Study Results

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Study 59 Summary Latest

This study was completed in 2018.

These tables summarize the measurements reported to the QA-SAC for Laboratory Intercomparison Study 59. A total of 75 laboratories reported measurements. Some measurements were missing or below the analytical detection limit (DL). N designates the number of reported values above the DL. At the center of each set of N measurements is the Median, which is the accepted target value of the set. Non-parametric Sigmas were estimated from the interquartile ranges and were used to calculate Z-scores. Good, Satisfactory, and Marginal categories are defined on Definitions and DQOs, where there is a table that lists the Data Quality Objectives.

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Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 67 5.21 0.09(6) 5.15 5.28 5.12 5.30 5.02 5.40 5.11 5.31
Conductivity μS/cm 65 4.0 0.3(7) 3.7 4.2 3.7 4.3 3.3 4.7 3.8 4.2
Acidity μeq/L 7 5.5 4.6(0) 5.2 11.4 1.0 10.0 0.0 14.6 4.2 6.8
Sulfate mg/L 58 0.224 0.016(3) 0.212 0.234 0.208 0.240 0.192 0.256 0.213 0.235
Nitrate mg/L 64 0.385 0.025(4) 0.362 0.395 0.360 0.409 0.334 0.435 0.366 0.403
Ammonium mg/L 60 0.059 0.007(8) 0.055 0.065 0.052 0.066 0.044 0.074 0.055 0.063
Fluoride mg/L 15 0.010 0.003(0) 0.009 0.013 0.008 0.012 0.005 0.015 0.008 0.012
Chloride mg/L 44 0.033 0.015(6) 0.029 0.050 0.018 0.048 0.002 0.064 0.030 0.036
Sodium mg/L 41 0.013 0.005(9) 0.011 0.018 0.008 0.018 0.002 0.024 0.012 0.014
Potassium mg/L 59 0.070 0.007(4) 0.065 0.075 0.063 0.077 0.056 0.084 0.056 0.084
Calcium mg/L 52 0.035 0.013(3) 0.031 0.048 0.022 0.048 0.009 0.061 0.030 0.040
Magnesium mg/L 47 0.007 0.003(7) 0.006 0.011 0.004 0.010 0.000 0.014 0.007 0.007
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 67 5.06 0.07(4) 5.01 5.11 4.99 5.13 4.92 5.20 4.96 5.16
Conductivity μS/cm 65 9.0 0.4(8) 8.7 9.3 8.6 9.4 8.1 9.9 8.4 9.6
Acidity μeq/L 7 10.0 6.6(7) 7.7 16.7 3.4 16.6 0.0 23.3 7.5 12.5
Sulfate mg/L 64 1.119 0.050(0) 1.077 1.143 1.069 1.168 1.019 1.218 1.063 1.174
Nitrate mg/L 65 0.710 0.029(3) 0.690 0.729 0.681 0.739 0.652 0.768 0.675 0.745
Ammonium mg/L 67 0.282 0.019(3) 0.269 0.295 0.263 0.301 0.244 0.320 0.263 0.301
Fluoride mg/L 17 0.024 0.003(3) 0.022 0.026 0.021 0.027 0.018 0.030 0.020 0.028
Chloride mg/L 63 0.292 0.014(1) 0.281 0.300 0.278 0.306 0.264 0.320 0.263 0.321
Sodium mg/L 64 0.141 0.009(5) 0.136 0.148 0.132 0.150 0.123 0.159 0.127 0.155
Potassium mg/L 59 0.081 0.009(6) 0.073 0.086 0.072 0.090 0.062 0.100 0.065 0.097
Calcium mg/L 63 0.149 0.012(6) 0.139 0.156 0.137 0.161 0.124 0.174 0.127 0.171
Magnesium mg/L 61 0.054 0.005(9) 0.049 0.057 0.049 0.059 0.043 0.065 0.049 0.059
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 68 5.96 0.15(9) 5.83 6.04 5.80 6.11 5.64 6.27 5.86 6.05
Conductivity μS/cm 66 16.4 0.6(7) 16.0 16.9 15.8 17.0 15.1 17.7 15.3 17.5
Acidity μeq/L 5 13.8 13.9(7) 1.1 19.9 0.0 27.7 0.0 41.7 10.4 17.2
Sulfate mg/L 64 1.917 0.063(2) 1.871 1.956 1.854 1.979 1.791 2.042 1.821 2.012
Nitrate mg/L 65 2.327 0.089(0) 2.263 2.382 2.239 2.415 2.150 2.504 2.211 2.443
Ammonium mg/L 68 0.960 0.032(6) 0.937 0.980 0.927 0.992 0.895 1.024 0.893 1.026
Fluoride mg/L 21 0.109 0.011(1) 0.104 0.119 0.098 0.120 0.087 0.131 0.088 0.130
Chloride mg/L 63 0.872 0.043(7) 0.830 0.889 0.829 0.915 0.785 0.959 0.785 0.959
Sodium mg/L 65 0.434 0.015(9) 0.420 0.441 0.419 0.449 0.403 0.465 0.391 0.477
Potassium mg/L 62 0.120 0.012(8) 0.110 0.127 0.108 0.132 0.095 0.145 0.096 0.144
Calcium mg/L 64 0.693 0.062(6) 0.650 0.734 0.630 0.755 0.568 0.817 0.589 0.796
Magnesium mg/L 61 0.132 0.006(7) 0.126 0.135 0.126 0.138 0.119 0.145 0.119 0.145