Study Results

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Study 68 Summary Latest

This study was completed in 2023.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 68. A total of 55 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 Feb 20, 2024.

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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 49 5.83 0.13(7) 5.71 5.89 5.70 5.96 5.56 6.10 5.73 5.93
Conductivity μS/cm 45 16.0 0.4(1) 15.7 16.2 15.6 16.4 15.2 16.8 14.9 17.1
Acidity μeq/L 5 1.9 5.1(5) 1.1 8.0 0.0 7.0 0.0 12.2 1.5 2.3
Sulfate mg/L 50 1.932 0.036(5) 1.910 1.958 1.896 1.968 1.859 2.005 1.836 2.028
Nitrate mg/L 50 2.334 0.053(0) 2.295 2.365 2.281 2.386 2.228 2.439 2.217 2.450
Ammonium mg/L 53 0.957 0.033(7) 0.937 0.982 0.924 0.990 0.890 1.024 0.891 1.023
Fluoride mg/L 16 0.044 0.002(8) 0.042 0.045 0.042 0.046 0.039 0.049 0.036 0.052
Chloride mg/L 50 0.879 0.027(6) 0.857 0.894 0.852 0.906 0.824 0.934 0.792 0.966
Sodium mg/L 50 0.437 0.019(8) 0.421 0.447 0.417 0.456 0.397 0.476 0.393 0.480
Potassium mg/L 50 0.120 0.009(3) 0.113 0.125 0.111 0.129 0.102 0.138 0.096 0.144
Calcium mg/L 49 0.515 0.053(0) 0.466 0.537 0.462 0.568 0.409 0.621 0.438 0.592
Magnesium mg/L 49 0.129 0.013(3) 0.118 0.136 0.116 0.142 0.103 0.155 0.117 0.141
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 4.63 0.05(6) 4.60 4.67 4.58 4.68 4.52 4.74 4.56 4.70
Conductivity μS/cm 45 22.0 0.8(2) 21.5 22.6 21.2 22.8 20.4 23.6 20.5 23.5
Acidity μeq/L 5 24.7 5.7(4) 20.2 27.9 19.0 30.4 13.3 36.1 18.6 30.8
Sulfate mg/L 50 2.518 0.061(2) 2.484 2.566 2.457 2.578 2.396 2.639 2.392 2.643
Nitrate mg/L 50 1.849 0.056(0) 1.808 1.883 1.794 1.904 1.738 1.960 1.757 1.941
Ammonium mg/L 53 0.614 0.029(3) 0.602 0.641 0.585 0.643 0.556 0.672 0.572 0.656
Fluoride mg/L 16 0.040 0.003(0) 0.038 0.042 0.037 0.042 0.034 0.045 0.032 0.047
Chloride mg/L 50 0.779 0.027(8) 0.763 0.800 0.752 0.806 0.724 0.834 0.702 0.856
Sodium mg/L 50 0.414 0.016(7) 0.400 0.422 0.397 0.430 0.381 0.446 0.373 0.454
Potassium mg/L 50 0.126 0.012(2) 0.119 0.135 0.114 0.138 0.102 0.150 0.101 0.151
Calcium mg/L 49 0.340 0.017(4) 0.327 0.350 0.323 0.357 0.306 0.374 0.289 0.391
Magnesium mg/L 49 0.097 0.007(4) 0.092 0.102 0.090 0.104 0.083 0.111 0.088 0.106
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 4.60 0.03(7) 4.58 4.63 4.57 4.63 4.53 4.67 4.53 4.67
Conductivity μS/cm 45 38.2 1.1(1) 37.4 38.8 37.1 39.3 36.0 40.4 35.6 40.8
Acidity μeq/L 5 26.2 8.0(8) 19.3 30.2 18.2 34.2 10.1 42.3 19.7 32.7
Sulfate mg/L 50 4.373 0.099(7) 4.317 4.451 4.274 4.472 4.174 4.572 4.155 4.591
Nitrate mg/L 50 2.174 0.042(6) 2.138 2.195 2.131 2.216 2.089 2.258 2.065 2.282
Ammonium mg/L 53 0.801 0.029(7) 0.781 0.821 0.772 0.830 0.742 0.860 0.745 0.857
Fluoride mg/L 15 0.051 0.003(0) 0.050 0.054 0.049 0.053 0.046 0.056 0.041 0.061
Chloride mg/L 50 3.658 0.078(2) 3.598 3.703 3.580 3.735 3.502 3.813 3.292 4.023
Sodium mg/L 50 2.280 0.060(6) 2.233 2.314 2.219 2.340 2.159 2.400 2.052 2.507
Potassium mg/L 50 0.394 0.017(6) 0.384 0.407 0.377 0.411 0.359 0.429 0.316 0.472
Calcium mg/L 49 0.621 0.021(1) 0.602 0.630 0.600 0.642 0.579 0.663 0.528 0.714
Magnesium mg/L 49 0.252 0.014(8) 0.239 0.258 0.238 0.266 0.223 0.281 0.227 0.277