Study Results
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 |