CORPORATE EHS SERVICES 

Duke Energy 

526 South Church Street 

Charlotte, NC 28202 

Mailing Address: 

EC13K / P.O. Box 1006 

Charlotte, NC 28201-1006 

January 31, 2012 

Via Electronic Mail 

Ronald P. Jordan 

U. S. EPA Headquarters 

Engineering & Analysis Division (4303T) 

Ariel Rios Building 

1200 Pennsylvania Avenue, N.W. 

Washington, DC 20460 

RE: Allen Sampling Episode Report No. 6561 (August 1-6, 2010)

Dear Mr. Jordan: 

Thank you for the opportunity to comment on the draft Sampling Episode Report (SER) 

for Allen Station’s (Allen) August 1-6, 2010 sampling event. We have done our best, 

given the amount of data provided and the relatively short time frame for review, to 

thoroughly review the data within the report. However, these comments should be 

considered preliminary, as we may, upon further consideration of the data, have 

additional comments. In addition to the comments below, please also find attached the 

SER with minor changes documented with track changes. 

Also, in addition to the analytical results in the SER, Allen supplied four additional 

samples taken in four separate months: October 2010, November 2010, December 

2010, and January 2011. Examination of the full data set is necessary to reach any 

general conclusions. For that reason, we urge the EPA to supply the additional data as 

soon as reasonably possible, so that we can evaluate the entire data set in the proper 

context. 

According to EPA, the focus of Episode 6561 was to characterize the purge stream 

entering the flue gas desulfurization (FGD) wastewater treatment system and the 

influent to and effluent from the FGD bioreactor treatment system. The primary goal of 

the sampling program is to characterize the untreated FGD wastewaters and effluent 

quality from technologies designed to treat the wastewater. It is our understanding that 

EPA will use the results from the 4-day sampling event conducted at Allen Steam 
Station as part of its evaluation to determine the best available technology (BAT) for the 

treatment of FGD wastewater for the revision to the steam electric effluent guidelines. 

We would like to emphasize that the effectiveness of the Allen FGD wastewater 

treatment system can change dramatically based on the constituents within the coal, the 

effectiveness of the air pollutant control technology (such as the performance of the 

FGD scrubber and the electrostatic precipitators), and other factors. Furthermore, 

future changes, including combustion of different coal types and new air pollutions 

control technology, and the addition of additives to enhance the removal of 

contaminants from the flue gas, could affect considerably the performance of the 

system. We consider the FGD system performance variability introduced by these and 

other factors to represent the normal range of treatment system effectiveness. This 4-

day sampling episode, as well as the Allen self-monitoring data previously submitted to 

EPA, most certainly has not adequately characterize the performance variability of the 

system under all of these different operating scenarios. 

As an example, only Central Appalachian coal was burned during the 4-day sampling 

event and during the collection of samples for the self-monitoring data previously 

submitted to EPA. Recently, the station conducted a test burn of a high sulfur blend, 

Illinois River Basin coal. Within days of the test burn beginning, increased oxidation 

reduction potential (ORP) values within the FGD purge (influent to the FGD wastewater 

treatment system) and within the FGD scrubber were observed. With the increased 

oxidizing environment within the scrubber, a noticeable chlorine smell was observed 

and an increase in free available oxidant (FAO) was detected within the scrubber purge. 

To prevent damage to the microbes within the bioreactors, the test burn was stopped 

immediately and the bioreactors were forced to be bypassed for several days until the 

FAO returned to acceptable levels. Within this higher oxidizing environment, some 

metals, including selenium, arsenic, and mercury increased their dissolved fraction. As 

a result, the effectiveness of the wastewater treatment system was compromised. 

During the test burn, total selenium and arsenic levels in the bioreactor effluent were 

considerably higher than prior to the test burn. If the test burn was allowed to continue 

and elevated ORP values were continuing to be observed, there was a concern that the 

increased oxidizing environment of the scrubber purge would cause substantial harm to 

the organisms in the bioreactors. With the potential for a higher dissolved fraction of 

metals constituents within the scrubber purge due to the increased ORP levels, there 

was an additional concern of elevated levels of Se, Hg and As to be discharged from 

the wastewater treatment system. This is a clear example of when the past 

performance of the wastewater treatment system may not be indicative of the current or 

future performance of the treatment system under different operating scenarios. 
Furthermore, as EPA is evaluating BAT for the treatment of FGD wastewater on a 

national level, other facilities may not be able to meet the same historical performance 

levels with a system similar to the Allen wastewater treatment system. As illustrated 

above, stations that burn different types of coal, such as a high sulfur coal, and have 

differing scrubber operating conditions, may not be able to achieve the performance 

levels achieved by the Allen treatment system. By relying only on a limited data set, 

which was collected under ideal conditions, the existing data mischaracterized the 

across-the-board effectiveness of treatment systems on a national level. Duke Energy 

encourages EPA to investigate these differences in the FGD systems and the ability of 

different wastewater treatment technologies to effectively treat the resulting wastewater 

prior to selecting BAT and establishing limits. 

I. General Comments

Wastewater Treatment Description 

Within Section 2 of the SER, Duke Energy requests the follow change to be made: 

• p. 2-3, Section 2.2.1 Physical/Chemical Separation 1st paragraph: EPA 

incorrectly states that reaction tank 2 was formerly used for organosulfide 

addition. Organosulfide has never been added to the system. Revise the 

sentence to read: “From the equalization tank, the wastewater enters three 

reaction tanks in series: reaction tank 1, in which lime is added to increase the 

pH to between 8.6 and 9.2 S.U.; reaction tank 2, designed for organosulfide 

addition, but which is only used to provide additional mixing; and reaction tank 3, 

in which ferric chloride is added.” 

 

• On page 2-4, Section 2.2.2 Biological Reactors 3rd paragraph: EPA states 

“Allen operates the bioreactors to achieve a negative oxidation reduction 

potential (ORP) within the system...” We suggest inserting “ideally” prior to 

“operates” within this sentence. Allen attempts to operate the bioreactors to 

achieve a negative ORP; the ORP, however, cannot always be controlled due to 

the variability of the ORP in the scrubber purge. The ORP in the scrubber purge 

can vary dramatically based on operating conditions. 

Comparison of UWAG and EPA Split Sample Study Data 

The data comparisons discussed here are from the EPA and Utility Water Act Group 

(UWAG) four day Split Sample Study (4DSSS) conducted at the Allen facility during 

August 1-6, 2010 
In general, the comments below use four-day averages of the data. The use of four-day 

averages is only for the purpose of assessing general trends. In using these averages, 

Duke Energy does not mean to endorse their use for all purposes. In many instances, 

data comparison should be done based on comparison of individual data points. We 

reserve the right to comment on individual data points, as we deem appropriate, in the 

future. 

Data Usability 

Duke Energy agrees with EPA’s efforts to identify and flag potentially erroneous (outlier) 

data points in the Allen data set. However, the identified outliers are still generally 

included in calculating four-day averages and other analyses. If a value is an outlier, 

then it should be discarded from the data set and not used for any purpose. 

Also, there is no discussion in the SER of how flagged data points will be used (or 

excluded) from consideration in calculating the new steam electric effluent guidelines. 

For example, data points flagged B, Est, F and T indicate potentially significant 

inaccuracies (bias) in the associated data. EPA should use the data related comments 

in this response, based on UWAG split sample data, to confirm those EPA data points 

that are clearly inaccurate, and to revise the SER to exclude the erroneous data points 

from calculations in the report and to exclude the erroneous data points from the 

database used to calculate the new steam electric effluent guidelines. 

Furthermore, statistical methods are available to systematically identify “outliers” which 

may then be excluded from a data set before further interpretation. Such tests provide 

a consistent method and rationale for rejecting or keeping data which is useful to ensure 

that the variability (present in every data set and associated with many sources of 

uncertainty) in the measurements is preserved. If such methods will not be applied 

here, then a clear and consistent narrative for how questionable data points are 

indentified and either considered or rejected during data interpretation, summaries, etc. 

should be provided. 

Inadequate Treatment System Design and Operational Descriptions and Data 

The SER lacks some basic technical information that is very important for a 

comprehensive understanding of the analytical results. This information is also key to 

understanding the conditions under which a certain level of treatment can be reliably 

achieved. Duke Energy urges EPA to provide (and, if necessary, collect) the following 

types of information, and to include them within the SER. 
System Design Information 

The SER should include, at a minimum, the following information 

1. Daily retention times for each stage of the treatment system; 

2. Dimensions and water volume sizes for all individual components of the 

treatment system, including each holding tank, reaction tank, clarifier, sand filter, 

and biological treatment unit; and 

3. A full description of all types of filter media used in the system. 

Some of the above information has been provided to EPA either prior to or during 

sampling events or through EPA’s Information Collection Request (ICR). Duke Energy 

urges EPA to integrate this information into the SER so that the data can be understood 

in the specific context of the Allen treatment system. 

System Operations Information 

In addition, EPA should provide information on the load of each operating unit prior to 

the sampling event, as well as, on each of the sampling days, which was supplied to 

EPA within the monitoring program engineering data submittal. While the SER states 

the design megawatt capacity of the facility, it does not indicate the actual megawatt 

output for each day of sampling. There is no way of determining, based on the SER, 

whether the facility was operating at full capacity. Daily actual load information is also 

important to understanding the sampling event results. 

Also, EPA’s study plan should have included a comprehensive study of the coal feed 

stock during each sampling event. It is clear that coal characteristics have a very 

substantial impact on FGD chemistry and wastewater treatment. While EPA gathered 

some information about coal constituents during the sampling events, it should have 

collected full information about levels of sulfur, metals, and chlorides in the coal, as well 

as the heating value of the coal being burned during the relevant period for the sampling 

event. 
Mercury reporting units 

In the draft SER, all metals data are reported in units of micrograms per liter (parts per 

billion, ppb), except mercury (Hg) data are reported in units of nanograms per liter 

(parts per trillion, ppt). This approach is unnecessarily confusing and gives the reader 

an initial impression that Hg levels in FGD wastewaters are very high and similar to 

those of the major cations reported such as calcium, magnesium and sodium. All 

metals data, including Hg data, should be reported in the same ppb units to avoid 

confusing the reader during even a cursory review of the data tables. 

Description of unfiltered metals data 

In the draft SER, all unfiltered metals sample data are referred to as “Total Metals.” 

This term is also used in the analytical narratives (Appendix B) for both EPA methods 

200.7 and 200.8. This is misleading and incorrect. Both EPA methods 200.7 and 200.8 

use the term “total recoverable metals” to describe the unfiltered metals data generated 

by the method. 

Dissolved metals and mercury data 

The accurate measurement of dissolved Hg and other metals in FGD wastewaters is 

challenging. EPA defines dissolved metals as metals, including Hg, associated with 

particles ≤ 0.45 μm or ionic that will pass through a 0.45 μm filter. This definition is an 

operational definition, and there are many types of filters rated at 0.45 μm (e.g., 

capsule, flat membrane, etc.). Hg and other metals associated with colloids (i.e., 

particles < 1 μm in size and the vast majority < 0.45 μm) can be an important fraction of 

the elements present in FGD wastewaters. The fraction of < 0.45 μm colloids removed 

(retained) during filtrations varies according to the type of filter used. The phenomenon 

is called colloidal trapping. Capsule filters tend to retain a larger fraction of the < 0.45 

μm colloids than do other filter types. This situation can lead to significant differences in 

“dissolved” metals and Hg data depending on the filter used. The EPA should consider 

this fact when evaluating and using dissolved metals or Hg data in developing the 

steam electric effluent guidelines. Differences in dissolved metals and Hg between EPA 

and UWAG split sample data were substantial for SP-1 and SP-3 during the sampling 

event. 

Analytical methods descriptions 

The analytical descriptions in section 4 and the analytical narratives omit some basic 

information that should be included and would be helpful in making data evaluations 
and comparisons. Section 4 should be revised to include basic analytical information 

that answers the following: 

1. How were the trace metals samples digested? Was a heated strong acid leach 

digestion patterned after EPA method 200.2 used, or some other alternative 

digestion? Were the metals samples preserved to pH < 2 at least 24 hours prior 

to digestion (total recoverable) or analysis (dissolved)? 

2. How were the Hg samples digested? Was the bromine monochloride digestion 

done at room temperature? Was it heated, by method 1631E appendix A? Was 

some other method used? 

3. Were individual grab samples for Hg and some other parameters flow-proportion 

composited? If so was the compositing done physically prior to analysis or was 

the “compositing” done arithmetically after the individual analysis of each 

sample? 

4. How are known interferences in FGD matrices controlled? For example, chloride 

is a known interference in the COD method and the concentration must be 

carefully controlled to achieve accurate results. 

5. More information is needed in the analytical narratives for matrix spikes and MS 

duplicates (MS/MSD) that fail. For example, if failed recoveries are close to the 

acceptance range (87% when the limit is 90 to 100%) then the data can be used 

with qualification. However, if the recoveries are significantly below the method 

acceptance criteria then the data should not be used. 

Description of sampling points (SP) 

Using only the description of a sampling point in many of the Appendix A tables is 

unnecessarily confusing. In the main body (e.g., sections 3, 4 & 5) of the SER, the data 

tables include both a description of the SP as well as the abbreviation (e.g., SP-2, SP-3, 

etc.). This minimizes the risk of confusion between the two SP’s with influent in the 

description (i.e., influent to wastewater treatment system and influent to bioreactor). It 

would be helpful if the SP abbreviation were included on the daily data tables in SER 

Appendix A. 
Calculating Averages 

EPA has chosen to calculate four-day averages of the major constituents throughout the 

SER. We question the validity of using four-day averages to characterize the data. For 

purposes of setting limits, the use of four-day averages would not be appropriate 

because it would minimize the variability among the data points. At best, the use of the 

four-day averages only provides a “snapshot” of general trends. For all other purposes, 

we urge EPA to avoid averaging the data points. 

Also, the EPA uses the following approach when calculating averages: “If at least one 

result was above the quantitation limit, then 1⁄2 the quantitation limit was used in the 

average calculation for all results that were less than the quantitation limit and the result 

is reported with a less than sign (“<”)” (SER page 4-1). This approach is not justified 

because it introduces arbitrarily estimated data into the calculations. A more consistent, 

justifiable and conservative approach would be to use the quantitation limit in the 

calculations as is done when all results are below the quantitation limit. 

Cyanide Interference 

All of the 40 CRF Part 136 approved cyanide methods are subject to numerous 

interferences, especially in complex sample matrices. The methods were originally 

designed for use with discharges from metal plating facilities where cyanide was known 

to be present. Most of the interferences result in false positives, and many of these are 

caused by sulfide and other reduced sulfur compounds which may be present in FGD 

wastewater. Other compounds that can cause false positives under the right conditions 

are organosulfides, thiosulfates, nitrites, and other nitrogen compounds. Some of these 

compounds can actually cause cyanide to be produced during the acid distillation 

procedure of the method. The procedures for removing interferences provided in the 

methods are often not effective, and complex samples, such as FGD wastewater, may 

also contain unknown interferences. It is entirely possible that most if not all of the 

reported cyanide detections could be sample matrix interferences. Therefore, EPA 

should use caution when interpreting its cyanide results. 
II. Specific Comments 

Data comparisons 

1. Low-level Mercury

Total recoverable and dissolved Hg in UWAG split samples were analyzed by Albion 

Environmental (AE). Dissolved Hg samples were filtered at AE under clean room 

conditions within 24 hours of collection using a 0.45 μm membrane filter with 5 μm prefilter approved for Clean Water Act use by the EPA Engineering and Analysis Division 

(EAD, ATP N99-0021 dated 6-7-2000). Samples with elevated solids were allowed to 

settle and the “clearer” supernatant was filtered for dissolved Hg. All Hg samples were 

subjected to a heated bromine monochloride digestion (i.e., sealed bottles in oven at ≥

50 °C for at least 6 hours) prior to analysis using a method compliant flow-injection 

instrument. A comparison of the EPA Hg data summarized in the SER and the 

comparable UWAG split sample data from the 4DSSS is presented in Table A-1. 

TABLE A-1. Comparison of 4-Day Averages of EPA & UWAG Split Sample 

Mercury Data 

Source -> UWAG EPA UWAG EPA 

Processing -> Total Rec. Total Rec. Diss. Diss. 

SP / Parameter -

> 

Hg (ppb) Hg (ppb) Hg (ppb) Hg (ppb)

SP-1 54.5 49.2 0.506 0.0319 

SP-2 1.09 1.04 0.257 0.342 

SP-3 0.0221 0.0218 0.00498 0.0220 

The UWAG and EPA Hg data agree well with the exception of dissolved Hg at SP-1 and 

SP-3. The SP-1 dissolved Hg disagreement is possibly a reflection of the type of 

filtration used by the EPA laboratory (Frontier Geosciences, FGS). The SER does not 

describe how the Allen dissolved Hg samples were filtered by FGS, and so it is not 

possible to evaluate this hypothesis further. Mercury associated with colloids (i.e., 

particles < 1 μm in size and the vast majority < 0.45 μm) can be an important fraction of 

the Hg present in FGD wastewaters. Colloidal Hg < 0.45 μm should be included in the 

filtered (dissolved) samples according to the EPA definition and not be retained 

(trapped) to a meaningful degree on the filter. The fraction of < 0.45 μm colloids 

removed (retained) during filtrations varies according to the type of filter used. Use of 

capsule filters and “clogging” of flat membrane filters can result in colloidal trapping and 

retain a considerable portion of the < 0.45 μm colloidal Hg present in a sample. 
The SER (section 4 and the analytical narrative in Appendix B) does not describe how 

FGS filtered the dissolved Hg samples. The FGS analytical narrative (Appendix B) is 

also confusing by its listing of a single EPA ID # and FGS Lab ID # for the four 

individual dissolved Hg grab samples collected in the field for each daily event. It is 

assumed that each individual Hg grab sample was filtered upon receipt and then 

composited in some fashion (also not described in the SER) to arrive at a final reported 

daily dissolved Hg concentration. This represents 20 separate filtrations to produce the 

five reported SP-3 dissolved Hg data points. It is possible that there was a consistent 

decimal point error made in calculating the final SP-3 dissolved Hg concentrations. 

Although unlikely, if this were the case then the EPA SP-3 average dissolved Hg 

concentration would be 0.0022 ppb. The 0.0022 ppb mean would be within about 

twofold - of the comparable UWAG average (0.00498 ppb) and well within potential 

variation associated with differences in the way the samples may have been filtered. 

Recent studies of mercury chemistry within FGD scrubbers may provide some insight 

into why mercury may routinely change phases, and thus why FGD wastewater systems 

may have variable mercury treatment results. Based on data from 15 different 

scrubbers, when the oxidation reduction potential (ORP) within the scrubber is high, 

more mercury tends to be in the dissolved phase (Allen et al., 2011). The more highly 

oxidizing the system, the greater the dissolved phase concentrations of mercury will be. 

Power plant operators are still attempting to understand ORP within their scrubbers. 

There appear to be many individual factors that may affect ORP, including, but not 

limited to, the presence of an SCR, load, level of sulfur within the coal, pH, and the 

quality of makeup water used in the scrubber. Because ORP routinely fluctuates within 

scrubbers, the mercury phase within the wastewater exiting the scrubber is variable. 

Therefore, the level of treatment possible at a given FGD wastewater treatment system 

can vary drastically over time. 

2. Total Phosphorus

EPA (TestAmerica, TA) and UWAG (Alabama Power Company, APC) used similar 

colorimetric methods to measure total phosphorus in the samples from the 4DSSS. TA 

used EPA method 365.1 and APC used SM4500P-E. EPA and UWAG phosphorus 

data were generally comparable except for the SP-1 (see Table A-2). The comparison 

suggests that the EPA data underestimates the total phosphorus concentration at SP-1. 

Barium, lead, and silver can interfere with the colorimetric orthophosphate determination 

by forming insoluble phosphates. Barium, and to a lesser extent lead levels, in FGD 

wastewaters (especially SP-1 matrices) are high enough to raise an interference 
concern for phosphorus analyses. No MS/MSD QC samples were performed by the 

EPA lab on SP-1 samples, but the phosphorus data at SP-1 may be biased low. 

TABLE A-2. Comparison of 4-Day Averages of EPA & UWAG Split Sample 

Phosphorus Data 

Source-> UWAG EPA 

Processing -> Total Total 

SP / Parameter 

-> 

Phosphoru

s 

 (ppm) 

Phosphorus 

(ppm)

SP-1 1.02 < 0.106 

SP-2 0.02 < 0.034 

SP-3 0.11 0.153 

3. Miscellaneous Issues

In the analytical narrative in Appendix B, FGS validates their EPA method 1631E 

calibration using a linear regression correlation factor criterion of > 0.995. This 

statement is misleading because method 1631E does not allow for a linear regression 

calibration curve. Rather, method 1631E uses a mean calibration factor (CFm), which 

is a simple arithmetic mean of the five or more individual calibration factors. The 

acceptance criteria for the method 1631E calibration are an RSD of < 15% for the five or 

more CF’s and recovery between 75-125% at the method reporting limit of 0.5 ppt. The 

SER analytical narrative should be revised to clarify this situation. 

In SER data Appendix A, the ratio of MDL to ML (reporting limit) for EPA method 200.7 

averages ~ 20 with a range of approximately 3 to 55. The expected ratio is 3-5 as 

shown for EPA method 200.8 MDL/ML’s listed in the SER. The reason for this 

aberration is not clear. Are the MDL’s too low or the ML’s too high for the elements with 

elevated ratios? 

All EPA chromium (Cr) data in the SER tables are qualified (flagged) “^” with the 

statement “ICV, CCV, ICB, CCB, ISA, ISB, CRI, or MRL standard: Instrument related 

QC exceeds the control limits.” However, the Test America (TA) EPA method 200.8 

analytical narrative (Appendix B) makes no mention of any quality control (QC) issues 

associated with the Cr analyses. Should the Cr data be flagged or not? If there are 
quality control concerns, then certainly these data may not be relied upon or used for 

any purpose. 

Sources 

Allen, Jonathan O., Eggert, Derek, and Tyree, Corey A. Effect of FGD Chemistry on 

Wastewater Composition, presented at Air Quality VII Conference, Arlington, VA, 

October 25, 2011.