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<br />N aftz and Spangler <br /> <br />ratio of 0.001, substanitialIy less than the modern <br />ocean-water value of 0.00344. In contrast, samples of <br />OFB are generally enriched in bromide relative to <br />N modern ocean water. Thil average bromide-to-chloride <br />~ ratio for the nine OFB'samples is 0.014, indicating <br />CD the influence of organic imaterial on the OFB waters. <br />01 'lbtal organic carbon (TqC) concentrations from five of <br />the OFB samples rangeq from 5.2 to 180 mg/L. <br />The bromide-to-chl~ride weight ratios of four <br />potential groups of end-member waters, plotted with <br />chloride concentrations,' are shown in Figure 5. The <br />four groups of end-member waters are defined as fol- <br />lows: (1) uncontaminated and upgradient water from <br />the Navajo aquifer, defirled by chloride concentrations <br />less than or equal to 6Q mg/kg; (2) OFB water from <br />the Paradox Formation,' in and adjacent to the study <br />area; (3) non-OFB water!from the Paradox Formation, <br />northeast of the study area; and (4) injection water <br />composed of a 50/50 mixlture of alluvial aquifer water <br />and OFB water. In ord~r to work with ratio values <br />larger than 1, the weight ratios are multiplied by <br />10,000. <br />Significant differenceS between the brine end-mem- <br />ber waters are shown in !Figure 5. The three non-OFB <br />samples from the ParadOx Formation have small bro- <br />mide-to-chloride weight !ratios that are less than 10. <br /> <br />In contrast, the nine OFB water s;lmples from the <br />Paradox Formation in and adjacent to the stlldy area <br />have bromide-to,chloride weight ratios much larger <br />than 10. Bromide-to-chloride weight ratios that <br />exceed 10 are typical of other OFBs in the United. <br />States and probably reflect decomposition of bromide- <br />enriched organic matter associated with oil reservoirs <br />(Whittemore, 1988). <br />Salinization of the water from the NavajO aquifer <br />with either of the brine end-member water.s or the <br />injection waters may be reflected in the direction of <br />change in the bromide-to-chloride weight ratio as the <br />chloride concentration increases. Salinization of low <br />chloride concentration (less than or equal to 60 <br />mg/kg) water from the Navajo aquifer with OFB <br />water would produce a water with equal or larger bro- <br />mide-to-chloride weight ratios (Figure 5). On the basis <br />of the bromide-to-chloride ratios of non-OFB waters <br />outside of the study area, salinization. of water from <br />the Navajo aquifer with non-OFB water would pro- <br />duce a water with smaller bromide-to-chloride weight <br />ratios (Figure 5). <br />A series of mixing models were constructed using <br />various bromide-to-chloride weight ratios of the <br />previously defined end-member waters to determine <br />which saline end-member may be contributing to the <br /> <br /> <br /> <br /> <br />~~ 1,000 t:J.. NAVAJO AQUIFER <br /> 'i1 SAN JUAN RIVER <br /> 0 ALLUVIAL AQUIFER <br />OD 100 . OIL-FIELD BRINE <br />~~ 0 NON-OIL-FIELD BRINE-- <br />10 Number above symbol <br />ffi~ refers to multiple samples <br />urf MODERN STANDARD <br />ZCI) 1 <br />~3 MEAN OCEAN WATER <br />0.1 <br />n t:J.. t:J.. <br /> t:J.. <br />0.01 <br />~ <br /> <br />0.001 <br />1 . 10 100 1,000 10,000 100,000 1;000,000 <br />CHLORIDE CONCENTRATION, IN MILLIGRAMS PER KILOGRAM <br /> <br />Figure 4. ~romide and Chloride Concentrations in Ground- and Surface-Water Samples Compared <br />with the Bromide-ta-Chloride Weight Ratio of Modern Standard Mean Ocean Water. ' <br /> <br />WATER RESOURCES BULLETIN <br /> <br />1126 <br /> <br /> <br />"."'''''--''.-,<-< . <br /> <br />,~ " 4.",' :,_", <br /> <br />'_.,~- <br />