Study Results

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Study Summary Ring Diagrams Tabular Summary Measurement Record

Study 65 Summary Latest

This study was completed in 2022.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 65. A total of 56 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 Aug 10, 2022.

Download study summaries for Sample 1, Sample 2, or Sample 3 as a CSV.

Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives
pH pH units 49 4.77 0.05(9) 4.73 4.81 4.72 4.82 4.66 4.88 4.70 4.84
Conductivity μS/cm 46 20.8 0.7(8) 20.1 21.1 20.0 21.5 19.2 22.3 19.3 22.2
Acidity μeq/L 4 17.6 6.3(6) 14.4 22.9 11.3 23.9 4.9 30.3 13.2 22.0
Sulfate mg/L 50 1.921 0.057(8) 1.880 1.957 1.864 1.978 1.806 2.036 1.825 2.017
Nitrate mg/L 49 0.966 0.030(4) 0.943 0.983 0.936 0.996 0.906 1.026 0.918 1.014
Ammonium mg/L 51 0.382 0.018(5) 0.371 0.396 0.364 0.400 0.345 0.419 0.356 0.408
Fluoride mg/L 15 0.054 0.008(2) 0.049 0.060 0.046 0.062 0.038 0.070 0.044 0.064
Chloride mg/L 50 2.021 0.066(0) 1.952 2.041 1.956 2.086 1.890 2.152 1.819 2.223
Sodium mg/L 49 1.109 0.035(6) 1.080 1.128 1.074 1.144 1.038 1.180 0.999 1.219
Potassium mg/L 49 0.213 0.015(6) 0.197 0.218 0.198 0.228 0.182 0.244 0.171 0.255
Calcium mg/L 49 0.267 0.016(7) 0.250 0.272 0.251 0.283 0.234 0.300 0.227 0.307
Magnesium mg/L 47 0.117 0.005(9) 0.111 0.119 0.112 0.122 0.106 0.128 0.106 0.128
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives
pH pH units 49 4.71 0.06(3) 4.67 4.75 4.65 4.77 4.59 4.83 4.64 4.78
Conductivity μS/cm 46 21.8 0.6(9) 21.5 22.4 21.2 22.4 20.5 23.1 20.3 23.3
Acidity μeq/L 4 17.9 3.6(1) 14.9 19.7 14.3 21.5 10.7 25.1 13.5 22.3
Sulfate mg/L 51 2.389 0.060(8) 2.343 2.425 2.329 2.449 2.268 2.510 2.270 2.508
Nitrate mg/L 50 1.219 0.033(0) 1.194 1.238 1.186 1.251 1.153 1.284 1.158 1.279
Ammonium mg/L 51 0.449 0.019(3) 0.436 0.462 0.430 0.468 0.411 0.487 0.418 0.480
Fluoride mg/L 14 0.020 0.006(3) 0.016 0.023 0.014 0.026 0.008 0.032 0.016 0.024
Chloride mg/L 51 1.594 0.045(2) 1.550 1.611 1.549 1.639 1.504 1.684 1.435 1.753
Sodium mg/L 49 1.020 0.033(4) 1.000 1.044 0.987 1.053 0.954 1.086 0.918 1.122
Potassium mg/L 49 0.178 0.012(2) 0.168 0.184 0.166 0.190 0.154 0.202 0.143 0.213
Calcium mg/L 50 0.233 0.014(6) 0.219 0.238 0.219 0.247 0.204 0.262 0.199 0.267
Magnesium mg/L 48 0.118 0.007(0) 0.112 0.120 0.111 0.124 0.104 0.131 0.106 0.129
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives
pH pH units 49 5.02 0.07(0) 4.97 5.06 4.95 5.09 4.88 5.16 4.92 5.12
Conductivity μS/cm 46 9.4 0.5(2) 9.1 9.8 8.9 9.9 8.4 10.4 8.8 10.0
Acidity μeq/L 4 10.4 5.0(4) 9.1 15.8 5.4 15.3 0.3 20.4 7.8 12.9
Sulfate mg/L 49 1.123 0.031(5) 1.097 1.139 1.092 1.154 1.060 1.186 1.067 1.179
Nitrate mg/L 49 0.711 0.023(0) 0.695 0.726 0.689 0.733 0.666 0.756 0.676 0.746
Ammonium mg/L 51 0.286 0.014(1) 0.275 0.294 0.272 0.300 0.258 0.314 0.266 0.306
Fluoride mg/L 15 0.025 0.006(7) 0.021 0.030 0.019 0.031 0.012 0.038 0.020 0.030
Chloride mg/L 50 0.294 0.017(0) 0.279 0.302 0.277 0.310 0.260 0.327 0.265 0.322
Sodium mg/L 49 0.143 0.011(1) 0.133 0.148 0.132 0.154 0.121 0.165 0.129 0.157
Potassium mg/L 48 0.082 0.009(1) 0.075 0.086 0.073 0.090 0.064 0.099 0.066 0.097
Calcium mg/L 48 0.151 0.017(4) 0.135 0.158 0.134 0.167 0.116 0.185 0.128 0.173
Magnesium mg/L 46 0.053 0.003(3) 0.052 0.056 0.050 0.056 0.047 0.059 0.048 0.058