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UJlI5J~ . CHLORIDE MASS BALANCE USING HYPERBOLIC MIXING MODEL IS IN GOOD AGREEMENT WITH MEASURED CONCENTRATIONS The 1)"Sr value and strontium concentration from 47 water samples from the Navajo aquifer and 5 samples of OFB were compared with the 4 constructed mixing lines. The mixing lines generally match the observed trends along flow paths I and 2 using water from the Upper Paleozoic aquifer as the source of salinity. The two mixing lines constructed using wells along flow path I (N I and N48) fit the observed trend of decreasing 1)"$r with increasing strontium concentration. The two mixing lines constructed using wells along flow path 2 (N38 and N44) also match the observed trend of increasing 1)"Sr with increasing strontium concentration. Estimated mixing ratios (water from the Upper Paleozoic aquifer:water from well N38) for wells plotting on the well N38 mixing line range from less than I :greater than 99 to 65:35 (vol:vol). The N48 and N38 mix lines were used to estimate mixing proportions between the Navajo aquifer end-member and Upper Paleozoic aquifer end-member water in potentially effected wells completed in the Navajo aquifer (table below). Mixing proportions estimated from the 1)"$r models were then used to calculate the chloride concentration expected in the affected wells. In general. calculated and measured chloride concentration in the effected wells are in close agreement (table below). With the exception of two sites, the calculated chloride concentration agreed within :!: 40 percent to :!: 15 percent of the measured cWoride concentration. This agreement between predicted and measured chloride concentrations provides an independent line of evidence supporting the hypothesis that water from the Upper Paleozoic aquifer may be the source of salinity in the Navajo aquifer. . Table . Proportion of injection water determined from the 087 Sr isotopic mixing models compared with measured and calculated chloride concentrations in water from two weLLs completed in the Navajo aquifer. [chloride concentration in milligrams per liter) Sample site Percent water from Up- per Paleo- zoic aquifer Percent fresh water Calculated chloride con- Measured centrationfrom chloride 1)"Sr mixing concentration model N2 N50 N52 N23 2 7 12 34 Well N48 mix line 98 190 93 520 88 1.100 66 1,200 140 420 710 2,000 . N39 N41 N46 N42 N35 N34 1.5 4 25 35 51 65 Well N38 mix line 98.5 130 96 100 75 1,100 65 890 49 3,600 35 3,200 110 250 1,500 2.000 3,000 3.800 Aneth Progress Report--February 1995