Study Results

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Study 64 Summary Latest

This study was completed in 2021.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 64. A total of 64 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 Apr 22, 2022.

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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 58 5.33 0.11(5) 5.28 5.43 5.22 5.43 5.10 5.55 5.23 5.42
Conductivity μS/cm 54 6.5 0.3(7) 6.4 6.9 6.2 6.8 5.8 7.2 6.1 6.9
Acidity μeq/L 8 4.7 4.9(5) 1.4 8.0 0.0 9.6 0.0 14.5 3.6 5.8
Sulfate mg/L 56 0.664 0.027(6) 0.641 0.677 0.636 0.691 0.609 0.718 0.631 0.696
Nitrate mg/L 58 0.747 0.028(0) 0.726 0.763 0.719 0.774 0.691 0.802 0.710 0.783
Ammonium mg/L 59 0.247 0.014(8) 0.239 0.259 0.233 0.261 0.218 0.276 0.230 0.264
Fluoride mg/L 17 0.058 0.006(3) 0.056 0.064 0.052 0.064 0.046 0.070 0.047 0.069
Chloride mg/L 57 0.175 0.012(2) 0.169 0.185 0.163 0.187 0.151 0.199 0.158 0.192
Sodium mg/L 56 0.108 0.009(3) 0.102 0.113 0.099 0.116 0.089 0.126 0.097 0.118
Potassium mg/L 51 0.032 0.006(7) 0.029 0.038 0.026 0.038 0.019 0.045 0.026 0.038
Calcium mg/L 56 0.194 0.018(5) 0.181 0.205 0.176 0.212 0.157 0.231 0.165 0.223
Magnesium mg/L 52 0.038 0.007(8) 0.035 0.045 0.031 0.045 0.023 0.053 0.035 0.041
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 58 5.75 0.12(8) 5.68 5.85 5.63 5.87 5.50 6.00 5.65 5.85
Conductivity μS/cm 54 8.8 0.4(6) 8.6 9.2 8.4 9.2 7.9 9.7 8.2 9.4
Acidity μeq/L 7 3.0 7.3(4) 1.5 11.4 0.0 10.3 0.0 17.6 2.3 3.7
Sulfate mg/L 55 0.954 0.035(6) 0.923 0.971 0.919 0.989 0.883 1.025 0.907 1.001
Nitrate mg/L 58 1.164 0.031(3) 1.143 1.185 1.133 1.194 1.101 1.226 1.106 1.221
Ammonium mg/L 59 0.482 0.023(0) 0.468 0.499 0.460 0.504 0.437 0.527 0.449 0.515
Fluoride mg/L 18 0.060 0.010(0) 0.055 0.068 0.050 0.069 0.040 0.079 0.048 0.071
Chloride mg/L 58 0.433 0.019(6) 0.424 0.450 0.413 0.452 0.394 0.471 0.390 0.475
Sodium mg/L 58 0.215 0.014(5) 0.204 0.223 0.201 0.229 0.187 0.243 0.194 0.236
Potassium mg/L 56 0.060 0.007(8) 0.055 0.065 0.052 0.067 0.044 0.075 0.048 0.071
Calcium mg/L 56 0.327 0.031(7) 0.300 0.342 0.296 0.358 0.264 0.390 0.278 0.376
Magnesium mg/L 57 0.066 0.007(4) 0.063 0.072 0.059 0.073 0.052 0.080 0.060 0.072
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 59 4.63 0.05(2) 4.59 4.66 4.58 4.68 4.53 4.73 4.56 4.70
Conductivity μS/cm 55 21.7 1.0(4) 21.1 22.5 20.7 22.7 19.7 23.7 20.2 23.2
Acidity μeq/L 9 22.9 12.5(6) 13.1 30.0 10.4 35.4 0.0 48.0 17.2 28.6
Sulfate mg/L 59 2.499 0.088(2) 2.439 2.558 2.411 2.587 2.323 2.675 2.375 2.623
Nitrate mg/L 59 1.837 0.070(4) 1.777 1.872 1.767 1.907 1.697 1.977 1.746 1.928
Ammonium mg/L 59 0.600 0.025(2) 0.586 0.620 0.575 0.625 0.550 0.650 0.558 0.642
Fluoride mg/L 18 0.039 0.009(6) 0.035 0.047 0.030 0.048 0.020 0.058 0.032 0.046
Chloride mg/L 60 0.764 0.029(5) 0.744 0.783 0.735 0.793 0.706 0.822 0.688 0.840
Sodium mg/L 58 0.412 0.017(2) 0.402 0.425 0.395 0.429 0.378 0.446 0.371 0.453
Potassium mg/L 57 0.128 0.015(2) 0.122 0.142 0.113 0.143 0.098 0.158 0.103 0.153
Calcium mg/L 57 0.339 0.019(3) 0.325 0.351 0.320 0.358 0.301 0.377 0.289 0.389
Magnesium mg/L 58 0.099 0.008(0) 0.095 0.105 0.092 0.106 0.084 0.114 0.090 0.108