LGVSD Fact Sheet

NPDES Permit NO. CA 0037851Attachment 6

Order No. R2-2003-XXXX

Attachment 6

Statistical Analysis of Effluent Data for Infeasibility Determination

(Chromium VI, Nickel, Lead, Copper, and Mercury)

Las Gallinas Valley Sanitary District

NPDES Permit No. CA 0037851 Order NO. R2-2003-XXXX

Fact Sheet

Software: MiniTab

Censored data analysis method: robust regression method

1. Chromium (VI)

There are a total of 29 chromium (V) effluent data points (during the discharge season from November 1998 through December 2002) with 14 non-detected values (Method detection limit (MDL) = 3 and 5 g/L, respectively). The data ranged from 2 to 10 g/L. Lognormal distribution fits the data above the MDLs.

Statistics estimates of the raw chromium data (regression method)

Variable N Mean Median TrMean StDev SE Mean

ESTIMATE 29 0.9437 0.9000 0.9176 0.4365 0.0811

Variable Minimum Maximum Q1 Q3

ESTIMATE 0.3917 2.2000 0.6041 1.0591

Statistics estimates of the log-transformed data:

Variable N Mean Median TrMean StDev SE Mean

ESTIMATE 29 -0.1495 -0.1054 -0.1551 0.4290 0.0797

Variable Minimum Maximum Q1 Q3

ESTIMATE -0.9373 0.7885 -0.5040 0.0567

Mean = 0.94 g/L

95th percentile = exp(mean+1.645*standard deviation) = 1.74 g/L

99th percentile = exp(mean+2.326*standard deviation) = 2.34 g/L

Figure 1. Probability Plot of Censored Chromium (VI) Effluent Data

Figure 2. Box Plot of Censored Chromium (VI) Effluent Data

2. Lead

19 out of 29 data points are non-detects

MDLs = 2.0, 2.5 g/L

Statistics estimates of the raw lead data (regression method)

Variable N Mean Median TrMean StDev SE Mean

ESTIMATE 29 0.3243 0.2185 0.2913 0.3098 0.0575

Variable Minimum Maximum Q1 Q3

ESTIMATE 0.0385 1.5000 0.1208 0.4500

Statistics estimates of the log-transformed lead data (regression method)

Variable N Mean Median TrMean StDev SE Mean

ESTIMATE 29 -1.493 -1.521 -1.498 0.881 0.164

Variable Minimum Maximum Q1 Q3

ESTIMATE -3.256 0.405 -2.115 -0.805

Mean = 0.32 g/L

95th percentile = exp(mean+1.645*standard deviation) = 0.96g/L

99th percentile = exp(mean+2.326*standard deviation) = 1.74 g/L

Figure 3. Probability Plot of Censored Lead Effluent Data

Figure 4. Box Plot of Censored Lead Effluent Data

3. Nickel

Total No. of data points = 29

Total No. of non-detects = 5

MDLs = 3, 4.5, 5.0 g/L

Statistics estimates of raw nickel data (regression method)

Variable N Mean Median TrMean StDev SE Mean

ESTIMATE 29 4.632 4.500 4.586 1.492 0.277

Variable Minimum Maximum Q1 Q3

ESTIMATE 2.314 8.200 3.640 5.500

Statistics estimates of log-transformed nickel data for percentile estimate (regression method)

Variable N Mean Median TrMean StDev SE Mean

ESTIMATE 29 1.4830 1.5041 1.4838 0.3245 0.0603

Variable Minimum Maximum Q1 Q3

ESTIMATE 0.8390 2.1041 1.2912 1.7006

Mean = 4.63 g/L

95th percentile = exp( mean + 1.645 StDev) = 7.51 g/L

99th percentile = exp( mean + 2.323 StDev) = 9.37 g/L

Figure 5. Probability Plot of Censored Nickel Effluent Data

Figure 6. Box Plot of Censored Nickel Effluent Data

4. Copper

No. of data points: 30 (all above detection limit)

Summary statistics of copper effluent data:

Variable N Mean Median TrMean StDev SE Mean

Cu 30 10.333 9.000 9.769 4.294 0.784

Variable Minimum Maximum Q1 Q3

Cu 5.000 25.000 7.000 12.250

Percentile estimates

95% CI 95% CI

Approximate Approximate

Percent Percentile Lower Limit Upper Limit

1.00 4.2314 3.3145 5.4020

2.00 4.6608 3.7266 5.8292

3.00 4.9555 4.0124 6.1203

4.00 5.1895 4.2407 6.3505

5.00 5.3879 4.4351 6.5454

6.00 5.5628 4.6069 6.7170

7.00 5.7207 4.7623 6.8721

8.00 5.8660 4.9054 7.0147

9.00 6.0013 5.0387 7.1478

10.00 6.1286 5.1642 7.2731

20.00 7.1631 6.1799 8.3027

30.00 8.0158 7.0013 9.1772

40.00 8.8243 7.7572 10.0382

50.00 9.6536 8.5034 10.9595

60.00 10.5609 9.2838 12.0137

70.00 11.6262 10.1548 13.3108

80.00 13.0101 11.2244 15.0800

90.00 15.2062 12.8134 18.0459

91.00 15.5288 13.0380 18.4954

92.00 15.8870 13.2853 18.9982

93.00 16.2903 13.5611 19.5689

94.00 16.7530 13.8741 20.2292

95.00 17.2967 14.2379 21.0125

96.00 17.9580 14.6749 21.9756

97.00 18.8058 15.2268 23.2259

98.00 19.9951 15.9871 25.0078

99.00 22.0240 17.2515 28.1169

99.87 28.0794 20.8336 37.8452 (interim limit)

99.90 28.8748 21.2868 39.1675

Mean = 10.33 g/L

95th percentile = 17.3 g/L

99th percentile = 22.0 g/L

99.87th percentile = 28g/L

Figure 7. Probability Plot of Copper Effluent Data

Figure 8. Box Plot of Copper Effluent Data

5. Mercury

Total of data points: 30 (all data are detected)

Summary statistics of mercury data:

Variable N Mean Median TrMean StDev SE Mean

hg 30 0.03517 0.03100 0.03342 0.01238 0.00226

Variable Minimum Maximum Q1 Q3

hg 0.01800 0.07700 0.02775 0.03750

Percentile estimates:

95% CI 95% CI

Approximate Approximate

Percent Percentile Lower Limit Upper Limit

1.00 1.69E-02 1.38E-02 0.020665

2.00 1.83E-02 1.52E-02 0.022018

3.00 1.92E-02 1.61E-02 0.022931

4.00 2.00E-02 1.69E-02 0.023648

5.00 2.06E-02 1.75E-02 0.024251

6.00 2.12E-02 1.81E-02 0.024780

7.00 2.17E-02 1.86E-02 0.025256

8.00 2.21E-02 1.91E-02 0.025692

9.00 2.26E-02 1.95E-02 0.026098

10.00 2.30E-02 1.99E-02 0.026479

20.00 2.61E-02 2.31E-02 0.029569

30.00 2.87E-02 2.57E-02 0.032143

40.00 3.11E-02 2.79E-02 0.034638

50.00 3.35E-02 3.02E-02 0.037269

60.00 3.61E-02 3.25E-02 0.040234

70.00 3.91E-02 3.50E-02 0.043824

80.00 4.30E-02 3.80E-02 0.048628

90.00 4.90E-02 4.25E-02 0.056480

91.00 4.98E-02 4.31E-02 0.057650

92.00 5.08E-02 4.38E-02 0.058954

93.00 5.19E-02 4.45E-02 0.060427

94.00 5.31E-02 4.54E-02 0.062121

95.00 5.45E-02 4.64E-02 0.064120

96.00 5.63E-02 4.75E-02 0.066561

97.00 5.85E-02 4.90E-02 0.069704

98.00 6.15E-02 5.11E-02 0.074134

99.00 6.67E-02 5.44E-02 0.081741

99.90 8.36E-02 6.48E-02 0.107758

Mean = 0.036g/L

95th percentile = 0.054g/L

99th percentile = 0.067 g/L

Figure 9. Probability Plot of Mercury Effluent Data

Figure 10. Box Plot of Mercury Effluent Data

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