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.   

Answers, provided by We Energies, appear in bold and italicized font.   

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:   

The process flow diagram (PFD) was included as Figure 6 in the comments submittal, dated

September 20, 2013.  For convenience, it is enclosed in Appendix A.

a. Data submitted with comments

i. Effluent from FGD Chemical Precipitation Wastewater Treatment System  

This sample point represents the split sample from the 2009 EPA Sampling

Event.  It is designated as “SP‐102” on the PFD.

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

This sample point is designated as “SP‐102” on the PFD.

iii. Effluent from the FGD Chemical Precipitation Wastewater Treatment System

This sample point represents the split sample from the 2009 EPA Sampling

Event.  It is designated as “SP‐102” on the PFD.

iv. Influent to FGD Chemical Precipitation Wastewater Treatment System   

This sample point represents the split sample from the 2009 EPA Sampling

Event.  It is designated as “SP‐1” on the PFD.

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

This sample point is designated as “SP‐2” on PFD.

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

This sample point is designated as “SP‐2” on PFD (same answer as “v”).

   

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

Effluent)  

This sample point is designated as “SP‐3” on PFD.
viii. Internal point within the FGD Wastewater Treatment System (Primary Clarifier

Effluent)

This sample point is designated as “SP‐3” on PFD (same answer as “vii”).

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

Clarifier Effluent)

This sample point is designated as “SP‐4” on PFD.

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

Clarifier Effluent)  

This sample point is designated as “SP‐4” on PFD (same answer as “ix”).

b. Response to EPA’s data request   

As discussed on our June 4, 2013, conference call, we used the same sample location

naming conventions for the additional data submitted in February 2014 as the original

comment submittal in September 2013.  We did not use the naming conventions

presented below.

i. FGD Purge

ii. Secondary Clarifier

iii. Chem Prep. Effluent

2. How were samples collected for the secondary clarifier?   

The secondary clarifier samples are collected from a sample tap.

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

All grab samples are single grabs.  We provided daily average values on the spreadsheet

submittal and noted in Column Q, “Qualifier Description” whether the amount was an average

of two (2) or more samples collected on the date.  The Total Mercury samples at the “Effluent

from FGD Wastewater Treatment System (SP 102)” represent the sample and field duplicate

collected at one time during the day.

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

obtain these values?   

The reporting limit and dilution factor were provided by the laboratory (We Energies

Laboratory Services).  These values were obtained from analytical and technical records

containing raw and derived data.  According to NR 149.47(1)(c), Wis. Adm. Code, laboratories

who perform tests for internal clients do not need to include all of the required elements in

their laboratory reports, as long as the laboratory retains and makes available to the

department, upon request, records that include the elements specified in the section.  
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)

Arsenic was analyzed using Analytical Method EPA 6020A, Inductively Coupled Plasma

Dynamic Reaction Cell Mass Spectrometry (ICP‐DRC‐MS), as allowed by Chapter NR 219 of the

Wisconsin Administrative Code, which specifies the analytical test methods and procedures

applicable to effluent limitations for discharges from point sources.  Both Methods (6020A and

200.8) use inductively coupled plasma‐mass spectrometry; however, Method 6020A is a more

recent method (2007) which includes additional QC as well as a performance‐based statement

as compared to the older  Method 200.8 (1994).    

The Wisconsin Department of Natural Resources (WDNR), authorized by the EPA to administer

the NPDES permit program in the state of Wisconsin, incorporated  SW‐846 methods (Test

Methods for Evaluating Solid Waste, Physical/Chemical Methods) into Chapter 219, Wis. Adm.

Code, in December 1993 and September 1995.  During the rulemaking period, the proposed

rules were sent to EPA Region V seeking comment.  No response from the Region was

received, so the WDNR enacted the rule change.  Later, EPA Region V inquired about the use of

SW‐846 methods for analyzing wastewater, and WDNR submitted a written response in

October 1997 (see Appendix B for the letter from D. Dinsmore and R. Weber (WDNR) to D.

Wesolowski (EPA Region V)).  As WDNR explained in the letter:

“The SW‐846 methods are technically equivalent to the approved wastewater

methods listed in NR 219.  Many SW‐846 methods utilize newer, more sensitive

technologies than existing methods.  The addition of the solid waste methods will

consolidate the number of references needed by laboratories certified under NR 149,

and will ensure accurate reporting of the methodology being used by registered and

certified laboratories.”

The letter continues:

“The background memo notes that the federal regulations do not include the SW‐846

methods in 40 CFR Part 136; however, we assert this move, while technically

approving more methods than the federal regulations, conforms to the [statutory]

provision allowing the Department to set more stringent requirements.  The SW‐846

methods include stricter quality control requirements for some analytes and utilize

more sensitive technologies than the currently approved methods.”      

The letter concludes:

“In summary, we believe that SW‐846 method conditions are equivalent or superior to

those in 40 CFR Part 136.  The more stringent quality control in these methods yields

higher quality data.”   

The following comparison of ICP‐MS Methods 6020A and 200.8 demonstrates that the analysis

and quality control elements contained within Method 6020A (and followed by We Energies
Laboratory Services when conducting arsenic analyses of Pleasant Prairie FGD wastewater)

are equivalent to or exceed those contained in Method 200.8.  A representative QC

demonstration of three samples analyzed for arsenic can be found in Appendix C.   

Element Method 6020A1   Method 200.82  

Instrument Quality Control Measures

Mass Calibration/Tuning 10.2 Perform daily prior to instrument

calibration in the regions of interest.

The mass calibration and resolution

parameters are required criteria which

must be met prior to any samples

being analyzed.  Mass calibration

criteria is +/‐ 0.1 amu with resolution

<0.9 amu full width at 10% peak

height. We Laboratory Services tunes

across the range of C12 ‐ Th232.

10.2.1 Conduct mass calibration and

resolution checks using the tuning

solution covering masses Mg24 ‐ 

Pb208. Adjust the spectrometer

resolution to produce a peak width of

0.75 amu at 5% height. Adjust if it has

shifted by more than 0.1 amu from

unit mass.

Daily Instrument Performance

Check

11.4 Following instrument

optimization, analyze the tuning

solution to monitor response for a

selection of elements covering mass

range of Mg24 ‐ U238 with a minimum

response required for each mass in

order to proceed with the analysis. A

minimum of 4 replicates should give

<5% RSD. Additional Internal: monitor

Oxide Ratio and Double Charged

Species with acceptance criteria of

<3% for each. Monitor background at

mass 5 and 220 with criteria of < 3

counts for each.

10.2.2 Instrument stability must be

demonstrated by running the tuning

solution a minimum of 5 times with

<5% RSD.

Instrument Calibration 10.4.2 Calibrate daily with a minimum

of a calibration blank and a single

standard. Use the average of at least 3

integrations  for both calibration and

sample analyses.

10.4 The instrument must calibrated

using the calibration blank and

calibration standards at one or more

concentration levels. A minimum of

three replicate integrations are

required for data acquisition.

Internal Standard 9.6 Control limit >70% of initial

calibration blank

Control limit 60‐125% of initial

calibration blank
Element Method 6020A1

   Method 200.82  

Initial Calibration Verification 7.8, 10.4.3 Initial Calibration

Verification (ICV) following instrument

calibration prepared from an

independent source at the mid‐point

of the calibration curve. QC limits are

+/‐ 10%.

7.8 Quality Control Sample (QCS). The

QCS should be obtained from a source

outside the laboratory.  

9.2.3 When beginning the use of this

method, on a quarterly basis or as

required to meet data quality needs,

verify the calibration standards and

acceptable instrument performance

with the QCS. To verify the calibration

standards the determined mean

concentration from three analyses of

the QCS must be within +/‐ 10% of the

stated QCS value. If the QCS is used for

determining acceptable on‐going

instrument performance, analysis of

the QCS prepared to a concentration

of 100 ug/L must be within +/‐ 10% of

the QCS value.

Initial calibration Blank 10.4.1.2 Analyze the calibration blank

(ICB) once following instrument

calibration; results should be <LOQ.

10.5 The rinse blank should be used to

flush the system between solution

changes for blanks, standards and

samples. Allow sufficient rinse time to

remove traces of the previous sample.

Low‐Level Initial Calibration

Verification

10.4.3 Low‐Level Initial Calibration

Verification (LLICV) following

instrument calibration prepared from

'same source' standards at the Level of

Quantitation (LOQ). Suggested QC

limits are +/‐ 30%.

No mention.

Continuing Calibration

Verification

10.4.4 Following every 10 samples and

at the end of the analysis, prepare the

Continuing Calibration Verification

(CCV) from 'same source' standards at

the mid‐point of the calibration curve.

QC limits +/‐ 10%.

7.8 Quality Control Sample (QCS). The

QCS should be obtained from a source

outside the laboratory. 9.2.3 If the QCS

is used for determining acceptable on‐

going instrument performance,

analysis of the QCS prepared to a

concentration of 100 ug/L must be

within +/‐ 10% of the QCS value.

Continuing Calibration Blank 10.4.4 Analyze the calibration blank

(CCB) following every 10 samples and

at the end of the analysis.; results

should be <LOQ.

10.5 The rinse blank should be used to

flush the system between solution

changes for blanks, standards and

samples. Allow sufficient rinse time to

remove traces of the previous sample.
Element Method 6020A1

   Method 200.82  

Low‐Level Continuing

Calibration Verification

10.4.4 Following instrument

calibration, prepare the LLCCV from

'same source' standards to

demonstrate accuracy as an additional

check at the low end of the calibration

curve. QC limits are +/‐ 30%.

No mention.

Interference Check Solutions 7.7, 10.5 The ICS is prepared to contain

known concentrations of interfering

elements that will demonstrate the

magnitude of interferences and

provide an adequate test of any

corrections.

No mention.

Interference Control (specific

to Arsenic)

Because Method 6020A is a

performance‐based method and

advances in ICP‐MS technology have

provided reaction cell (DRC) and

collision cell (CRC) technology for

reducing polyatomic interferences, we

utilize the DRC with oxygen as the

reaction cell gas and analyze Arsenic

at Mass 91 as AsO91 which effectively

moves monoisotopic arsenic Mass 75

away from the ArCl75 interference.  

Sections 4.1.1 and 4.1.3 discuss

isobaric and polyatomic interferences

and the need to use mathematical

equations to correct for.

Method Detection Limit

determination

MDLs are determined following 40 CFR

Part 136 Appendix B.

9.2.1 describes initial demonstration

of performance data which includes

MDL determinations.

Linear Range determination Yes, section 10.6 Same as above, see 9.2.1.

Sample Quality Control Measures:

Laboratory Method (Reagent)

Blank

7.6.2, 9.8 For each batch of samples

processed, prepare and analyze a

Laboratory Reagent Blank which must

be carried through the entire sample

preparation and analysis process. QC

limits are +/‐ the MDL or <10% of

sample concentration.

7.6.2 Must contain all the reagents in

the same volumes as used in

processing samples. The LRB must be

carried through the entire sample

preparation scheme as the samples

including digestion, when applicable.

QC limits are +/‐ the MDL or <10% of

sample concentration.

Laboratory Control Sample 9.9 For each batch of samples

processed, prepare and analyze a

Laboratory Control Sample (LCS) which

must be carried through the entire

sample preparation and analysis

process. QC limits are +/‐ 20%. In

addition We Laboratory Services

processes a LCS‐Duplicate as a way to

monitor both accuracy and precision

(<20 RPD).

7.9 Laboratory Fortified Blank (LFB).

The LFB must be carried through the

entire preparation scheme as the

samples including sample digestion,

when applicable. 9.3.3 Default

recovery QC limit of 85‐115%.
Element Method 6020A1

   Method 200.82  

Matrix Spike/Matrix Spike

Duplicate

9.10 For each batch of samples

processed, prepare and analyze a

Matrix Spike (MS) and a Matrix Spike

Duplicate (MSD) which must be

carried through the entire sample

preparation and analysis process.

Default QC limits are +/‐ 25% recovery

and <20 RPD.

9.4.2 Laboratory Fortified Matrix

(LFM): The laboratory must add a

known amount of analyte to a

minimum of 10% of the routine

samples. The LFM must be carried

through sample preparation

procedures. 9.4.3 Default recovery QC

limit of 70‐130%.

Additional QC:  

Post‐Digestion spike addition yes No mention.

Dilution Test yes No mention.

1 Method 6020A, Inductively Coupled Plasma‐Mass Spectrometry, Revision 1, February 2007.    2 Method 200.8, Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma – Mass

Spectrometry, J.T. Creed, C.A. Brockhoff, and T.D. Martin, Revision 5.4, 1994.   

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)?  

Yes

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.

Only one field was available for the MDL, so we presumed EPA wanted one numerical

value.  We chose to provide the highest MDL as this is the most conservative data point.  It

appears that the 5/24/10 FGD WWTS Effluent – SP102 MDL was in error and that we

should have reported fifteen (15) rather than fourteen (14).  Additionally, the lower MDL

for the 8/5/2008 FGD WWTS Effluent – SP102 sample (1.2) does not account for the

dilution factor (50).  Therefore, the lab reports should have reported an MDL of sixty (60)

for both samples.  

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

Type of Wastewater Date Analyte Procedure Units

Non‐

Detect

Indicator Amount

EPA

Calculated

Average
Type of Wastewater Date Analyte Procedure Units

Non‐

Detect

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

Non‐

Detect

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.  

The MDL reported in the data table is correct for samples listed through 8/10/2009 and

reflects the dilution factor adjusted MDL. The MDL listed in the data table for samples

11/19/2009 through 5/5/2010 should be 28 as was correctly reported in the lab report.

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

Type of Wastewater Date Analyte Procedure Units

Non‐

Detect

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?   

After further investigation, the November 2007 (11/6/2007 – 11/15/2007) data represent

primary clarifier effluent AFTER additional jar testing.  We would agree that this data should

not be used by EPA in its rulemaking.  On March 30 and 31, 2009, additional jar testing was

conducted to further optimize treatment of the wastewater treatment system.  With the

exception of one data point, “P4 FGD WWTP Sec. Clar. Effluent 41C” on 3/30/2009 (which

represents secondary clarifier effluent after jar testing), the remaining data represent primary
or secondary clarifier effluent.   Therefore, the March 30, 2009, secondary clarifier effluent

mercury data should be revised as follows:   

Parameter Original Submittal to EPA Revision

Total Mercury (ng/L) 1850 1800

Dissolved Mercury (ng/L) 1600 1600

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?   

These samples represent secondary clarifier effluent.  The designation of “dump valve” versus

“sample tap” was used to differentiate exactly where the sample was collected.  The main

function of the dump valve is to “dump” the secondary clarifier effluent back to the sump and

re‐route the treated wastewater to the beginning of the treatment system.  The “dump valve”

can be used as an alternate sampling point for secondary clarifier effluent; however, it is not

designed for sampling.  It is a line approximately 2 1⁄2 inches in diameter (as opposed to the

“Sample Tap” line which is approximately 1⁄2 inch in diameter).  Additionally, the dump valve

precedes the sample line and instrumentation skid (i.e., pH and turbidity meters).   

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

“Sample Tap.” What does this sample represent?  

This sample represents secondary clarifier effluent.  The designation of “dump valve” versus

“sample tap” was used to differentiate exactly where the sample was collected.  The sample

tap is the predominant location where samples of secondary clarifier effluent are collected.
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?   

Eleven (11) is the correct MDL value.  The laboratory report did not account for the dilution

factor (25).  Yes, the duplicate sample should 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.   

The laboratory report did not account for the dilution factor (25) when reporting the MDL for

the duplicate sample.  Thus the dilution factor adjusted MDL for the duplicate should be 18

ng/L (0.72 ng/L x 25).   

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.)   

The hydrochloric acid feed to Reaction Tank #2 was implemented in November, 2007.

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)?   

Chemical Technician

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

used)?   

Modified clean hands protocol (i.e., precautions taken, gloves worn but not Tyvek

suits)

c. Where are the samples taken for analysis?   

Samples are taken to the plant lab.
d. Who performs the analysis (e.g., position title)?   

Chemical Technician

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

The analysis procedure is documented in a written procedure.  Training is given by

more experienced chemical technicians who then observe the newly trained technician

perform the analyses for the first week before allowing him/her to perform the

analyses independently.

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

The analyzer can produce results within 4 to 5 minutes of starting the analysis.  

However, the analyzer takes about 15 minutes to warm up, then blanks and duplicate

standards are analyzed before the sample is analyzed, bringing the total elapsed time

to around a half hour.  

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

Results are typically available within one to three hours of sample collection,

depending on whether the technician collects the FGD wastewater samples near the

beginning or end of his/her rounds.

We note that the Direct‐Combustion Mercury Analyzer (DMA) for FGD wastewater

analysis has limitations regarding the accuracy of the analysis, especially at a lower

bound concentration of 140 ng/L.   The DMA calibration protocol is based on

introducing a known mass (ng) amount of mercury into the analyzer and measuring

the instrument response for each known level. The calibration protocol developed for

screening FGD wastewater uses standards at the following levels: 0.025, 0.05, 0.10,

0.20, 0.30 ng Hg. A method detection limit study has shown that the LOQ is equivalent

to 0.014 ng Hg. From our experience, the complex matrix of secondary clarifier effluent

limits the volume of sample that can be introduced into the analyzer without

prematurely fouling the catalyst tube inside the analyzer. For daily screening of the

secondary clarifier effluent we limit the volume to 0.1 mL of sample. Thus, the lower

limit of quantitation is 0.014ng/0.1 mL or 140 ng/L. For daily screening of the

secondary clarifier effluent with an existing limit of 1500 ng/L, this method is

sufficient. However, experience has shown that accurate quantitation of levels below

140 ng/L would not be achievable with this analyzer for this given matrix.  We bring

this to EPA’s attention because EPA’s proposed daily maximum limitation of 119 ng/L

is lower than what can be accurately measured by the DMA.     

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

effluent (SP‐102)?  

The pollutant characteristics would not be expected to differ significantly.  The secondary

clarifier effluent flows into the two wastewater effluent tanks (in series), and effluent from

the tanks is sampled at SP‐102.  The concentrations measured at the two sampling points
may differ slightly due to timing, settling or re‐suspension in the tanks, and/or analytical

variability.  The form or speciation of the constituents being analyzed would not be expected

to differ between the two sampling points.

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?   

In general, mercury concentrations are higher following periods when the wastewater

treatment system (WWTS) has been shut down or in recirculation mode with no discharge.  

The WWTS is typically shut down each weekend for cleaning, so concentrations may be higher

at the beginning of the week than later in the week.  During the winter months, when plant

effluent is recirculated to the intake for deicing, the WWTS discharges only sporadically and

concentrations tend to be higher when it does discharge due to the buildup of fine, colloidal

particles that are difficult to remove.  Occasionally, the mercury concentration will increase as

a result of a chemical feed problem (e.g., the polymer feed pump becomes plugged).  

Additional notes pertaining to the specific dates listed are included below.  

a. Mercury data for 2007 at highly elevated concentrations

During this period of initial startup, the WWTS was being tuned to improve mercury

removal prior to beginning to discharge on a regular basis in November, 2007.  

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)

The WWTS was in recirculation mode and was not discharging from 1/27 to 2/2.  1/31

was a Monday, so these higher concentrations are likely the result of WWTS startup

after a weekend shutdown.

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

These are the first days of discharge after five days of no discharge, and likely reflect

WWTS startup conditions.

d. 3/18/11 (665 ng/L) – CP effluent  

This may reflect a problem with chemical feed.

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

The WWTS was shut down 1/23/12 for repairs and began discharging again on

1/31/12; therefore, these results likely reflect higher startup concentrations trending

down with time.
f. 6/13/12 (2900 ng/L) – CP effluent  

This was an exceedance of the 1500 ng/L BPJ limit that occurred upon startup after a

dual‐unit outage and a 4‐week FGD system shutdown.  Storage of the FGD absorber

slurry in a holding tank for 4 weeks without aeration during a period of warm ambient

temperatures led to reduction and dissolution of some of the oxidized, particulate

mercury.  The abnormally high proportion of dissolved mercury in the FGD blowdown

following the outage proved difficult for the WWTS to remove.  The WWTS was then

operated in recirculation mode for several days such that wastewater containing

organosulfide was recirculated back to the absorbers to aid in precipitation of the

mercury.   

g. 6/18/12 (8300 ng/L) – secondary clarifier  

This was during the recirculation period described in f above.

h. 6/28/12 (640 ng/L) – CP effluent  

The mercury concentration was in the process of coming down following the outage‐

related exceedance.

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

The WWTS had been taken out of service in December, 2012 and hadn’t discharged in

a month.  These concentrations likely reflect startup conditions.

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

In our February 10, 2014, submittal, we indicated that the switch occurred in April 2010.  Upon

further review of our records, the switch to the Nalmet organosulfide occurred during the

week of March 30, 2009.   

Additional Questions posed by EPA during June 4, 2014 conference call:

18. Why was the specific organosulfides changed?  Was the Nalmet product more effective at

removing mercury compared to TMT 15?  Why is Metclear being used instead of Nalmet?    

Both the Nalmet 1689 (Nalmet) and Metclear MR2405 (Metclear) products performed better

than the TMT 15.  While it is difficult to quantify the degree of effectiveness (since the mercury

concentration in the FGD absorber blowdown fluctuates), we estimate that the Nalmet

organosulfide could achieve a 100 to 200 ppt improvement in mercury reduction compared to

treatment using TMT 15.   The mercury removal performance of the Nalmet and Metclear

organosulfides are similar.  Jar testing in November 2009 resulted in slightly better dissolved

mercury removal using the Metclear organosulfide; however, the full‐scale test of the

Metclear organosulfide (October – December 2010) showed that the mercury removal was
comparable to the Nalmet organosulfide.  The Nalmet organosulfide was used December 30,

2010 until February 16, 2012.  At that time, the switch was made to the Metclear

organosulfide based on a business decision from a Supply Chain standpoint.   

19. Why is cleaning of the wastewater treatment system performed?  What does cleaning entail?

Weekly cleaning of the secondary clarifier is performed to avoid thick, hard calcium scale

buildup from forming on the incline sections of the clarifier.  Weekly cleaning entails draining

the secondary clarifier and rinsing it with a hose.  The entire wastewater treatment system is

cleaned annually for scale removal.  Without regular cleanings, excessive scale would build up

and affect the performance of the clarifier.  The scale would then need to be removed by

pressure washing or mechanical scraping.   

20. What causes higher levels of mercury in the FGD effluent after periods of wastewater treatment

shutdown (during start‐up conditions)?   

When the FGD wastewater treatment system is shut down for regular cleanings or as part of

an outage, the FGD absorber slurry recirculates until it can be sent to the treatment system.  

During this time, fine colloidal particles build up, and these fine particles are more difficult to

remove in the physical‐chemical treatment system.  Additionally, our experience has been that

some particulate mercury in the absorber converts to dissolved mercury, especially without

aeration and during periods of warm ambient temperatures.   The combination of fine

particles and higher load of dissolved mercury results in a higher loading of mercury to the

treatment system.   

21. Is there something being done in particular after an outage or during start‐up to reduce mercury

concentrations within the treatment system?

The secondary clarifier effluent is recirculated to the FGD absorber or treatment system

equalization tank until the effluent mercury concentrations are below the WPDES permit best

professional judgment limit of 1500 ppt.  Time is necessary to process (and re‐process)

wastewater until the chemical‐physical reactions can achieve the BPJ limit.    

22. P4 FGD wastewater currently has a BPJ mercury limit of 1500 ppt.  What is the target value for

treatment of mercury within the treatment system?

P4 treats the FGD wastewater and aims to remove as much mercury as possible below the

1500 ppt BPJ limit.  The target Total Mercury concentration is 1000 ppt.  The results of the

mercury sample analysis dictate whether the treatment system effluent is discharged or

recirculated.  Secondary clarifier effluent samples are collected (usually from the sample tap)

and analyzed using the Direct‐Combustion Mercury Analyzer (in‐plant analyzer).  The three

scenarios are as follows:

‐ If the Total Mercury concentration of the secondary clarifier effluent is <1000 ppt, the

effluent discharges continuously.   

‐ If the Total Mercury concentration of the secondary clarifier effluent is between 1000 and

1500 ppt, then continuous discharge ceases.  The effluent tanks are filled to capacity and

an additional sample is collected of the wastewater from the effluent tank.  If the Total
Mercury concentration is <1500 ppt, then the effluent batch discharges.  If, however, the

Total Mercury concentration is >1500 ppt, then the wastewater is recirculated to the FGD

absorber or treatment system equalization tank for re‐processing through the chemical‐

physical treatment system.  

‐ If the Total Mercury concentration of the secondary clarifier effluent is >1500 ppt, then

the wastewater is recirculated to the FGD absorber or treatment system equalization tank

for re‐processing through the chemical‐physical treatment system.  

In addition to using the Total Mercury concentration to make decisions whether to discharge

or recirculate, turbidity and pH are also used.  Turbidity and pH are measured after the

secondary clarifier and effluent tanks.  Trip points have been established in the logic to

automatically divert the effluent to the FGD absorber or treatment system equalization tank if

the levels are not within an acceptable range.    

23. The mercury data indicates that when the organosulfide was switched from TMT‐15 to

Nalmet/Metclear, mercury removal was better.  Yet, in the last year or two, the data shows

more “scatter” in the mercury concentration.  Any insight into why this is the case?   

In general, mercury concentrations are higher following periods when the wastewater

treatment system (WWTS) has been shut down or in recirculation mode with no discharge.  

The higher sample results may represent those time periods following shut down or

recirculation.  The WWTS is typically shut down each weekend for cleaning, so concentrations

may be higher at the beginning of the week than later in the week.   

During the winter months, when the combined effluent is directed to a warming line

immediately adjacent to the intake for deicing purposes, the FGD WWTS effluent is typically

not discharged; rather, it is recirculated to the absorber or to the equalization tank.  This is

because the recirculated FGD wastewater impacts cooling tower chemistry and can lead to

elevated levels of Total Residual Chlorine (TRC) detected.1

  When the FGD WWTS effluent does

discharge, concentrations of mercury tend to be higher due to the buildup of fine, colloidal

particles that are difficult to remove.  During the past winter, the FGD WWTS discharged only

sporadically because the extended periods of colder weather required the frequent use of the

warming line.

Occasionally, the mercury concentration will increase as a result of a chemical feed problem

(e.g., the polymer feed pump becomes plugged).   

While the Total Mercury concentrations improved with the organosulfide switch from TMT 15

to Nalmet, the typical concentrations achieved were still above EPA’s proposed monthly

average limitation of 119 ng/L, regardless of whether Nalmet or Metclear organosulfides were

in use (see Figure 1).

                                                            

1 Pleasant Prairie’s WPDES Permit regulates TRC concentrations in cooling tower blowdown.  
Figure 1: Pleasant Prairie Power Plant FGD WWTP Effluent Total Mercury Concentration with periods of organosulfide chemical additi

1

10

100

1000

10000

Total Mercury Concentration (ng/L)

Sample Date

PPPP FGD WWTP Effluent ‐ Total Mercury Concentration

FGD WWTP EProposed DaiProposed Mo

TMT 15 Nalmet 1689 Nalmet 1689

MetclearMR2405

Metclear MR2405
Appendix A:  Pleasant Prairie Power Plant FGD WWTS Process Flow Diagram

   
E M

2008

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ONE LINE DIAGRAM

WASTE WATER TREATEMENT - 2

UNIT 31

PLEASANT PRAIRIE POWER PLANT

678529

PP K 000

678529.dgn

VENDOR No:

 

 

 

 

 

 

RELATED DRAWINGS

SB2007version01

 

 

 

 

 

 

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We Energies

Milwaukee, WI 53203

231 W. Michigan St

SB2010v01

DOCUMENT NO.

FILE NAME:

PLANT ID: 06283

PLEASANT PRAIRIE POWER PLANT

D-2

TANK 2

REACTION

WWT-2

ACID

HYDROCHLORIC

ORGANOSULFIDE

CP-2-1

TANK 1

REACTION

CP-1-1

POLYMER

TANK

EQUALIZATION

EQ-P

CL-P-1

CLARIFIER

PRIMARY 

LIME

TANK 3

REACTION

CP-3-1

CL-S-1

TANKS

STORAGE

WASTEWATER

TREATED

TANK

SLUDGE HOLDING

FP-1

PRESS

FILTER

SUMP

FILTRATE

CHLORIDE

FERRIC POLYMER

TANK

MIX

FLASH

TANK

FLOCCULATION CLARIFIER

SECONDARY

PH-3

ACID

HYDROCHLORIC

HT

DISCHARGE

EFFLUENT TO

SP-102 TREATED

RECYC-FGDAB

TO FGD ABSORBER

RECYCLE

EFFLUENT

TREATED

INDICATES A SAMPLING POINT

TO SLUDGE DISPOSAL

[LANDF]

199 dpy

17 hpd

40 gpm

 EFF-4

[OUTFALL 001]

199 dpy

57gpm, 12 hpd,

SCRBP

OVERFLOW

HYDROCYCLONE

SECONDARY

SLDG: 5.7 TPD DRY
Appendix B:  Letter from D. Dinsmore and R. Weber (WDNR) to D. Wesolowski (EPA Region V)

explaining why SW‐846 Methods are approved for analyzing wastewater samples under NR

219, Wis. Adm. Code

   



Appendix C:  Representative Arsenic QC demonstration using Method 6020A
PPPP SP102

Sample Analysis QC Summary

Collect Date 3/14/13

Analysis Date 3/20/13

Sample Collect LIMS Prep. Prep. Prep. Analysis Analysis 

Desc. Date

Sample

ID Method Date Batch Date Method Analyte Mass Result Units D

SP102 3/14/13 AD66415 EPA3005A 3/19/13 4566 3/20/13 EPA 6020A DRC‐O2‐ICPMS Arsenic AsO‐91 9.9 ug/L 1

Instrument/Analysis QC:

Cal. Cal. Result Amt. %Rec Result Result Amt. %Rec Result Amt. %Rec Result Amt. Res

Date Stds. ICV ICV ICV ICB LOQ‐CCV LOQ‐CCV LOQ‐CCV LL‐CCV LL‐CCV LL‐CCV ICS‐A ICS‐A ICS‐

3/20/13 0, 20 9.68 10 97 <0.0043 0.112 0.1 112 0.98 1 98 0.010 0 5.3

Instrument/Analysis QC:

Result Amt. %Rec Result Result Amt. %Rec Result Result Amt. %Rec Result

CCV1 CCV1 CCV1 CCB1 CCV2 CCV2 CCV2 CCB2 CCV3 CCV3 CCV3 CCB3

9.96 10 100 <0.0043 10.26 10 103 <0.0043 10.26 10 103.00 <0.0043

Result Amt. %Rec Result Result Amt. %Rec Result

CCV4 CCV4 CCV4 CCB4 CCV5 CCV5 CCV5 CCB5

10.21 10 102 <0.0043 10.46 10 105.00 <0.0043

Sample Prep Batch QC:

Result Amt. %Rec

ERA‐WP

ERA‐

WP ERA‐WP Result Spike Mean Dil. Spike Me

Cert. Cert. Cert. Prep. Result Result Amt. %Rec RPD LIMS ID Result Result Result Amt. %R

Ref. Std.

Ref.

Std. Ref. Std. Blank LCS LCSD LCS/LCSD LCS/LCSD LCS/LCSD MS/MSD Sample MS MSD MS/MSD MS/

WP204

3.53 3.47 102 <0.043 4.05 4.04 4 101 0.2 AD66403 0.22 4.46 4.55 4 10

AD66414 0.49 4.72 4.80 4 10
PPPP SP102

Sample Analysis QC Summary

Collect Date 3/27/13

Analysis Date

4/8/13

Sample Collect LIMS Prep. Prep. Prep. Analysis Analysis 

Desc. Date

Sample

ID Method Date Batch Date Method Analyte Mass Result Units D

SP102 3/27/13 AD66840 EPA3005A 4/5/13 4583 4/8/13 EPA 6020A DRC‐O2‐ICPMS Arsenic AsO‐91 10 ug/L 2

Instrument/Analysis QC:

Cal. Cal. Result Amt. %Rec Result Result Amt. %Rec Result Amt. %Rec Result Amt. Res

Date Stds. ICV ICV ICV ICB LOQ‐CCV LOQ‐CCV LOQ‐CCV LL‐CCV LL‐CCV LL‐CCV ICS‐A ICS‐A ICS‐

4/8/13 0, 20 10.14 10 101 <0.0043 0.10 0.1 100 0.99 1 99 0.023 0 5.3

Instrument/Analysis QC:

Result Amt. %Rec Result Result Amt. %Rec Result Result Amt. %Rec Result

CCV1 CCV1 CCV1 CCB1 CCV2 CCV2 CCV2 CCB2 CCV3 CCV3 CCV3 CCB3

10.04 10 100 <0.0043 10.39 10 104 <0.0043 10.58 10 106 <0.0043

Result Amt. %Rec Result Result Amt. %Rec Result

CCV4 CCV4 CCV4 CCB4 CCV5 CCV5 CCV5 CCB5

10.49 10 105 <0.0043

Sample Prep Batch QC:

Result Amt. %Rec

ERA‐WP

ERA‐

WP ERA‐WP Result Spike Mean Dil. Spike Me

Cert. Cert. Cert. Prep. Result Result Amt. %Rec RPD LIMS ID Result Result Result Amt. %R

Ref. Std.

Ref.

Std. Ref. Std. Blank LCS LCSD LCS/LCSD LCS/LCSD LCS/LCSD MS/MSD Sample MS MSD MS/MSD MS/M

WP204

3.56 3.47 103 <0.043 4.39 4.11 4 106 6.6 AD66944 0.14 4.53 4.54 4 11
PPPP SP102

Sample Analysis QC Summary

Collect Date 4/10/13

Analysis Date 4/24/13

Sample Collect LIMS Prep. Prep. Prep. Analysis Analysis 

Desc. Date

Sample

ID Method Date Batch Date Method Analyte Mass Result Units D

SP102 4/10/13 AD67296 EPA3005A 4/19/13 4597 4/24/13 EPA 6020A DRC‐O2‐ICPMS Arsenic AsO‐91 6.8 ug/L 2

Instrument/Analysis QC:

Cal. Cal. Result Amt. %Rec Result Result Amt. %Rec Result Amt. %Rec Result Amt. Res

Date Stds. ICV ICV ICV ICB LOQ‐CCV LOQ‐CCV LOQ‐CCV LL‐CCV LL‐CCV LL‐CCV ICS‐A ICS‐A ICS‐

4/24/13 0, 20 10.18 10 102 <0.0043 0.095 0.1 95 0.99 1 99 0.0081 0 5.4

Instrument/Analysis QC:

Result Amt. %Rec Result Result Amt. %Rec Result Result Amt. %Rec Result

CCV1 CCV1 CCV1 CCB1 CCV2 CCV2 CCV2 CCB2 CCV3 CCV3 CCV3 CCB3

9.78 10 98 <0.0043

Result Amt. %Rec Result Result Amt. %Rec Result

CCV4 CCV4 CCV4 CCB4 CCV5 CCV5 CCV5 CCB5

Sample Prep Batch QC:

Result Amt. %Rec

ERA‐WP

ERA‐

WP ERA‐WP Result Spike Mean Dil. Spike Me

Cert. Cert. Cert. Prep. Result Result Amt. %Rec RPD LIMS ID Result Result Result Amt. %R

Ref. Std.

Ref.

Std. Ref. Std. Blank LCS LCSD LCS/LCSD LCS/LCSD LCS/LCSD MS/MSD Sample MS MSD MS/MSD MS/

WP204

3.66 3.47 105 <0.11 1.63 1.60 1.6 101 1.8 AD67296 0.27 5.30 5.44 5 10