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• indicates, and not what the individual values observed are, More data <br />will be needed to determine the long-term TDS trend at this well. Also, <br />the 950 mg/1 value observed at this well was determined gravimetrically <br />(i.e., dry a water sample and weigh the residue). According to Hem <br />(1989, pg. 157), .,. it is not uncommon for water high in calcium and <br />sulfate concentrations to yield a residue after drying an hour at 180°C <br />that exceeds the computed dissolved solids by several hundred milligrams <br />pex liter" and also, "In many instances, especially if.the concentration <br />is greater than 1000 mg/1, the calculated dissolved-solids value may be <br />preferable to the residue-on-evaporation value". The calculated <br />dissolved solids value is determined by adding up all the concentrations <br />for all of the various dissolved constituents. The, cal cula ted~TDS value <br />for this well was 922 mg/1, which exceeds the PHC predicted value by <br />only 159. <br />At Armand Draw alluvial well YAAL19, the TDS value observed in May was <br />3080 mg/1 gxavimetric (3030 mg/1 calculated(. The gravimetric value <br />exceeds the predicted value of 2036 mg/1 by SlB. This increase may be <br />caused by the same climatic conditions noted in the previous paragraph. <br />At Grassy Creek alluvial well YGAL15, the TDS value observed in May was <br />4950 mg/1. However, TDS value observed in May upstream at Well YGAL16 <br />(NPDESII alluvium) was only 720 mg/1. Since NPDESII is the only <br />discharge coming from the Yoast Mine into this portion of Grassy Creek, <br />the elevated TDS values at Well YGAL15 must have a source other than <br />Yoast Mine discharges. <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 Y552, and on Grassy <br />Creek at Sites YSGFS and YSGS. These surface water sites are monitored <br />monthly (March to October) for flow and field parameters (pH, <br />temperature, and electrical conductivity (EC]). NPDES Discharge Point <br />• 012 is monitored weekly for flow and pH. All three NPDES sites are <br />monitored monthly for NPDES parameters and field parameters. Samples <br />9 <br />