Study Results
Study 67 Summary Latest
This study was completed in 2023.
These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 67. A total of 63 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 Aug 23, 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 | 56 | 4.44 | 0.05(2) | 4.39 | 4.46 | 4.39 | 4.49 | 4.34 | 4.54 | 4.37 | 4.51 |
Conductivity | μS/cm | 51 | 24.5 | 1.3(3) | 23.7 | 25.5 | 23.2 | 25.8 | 21.9 | 27.1 | 22.8 | 26.2 |
Acidity | μeq/L | 5 | 36.3 | 6.4(1) | 35.4 | 44.0 | 29.9 | 42.7 | 23.5 | 49.1 | 27.3 | 45.3 |
Sulfate | mg/L | 55 | 2.312 | 0.065(2) | 2.282 | 2.370 | 2.247 | 2.377 | 2.182 | 2.442 | 2.197 | 2.427 |
Nitrate | mg/L | 57 | 2.160 | 0.072(6) | 2.108 | 2.206 | 2.088 | 2.232 | 2.015 | 2.305 | 2.052 | 2.268 |
Ammonium | mg/L | 58 | 0.483 | 0.015(9) | 0.473 | 0.494 | 0.467 | 0.498 | 0.451 | 0.514 | 0.449 | 0.516 |
Fluoride | mg/L | 18 | 0.106 | 0.007(6) | 0.102 | 0.112 | 0.098 | 0.113 | 0.091 | 0.120 | 0.085 | 0.126 |
Chloride | mg/L | 58 | 0.300 | 0.015(0) | 0.290 | 0.310 | 0.285 | 0.315 | 0.270 | 0.330 | 0.270 | 0.330 |
Sodium | mg/L | 54 | 0.200 | 0.010(6) | 0.194 | 0.208 | 0.190 | 0.210 | 0.179 | 0.221 | 0.180 | 0.220 |
Potassium | mg/L | 49 | 0.048 | 0.006(7) | 0.044 | 0.053 | 0.042 | 0.054 | 0.035 | 0.061 | 0.039 | 0.057 |
Calcium | mg/L | 53 | 0.280 | 0.018(5) | 0.266 | 0.291 | 0.262 | 0.298 | 0.243 | 0.317 | 0.238 | 0.322 |
Magnesium | mg/L | 54 | 0.058 | 0.003(9) | 0.055 | 0.060 | 0.055 | 0.061 | 0.051 | 0.065 | 0.053 | 0.063 |
Measurement | Units | N | Median | Sigmaest. |
Good 25th to 75th percentiles |
Satisfactory Median ± Sigma |
Marginal Median ± 2 Sigma |
Meets Data Quality Objectives |
||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | pH units | 56 | 4.95 | 0.08(2) | 4.89 | 5.00 | 4.87 | 5.03 | 4.79 | 5.11 | 4.88 | 5.02 |
Conductivity | μS/cm | 51 | 7.1 | 0.3(7) | 6.8 | 7.3 | 6.8 | 7.4 | 6.4 | 7.8 | 6.7 | 7.5 |
Acidity | μeq/L | 5 | 11.7 | 17.5(7) | 9.9 | 33.5 | 0.0 | 29.2 | 0.0 | 46.8 | 8.8 | 14.6 |
Sulfate | mg/L | 53 | 0.570 | 0.031(5) | 0.543 | 0.585 | 0.539 | 0.601 | 0.507 | 0.633 | 0.542 | 0.598 |
Nitrate | mg/L | 56 | 0.580 | 0.034(7) | 0.548 | 0.594 | 0.545 | 0.614 | 0.511 | 0.648 | 0.551 | 0.608 |
Ammonium | mg/L | 55 | 0.113 | 0.008(9) | 0.109 | 0.121 | 0.105 | 0.121 | 0.096 | 0.130 | 0.106 | 0.120 |
Fluoride | mg/L | 13 | 0.005 | 0.003(7) | 0.005 | 0.009 | 0.002 | 0.008 | 0.000 | 0.012 | 0.004 | 0.006 |
Chloride | mg/L | 53 | 0.075 | 0.012(6) | 0.069 | 0.086 | 0.063 | 0.087 | 0.050 | 0.100 | 0.068 | 0.082 |
Sodium | mg/L | 45 | 0.039 | 0.004(8) | 0.036 | 0.042 | 0.035 | 0.043 | 0.030 | 0.048 | 0.036 | 0.042 |
Potassium | mg/L | 38 | 0.021 | 0.003(2) | 0.020 | 0.024 | 0.018 | 0.024 | 0.015 | 0.027 | 0.017 | 0.025 |
Calcium | mg/L | 48 | 0.054 | 0.008(0) | 0.051 | 0.061 | 0.047 | 0.061 | 0.039 | 0.069 | 0.046 | 0.062 |
Magnesium | mg/L | 43 | 0.016 | 0.003(0) | 0.015 | 0.019 | 0.014 | 0.018 | 0.011 | 0.021 | 0.015 | 0.017 |
Measurement | Units | N | Median | Sigmaest. |
Good 25th to 75th percentiles |
Satisfactory Median ± Sigma |
Marginal Median ± 2 Sigma |
Meets Data Quality Objectives |
||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | pH units | 56 | 5.25 | 0.08(5) | 5.20 | 5.30 | 5.17 | 5.33 | 5.08 | 5.42 | 5.15 | 5.35 |
Conductivity | μS/cm | 51 | 8.3 | 0.3(7) | 8.0 | 8.5 | 8.0 | 8.6 | 7.6 | 9.0 | 7.8 | 8.8 |
Acidity | μeq/L | 5 | 5.4 | 10.3(4) | 5.1 | 19.0 | 0.0 | 15.7 | 0.0 | 26.0 | 4.1 | 6.7 |
Sulfate | mg/L | 53 | 0.942 | 0.029(7) | 0.918 | 0.958 | 0.913 | 0.971 | 0.883 | 1.001 | 0.895 | 0.989 |
Nitrate | mg/L | 56 | 1.059 | 0.030(8) | 1.038 | 1.078 | 1.029 | 1.089 | 0.998 | 1.120 | 1.007 | 1.111 |
Ammonium | mg/L | 57 | 0.395 | 0.017(4) | 0.384 | 0.407 | 0.378 | 0.412 | 0.361 | 0.429 | 0.368 | 0.422 |
Fluoride | mg/L | 14 | 0.019 | 0.002(6) | 0.017 | 0.020 | 0.017 | 0.021 | 0.014 | 0.024 | 0.016 | 0.022 |
Chloride | mg/L | 55 | 0.194 | 0.011(9) | 0.185 | 0.201 | 0.183 | 0.205 | 0.171 | 0.217 | 0.175 | 0.213 |
Sodium | mg/L | 54 | 0.103 | 0.006(9) | 0.097 | 0.106 | 0.097 | 0.109 | 0.090 | 0.116 | 0.093 | 0.113 |
Potassium | mg/L | 48 | 0.036 | 0.006(7) | 0.034 | 0.043 | 0.030 | 0.042 | 0.023 | 0.049 | 0.029 | 0.043 |
Calcium | mg/L | 52 | 0.175 | 0.024(5) | 0.158 | 0.191 | 0.151 | 0.199 | 0.127 | 0.223 | 0.149 | 0.201 |
Magnesium | mg/L | 53 | 0.041 | 0.003(0) | 0.039 | 0.043 | 0.039 | 0.043 | 0.036 | 0.046 | 0.037 | 0.045 |