Study Results
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 Apr 30, 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 | 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 |