Study Results

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Study Summary Ring Diagrams Tabular Summary Measurement Record

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.

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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 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