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 & Analysi s Division (4303T) Ariel Rios Building 1200 Pennsylvania Avenue, N.W. Washington, DC 20460

RE: Allen Sampling Episode Re port 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 dat a provided and the relatively shor t time frame fo r review, to thoroughly review the data within the repor t. However, these comments should be considered preliminary, as we may, upon further consideration of the data, have
additional comments. In addition to the comm ents 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, Nove mber 2010, December 2010, and January 2011. Exami nation of the full data set is necessary to reach any general conclusions. For that reason, we urge the EPA to s upply the additional data as soon as reasonably possible, so that we c an evaluate the entire dat a set in the proper
context.

According to EPA, the focus of Episode 6 561 was to characterize the purge stream entering the flue gas desulfurization (FGD ) wastewater treatment system and the
influent to and effluent from t he FGD bioreactor treatment syst em. The primary goal of the sampling program is to characterize the untreated FGD wa stewaters and effluent quality from technologies design ed to treat the wastewater. It is our understanding that
EPA will use the results from the 4-day sampling event conducted at Allen SteamStation as part of its evaluat ion to determine the best available technology (BAT) for the
treatment of FGD wastewater fo r the revision to the steam elec tric effluent guidelines.

We would like to emphasize that the effe ctiveness of the All en FGD wastewater treatment system can change dramatically bas ed 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 precipitat ors), and other factors. Furthermore, future changes, including combustion of di fferent coal types and new air pollutions control technology, and the addition of additives to enhance the removal of contaminants from the flue gas, could a ffect considerably the performance of the system. We consider the FGD system per formance 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 dat a previously submitted to EPA, most certainly has not adequately charac terize the performance variability of the system under all of these different operating scenarios.

As an example, only Centra l Appalachian coal was bur ned during the 4-day sampling event and during the collectio n of samples for the self-monitoring data previously submitted to EPA. Recently, the station conducted a test bur n 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 (F AO) was detected within the scrubber purge. To prevent damage to the microbes within t he 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 me rcury increased their dissolved fraction. As a result, the effectiveness of the wastewat er treatment system was compromised. During the test burn, total selenium and ars enic levels in the bioreactor effluent were considerably higher than prior to the test bur n. 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 pur ge 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 wastew ater treatment system may not be indicative of the current or future performance of the treatment syst em under different operating scenarios.Furthermore, as EPA is evaluating BAT fo r 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 wa stewater treatment s ystem. 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 idea l conditions, the existing data mischaracterized the across-the-board effectiveness of treatment syst ems on a national level. Duke Energy encourages EPA to investigate t hese differences in the FGD systems and the ability of
different wastewater treatment technologies to effectively tr eat the resulting wastewater prior to selecting BAT and establishing limits.

I. General Comments

Wastewater Treatment Description

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

• p. 2-3, Section 2.2.1 Ph ysical/Chemical Separation 1 st paragraph: EPA incorrectly states that reaction t ank 2 was formerly used for organosulfide addition. Organosulfide has never been added to the system. Revise the sentence to read: “From the equalizatio n 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 Biol ogical Reactors 3 rd paragraph: EPA states “Allen operates the bioreactors to ac hieve a negative oxidation reduction potential (ORP) within the syst em...” We suggest insert ing “ideally” prior to “operates” within this sentenc e. Allen attempts to op erate 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. T he ORP in the scrubber purge can vary dramatically bas ed on operating conditions.

Comparison of UWAG and EPA Split Sample Study Data

The data comparisons discussed here are fr om the EPA and Utility Water Act Group (UWAG) four day Split Sample Study (4DSSS) conducted at the Allen facility during August 1-6, 2010In general, the comments below use four-day av erages 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 com parison of individual data points. We reserve the right to comment on individual da ta points, as we deem appropriate, in the
future.

Data Usability

Duke Energy agrees with EPA’s efforts to identify and flag pot entially 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 el ectric 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 samp le 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 dat a points from the
database used to calculate the new steam electric effluent guidelines.

Furthermore, statistical methods are available to systematically ident ify “outliers” which may then be excluded from a data set before fu rther 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 asso ciated with many sources of uncertainty) in the measurements is preser ved. If such methods will not be applied here, then a clear and consistent narrati ve for how questionable data points are
indentified and either c onsidered or rejected during data interpretation, summaries, etc. should be provided.

Inadequate Treatment System Design an d Operational Descriptions and Data

The SER lacks some basic technical information that is very important for a comprehensive understanding of the analytical resu lts. 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 provi de (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 mi nimum, the following information

1. Daily retention times for eac h 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 us ed 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 operatin g at full capacity. Daily actual load information is also important to understanding the sampling event results.

Also, EPA’s study plan should have includ ed 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 wa stewater treatment. While EPA gathered
some information about coal constituents dur ing the sampling events, it should have
collected full information about leve ls 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 dat a are reported in units of mi crograms per liter (parts per billion, ppb), except mercur y (Hg) data are r eported in units of nanograms per liter (parts per trillion, ppt). Th is 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 cu rsory review of the data tables.

Description of unfiltered metals data

In the draft SER, all unfiltered metals sample data are referr ed 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 incorre ct. 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 μ m or ionic that wil l pass through a 0.45 μ m filter. This definition is an operational definition, and there are many types of filters rated at 0.45 μ m (e.g., capsule, flat membrane, et c.). Hg and other metals associated with colloids (i.e., particles < 1 μ m in size and the vast majority < 0.45 μ m) can be an important fraction of the elements present in FGD wast ewaters. The fraction of < 0.45 μ m colloids removed (retained) during filtrations varies according to the type of filter us ed. The phenomenon is called colloidal trappi ng. Capsule filters tend to retain a larger fraction of the < 0.45

μ m colloids than do other f ilter types. This situation can le ad to significant differences in “dissolved” metals and Hg dat a depending on the filter used. The EPA should consider this fact when evaluating and using dissol ved metals or Hg dat a in developing the steam electric effluent guidelines. Differenc es in dissolved metals and Hg between EPA and UWAG split sample data we re 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 woul d be helpful in making data evaluationsand comparisons. Section 4 should be revi sed 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 pres erved to pH < 2 at least 24 hours prior to digestion (total recover able) or analysis (dissolved)?

2. How were the Hg sample s digested? Was the bromi ne 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 paramet ers flow-proportion composited? If so was the compositing d one physically prior to analysis or was the “compositing” done arit hmetically 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 analyti cal narratives for matr ix 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 sampl ing points (SP)

Using only the description of a sampling poin t in many of the A ppendix A tables is unnecessarily confusing. In t he main body (e.g., sections 3, 4 & 5) of the SER, the data tables include both a descripti on of the SP as well as the abbreviation (e.g., SP-2, SP-3, etc.). This minimizes the risk of confus ion between the two SP’s with influent in the description (i.e., influent to wastewater treat ment 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 aver ages 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 av eraging 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 resu lts that were less than the quant itation limit and the result is reported with a less than sign (“<”)” (SER page 4-1). This appr oach 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 resu lts are below the quantitation limit.

Cyanide Interference

All of the 40 CRF Part 136 approved cyani de methods are subject to numerous interferences, especially in complex sample matrices. The methods were originally designed for use with discharges from metal pl ating facilities where cyanide was known to be present. Most of the interferences resu lt 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 t hat 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. T he procedures for removing interferences provided in the methods are often not effective, and comple x samples, such as FGD wastewater, may
also contain unknown interferences. It is ent irely possible that most if not all of the reported cyanide detections coul d be sample matrix interf erences. Therefore, EPA should use caution when interp reting 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 samp les were filtered at AE under clean room
conditions within 24 hours of collection using a 0.45 μ m membrane filter with 5 μ m prefilter approved for Clean Water Act use by the EPA Engineering and Analysis Division (EAD, ATP N99-0021 dated 6-7-2000). Sample s 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) pr ior 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 t he 4DSSS is presented in Table A-1.

TABLE A-1. Comparison of 4-Day A verages 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 dissol ved Hg disagreement is possibly a reflection of the type of filtration used by the EPA labor atory (Frontier Geosciences, FGS). The SER does not describe how the Allen dissolved Hg samples we re filtered by FGS, and so it is not possible to evaluate this hypothesis further . Mercury associated with colloids (i.e., particles < 1 μ m in size and the vast majority < 0.45 μ m) can be an important fraction of the Hg present in FGD wastew aters. Colloidal Hg < 0.45 μ m should be included in the filtered (dissolved) samples according to the EPA definition and not be retained (trapped) to a meaningful degree on th e filter. The fraction of < 0.45 μ m colloids removed (retained) during filtrations varies acco rding to the type of filter used. Use of capsule filters and “clogging” of flat membrane f ilters can result in colloidal trapping and retain a considerable portion of the < 0.45 μ m colloidal Hg present in a sample.The SER (section 4 and the analytical narrati ve in Appendix B) d oes 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 samp les collected in the field for each daily event. It is assumed that each individual Hg grab sa mple was filtered upon receipt and then composited in some fashion (also not descri bed in the SER) to arrive at a final reported daily dissolved Hg concentration. This repr esents 20 separate filtra tions 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 ca se then the EPA SP-3 average dissolved Hg concentration would be 0.0022 ppb. The 0.0022 ppb mean woul d be within about twofold - of the comparable UWAG aver age (0.00498 ppb) and we ll within potential
variation associated with differences in t he way the samples may have been filtered.

Recent studies of mercury chemistry withi n FGD scrubbers may provide some insight into why mercury may routinely change phase s, and thus why FGD wastewater systems may have variable mercury treatment resu lts. Based on data from 15 different scrubbers, when the oxidation reduction potential (ORP) withi n the scrubber is high, more mercury tends to be in the dissolved phase (Allen et al., 2011). The more highly oxidizing the system, the great er 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 indivi dual 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 with in 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 (Alabam a Power Company, APC) used similar colorimetric methods to measure total phosphor us in the samples fr om 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 Tabl e A-2). The comparison suggests that the EPA data underestimates the total phosphorus concentration at SP-1. Barium, lead, and silver can interfere with th e 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 interferenceconcern for phosphorus analyses. No MS/MSD QC samples were performed by the EPA lab on SP-1 samples, but the phosphor us data at SP-1 may be biased low.

TABLE A-2. Comparison of 4-Day A verages 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 correlati on 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 calib ration factors. The acceptance criteria for the method 1631E calibra tion are an RSD of < 15% for the five or more CF’s and recovery between 75-125% at t he method reporting limit of 0.5 ppt. The SER analytical narrative should be re vised 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 list ed 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 t ables are qualified (f lagged) “^” with the statement “ICV, CCV, ICB, CC B, ISA, ISB, CRI, or MRL standard: Instrument related QC exceeds the control limits.” However, the Test America (T A) EPA method 200.8 analytical narrative (Appendix B) makes no m ention of any quality control (QC) issues associated with the Cr analyse s. Should the Cr data be fl agged or not? If there arequality control concerns, then certainly thes e data may not be relied upon or used for

any purpose.

Sources Allen, Jonathan O., Eggert, De rek, and Tyree, Corey A. Effect of FGD Chemistry on Wastewater Composition , presented at Air Quality V II Conference, Arlington, VA, October 25, 2011.