Study Results

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Study 62 Summary Latest

This study was completed in 2020.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 62. A total of 67 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. Go to Definitions and DQOs for a description of Good, Satisfactory, and Marginal, and for a list of the Data Quality Objectives.

Study last updated on Mar 16, 2021.

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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 60 5.24 0.10(6) 5.19 5.33 5.13 5.34 5.03 5.44 5.14 5.33
Conductivity μS/cm 58 11.2 0.6(1) 10.9 11.7 10.6 11.8 10.0 12.4 10.5 11.9
Acidity μeq/L 5 5.6 9.5(6) 2.3 15.2 0.0 15.1 0.0 24.7 4.2 7.0
Sulfate mg/L 62 1.321 0.039(5) 1.298 1.350 1.282 1.359 1.242 1.399 1.255 1.386
Nitrate mg/L 62 1.479 0.055(4) 1.426 1.500 1.424 1.534 1.369 1.589 1.406 1.552
Ammonium mg/L 63 0.485 0.022(2) 0.472 0.502 0.463 0.507 0.441 0.529 0.452 0.518
Fluoride mg/L 22 0.115 0.010(2) 0.106 0.119 0.105 0.124 0.095 0.134 0.092 0.137
Chloride mg/L 63 0.349 0.009(6) 0.343 0.356 0.340 0.358 0.330 0.368 0.315 0.383
Sodium mg/L 59 0.214 0.008(9) 0.207 0.219 0.206 0.222 0.197 0.231 0.193 0.235
Potassium mg/L 57 0.061 0.006(3) 0.056 0.064 0.055 0.067 0.049 0.073 0.049 0.073
Calcium mg/L 60 0.380 0.038(7) 0.346 0.398 0.341 0.418 0.303 0.456 0.323 0.436
Magnesium mg/L 58 0.072 0.006(1) 0.067 0.075 0.066 0.077 0.060 0.083 0.065 0.078
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 60 5.15 0.11(5) 5.11 5.25 5.04 5.26 4.93 5.37 5.05 5.25
Conductivity μS/cm 58 4.4 0.3(9) 4.1 4.6 4.1 4.7 3.7 5.1 4.1 4.7
Acidity μeq/L 5 7.2 5.5(2) 5.6 13.0 1.7 12.7 0.0 18.2 5.4 9.0
Sulfate mg/L 57 0.270 0.017(0) 0.256 0.279 0.253 0.287 0.236 0.304 0.257 0.283
Nitrate mg/L 60 0.331 0.022(4) 0.316 0.345 0.309 0.352 0.286 0.375 0.314 0.347
Ammonium mg/L 60 0.077 0.011(1) 0.068 0.082 0.066 0.088 0.055 0.099 0.072 0.082
Fluoride mg/L 16 0.011 0.002(2) 0.010 0.013 0.009 0.013 0.007 0.015 0.009 0.013
Chloride mg/L 51 0.039 0.011(1) 0.035 0.050 0.028 0.050 0.017 0.061 0.036 0.042
Sodium mg/L 39 0.016 0.003(7) 0.015 0.020 0.013 0.019 0.009 0.023 0.015 0.017
Potassium mg/L 40 0.011 0.007(2) 0.008 0.017 0.004 0.017 0.000 0.024 0.009 0.012
Calcium mg/L 50 0.045 0.012(2) 0.040 0.056 0.033 0.056 0.021 0.068 0.038 0.051
Magnesium mg/L 46 0.009 0.001(9) 0.008 0.010 0.008 0.010 0.006 0.012 0.009 0.009
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 60 4.76 0.07(0) 4.73 4.81 4.69 4.83 4.62 4.90 4.69 4.83
Conductivity μS/cm 58 11.4 0.4(6) 11.0 11.6 11.0 11.8 10.5 12.3 10.7 12.1
Acidity μeq/L 5 19.5 7.0(4) 17.4 26.9 12.5 26.5 5.5 33.5 14.7 24.3
Sulfate mg/L 61 1.024 0.042(3) 0.996 1.053 0.982 1.066 0.940 1.108 0.973 1.075
Nitrate mg/L 62 1.055 0.053(6) 1.009 1.081 1.002 1.108 0.948 1.162 1.003 1.107
Ammonium mg/L 61 0.205 0.013(3) 0.197 0.215 0.192 0.218 0.179 0.231 0.191 0.219
Fluoride mg/L 19 0.020 0.001(5) 0.019 0.021 0.019 0.021 0.018 0.022 0.016 0.024
Chloride mg/L 58 0.118 0.008(5) 0.114 0.125 0.109 0.126 0.101 0.134 0.106 0.129
Sodium mg/L 57 0.080 0.008(5) 0.072 0.083 0.072 0.088 0.063 0.097 0.072 0.088
Potassium mg/L 50 0.030 0.003(7) 0.028 0.033 0.027 0.033 0.023 0.037 0.024 0.036
Calcium mg/L 59 0.109 0.011(1) 0.101 0.116 0.098 0.120 0.087 0.131 0.093 0.125
Magnesium mg/L 55 0.043 0.002(2) 0.041 0.044 0.041 0.045 0.039 0.047 0.039 0.047