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<br />b, <br /> <br />e <br /> <br />e <br /> <br />~ <br /> <br />Salinitv Monitorin~ and Decision MakinR Process in Support of Minute 242 <br /> <br />The goal or objective of Minute 242 is to maintain a salinity differential <br />between the flew arriving at Imperial Dam and the flow crossing the Northerly <br />International B(,undary (NIB) with Mexico. This differential cannot exceed an <br />annual average of 115 plus or minus 30 parts per million (ppm) total dissolved <br />solids (TDS). To meet this goal or objective, the Bureau of Reclamation <br />(Reclamation) and International Boundary and Water Commission (IBWC) monitor <br />the flow and salinity at Imperial Dam and NIB. A description of the <br />assumptions used in calculating the salinity differential, the monitoring, and <br />possible actions that can be taken to assure that the goals of Minute 242 are <br />met (prior to full Yuma D~salting Plant operation) are provided below. <br /> <br />The differential is-calculated as the difference (NIB - Imperial Dam) of flow <br />weighted average annual salinity values for the calendar year. The monthly <br />flow weighted salinity values are calculated as the summation of the product <br />(Q x PPM) obtained from the flow times the salinity for each day, divided by <br />the summation of the flow for the month. The summation of the flow and of the <br />flow times salinity is in turn accumulated for the calendar year. The flow <br />weighted average annual salinity value is this annual summation of flow times <br />salinity divided by the summation of flow for the calendar year. <br /> <br />The objective differential is 115 pprn for the year. Actions are not expected <br />to be taken until the annual differential is projected to be above the maximum <br />allowable value of 145 (115 + 30) pprn. Any actions that might be taken would <br />have the objective of providing an annual salinity differential of no less than <br />115 ppm and no greater than 145 ppm. Daily and monthly differentials may <br />exceed 145 ppm. <br /> <br />At Imperial Dam, flow is measured by the United States Geological Su~vey (USGS) <br />and daily water samples are collected by the Imperial Irrigation District. At <br />NIB, the IBWC measures flow and collects daily water samples (excluding <br />holidays and weekends). The water samples are analyzed at the Reclamation <br />contract laboratory at the Yuma Desalting Plant in Yuma, Arizona. Reclamation <br />and IBWG perso~~el monitor electrical conductivity (EG) on a daily basis, and <br />the laboratory personnel perform a complete chemical analysis, including TDS by <br />evaporation and summation of ions, on the first and third Mondays of each <br />month. The TDS value from the summation of ions is used for the differential <br />calculaticn made by Reclamation using approximately 1/2 the bicarbonate value. <br /> <br />The salinity values for each day are computed from daily flow and EC <br />measurements converted to TDS with a conversion factor (EG to TDS) calculated <br />from the complete laboratory analyses. The calculations for the EC to IDS <br />factor and monthly salinity value are coordinated ~ith IB~C to assure a <br />consistent record. <br /> <br />At present, two tools are used by Reclamation to project the salinity <br />differential for the coming year. These are a FORTRAN program known as <br />