Study Results
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 Oct 4, 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(6) | 4.74 | 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 | 1.919 | 0.056(7) | 1.880 | 1.956 | 1.862 | 1.975 | 1.806 | 2.031 | 1.823 | 2.014 |
Nitrate | mg/L | 49 | 0.965 | 0.029(3) | 0.943 | 0.982 | 0.936 | 0.994 | 0.907 | 1.023 | 0.917 | 1.013 |
Ammonium | mg/L | 51 | 0.382 | 0.018(5) | 0.369 | 0.394 | 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 | 0.063(8) | 1.955 | 2.041 | 1.958 | 2.084 | 1.894 | 2.148 | 1.819 | 2.223 |
Sodium | mg/L | 49 | 1.111 | 0.037(4) | 1.083 | 1.133 | 1.074 | 1.148 | 1.037 | 1.185 | 1.000 | 1.222 |
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 | 0.05(9) | 4.67 | 4.74 | 4.66 | 4.76 | 4.60 | 4.82 | 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 | 2.390 | 0.057(8) | 2.347 | 2.425 | 2.333 | 2.447 | 2.275 | 2.505 | 2.271 | 2.509 |
Nitrate | mg/L | 50 | 1.223 | 0.030(4) | 1.198 | 1.238 | 1.193 | 1.253 | 1.163 | 1.283 | 1.162 | 1.284 |
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 | 0.043(0) | 1.550 | 1.608 | 1.552 | 1.636 | 1.509 | 1.679 | 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 | 0.014(8) | 0.164 | 0.184 | 0.164 | 0.192 | 0.149 | 0.207 | 0.143 | 0.213 |
Calcium | mg/L | 50 | 0.233 | 0.016(3) | 0.216 | 0.238 | 0.217 | 0.249 | 0.201 | 0.265 | 0.199 | 0.267 |
Magnesium | mg/L | 48 | 0.118 | 0.006(5) | 0.112 | 0.120 | 0.112 | 0.123 | 0.105 | 0.130 | 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 |