n-
<br />trations of nohle WISl..'S su~...'st.... a templ..'r.\Iure suppression
<br />rangin~ from ;-9'C during the last gbci:11 period
<br />(Aeschbach-Hertig et al.. 10(0). :Sohle ga:-. tt"lllpcr.ltures in
<br />the south-centr31 and southwestern U.S, dllfin~ the \;I~t
<br />glacial period were approximatdr :;'C cookr th;1O
<br />Holon'ne tell1per.nur....~ (Stule t-'t ;II., 1991; Clark d al..
<br />199K), consistent with other c..timalt.'s of l'ontinl..'ntal tem-
<br />per.Hure change and local gbcial-clinutt" recunstmctions
<br />(.\1uhs et a!., 1(99).
<br />
<br />METHODS
<br />
<br />Samplin~
<br />
<br />Six samples wefe l'ollectnl from kx:;lliun.'i that lie along
<br />a tr.mseCl p;lr:illld to the pre...urneu mOlkrn ,!o:fuundw3tl:'r
<br />now palh heginnin~ ne;lr tilt' sOllth...'rn oulcrop of the
<br />~Iquifer:'o (Fi~, 1), 111t' ,~Jmple.~ were uJlleckd from ground-
<br />watt'r of the Ar.:lpaho... and Denver aquifer;, nt'ar P:lfker.
<br />Colorado during the ~pring of 2001 ;lnd ne:lr Aurora anu
<br />[xlOala (n..."ar Colorado ~prings), Colur.Jdo durinll the
<br />~pring of 2(X~5 I Tahle I). One,liwr \Vatl..'r :'oampiL's Wt're
<br />analyzlO"d for dh.~olved inorganic ...';\fl-xm (DIC) i."-OlOpes hy
<br />atomic mas...-sp...'cuomcuy al Ikt:1 :\nal}"tical LIhs, Ih:;,ults
<br />of DiC :Illaly~i;, .Ire fl..'pOI"tl'd in pcf('....nt mOl!...'rn Glrhon
<br />(POlO for HC and delta l3-culxlO per mil \l-'DB IOl:lC '%0)
<br />for rdati\"(~ UC/l~C. S~lmpks for di:'o~oln.d !o(.IS analy~es
<br />w...'re collected follo\ving Ihc prolOcol outlmed hy :-o.l.:mning
<br />et a!. (2()()3) :md were an:llyzt--d hy the :'\ohk- Gas Llhora-
<br />{{)IT at the Univt'rslty of ('tah for 2li.,\~ .i~02' 211:\'e. lilAr,
<br />l'>IKr. .~Ht' anJ\He. Results of the Ji......olv'ed g.ls ;lOalysis arc
<br />r""p<lrted in mol.lr-fraction (unit-less) and precision of mea-
<br />surement.'i i.-; a f...,\\ iX'rn:nL Additional fidd mea:-.tIfemenl<,
<br />of fempt'"ratun~ IT) ;lml tot:lI Jissolwd gas pn5Sure (PllX,)
<br />of the groundwater were made. :\ lktailcd dcsLriplion of
<br />the samplin,g prol..'edure :Ind ;lIlaly"i" may IX' found in
<br />:'\:o\'otny (2rxH~.
<br />
<br />A 0
<br />
<br />20
<br />
<br />i:L...
<br />
<br />, "
<br />
<br />
<br />LEGEND
<br />o SampleLocebOf1
<br />o AtlurferOulcrop
<br />UrbanAloa
<br />
<br />Pot.ntrom.tric: Surtac:.:
<br />Incremel'1lsofl00!'l1l'om
<br />hi9" (dal'k) 10 low (l9ht)
<br />surfaceCO'llOU'
<br />
<br />figure 1, General locations of groundwatPf samples with 197B
<br />pOlentiOmetric surface of Arapahoe aquifer (Robson, 1987) for
<br />reference.
<br />
<br />Carbon-14 Activity Dilution and Determination of
<br />Residence Time
<br />
<br />Additional sources of carl-xm exist in most ;Iquifcrs and
<br />("'.In t:au'\t" dilUlion of thc !-IC acth-ilY. nu:rd(m:~. a corret:-
<br />[ion for tht" interal'1ion of thest.' SOtlfCI:'S with grollndwatl'r
<br />wa~ :Jpplk'd prior 10 Ihe cakubtion of resid....nn: time. Cor-
<br />rection mt'th(xb in\"olving mas..'i-habnce of oC/t!C (e,g.,
<br />Pcarson and Swar;;enki. 1<)74) wt"rt' not u-.ed; ratios of
<br />thes...' j'i010jkS in lhe potential SOtlft:l'.~ of carbon in Ihe
<br />aquifer:-. and rechargt" arca :Ire not known J.nd the infer-
<br />ence of theSl' from other information i.... unrdiahle.
<br />ReSOtlfl'es wert" unJ\'ailahle for i"otopk-exdl:Jn~e or reac-
<br />tion path motlds, and'iO thes...' melhod~ wt"re not u,'iI.:'d. :\
<br />non-~ite-spt:cific l'mpirit:ally-deri\"ed dilution quollcnt
<br />equal [0 OB; of the inilial ~roundwat...'r sample acti\'ity was
<br />used IU correct the HC ani\'i!ies 1 Vogel, 19-0). while lhis
<br />corre...1ion does not physkally reprt".~l'nt He dilution in the
<br />aquifers, other n~~earch indicatt's that Jifft"rcncl:'" betwel..'n
<br />thb ~impll..', empirical correuion :llld more sophisticlll"<.i
<br />approaches are not si!o!nilk':lllt in the lower Tertia!"}'
<br />;lquifl:'r~ of the ~;In JU,1O Basin (Phillips l'[ aI., 19H9l, a
<br />hytlrogeologlc and hydroch...'mical selling "lmil:tr to the
<br />Ar:Jp:.lhOl' and Den\"(:r aquifers
<br />
<br />163
<br />
<br />The Roc~~ \Iounl:un A"""OJhon "r G""loJ.:,>I,
<br />
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