Questions for Pleasant Prairie

The following questions relate to EPA’s review of the analytical data We Energies provided with 

comments on the proposed effluent guidelines and in response to EPA’s request for additional data.

1. Using the process flow diagram included in We Energies’ 2/10/2014 letter, please identify the 

location for each sample point associated with data submitted with comments or in response to 

EPA’s data request:

a. Data submitted with comments

i. Effluent from FGD Chemical Precipitation Wastewater Treatment System

ii. Effluent from FGD Wastewater Treatment System (SP 102)

iii. Effluent from the FGD Chemical Precipitation Wastewater Treatment System

iv. Influent to FGD Chemical Precipitation Wastewater Treatment System

v. Influent to FGD Wastewater Treatment System (Reaction Tank #1 Influent)

vi. Influent to FGD Wastewater Treatment System (for Reaction Tank #1 Influent)

vii. Internal Point within the FGD Wastewater Treatment System (Primary Clarifier 

Effluent)

viii. Internal point within the FGD Wastewater Treatment System (Primary Clarifier 

Effluent)

ix. Internal Point within the FGD Wastewater Treatment System (Secondary 

Clarifier Effluent)

x. Internal point within the FGD Wastewater Treatment System (Secondary

Clarifier Effluent)

b. Response to EPA’s data request

i. FGD Purge

ii. Secondary Clarifier

iii. Chem Prep. Effluent

2. How were samples collected for the secondary clarifier?

3. Are all grab samples single grabs or are there composites of multiple grabs?

4. EPA was not able to verify the RL or dilution factor in the lab reports. How did Pleasant Prairie 

obtain these values?

Analytical Data Provided in Comments 

5. Why was arsenic measured using Method 6020A, since it is not included in 40 CFR Part 136 as a 

CWA-approved method? (note that 6020A was also used to analyze samples of secondary 

clarifier effluent, provided in response to EPA’s data request) 

6. As noted in the analytical spreadsheet, We Energies provided the average result when multiples 

samples were collected from the same sampling location on the same day.

a. There are several instances where the calculated average mercury value should end in a 

decimal (i.e., XX.5), which differs from the spreadsheet entry. Do you agree the 

discrepancy is due to We Energies rounding the value down to the nearest integer (see 

Table 1)?
b. On a few days, where multiple samples from the same sampling location were collected 

for an analyte, the two samples were averaged together but the MDL for only one of the 

individual samples was included in the analytical spreadsheet (see Table 2). Please 

explain the reasoning for which MDL was provided in the analytical spreadsheet. 

Table 1. Pleasant Prairie Averaged Values and EPA Calculated Average Values

Type of Wastewater Date Analyte Procedure Units

NonDetect 

Indicator Amount

EPA

Calculated 

Average

FGD WWTS Effluent - SP 102 5/25/2010 Mercury Total ng/L D 374 374.5

FGD WWTS Effluent - SP 102 6/9/2010 Mercury Total ng/L D 92 92.5

FGD WWTS Effluent - SP 102 7/7/2010 Mercury Total ng/L D 94 94.5

FGD WWTS Effluent - SP 102 11/23/2010 Mercury Total ng/L D 56 56.5

FGD WWTS Effluent - SP 102 12/15/2010 Mercury Total ng/L D 64 64.5

FGD WWTS Effluent - SP 102 6/21/2011 Mercury Total ng/L D 92 92.5

FGD WWTS Effluent - SP 102 6/28/2011 Mercury Total ng/L D 68 68.5

FGD WWTS Effluent - SP 102 7/13/2011 Mercury Total ng/L D 58 58.5

FGD WWTS Effluent - SP 102 7/26/2011 Mercury Total ng/L D 92 92.5

FGD WWTS Effluent - SP 102 12/28/2011 Mercury Total ng/L D 88 88.5

FGD WWTS Effluent - SP 102 12/30/2011 Mercury Total ng/L D 100 100.5

FGD WWTS Effluent - SP 102 11/13/2012 Mercury Total ng/L D 94 94.5

FGD WWTS Effluent - SP 102 11/14/2012 Mercury Total ng/L D 88 88.5

FGD WWTS Effluent - SP 102 4/10/2013 Mercury Total ng/L D 78 78.5

FGD WWTS Effluent - SP 102 4/24/2013 Mercury Total ng/L D 80 80.5

Table 2. Pleasant Prairie Averaged Values with Different MDLs for the Averaged Samples

Type of Wastewater Date Analyte Procedure Units

NonDetect 

Indicator Amount

MDL in 

Data 

Table

MDL in 

Lab 

Report

FGD WWTS Effluent - SP 102 8/5/2008 Mercury Total ng/L D 335 60 1.2, 60 

FGD WWTS Effluent - SP 102 5/24/2010 Mercury Total ng/L D 340 14 14, 15

Primary Clarifier Effluent 6/17/2008 Arsenic Total ug/L < [blank] 4.7

4.7, 2.4,

2.4

Primary Clarifier Effluent 3/30/2009 Mercury Dissolved ng/L D 3,500 25 12, 25
7. There are several discrepancies between the MDL values reported in the analytical spreadsheet 

compared to the MDL cited in the lab report (see Table 3). Please confirm which MDL value is 

correct for these data samples.

Table 3. Pleasant Prairie MDL Value Discrepancies between Analytical Spreadsheet and Lab Reports

Type of Wastewater Date Analyte Procedure Units

NonDetect 

Indicator Amount

MDL in 

Data 

Table

MDL in 

Lab 

Report

Reaction Tank #1 Influent 12/18/2007 Mercury Dissolved ng/L D 2,400 50 1

Reaction Tank #1 Influent 8/4/2008 Mercury Dissolved ng/L D 2,300 60 1.2

Secondary Clarifier 

Effluent* 10/28/2008 Mercury Total ng/L D 530 16 0.63

Secondary Clarifier 

Effluent 7/10/2009 Mercury Total ng/L D 340 12 0.5

Secondary Clarifier 

Effluent 8/7/2009 Mercury Total ng/L D 410 14 0.57

Secondary Clarifier 

Effluent 8/10/2009 Mercury Total ng/L D 470 14 0.57

Secondary Clarifier 

Effluent 8/10/2009 Mercury Dissolved ng/L D 47 14 0.57

Primary Clarifier Effluent 11/19/2009 Mercury Dissolved ng/L D 220 25 28

Primary Clarifier Effluent 11/24/2009 Mercury Dissolved ng/L D 260 25 28

Primary Clarifier Effluent 12/21/2009 Mercury Dissolved ng/L D 730 25 28

Primary Clarifier Effluent 4/16/2010 Mercury Dissolved ng/L D 390 25 28

Primary Clarifier Effluent 5/5/2010 Mercury Dissolved ng/L D 440 25 28

*Dump valve

8. The primary clarifier effluent and secondary clarifier effluent results for mercury from 

11/6/2007 through 11/15/2007 and 3/30/2009 through 3/31/2009 note that “Jar testing may 

have been conducted on this date.” Do these sample results represent the primary clarifier 

effluent or the primary clarifier effluent after additional jar testing?

9. The secondary clarifier effluent results for mercury on 10/28/2008, 10/29/2008, and 3/16/2009 

notes that the sample is “Dump Valve.” What does this sample represent?

10. The secondary clarifier effluent result for mercury on 10/29/2008 notes that the sample is 

“Sample Tap.” What does this sample represent?
Analytical Data Provided in Data Request 

11. The total mercury and total mercury field duplicate for the FGD WWTS Effluent – SP 102 on 

8/6/2013 both have a reported MDL of 0.45 ng/L in the lab report. However, according to the 

analytical spreadsheet, the MDL is reported as 11 ng/L. Because of the elevated MDL, the 

duplicate sample was treated as a J-value in the calculation of the average. Which MDL values

are correct? Should the duplicate sample be considered a J-value?

12. For the total mercury result from the FGD WWTS Effluent – SP 102 on 10/29/2013, the native 

and duplicate sample were averaged together. However, only the native sample MDL (18 ng/L) 

was reported in the spreadsheet. The duplicate sample MDL was 0.72 ng/L. Please explain the 

reasoning for why the native sample MDL was provided in the analytical spreadsheet.

Additional Questions

13. Pleasant Prairie stated that hydrochloric acid is added to Reaction Tank #2 at a dose 

concentration of 0.012 g/L and dosage rate of 1.9 gpd. When did Pleasant Prairie begin adding 

hydrochloric acid to Reaction Tank #2? (EPA’s understanding is that during the initial operation 

of the system, the plant was only adding hydrochloric acid downstream of the secondary 

clarifier.)

14. Please provide a general timeline for the collection and analysis of the mercury samples that are 

analyzed using the in-plant analyzer (i.e., the DMA 80 Hg Analyzer). Please include enough 

detail to answer the following questions:

a. Who collects the mercury samples (e.g., position title)?

b. What type of handling procedures are used (i.e., are clean hands/dirty hands protocols 

used)?

c. Where are the samples taken for analysis?

d. Who performs the analysis (e.g., position title)?

e. What type of experience is required to perform the analysis?

f. How long after the analysis is started are the results available?

g. How long after the sample is collected are the results available?

15. Would pollutant characteristics of the secondary clarifier effluent differ from phys-chem 

effluent (SP-102)?

16. We observed several results at substantially higher concentrations relative to the other effluent 

values. What was happening with plant processes, coal sources, treatment system operation? 

What actions were taken in response to these observed concentrations? 

a. Mercury data for 2007 at highly elevated concentrations

b. 1/31/11 (1440 ng/L) and 2/1/11 (970 ng/L) – secondary clarifier (compare to data for 

2/3 and 2/4)

c. 2/15/11 (780 ng/L) and 2/16/11 (615 ng/L) – CP effluent

d. 3/18/11 (665 ng/L) – CP effluent

e. 2/3/12 (815 ng/L) and 2/4/12 (705 ng/L) – CP effluent

f. 6/13/12 (2900 ng/L) – CP effluent

g. 6/18/12 (8300 ng/L) – secondary clarifier
h. 6/28/12 (640 ng/L) – CP effluent

i. 1/3/13 (360 ng/L clarifier effluent; 855 ng/L CP effluent)

17. What day did the plant switch from TMT-15 to Nalmet?