Study Results

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Study 61 Summary Latest

This study was completed in 2019.

These tables summarize the measurements reported to the QA-SAC for Inter-laboratory Comparison Study 61. A total of 72 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 Nov 28, 2019.

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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 66 4.63 0.04(8) 4.61 4.67 4.59 4.67 4.54 4.72 4.56 4.70
Conductivity μS/cm 61 36.9 1.0(4) 36.1 37.5 35.9 37.9 34.9 38.9 34.4 39.4
Acidity μeq/L 7 27.1 7.4(9) 19.9 30.0 19.7 34.5 12.2 42.0 20.4 33.8
Sulfate mg/L 64 4.254 0.098(4) 4.173 4.305 4.156 4.352 4.058 4.450 4.042 4.466
Nitrate mg/L 66 2.127 0.051(9) 2.103 2.172 2.075 2.178 2.023 2.230 2.021 2.232
Ammonium mg/L 68 0.777 0.036(3) 0.750 0.798 0.741 0.813 0.705 0.849 0.723 0.831
Fluoride mg/L 18 0.048 0.004(1) 0.046 0.051 0.044 0.052 0.040 0.056 0.039 0.057
Chloride mg/L 64 3.571 0.080(1) 3.512 3.620 3.491 3.651 3.411 3.731 3.214 3.928
Sodium mg/L 65 2.235 0.066(7) 2.173 2.262 2.169 2.301 2.102 2.368 2.012 2.458
Potassium mg/L 64 0.387 0.016(7) 0.373 0.395 0.370 0.403 0.354 0.419 0.310 0.463
Calcium mg/L 62 0.597 0.032(6) 0.573 0.616 0.565 0.629 0.532 0.662 0.508 0.686
Magnesium mg/L 61 0.247 0.009(3) 0.240 0.252 0.238 0.256 0.229 0.265 0.223 0.271
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 66 4.46 0.05(2) 4.43 4.50 4.41 4.50 4.36 4.55 4.39 4.52
Conductivity μS/cm 61 23.0 0.8(9) 22.3 23.5 22.2 23.8 21.3 24.7 21.4 24.6
Acidity μeq/L 7 38.5 2.8(2) 36.2 40.0 35.7 41.3 32.9 44.1 28.9 48.1
Sulfate mg/L 65 2.136 0.076(0) 2.089 2.191 2.061 2.211 1.985 2.287 2.030 2.242
Nitrate mg/L 65 2.006 0.055(2) 1.964 2.038 1.951 2.061 1.896 2.116 1.906 2.106
Ammonium mg/L 66 0.448 0.020(9) 0.436 0.464 0.427 0.468 0.406 0.489 0.417 0.478
Fluoride mg/L 20 0.101 0.003(7) 0.098 0.103 0.097 0.104 0.094 0.107 0.081 0.120
Chloride mg/L 63 0.284 0.016(3) 0.276 0.298 0.268 0.300 0.252 0.316 0.256 0.312
Sodium mg/L 61 0.186 0.013(3) 0.174 0.192 0.173 0.199 0.160 0.212 0.168 0.204
Potassium mg/L 57 0.043 0.009(3) 0.040 0.052 0.034 0.052 0.025 0.061 0.035 0.051
Calcium mg/L 60 0.258 0.020(0) 0.239 0.265 0.238 0.277 0.218 0.297 0.219 0.296
Magnesium mg/L 56 0.054 0.003(7) 0.051 0.056 0.051 0.057 0.047 0.061 0.049 0.059
Measurement Units N Median Sigmaest.

Good

25th to 75th percentiles

Satisfactory

Median ± Sigma

Marginal

Median ± 2 Sigma

Meets Data Quality Objectives

pH pH units 66 5.10 0.05(9) 5.07 5.15 5.05 5.15 4.99 5.21 5.00 5.20
Conductivity μS/cm 60 6.4 0.2(8) 6.3 6.6 6.2 6.6 5.9 6.9 6.0 6.8
Acidity μeq/L 7 9.0 7.3(4) 7.7 17.6 1.7 16.3 0.0 23.6 6.8 11.2
Sulfate mg/L 61 0.589 0.025(6) 0.572 0.606 0.564 0.614 0.538 0.640 0.560 0.618
Nitrate mg/L 64 0.671 0.024(5) 0.653 0.685 0.647 0.694 0.622 0.719 0.637 0.704
Ammonium mg/L 66 0.212 0.011(9) 0.205 0.220 0.201 0.223 0.189 0.235 0.198 0.226
Fluoride mg/L 18 0.035 0.004(6) 0.032 0.038 0.030 0.039 0.026 0.043 0.028 0.041
Chloride mg/L 56 0.085 0.011(7) 0.082 0.097 0.074 0.096 0.062 0.108 0.077 0.093
Sodium mg/L 50 0.045 0.005(9) 0.040 0.048 0.040 0.050 0.034 0.056 0.041 0.049
Potassium mg/L 42 0.019 0.007(4) 0.016 0.025 0.012 0.025 0.004 0.033 0.015 0.022
Calcium mg/L 56 0.104 0.016(3) 0.089 0.111 0.088 0.119 0.071 0.136 0.088 0.119
Magnesium mg/L 49 0.021 0.002(6) 0.019 0.022 0.019 0.023 0.016 0.026 0.019 0.023