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At Annand Draw alluvial well YAAL14, the TDS value observed in May was • <br />2820 mg/1. This value exceeds the predicted value of 2036 mg/1 by 39~. <br />The PHC predictions are based on long-term average values. Individual <br />TDS measurements will vary from year to year due to climatic conditions. <br />Precipitation values were below average in previous years. What is <br />important is what the long-term trend indicates, and not what the <br />individual values observed are. More data will be needed to determine <br />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 2710 mg/1, <br />which exceeds the PHC predicted value by 33~. <br />At Grassy Creek alluvial well YGAL15, the TDS value observed in May was <br />5350 mg/1 (5110 mg/1 calculated). This value exceeds the predicted value <br />of 3548 mgll by 51$. However, TDS value observed in May, upstream at <br />Well YGAL16 (NPDESll alluvium), was only 1130 mg/1. Since NPDESII is the <br />only discharge coming from the Yoast Mine into this portion of Grassy <br />Creek, the elevated TDS values at Well YGAL15 must have a source other <br />than 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 YSS2, and on Grassy <br />Creek at Sites YSGFS and YSGS. These surface water sites are monitored <br />monthly (April to October), or triannually, for flow and field <br />parameters (pH, temperature, and electrical conductivity [EC]). NPDES • <br />Discharge Points 012, 013 and 014 are monitored weekly for flow and pH. <br />9 <br />