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area surrounding Yoast, ground water is not being pumped for irrigation <br />or livestock watering purposes, nor has the CDOH classified any aquifer <br />in this region for any use. The above discussion is provided only to <br />serve as a comparative basis to judge ground water quality. <br />In the Probable Hydrological Consequences (PHC, Tab 17, Attachment 17-5) <br />section of the Yoast Mine PAP, predictions were made as to the expected <br />TDS increases to be observed at various monitoring wells. The following <br />table outlines these predictions along with this year's observed average <br />values (annual average for bedrock wells, May-September average for <br />alluvial wells). <br />Well Predicted TDS values (mg/1) <br />YOV28 2587 <br />YOV29 3201 <br />YOV30 3201 <br />YW28 3045 <br />YW29 2570 <br />YW30 2570 <br />YAAL14 2036 <br />YGAL15 3548 <br />YGAL16 1296 <br />YSAL1 798 <br />This years average TDS (mg/1) <br />830 <br />Dry <br />1040 <br />910 <br />500 <br />530 <br />2520 <br />5700 <br />790 <br />1030 <br />The TDS value in May at Well YSAL1 was 1030 mg/1, which exceeds the <br />predicted value of 798 mg/1 by 29~. The PHC predictions are based on <br />long-term average values. Individual TDS measurements will vary from <br />year to year due to climatic conditions. As mentioned previously in the <br />Meteorological section, precipitation values were below average for the <br />past several years. What is important is what the long-term trend <br />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 1030 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 /> <br />• <br />• <br />8 <br />