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Kim ey>>> Horn Page 22 <br />was sufficient bicarbonate that allowed a protective film to form on the pipe wall. Increasing the pH to above <br />pH 8.0 significantly reduces the copper solubility of water (AWWARF 1985; McNally, et. al., 1993). IRCU <br />maintains relatively moderate alkalinity concentration (--60 mg/L as CaCO3) at the Point -of -Entry to the <br />distribution system at Hobart and Oslo. <br />IRCU has maintained compliance with copper concentrations less than 90th percentile action level of 1.3 <br />mg/L. Since 2011, the copper sample results in the 50th, 75th, and 90th percentile have increased slightly <br />up until 2015, with a marked increase in the May 2016 data. There was a slight increase from 2011 to <br />2014, and from 2014 to 2015. The copper levels from 2015 to May 2016 showed a greater increase, where <br />the 90th percentile of copper levels in the distribution system quadrupled. The December 2016 exhibited <br />a 25% decrease in the 90th percentile values obtained in May 2016. The reduction in copper concentrations <br />may be contributed to the increase in alkalinity and hardness in the finished water implemented in <br />September 2016. Although this is an improvement, the statistical values are still currently higher than those <br />observed in sampling prior to May 2016. <br />Table 4: IRCU - Copper Sample Tap Results <br />Sampling <br />Date <br />Average <br />(mg/L) <br />Maximum <br />(mg/L) <br />50th <br />Percentile <br />(mg/L) <br />75th <br />Percentile <br />(mg/L) <br />90th <br />Percentile <br />(mg/L) <br />Action <br />Level <br />(mg/L) <br />Sample <br />Size <br />Aug -11 <br />0.008 <br />0.150 <br />0.002 <br />0.007 <br />0.017 <br />1.3 <br />50 <br />Aug -1 4 <br />0.019 <br />0.120 R <br />0.012 <br />0.025 <br />0.038 <br />1.3 <br />50 <br />Dec -15 <br />0.022 <br />0.075 <br />0.015 <br />0.033 <br />0.051 <br />1.3 <br />50 <br />May -16 <br />0.075 <br />0.350 <br />0.040 <br />0.115 <br />0.202 <br />1.3 <br />50 <br />Dec -16 <br />0.071 <br />0.300 <br />0.048 <br />0.084 <br />0.151 <br />1.3 <br />50 <br />Aug -19 <br />0.086 <br />0.370 <br />0.075 <br />0.130 <br />0.178 <br />1.3 <br />52 <br />RIN <br />