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<br />. . <br /> <br />N <br />N <br />o <br />en <br /> <br />USING HAIj,OGEN RATIOS AND ISOTOPIC SIGNATURES TO EV ALUA TE <br />THE EFFIQIENCY OF ON-GOING SALINITY REDUCTION PROJECTS IN <br />THE COLQRADO RIVER BASIN <br /> <br />J <br />)'j <br />,,1 <br /> <br />,), <br /> <br />i <br /> <br />Prepared by U,S, Geological Survey/Utah District <br /> <br />I. Introductlon <br />To date (199$), there has been limited information on how efficient salinity control <br />projects in the Colorado River basin have been. Halogen (bromide-to-chloride and iodide- <br />to-chloride) ratios and isotopic (strontium, boron, oxygen, sulphur, uranium, and lithium) <br />values can provide very distinct "chemical fingerprints" that can be used to identify and <br />monitor the proportion of salt load from various salinity control projects into the Colorado <br />River system, The halogen ratio or isotopic value difference between a saline source water <br />and the receihng water can be much larger than the difference in dissolved-solids <br />concentration (Fig. I). Larger differences in end-member compositions can then be used <br />to more accutately evaluate the efficiency of salinity reduction projects in longer <br />downstream reaches than would be possible using only major-ion chemical composition, <br />Isotopic vall\es are not related to concentration; therefore, they can provide an <br />independent check on mass balance. Finally, distinct chemical fingerprints from individual <br />salinity control projects could potentially be used to evaluate cumulative efficiencies at <br />downstream stations, This differentiation in salinity sources would not be possible using <br />only dissolved-solids concentration. <br /> <br />:-"! <br /> <br />J <br /> <br />II. Objectives <br />The overall objective is to determine salt load reduction resulting from on-going salinity <br />control proje'cts and establish a means of evaluating future projects in the Colorado River <br />Basin, Specific objectives are to utilize halogen concentrations and selected isotopes at <br />two ongoing 'Salinity control projects to (I) chemically "fingerprint" salinity sources in <br />discharging and receiving waters and (2) monitor the success of salt-load reductions at <br />downstream gages. <br /> <br />III. GeneraUzed approach <br />Two ongoing salinity control projects will be selected. Favorable characteristics for <br />selection will inGlude large potential differences in the geochemical signature between end- <br />member wat~r samples and location of existing USGS gaging stations. End-member water <br />samples, including saline sources and upstream and downstream receiving sources, will be <br />analyzed fodselected chemical and isotopic constituents (possibly including bromide, <br />chloride, iodide, and selected isotopes of strontium, boron, oxygen, sulphur, uranium, and <br />lithium) during baseflow conditions as well as during runoff events prior to the initiation of <br />the salinity control project. Discharge will be measured during sample collection. <br /> <br />, <br />J <br />,}j; <br /> <br />After this initial sampling program, the geochemical constituent(s) representing the largest <br />differences ih end-member compositions will be selected and included in a monitoring <br />program at gaged sites located immediately upstream and downstream of the salinity <br />control proj~cts. The monitoring data will be input into mixing models to quantitatively <br />evaluate the success of the salinity control project over a selected time period. <br /> <br />, <br /> <br />