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<br /> -40 <br />N <br />..... -50 <br />(0 <br />(0 <br /> -60 <br /> ...;l -70 <br /> """" <br /> ~ <br /> ~ -80 <br /> ~ <br /> ~ <br /> Z -90 <br /> """" <br /> ... <br /> ~ -100 <br /> tJO <br /> -110 <br /> -120 <br /> <br />N aftz and Spangler <br /> <br /> <br />, <br /> <br /> <br />.../'/ ~ ARID-ZONE <br />.... METEORIC <br />,/ WATER LINE <br />, 2. <br />. <br /> <br />//.6. . <br /> <br />/;i' <br /> <br />NORTH AMERICAN <br />METEORIC WATER ........... <br />LINE <br /> <br />b.. NA V AlO AQUIFER <br />V SAN JUAN RIVER <br />o ALLUVIAL AQUIFER <br />. OIL-FIELD BRINE-- <br />Number above symbol <br />refers to multiple samples <br /> <br />-130 <br />-1;8 -16 -14 -12 -10 -8 <br /> <br />-6 <br /> <br />-4 <br /> <br />-2 <br /> <br />o <br /> <br />2 <br /> <br />4 <br /> <br />(5180, IN PERMIL <br /> <br />the North American (Craig, 1961) and arid-zone <br />(Welch and Preissler, 1986) meteoric water lines (Fig- <br />ure 8). Most of the samples from the Navajo aquifer <br />with a 1)180 value less th'an ,13.5 permil plot close to <br />the North American me~eoric water line (Figure 8). <br />The isotopically light sigriature ofthese waters, which <br />plot above the arid-zone meteoric water line, reflects <br />the dominant contributio~ of recharge from snowmelt <br />in the high-elevation mouintain ranges adjacent to the <br />study area. As water from the Navajo aquifer becomes <br />isotopically enriched, thl! samples consistently fall <br />below the North American meteoric water line, char- <br />acteristic of mixing meteoric recharge water with iso- <br />topically enriched watei from an evaporite basin. <br />OFB samples collected in; the study area are isotopi- <br />cally enriched relative tolall other samples collected <br />in the study area and plot considerably below both <br />meteoric water lines, typical of water from Paradox <br />Formation evaporites that formed in a closed basin. <br /> <br />WATER RESOURCES BU4LETIN <br /> <br />, ,1 .1. <br /> <br />Figure 8. The S1S0 and SD Values from Ground- and Surface-Water Samples Collected in the Study <br />~rea Compared with the North American and Arid-Zone Meteoric Water Lines. <br /> <br />Water samples from the San Juan River and adja- <br />cent alluvium have similar isotopic values and plot <br />close to the North American meteoric water lille. The <br />slight variation in the two samples from the Sa:n Juan <br />River is caused by seasonal isotopic variatiolls. The <br />isotopically enriched sample was taken during <br />November and represents a larger component of iso- <br />topically enriched spring and summer precipitation <br />relative to the other sample taken in March, repre- <br />senting a larger component of isotopically lighter win, <br />ter precipitation. The water sample from the alluvium <br />has an isotopic composition midway between the two <br />river samples, representing the average isotopic com- <br />position of the San Juan River. <br />A mixing line was constructed to best fit the trend <br />shown by the isotopically enriched samples fr6m the <br />Navajo aquifer (graph A, Figure 9). The mixing line <br />has a smaller slope relative to the North Americlln <br />meteoric water line, indicative of mixing with a'highly <br /> <br />1130 <br /> <br />c,_~ w.,c..: ,_-~'';;'-",I.ii, <br /> <br /><-, <br /> <br />~; <br /> <br /> <br />r <br />f <br />, <br />t <br />I <br />(l <br />11 <br />J <br /> <br />" <br />! <br />:~l <br />:U <br />a <br />U <br />.~ <br />.~ <br /> <br />