Study Results

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Study Summary Ring Diagrams Tabular Summary Measurement Record

Study 66 Summary Latest

This study was completed in 2022.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 66. A total of 58 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 9, 2023.

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 53 4.59 0.04(8) 4.55 4.61 4.55 4.63 4.50 4.68 4.52 4.66
Conductivity μS/cm 49 15.6 0.8(9) 15.0 16.2 14.8 16.4 13.9 17.3 14.6 16.6
Acidity μeq/L 5 28.2 8.9(0) 24.9 36.8 19.4 37.0 10.5 45.9 21.2 35.2
Sulfate mg/L 51 1.346 0.028(9) 1.330 1.369 1.318 1.374 1.289 1.403 1.279 1.413
Nitrate mg/L 52 1.053 0.037(2) 1.028 1.077 1.016 1.090 0.979 1.127 1.001 1.105
Ammonium mg/L 54 0.220 0.012(6) 0.214 0.230 0.208 0.232 0.195 0.245 0.205 0.235
Fluoride mg/L 14 0.051 0.007(8) 0.045 0.055 0.044 0.058 0.036 0.066 0.041 0.061
Chloride mg/L 52 0.283 0.012(8) 0.271 0.288 0.270 0.295 0.257 0.308 0.255 0.310
Sodium mg/L 53 0.153 0.010(0) 0.146 0.159 0.143 0.163 0.133 0.173 0.138 0.168
Potassium mg/L 44 0.031 0.007(0) 0.026 0.034 0.024 0.037 0.017 0.044 0.025 0.036
Calcium mg/L 53 0.114 0.014(5) 0.104 0.123 0.100 0.128 0.086 0.142 0.097 0.131
Magnesium mg/L 47 0.033 0.004(4) 0.029 0.035 0.029 0.037 0.025 0.041 0.030 0.036
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives
pH pH units 53 4.45 0.03(7) 4.42 4.47 4.42 4.48 4.38 4.52 4.38 4.52
Conductivity μS/cm 49 42.9 1.6(7) 41.3 43.5 41.3 44.5 39.6 46.2 39.9 45.9
Acidity μeq/L 5 35.2 9.1(2) 34.7 47.0 26.1 44.3 17.0 53.4 26.4 44.0
Sulfate mg/L 52 5.294 0.098(2) 5.196 5.327 5.196 5.392 5.098 5.490 5.030 5.558
Nitrate mg/L 52 4.016 0.078(6) 3.963 4.068 3.937 4.094 3.859 4.172 3.815 4.216
Ammonium mg/L 54 1.320 0.058(4) 1.283 1.361 1.262 1.378 1.204 1.436 1.228 1.412
Fluoride mg/L 16 0.056 0.004(8) 0.053 0.058 0.052 0.060 0.047 0.065 0.045 0.067
Chloride mg/L 52 2.070 0.061(3) 2.028 2.110 2.009 2.131 1.948 2.192 1.863 2.277
Sodium mg/L 53 1.306 0.043(0) 1.265 1.323 1.264 1.348 1.221 1.391 1.176 1.436
Potassium mg/L 53 0.287 0.016(7) 0.273 0.295 0.271 0.303 0.254 0.320 0.230 0.344
Calcium mg/L 53 0.781 0.046(0) 0.734 0.796 0.736 0.826 0.690 0.872 0.664 0.898
Magnesium mg/L 53 0.244 0.010(7) 0.236 0.250 0.234 0.254 0.223 0.265 0.220 0.268
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives
pH pH units 53 4.85 0.04(4) 4.84 4.89 4.81 4.89 4.77 4.93 4.78 4.92
Conductivity μS/cm 49 13.2 0.5(2) 12.9 13.6 12.7 13.7 12.2 14.2 12.3 14.1
Acidity μeq/L 5 14.6 7.5(2) 13.5 23.6 7.1 22.1 0.0 29.6 11.0 18.2
Sulfate mg/L 52 1.443 0.035(8) 1.419 1.466 1.408 1.478 1.372 1.514 1.371 1.515
Nitrate mg/L 53 0.632 0.025(6) 0.610 0.644 0.607 0.657 0.581 0.683 0.601 0.663
Ammonium mg/L 55 0.247 0.014(1) 0.238 0.257 0.233 0.261 0.219 0.275 0.230 0.264
Fluoride mg/L 13 0.005 0.001(5) 0.004 0.006 0.004 0.006 0.003 0.007 0.004 0.006
Chloride mg/L 53 0.791 0.023(0) 0.774 0.804 0.769 0.813 0.746 0.836 0.712 0.870
Sodium mg/L 54 0.472 0.024(5) 0.452 0.484 0.448 0.496 0.424 0.520 0.425 0.519
Potassium mg/L 53 0.106 0.009(6) 0.098 0.111 0.097 0.115 0.087 0.125 0.085 0.127
Calcium mg/L 54 0.163 0.011(7) 0.154 0.169 0.152 0.174 0.140 0.186 0.139 0.187
Magnesium mg/L 54 0.076 0.006(1) 0.070 0.078 0.070 0.082 0.064 0.088 0.069 0.083