Study Results

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Study Summary Ring Diagrams Tabular Summary Measurement Record

Study 69 Summary Latest

This study was completed in 2024.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 69. 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 Sep 3, 2024.

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 4.44 0.04(1) 4.42 4.47 4.40 4.48 4.36 4.52 4.37 4.51
Conductivity μS/cm 44 43.3 1.1(9) 42.5 44.1 42.1 44.4 40.9 45.6 40.3 46.2
Acidity μeq/L 5 33.8 5.1(5) 31.5 38.4 28.7 38.9 23.5 44.1 25.4 42.2
Sulfate mg/L 47 5.418 0.106(7) 5.356 5.500 5.312 5.524 5.205 5.631 5.148 5.688
Nitrate mg/L 48 4.137 0.097(5) 4.056 4.187 4.040 4.233 3.942 4.331 3.930 4.343
Ammonium mg/L 50 1.360 0.048(7) 1.319 1.384 1.312 1.408 1.263 1.457 1.265 1.455
Fluoride mg/L 13 0.057 0.005(2) 0.052 0.059 0.052 0.062 0.047 0.067 0.046 0.068
Chloride mg/L 48 2.136 0.042(8) 2.097 2.154 2.094 2.178 2.051 2.221 1.923 2.349
Sodium mg/L 47 1.329 0.046(7) 1.289 1.352 1.283 1.375 1.236 1.422 1.197 1.461
Potassium mg/L 47 0.290 0.016(3) 0.276 0.298 0.274 0.306 0.258 0.322 0.232 0.348
Calcium mg/L 47 0.799 0.044(5) 0.761 0.821 0.755 0.843 0.711 0.887 0.680 0.918
Magnesium mg/L 47 0.251 0.010(4) 0.242 0.256 0.241 0.261 0.231 0.271 0.226 0.276
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 5.80 0.13(0) 5.70 5.87 5.68 5.92 5.55 6.05 5.70 5.90
Conductivity μS/cm 44 16.5 0.5(0) 16.1 16.7 16.0 16.9 15.5 17.4 15.3 17.6
Acidity μeq/L 6 2.9 2.2(6) 1.5 4.5 0.6 5.1 0.0 7.3 2.2 3.5
Sulfate mg/L 48 1.938 0.052(1) 1.898 1.967 1.886 1.989 1.834 2.041 1.841 2.034
Nitrate mg/L 49 2.357 0.059(7) 2.318 2.398 2.298 2.416 2.238 2.476 2.240 2.474
Ammonium mg/L 50 0.966 0.022(6) 0.953 0.983 0.944 0.988 0.921 1.011 0.899 1.033
Fluoride mg/L 16 0.116 0.008(5) 0.108 0.118 0.108 0.124 0.099 0.133 0.093 0.139
Chloride mg/L 49 0.884 0.031(1) 0.857 0.899 0.853 0.915 0.822 0.946 0.796 0.972
Sodium mg/L 47 0.438 0.016(3) 0.426 0.448 0.422 0.454 0.406 0.470 0.395 0.481
Potassium mg/L 47 0.121 0.004(4) 0.118 0.124 0.117 0.125 0.113 0.129 0.097 0.145
Calcium mg/L 46 0.604 0.055(2) 0.548 0.622 0.549 0.658 0.494 0.713 0.513 0.694
Magnesium mg/L 46 0.128 0.010(7) 0.119 0.133 0.117 0.138 0.107 0.148 0.115 0.140
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 4.72 0.04(8) 4.70 4.76 4.68 4.76 4.63 4.81 4.65 4.79
Conductivity μS/cm 44 12.1 0.4(3) 11.9 12.4 11.7 12.5 11.3 12.9 11.3 12.9
Acidity μeq/L 5 17.9 3.6(0) 16.6 21.4 14.4 21.4 10.8 25.0 13.5 22.3
Sulfate mg/L 46 1.022 0.044(7) 0.984 1.044 0.977 1.066 0.933 1.110 0.971 1.072
Nitrate mg/L 48 1.051 0.043(7) 1.030 1.088 1.008 1.094 0.964 1.138 0.999 1.103
Ammonium mg/L 50 0.209 0.014(5) 0.201 0.220 0.195 0.222 0.180 0.237 0.194 0.223
Fluoride mg/L 10 0.018 0.002(4) 0.016 0.019 0.016 0.019 0.013 0.022 0.014 0.021
Chloride mg/L 46 0.118 0.009(3) 0.112 0.124 0.109 0.127 0.100 0.136 0.107 0.129
Sodium mg/L 45 0.079 0.006(7) 0.074 0.082 0.073 0.085 0.066 0.092 0.072 0.086
Potassium mg/L 44 0.032 0.008(5) 0.027 0.037 0.023 0.040 0.015 0.048 0.026 0.037
Calcium mg/L 47 0.113 0.023(0) 0.096 0.127 0.091 0.135 0.068 0.158 0.097 0.129
Magnesium mg/L 46 0.043 0.006(7) 0.039 0.048 0.036 0.049 0.030 0.055 0.039 0.046