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: Miami Fort Sampling Episode Report No. 6560, July 11-16, 2010 

Dear Mr. Jordan: 

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

for the Miami Fort July 11-16, 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. 

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

samples taken in four separate months: September 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 EPA to supply the additional data as 

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

context. 

I. General Comments

Facility Overview and Wastewater Treatment Description 

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

• On page 2-1, Section 2 (Facility Overview, 5th paragraph) incorrectly states 

that Miami Fort has had issues with blue plume stack emissions. This is not 

the case; lime is injected as a precautionary measure. We suggest revising 
the sentence to read: “Miami Fort injects lime into the flue gas between the 

air heater and the ESP to control sulfur trioxide emissions.” 

• On page 2-3, Section 2.2 (FGD Wastewater Treatment System, 3rd

paragraph) creates confusion around the use of ferric chloride, which had 

been discontinued as an additive by the time of the July 2010 sampling. We 

suggest revising the sentence to read: “Miami Fort tested the effectiveness 

of the Nalmet® 1689 by adjusting the feed rate and addition amounts, in 

combination with other FGD wastewater treatment additives (i.e., polymer).” 

Data Usability 

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

data points in the Miami Fort 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. 

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 to 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. 

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 urges 

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

specific context of the Miami Fort 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. While the SER states the 

design megawatt capacity of Miami Fort, 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 sampling and analysis 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 considerable 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 that 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 such as calcium, magnesium and sodium. All metals, 

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

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 mercury (Hg) and 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.). Metals, including Hg, associated with colloids (i.e. particles < 1 

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

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 data, including Hg, in developing 

the steam electric effluent guidelines. 

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 that answers 

the following questions: 

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 used? 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 were the dissolved Hg samples filtered? 

5. How were biphasic solids samples digested and analyzed for metals and Hg? 

6. How were biphasic solids analyzed for classical parameters? 

7. 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. 

8. 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. 

Qualification (Flagging) of Calculated (Reconstructed) Biphasic Data 

The EPA SP-1 MF samples were analyzed using biphasic separations. The samples 

were separated into solid and liquid phases by centrifugation (Hg) or pressure filtration 

(classicals and metals). The two phases were analyzed separately and a single total 

aqueous concentration was calculated (reconstructed) using formula 4.1 (SER page 4-

2). For many classical parameters and some metals, the data for one or both phases of 

a sample were qualified as estimates based on a variety of quality control (QC) issues 

including exceeding analytical holding time (H-Flag), exceeding the preservation holding 

time (P-Flag), parameter detected in the method blank (B-Flag), etc. In the summary 

data tables in section 4 and also in the data appendix A, the calculated total data point 

is listed with no qualification (flags) even though one or both of the component (parent) 

phase samples were qualified. A good example is Table A-5 and Table 4-1. For SP-1 

day one both phase components samples for nitrate/nitrite and TKN are qualified as 

estimates with various flags. However, the total (calculated) nitrate/nitrite (71.7 mg/L) 

and TKN (40.5 mg/L) data points show no data flags in either the top of Table A-5 or at 

all in table 4-1. This presentation approach is not correct and gives the mistaken 

impression that the final total data points have no associated QC issues (qualifications). 

Any data qualifications (flags) associated with either of the parent (phase) samples 

should be carried forward and also shown with the associated total (calculated) value. 

The SER should be revised to correct this oversight. 

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. 

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 Interferences 

All of the 40 CFR 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. 

The cyanide results reported by EPA for Miami Fort could be biased high due to the 

organosulfide addition in the chemical treatment system. The organosulfide compound 

used for treatment may not be detected in the sulfide interference check by the usual 

method procedures. In addition, these compounds will break down into simple sulfide 

during the acid digestion and cause an interference. It may be noteworthy that there 

was very little cyanide detected in the Belews Creek and Allen FGD wastewaters. 

These facilities do not use organosulfide addition in their physical/chemical treatment 

system. Therefore, analytical results showing that cyanide is present in FGD 

wastewaters may be a false positive due to interferences. 

II. Specific Comments 

1. Low-level Mercury

The EPA unfiltered SP-1 data exhibit a high degree of variability, i.e. RSD 53%. The 

unfiltered mercury data cannot be properly evaluated with the information given in the 

SER. The Frontier Geosciences (FGS) analytical narrative (Appendix B) only lists EPA 

method 1631E which is not approved for the analysis of solids. No mention is made of 

how the biphasic solids were digested or analyzed. Without this information, including 

the associated QC data, an appropriate evaluation cannot be conducted. The SER 

should be revised to include a description of the solids Hg digestion and analytical 

procedures. 

The dissolved Hg results, especially SP-1, could be affected by colloidal trapping 

depending on how the EPA samples were filtered. The SER, however, does not include 

a discussion on how the EPA samples were filtered; a proper evaluation, therefore, of 

the Hg data cannot be made. The SER should be revised to include a description of 

the type of filter and procedure used by FGS to filter the EPA dissolved Hg samples. 

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 and control ORP within their 

scrubbers. There appear to be many 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 

individual scrubbers (and varies between scrubbers of different designs), 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 extensively 

over time. 

2. Low-level Selenium

The EPA TestAmerica (TA) analytical narrative raises concerns about potential 

analytical bias in the EPA SP-2 dissolved Se data. For example, “the dissolved 

selenium result of 530 μg/L for sample 71748 FGD Effluent Day 4 (280-5438-1) is 

greater than the total selenium value of 480 μg/L reported for the same sample.” Also 

the EPA SP-2 dissolved Se MS/MSD was invalid (Flagged 4). The TA analytical 

narrative only states that for such invalid spikes “many spike recoveries were outside 

the method control limits of 70–130%.” It would be helpful to know the percent 

recoveries of the EPA SP-2 dissolved Se MS/MSD spikes. If the spike recoveries were 

> 130% it could indicate a potential analytical overestimation of the dissolved Se data. 

Finally, a post digestion Se spike failed (69 % recovery) on the day 3 SP-2 sample (not 

stated if total recoverable or dissolved). This is another indication of potential analytical 

bias in the EPA SP-2 Se data. 

3. Nitrogen Related Parameters

 The EPA laboratory (TestAmerica, TA) performed separate nitrogen analyses on 

biphasically separated filtrate and solids phases. The EPA (TA) used the two separate 

phase data to calculate a single “reconstructed” value for ammonia, nitrogen and TKN in 

each sample. The three nitrogen methods used (i.e. EPA methods 350.1, 353.2 and 

351.2) are all aqueous methods. There is no description of how the solid phase 

samples were prepared for analysis. Presumably TA used some sort of aqueous 

extraction (elutriate type) procedure to produce an aqueous extract of the solids that 

could then be analyzed by the various methods. This procedure should be described 

briefly in SER section 4.1. Also all SP-1 aqueous and solid phase nitrogen species 

samples were qualified as estimated values for exceeding holding times (H-Flag), 

exceeding preservation time (P-Flag) and blank issues for some (B-Flag). However, 

that flagging is absent from the summary table 4-1 and in Appendix A data tables A-5 to 

A-8 for the reconstructed total values. This is a mistake which should be corrected in 

the SER. The flags associated with the component samples should also be associated 

with any calculated total values derived from those component (phase) samples. 

Because all the EPA SP-1 nitrogen data are considered estimates, the EPA should use 

the SP-1 total (reconstructed) nitrogen species data with caution. 
4. Miscellaneous Issues

In the analytical narrative in Appendix B, Frontier Geosciences (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. FGS may want to revise the analytical narrative to clarify this situation. 

In the 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? 

Many of the 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. 

The Appendix A data tables for the SP-1 biphasic separation (i.e. Tables A-1, A-2, A-3 

and A-4) contain a concentration units error for the aqueous metals data. The aqueous 

metals data listed in those tables are in micrograms per liter (parts per billion, ppb) and 

not milligrams per liter (parts per million, ppm) as indicated at the top of the table. It 

appears that the solid phase metals data units are correctly listed as ppm. However, 

when listing solids metals data it is important to indicate whether the solids 

concentrations are on a wet or dry weight basis. The simplest correction for the 

affected Appendix A tables would be to change the “Total Metals” sub-heading to read 

“Total recoverable metals (aqueous and total result in ug/L and solid results in mg/kg 

dry weight).” 

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. 

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