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the long-term TDS trend at this well. Also, the value observed at this <br />well was determined gravimetrically (i.e., dry a water sample and weigh <br />the residue). According to Hem (1989, pg. 157), "... it is not uncommon <br />for water high in calcium and sulfate concentrations to yield a residue <br />after drying an hour at 180°C that exceeds the computed dissolved solids <br />by several hundred milligrams per liter" and also, "In many instances, <br />especially if the concentration is greater than 1000 mg/1, the <br />calculated dissolved-solids value may be preferable to the residue-on- <br />evaporation value". The calculated dissolved solids value is determined <br />by adding up all the concentrations for all of the various dissolved <br />constituents. The calculated TDS value for this well was 2530 mg/1, <br />which exceeds the PHC predicted value by 24°s. <br />At Grassy Creek alluvial well YGAL15, the TDS value observed in May was <br />5470 mg/1 (5190 mg/1 calculated). This value exceeds the predicted value <br />of 3548 mg/1 by 54%. However, the TDS value observed in May upstream at <br />Well YGAL16 (Pond 011 alluvium), was only 1340 mg/1. Since Pond 011 is <br />the only discharge coming from the Yoast Mine into this portion of <br />Grassy Creek, the elevated TDS values at Well YGAL15 must have a source <br />other than Yoast Mine discharges. <br />At Sage Creek alluvial well YSAL1, the TDS value observed in May was <br />1230 mg/1 (1200 mg/1 calculated). This value exceeds the predicted value <br />of 798 mg/1 by 54%. However, the TDS value observed in May upstream at <br />Well YSAL3 (directly below Pond 012), was only 1030 mg/1, which exceeds <br />the predicted value by 29%. <br />Surface Water <br />A summary of surface water sites is provided in Table 7. Stream <br />monitoring occurs on Sage Creek at Sites YSSF3 and YSS2, and on Grassy <br />Creek at Sites YSGF5 and YSGS. These surface water sites are monitored <br />triannually for flow and field parameters (pH, temperature, and <br />electrical conductivity [EC]) NPDES Discharge Points 013 and 014 are <br />monitored weekly for flow and pH. All five NPDES sites are monitored <br />monthly for NPDES parameters and field parameters. Samples obtained at <br />8 <br />