1 

Memorandum 

Review of Analytical Methods Used for Industry Self-Monitoring Data Considered for FGD 

Wastewater Effluent Limits 

December 8, 2014 

U.S. EPA, Office of Water, Office of Science and Technology, Engineering and Analysis 

Division 

1 Introduction 

In addition to the data EPA used at proposal to calculate effluent limitations for flue gas 

desulfurization (FGD) wastewater, EPA evaluated industry self-monitoring data that were 

submitted along with comments on the proposed rule in 2013, and self-monitoring data that were 

submitted in response to data request letters sent by EPA in 2013 and 2014. In order to assess 

the quality of the industry self-monitoring data received and to determine whether or not to 

include the effluent data in its calculations, EPA gathered all available information about the 

analytical method used and relevant FGD system and treatment system process operations 

associated with the data. 

This memorandum discusses whether, based on an initial review of the analytical methods used 

and information about how the analyses were performed, the industry self-monitoring effluent 

data are considered generally acceptable for use in calculating effluent limits. This initial review 

evaluated whether the methods used were appropriate, were sufficiently sensitive1

 to measure 

pollutant concentrations, and that the reported results reflect proper sampling and analytical 

practices and that the effluent data appear to be valid for use in calculating effluent limits. 

This evaluation was limited to a review of self-monitoring data appropriate for EPA to consider 

using to calculate effluent limits based on the operation of either (1) chemical precipitation/iron 

coprecipitation treatment technology; or (2) chemical precipitation/iron coprecipitation followed 

by anoxic/anaerobic biological treatment technology.2

 As such, discussion is limited to effluent 

data for the following pollutants under these technology bases: arsenic, mercury, selenium and 

nitrate-nitrite. EPA evaluated self-monitoring data from four plants that operate chemical 

precipitation/iron coprecipitation treatment technology: Hatfield’s Ferry Power Station, 

Keystone Generating Station, Miami Fort Station, and Pleasant Prairie Power Plant. Also, EPA 

evaluated self-monitoring data from two plants that operate chemical precipitation/iron 

coprecipitation followed by anoxic/anaerobic biological treatment technology: Belews Creek 

Steam Station and Allen Steam Station. 

 

1

 For data used to calculate effluent limits for the steam electric effluent guidelines, a sufficiently sensitive reporting 

limit (or a sufficiently sensitive analytical method) means that the analytical method is capable of and was used in a 

manner that most analytical results were above the level of quantitation. In instances where most analytical results 

were below the level of quantitation, sufficiently sensitive means that EPA is not aware of any other method 

approved in 40 CFR Part 136 that can produce substantially lower reporting limits for analyses of FGD wastewater. 2

 EPA did not receive self-monitoring data for vapor-compression evaporation treatment of FGD or gasification 

wastewater subsequent to publishing proposed revisions to the effluent guidelines. 
2 

In addition to the initial data assessment described in this memorandum, consistent with the 

methodology used at proposal, EPA thoroughly evaluated the available data for each plant to 

identify any data that should not be used when deriving effluent limits due to: (1) the samples 

being collected during the initial commissioning period for the treatment system prior to 

reaching steady state (or quasi-steady state) operation; (2) the analytical results being identified 

as questionable due to quality control issues, abnormal conditions or treatment upsets, or 

analytical anomalies; or (3) other relevant factors. The results of this additional evaluation are 

described in the memorandum Effluent Limitations for FGD Wastewater, Gasification 

Wastewater, and Combustion Residual Leachate for the Final Effluent Limitations Guidelines 

and Standards for the Steam Electric Rulemaking, (hereafter referred to as the “Effluent 

Limitations Memorandum”). 

2 Analytical Methods Associated with the Industry Self-Monitoring Data 

2.1 Arsenic and Selenium by EPA Method 200.8 

EPA used EPA Method 200.8, in conjunction with a collision cell, to analyze samples collected 

during EPA’s sampling episodes, as well as the samples collected by industry as directed by EPA 

under authority of section 308 of the Clean Water Act. EPA has approved Method 200.8 for the 

measurement of arsenic and selenium in wastewaters subject to compliance monitoring under the 

National Pollutant Discharge Elimination System (NPDES) in 40 CFR Part 136. These data 

were used to develop effluent limits for proposed revisions to the effluent guidelines. 

EPA Method 200.8 utilizes inductively coupled plasma (ICP) and mass spectrometry (MS) to 

determine metals in acid digestates from aqueous samples. The method includes a strong-acid 

digestion procedure that is used to prepare the sample for instrumental analysis. 

Using the MS detector with the ICP provides greater sensitivity for many metals, including 

arsenic, in comparison to the ICP-AES system used in EPA Method 200.7. Method 200.8 also 

employs internal standards (non-target metals added to the samples) to improve the quantitative 

accuracy. The use of the MS detector avoids the spectral interferences common to the ICP-AES 

methods, but there are other interferences specific to this detector. The most prominent potential 

interferences are isobaric elemental interferences, which are caused by isotopes of different 

elements forming atomic ions with the same nominal mass-to-charge ratio (m/z), and isobaric 

molecular and doubly-charged ion interferences, which are caused by ions consisting of more 

than one atom or charge, respectively. 

Most of these interferences have been well studied and reported in the literature. For arsenic in 

particular, the argon gas (as 40Ar) used to create the plasma in the ICP can combine with chloride 

(as 35Cl) in the sample to form ArCl+. ArCl+ has a nominal m/z of 75, the same m/z as the most 

prominent arsenic isotope, 75As. As with EPA Method 200.7, correction factors can be 

developed for the instrument data system to compensate for the expected interferences. 

The potential physical interferences in EPA Method 200.8 arise when high levels of dissolved 

solids in the digested sample affect the nebulizing system in the instrument. The most common 
3 

approach to overcoming the physical effects of dissolved solids is to dilute the sample digestate 

prior to analysis, thereby raising the reporting limits. However, these interferences can be 

reduced by using a nebulizer on the instrument that is designed to handle high dissolved solids 

loads. 

Concerns about the various potential interferences in FGD wastewaters led EPA to develop a 

laboratory standard operating procedure (SOP) which uses a collision cell in conjunction with 

the ICP-MS procedure. This approach (or a similar approach using a dynamic reaction cell, or 

“DRC”) is highly effective at resolving the potential interference effects. The collision cell and 

DRC act by affecting the ions exiting the ICP portion of the instrument on the way to the MS 

detector. A gas is introduced into the ion stream that either collides with (collision cell) or reacts 

with (in DRC) the molecular ions formed from two non-target elements, so that those 

interferences do not enter the MS detector with the same m/z as the target analyte. 

Analyses of arsenic and selenium conducted without the use of a collision cell (or a dynamic 

reaction cell) may result in high-biased data for these analytes as a result of those interferences. 

For this reason, results generated using EPA Method 200.8 without the collision cell or dynamic 

reaction cell are generally unacceptable for calculating effluent limits for the steam electric 

effluent guidelines. Data collected using Method 200.8 with a collision cell or dynamic reaction 

cell are generally acceptable for these purposes, provided that the laboratories achieved a 

sufficiently sensitive reporting limit and further evaluation of the data as described in section 3.1 

does not identify other reasons for excluding the data, such as treatment system upsets or other 

factors. 

2.2 Arsenic by EPA Method 200.7 

EPA Method 200.7 utilizes inductively coupled plasma (ICP) equipped with an atomic emission 

spectroscopy (AES) detector to determine metals in aqueous samples. EPA has approved Method 

200.7 for the measurement of arsenic and selenium in wastewaters subject to compliance 

monitoring under the National Pollutant Discharge Elimination System (NPDES) in 40 CFR Part 

136. The method advises users that there can be physical, chemical, and spectral interferences 

present in some samples that will affect the ability of the method to produce accurate data for 

some metals. 

The physical interferences noted in the method include changes in viscosity and surface tension 

that can cause significant inaccuracies, especially in samples containing high dissolved solids. 

These interferences can be reduced by using a nebulizer on the instrument that is designed to 

handle high dissolved solids loads, by diluting the sample, or by using an internal standard. High 

dissolved solids may also cause salt buildup at the tip of the nebulizer, which affects aerosol flow 

rate and causes instrumental drift. This problem can be controlled by a high-solids nebulizer, 

wetting the argon prior to nebulization, using a tip washer, or diluting the sample. 

While not normally significant, the method notes that chemical interferences include molecularcompound formation, ionization effects, and solute-vaporization effects. These potential 

chemical interferences are highly dependent on matrix type and the specific analyte element, and 
4 

if present, may be minimized by techniques such as “matrix matching” of the samples and 

standards and the use of the method of standard additions. 

Spectral interferences are those that affect the atomic emissions of the target analytes after they 

are excited by the energy of the plasma. They may be caused by instrument background, stray 

light, and overlap of the wavelengths of light emitted by the target analytes. The method 

specifically addresses these spectral interferences through the analysis of standards containing 

the known interferences from co-occurring metals in the digested sample. The instrument data 

system can be used to develop “inter-element correction factors” that compensate for these 

interferences. The presence of aluminum, cobalt, iron, nickel, or vanadium may produce 

emissions at the 193.759 nm atomic emission line for arsenic, and thus bias the results for arsenic 

by this method. 

The most common solution to the potential physical interferences from dissolved solids is to 

dilute the original sample or its digestate for analysis. However, this dilution reduces the 

sensitivity of Method 200.7 and is reflected in increased reporting limits. 

Data collected using Method 200.7 are generally acceptable for calculating effluent limits, 

provided that the laboratories achieved a sufficiently sensitive reporting limit, there are no 

indications of analytical interferences, and further evaluation of the data (described in section 

3.1) does not identify other reasons for excluding the data, such as treatment system upsets or 

other factors. 

2.3 Arsenic by EPA Methods 6020 or 6020A (SW 846) 

Method 6020A was issued by the Office of Resource Conservation and Recovery (ORCR) in 

2007 as part of the SW-846 methods manual. Method 6020A utilizes inductively coupled 

plasma (ICP) and mass spectrometry (MS) to determine metals in acid digestates from samples 

of various matrices, including aqueous and solid samples. Method 6020A covers only the 

determinative (instrumental analysis) portions of the analytical process. It must be coupled with 

digestion of the sample matrix using strong acids as described in one of the SW-846 sample 

preparation methods in the 3000-Series, e.g., Method 3005A, 3010A, or 3015A, which differ in 

the equipment used to heat the sample during the digestion process. When coupled with one of 

these sample preparation methods, Method 6020A is similar to Method 200.8 from the Office of 

Water. The differences are largely a function of the fact that the SW-846 methods manual is 

issued as guidance for monitoring compliance with ORCR solid waste regulations, and thus does 

not contain quality control requirements of the rigor that are typical of an Office of Water 

compliance monitoring method. 

Method 6020 is an earlier version of the SW-846 ICP/MS procedure, issued in 1994. Although it 

uses the same ICP/MS instrumentation, it was a simpler version of the procedure than the later 

revision, Method 6020A. It lacked a multi-point instrument calibration and detailed calibration 

instructions, contained fewer target metals, and provided less detailed discussions of quality 

control. EPA no longer provides copies of Method 6020 on its website since it has been 

superseded by Method 6020A. EPA has not approved Methods 6020 and 6020A for NPDES 

compliance monitoring in 40 CFR Part 136. 
5 

As with Method 200.8, using the MS detector with the ICP in Method 6020A provides greater 

sensitivity for many metals, including arsenic, in comparison to the ICP-AES system used in 

Method 200.7. The method also employs internal standards (non-target metals added to the 

samples) to improve the quantitative accuracy. The use of the MS detector avoids the spectral 

interferences common to the ICP-AES methods, but there are other interferences specific to this 

detector. The most prominent potential interferences are isobaric elemental interferences, 

described above in section 2.1. 

The potential physical interferences in Method 6020A are similar to those in Methods 200.7 and 

200.8, arising when high levels of dissolved solids in the digested sample affect the nebulizing 

system in the instrument. As with Method 200.8, the most common approach to overcoming the 

physical effects of dissolved solids is to dilute the sample digestate for analysis, raising the 

reporting limits. 

The “guidance” aspect of SW-846 methods affords the opportunity to utilize additional 

instrumental components as part of the ICP-MS system. Two related components are a dynamic 

reaction cell (DRC) or a collision cell accessory that can be used to overcome some of the 

interferences. Both of these accessories act by affecting the ions exiting the ICP portion of the 

instrument on the way to the MS detector. A gas is introduced into the ion stream that either 

reacts with (in DRC) or collides with (collision cell) the molecular ions formed from two nontarget elements, such that those interferences do not enter the MS detector with the same m/z as 

the target analyte. 

Arsenic concentration data submitted by industry collected using Method 6020A will not 

generally be considered acceptable for calculating effluent limits unless the laboratories achieved 

a sufficiently sensitive reporting limit and the method was approved for compliance monitoring 

by the permitting authority. Additionally, as is the case with data collected using Method 200.8, 

results generated using Method 6020A without the collision cell or DRC are generally not 

acceptable for calculating effluent limits for the steam electric effluent guidelines. 

As noted above, Method 6020 does not include many of the quality control requirements that are 

part of Method 6020A. Because of the limited quality control associated with this method and 

that the method is not approved for NPDES compliance monitoring under 40 CFR Part 136, data 

collected using Method 6020 are generally not acceptable for use in calculating effluent limits. 

2.4 Mercury by EPA Method 1631E 

EPA Method 1631E utilizes a cold vapor atomic fluorescence instrument to determine mercury 

in aqueous samples. The method involves adding bromine monochloride (BrCl) to the sample to 

oxidize all mercury in the sample to the Hg+2 ion. After oxidation, hydroxylamine hydrochloride 

(NH2OH•HCl) is added to the sample to destroy any free halogens remaining from the BrCl 

treatment. Stannous chloride (SnCl2) is added to convert the Hg+2 ions to volatile elemental 

mercury (Hg0

). The Hg0 is separated from solution by either purging with nitrogen, helium, or 

argon, or by vapor/liquid separation, and is collected on a series of two gold traps. The mercury 
6 

is then thermally desorbed from the gold trap into an inert gas stream that carries it into the cell 

of a cold-vapor atomic fluorescence spectrometer (CVAFS) for detection. 

The method contains extensive quality control procedures designed to ensure efficacy of the 

sample preparation, purging, and detection systems. The nominal quantitation limit for Method 

1631E is 0.5 ng/L, three orders of magnitude lower than the detection limit for Method 245.1. 

EPA has approved Method 1631E for the measurement of mercury in wastewaters for NPDES 

compliance monitoring in 40 CFR Part 136. 

EPA used EPA Method 1631E to analyze samples collected during EPA’s sampling episodes, as 

well as the samples collected by industry as directed by EPA under authority of section 308 of 

the Clean Water Act. These data were used to develop effluent limits for proposed revisions to 

the effluent guidelines. Industry self-monitoring data collected using Method 1631E are 

generally acceptable for calculating effluent limits for the final ELG rulemaking, provided that 

the laboratories achieved a sufficiently sensitive reporting limit, there are no indications of 

analytical interferences, and further evaluation of the data (described in section 3.1) does not 

identify other reasons for excluding the data, such as treatment system upsets or other factors. 

2.5 Mercury by EPA Method 245.7 

Like EPA Method 1631E, Method 245.7 utilizes an atomic fluorescence detector to achieve 

much greater sensitivity than the atomic absorption detector used in EPA Method 245.1 and SM 

3112B. However, Method 245.7 uses liquid-gas separation and a dryer tube to separate the 

mercury from the sample matrix, while Method 1631 purges the mercury and collects it on a 

gold trap. Method 245.7 also contains the same extensive suite of quality control operations as 

Method 1631E that are designed to ensure that the method is capable of measuring mercury at 

very low levels without background contamination from mercury in other sources, including the 

laboratory itself. EPA has approved Method 245.7 for the measurement of mercury in 

wastewaters subject to compliance monitoring under the National Pollutant Discharge 

Elimination System (NPDES) in 40 CFR Part 136. 

The nominal quantitation limit for Method 245.7 is 5 ng/L. Therefore, while not quite as 

sensitive as Method 1631E, Method 245.7 can produce valid results in the same general range of 

mercury concentrations. EPA’s review of the industry data generated using Method 245.7 found 

only a few non-detects among the observations, which minimizes concerns about how to 

incorporate the Method 245.7 results with those from Method 1631E. 

Industry self-monitoring data collected using Method 245.7 are generally acceptable for 

calculating effluent limits, provided that the laboratories achieved a sufficiently sensitive 

reporting limit, there are no indications of analytical interferences, and further evaluation of the 

data (described in section 3.1) does not identify other reasons for excluding the data, such as 

treatment system upsets or other factors. 

2.6 Mercury by EPA Method 245.1 
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EPA Method 245.1 uses a cold vapor atomic absorption (CVAA) procedure to analyze samples. 

It involves purging an aqueous sample with air to sweep mercury from the sample into a quartz 

absorption cell. A light source set to 253.7 nm, the characteristic absorption wavelength for 

elemental mercury, passes light through the absorption cell and onto an atomic absorption 

detector system. The absorption of light as it passes through the cell is proportional to the 

concentration of the absorbing species (mercury) and is used to determine the concentration in 

the sample. EPA has approved the method for the measurement of mercury for NPDES 

compliance monitoring in 40 CFR Part 136. 

EPA collected its mercury data for the rulemaking using EPA Method 1631E, which utilizes an 

atomic fluorescence detector to achieve much greater sensitivity than the atomic absorption 

detector used in Method 245.1. Method 245.1 was approved by EPA in 1974 and typically can 

achieve measurements of mercury down to 200 ng/L. EPA approved Method 1631E in 2002. 

This newer method has a nominal quantitation level of 0.5 ng/L, making it 400 times more 

sensitive than Method 245.1. 

In a memorandum issued by EPA’s Office of Wastewater Management, EPA advised permitting 

authorities to ensure that sufficiently-sensitive analytical methods are used when deciding 

whether to set a permit limitation for mercury and for sampling and analysis of mercury pursuant 

to the monitoring requirements within a NPDES permit3

. In the memorandum, EPA noted that 

Method 245.1 is “not likely to be sensitive enough to detect or quantify the concentration of 

mercury in the discharge” at levels that match the effluent limitations that may be established by 

a permit. That assessment is consistent with data EPA has collected during this rulemaking, 

showing that Method 245.1 typically is not sensitive enough to quantify mercury concentrations 

in the effluent from FGD wastewater treatment systems. Because of this, data collected using 

Method 245.1 are generally unacceptable for calculating effluent limits for FGD wastewater. 

2.7 Mercury by Standard Method 3112B 

Standard Method 3112B (SM 3112B) is a method published jointly by the American Public 

Health Association, American Water Works Association, and Water Environment Federation as 

part of Standard Methods for the Examination of Water and Wastewater. EPA has approved 

Method 3112B for the measurement of mercury for NPDES compliance monitoring in 40 CFR 

Part 136. 

The method does not provide example detection or reporting limits. However, functionally, SM 

3112B is very similar to EPA Method 245.1, and the nominal detection limit for Method 245.1 is 

approximately 200 ng/L, which suggests that SM 3112B is capable of producing mercury results 

at similar levels. SM 3122B also employs quality control operations similar to those in EPA 

Method 245.1. 

EPA collected its mercury data using EPA Method 1631E, which utilizes an atomic fluorescence 

detector to achieve much greater sensitivity than the atomic absorption detector used in SM 

3112B. The nominal quantitation limit for Method 1631E is 0.5 ng/L. Method 1631E also 

 

3 James A. Hanlon, Director, Office of Wastewater Management. “Analytical Methods for Mercury in National 

Pollutant Discharge Elimination System (NPDES) Permits,” August 23, 2007. 
8 

incorporates a larger suite of quality control operations than SM 3112B or Method 245.1 that are 

designed to ensure that the method is capable of measuring mercury at very low levels without 

background contamination from mercury in other sources, including the laboratory itself. 

SM 3112B is typically not sensitive enough to quantify the concentration of mercury present in 

FGD wastewater treatment system effluent. As a result, data collected using SM 3112B are 

generally unacceptable for calculating effluent limits for FGD wastewater. 

2.8 Nitrate-Nitrite by EPA Method 353.2 

Nitrate (NO3

-

) and nitrite (NO2

-

) are two ionic forms of oxidized nitrogen that frequently occur in 

wastewaters. These two pollutants can be important nutrients for aquatic plants, and therefore, 

EPA regulates them to reduce eutrophication of rivers, streams, and lakes receiving wastewater 

discharges. Under routine conditions in wastewaters and receiving waters, oxidation-reduction 

reactions can rapidly lead to conversion of nitrite to nitrate. Therefore, and as is the case for the 

steam electric effluent guidelines, EPA tends to regulate these nitrogen forms as the combined 

parameter called “nitrate-nitrite (as N).”4

EPA Method 353.2 is a colorimetric procedure for determining nitrate-nitrite in aqueous 

samples. The method uses cadmium as a reducing agent to convert all of the nitrate in the 

sample to nitrite. The nitrite that was originally present in the sample, plus any reduced nitrate, 

reacts with two reagents to form a colored azo (nitrogen containing) dye. The intensity of the 

color is proportional to the nitrate-nitrite concentration in the sample and is measured with a 

colorimeter. EPA Method 353.2 is approved for NPDES compliance monitoring in 40 CFR Part 

136 and was used to analyze the EPA-collected samples and CWA 308 samples used to calculate 

effluent limits for the proposed rule. 

Data collected using Method 353.2 are generally acceptable for calculating effluent limits, 

provided that the laboratories achieved a sufficiently sensitive reporting limit, there are no 

indications of analytical interferences, and further evaluation of the data (described in section 

3.1) does not identify other reasons for excluding the data, such as treatment system upsets or 

other factors. 

3 Plant-Specific Review of Self-Monitoring Data 

3.1 Data Evaluations 

 

4

 Industry submitted also submitted effluent data for nitrate that had been analyzed using either EPA Method 300.0 

or Hach test kits. The Method 300.0 and Hach test kit data measure the concentration of nitrate alone, and not the 

combined parameter nitrate-nitrite, and therefore these data would underestimate the value for the combined 

parameter nitrate-nitrite. Since the parameter that would be regulated is the combined nitrate-nitrite, and not nitrate 

alone, the Method 300.0 and Hach test kit data do not provide sufficient information about the regulated parameter 

and are not acceptable for calculating effluent limits for nitrate-nitrite in FGD wastewater. 
9 

Plant-specific considerations arise when engineering, laboratory, or other factors influence the 

sensitivity of the method used or the quality of the data obtained. This section discusses the 

sources of industry self-monitoring data, which analytical methods were used, and whether the 

data are acceptable for calculating effluent limits. Section 2 discussed whether or not a method 

is acceptable in general, however this section evaluates specific factors related to the data for 

each plant to determine whether they are appropriate for calculating effluent limits based on the 

considerations discussed in section 2. 

In sections 3.2 through 3.5, EPA discusses the self-monitoring data from four plants that operate 

chemical precipitation/iron coprecipitation treatment technology: Hatfield’s Ferry Power Station, 

Keystone Generating Station, Miami Fort Station, and Pleasant Prairie Power Plant. Sections 3.6 

and 3.7 discuss the self-monitoring data from two plants that operate chemical precipitation/iron 

coprecipitation followed by anoxic/anaerobic biological treatment technology: Belews Creek 

Steam Station and Allen Steam Station. 

The conclusions in this document about data acceptability only apply to the assessments 

described herein. In addition to assessing whether the industry self-monitoring data described in 

this memorandum are generally acceptable for use (as discussed in section 2 and sections 3.2 

through 3.7), EPA thoroughly evaluated the available data for each plant to identify any data that 

should not be used when deriving effluent limits due to: (1) the samples being collected during 

the initial commissioning period for the treatment system; (2) the analytical results being 

identified as questionable due to quality control issues, abnormal conditions or treatment upsets, 

or analytical anomalies; or (3) other relevant factors. Therefore, while this document may deem 

data to be acceptable, additional evaluation may have led EPA to determine otherwise. The final 

determination as to whether EPA determined the data are acceptable for calculating effluent 

limits for the final rule is presented in the Effluent Limitations Memorandum, along with the 

results of this additional evaluation and plots of the data. 

3.2 Hatfield’s Ferry Power Station 

FirstEnergy’s Hatfield’s Ferry Power Station operates a chemical precipitation system to treat the 

FGD wastewater. This facility is one of the BAT plants used by EPA to calculate limits for both 

the proposed and final rule. EPA collected data from Hatfield’s Ferry during an EPA sampling 

episode and from samples collected by industry as directed by EPA (i.e., “CWA 308 samples”). 

In their comments on the proposed rule, UWAG submitted plant self-monitoring data for arsenic 

(EPA Method 200.7) and mercury (EPA Method 245.7) for the effluent from the chemical 

precipitation treatment system. 

FirstEnergy also submitted self-monitoring data for arsenic (EPA Methods 200.7 and 200.8) and 

mercury (EPA Methods 245.7 and 245.1) for the effluent from the chemical precipitation 

treatment system. These data were submitted in response to a letter from EPA requesting the 

company to provide existing analytical data for the treatment system. 

Hatfield’s Ferry Power Station was decommissioned in late 2013. FirstEnergy advised EPA that 

data associated with samples collected after October 6, 2013, the last day Hatfield’s Ferry 
10 

generated electricity, are not representative of typical FGD wastewater treatment system effluent 

(DCN SE04679). 

3.2.1 Arsenic 

Arsenic by EPA Method 200.7 

Both UWAG and FirstEnergy provided arsenic data using Method 200.7. The data submitted by 

UWAG spans the period 7/7/2009 through 10/25/2011 and is a subset of the data provided by 

FirstEnergy. The Method 200.7 data provided by FirstEnergy includes analysis results from two 

company laboratories: Allegheny lab spanning 6/30/2009 through 11/29/2011, and FirstEnergy’s 

Beta lab spanning 12/6/2011 through 12/10/2013. 

Data collected after 10/6/2013 are associated with the decommissioning period for Hatfield’s 

Ferry and are not representative of typical FGD wastewater treatment system effluent. 

Therefore, the arsenic data for 10/8/2013 (the first sampling date during the decommissioning 

period) through 12/10/2013 are not acceptable for use in calculating effluent limits. 

As discussed in section 2.2, data collected using Method 200.7 are generally acceptable for use 

in developing effluent limits, provided the laboratories achieved a sufficiently sensitive reporting 

limit, there are no indications of analytical interferences, and evaluation of the data does not 

identify other reasons for excluding the data, such as treatment system upsets or other factors. 

The data from the Allegheny lab do not appear to be adversely affected by the types of 

interferences generally observed with Method 200.7 for FGD wastewater, as indicated by (1) the 

ability of the laboratory to achieve low reporting limits (i.e., MDL of 2 ug/L and quantified 

values as low as 3 ug/L reported to the permitting authority for compliance monitoring); (2) the 

consistency between values reported by the Allegheny lab and the values reported by a 

commercial lab under contract to EPA that analyzed samples from the EPA sampling episode 

and the CWA 308 samples, as well as the split samples collected and analyzed by UWAG on 

behalf of FirstEnergy during the EPA sampling episodes and CWA 308 sampling; and (3) the 

values reported by the Allegheny lab being consistent with the observed performance of 

chemical precipitation/iron coprecipitation for FGD wastewater generally, especially by power 

plants operating treatment systems that represent the BAT level of performance (for example, see 

the treatment system effluent concentrations for Miami Fort, Pleasant Prairie, and Keystone, and 

the chemical precipitation effluent for Belews Creek and Allen). For these reasons, the arsenic 

data from the Allegheny lab (for 6/30/2009 through 11/29/2011) are acceptable for calculating 

effluent limits, subject to the additional data evaluations described in section 3.1. 

Conversely, the data from the Beta lab bear stark contrast to the data from the Allegheny lab (and 

thus, data for Hatfield’s Ferry from other labs). The Allegheny lab provides approximately 2.5 

years of arsenic data for Hatfield’s Ferry, with 60 percent of observations below 10 ug/L. In fact, 

only one observation for effluent arsenic (out of 127 observations) from the Allegheny lab is 

above 20 ug/L. The Beta lab data, however, exhibit a strikingly different pattern which began 

with its first sample result (Beta’s first arsenic result of 159 ug/L on 12/6/2011, as compared to 

Allegheny’s last arsenic result of 8 ug/L on 11/29/2011). The data from Beta lab were routinely 
11 

in the upper double-digit parts-per-billion or even triple-digit parts-per billion. Only two 

observations for effluent arsenic (out of 106 observations) were below 10 ug/L, and 37 percent of 

observations were reported at or higher than 100 ug/L (a number of these were substantially 

higher than 100 ug/L, with the highest at 424 ug/L). All of the reasons explained above as to why 

the Allegheny lab results are acceptable help to explain why the Beta lab results are questionable. 

The Beta lab results are inconsistent with the effluent concentrations observed for chemical 

precipitation treatment systems and are particularly suspect given that this radically different 

pattern of data coincided with FirstEnergy shifting analyses to the Beta lab. FirstEnergy was 

unable to explain the unusual results from the Beta lab and noted there were no known processrelated reasons (e.g., changing coal type, modifications to FGD scrubber or treatment system 

operation) that would explain a change in effluent quality. These factors suggest that the Beta lab 

data very likely reflect quality control issues related to analytical interferences that would impart 

a high bias to the arsenic results, such as those noted above in section 2. For these reasons, the 

arsenic data from the Beta lab (for 12/6/2011 through 10/1/2013)5

 are not acceptable for use.6

Arsenic by EPA Method 200.8 

FirstEnergy provided arsenic data analyzed by the Beta lab using Method 200.8 for three days in 

late 2012. The concentrations associated with these data are at unusually high levels for effluent 

from a chemical precipitation treatment system. As noted above in section 2.1, Method 200.8 is 

an ICP-MS method that is subject to isobaric elemental interferences, including interferences that 

can result in high-biased results for arsenic. Concerns about potential interferences such as these 

led EPA to develop a laboratory standard operating procedure (SOP) which uses a collision cell 

in conjunction with the ICP-MS procedure. Use of the collision cell (or a dynamic reaction cell) 

is highly effective at resolving such interference effects. FirstEnergy confirmed that the Method 

200.8 analyses from the Beta lab did not include the use of either a collision cell or dynamic 

reaction cell, supporting EPA’s conclusion that the results provided by FirstEnergy very likely 

reflect quality control issues related to analytical interferences such as those noted above in 

section 2 (DCN SE04316A6). Because of this, FirstEnergy’s Method 200.8 data for arsenic for 

these three days are not acceptable for calculating effluent limits. 

3.2.2 Mercury 

Mercury by EPA Method 245.7 

Both UWAG and FirstEnergy provided mercury data using Method 245.7. The data submitted 

by UWAG with their comments on the proposed rule spans the period 7/7/2009 through 

10/25/2011 and is a subset of the data provided by FirstEnergy. The data from FirstEnergy was 

provided in response to an EPA request for data and spans the period 6/30/2009 through 

12/10/2013. 

 

5

 10/1/2013 is the last date that samples were collected for arsenic prior to the start of the decommissioning period. 6

 In addition, as noted earlier in this section, arsenic data from the Beta lab for the period 10/8/2013 through 

12/10/2013 are associated with the decommissioning period for Hatfield’s Ferry Power Station and, since the data 

are not representative of typical FGD operation, are not acceptable for use in calculating effluent limits. 
12 

Data collected after 10/6/2013 are associated with the decommissioning period for Hatfield’s 

Ferry and are not representative of typical FGD wastewater treatment system effluent. 

Therefore, the mercury data for 10/8/2013 through 12/10/2013 are not acceptable for use in 

calculating effluent limits. 

As discussed in section 2.5, industry self-monitoring data collected using Method 245.7 are 

generally acceptable for effluent limits provided that the laboratories achieved a sufficiently 

sensitive reporting limit. The reporting limits associated with Hatfield’s Ferry’s 245.7 data are 

sufficient for the purposes of the steam electric ELG rulemaking because the laboratory results 

for most samples were reported at levels above the level of quantitation. Therefore, the Method 

245.7 mercury data from Hatfield’s Ferry (for 6/30/2009 through 10/1/2013)7

 are acceptable for 

calculating effluent limits, subject to the additional data evaluations described in section 3.1. 

Mercury by EPA Method 245.1 

FirstEnergy provided mercury data analyzed by Method 245.1 for three days in late 2012, 

including a nondetect observation on 11/29/2012 (reporting limit of 200 ng/L). As discussed in 

section 2.6, Method 245.1 often is not sensitive enough to measure the mercury present in 

treatment system effluent and therefore data using this method are generally unacceptable for 

calculating effluent limitations for FGD wastewater. Most of the observations in the weeks 

preceding the 11/29/2012 observation were below 200 ng/L, as was the observation immediately 

following that date, demonstrating that Method 245.1 is not sensitive enough to reliably measure 

the concentration of mercury in the treatment system effluent.8

 Therefore, FirstEnergy’s Method 

245.1 mercury data for these three days are not acceptable for calculating effluent limits. 

3.3 Keystone Generating Station 

NRG Energy’s Keystone Generating Station operates a chemical precipitation system to treat the 

FGD wastewater. This facility is one of the BAT plants used by EPA to calculate limits for the 

proposed and final rules. EPA collected data from Keystone during an EPA sampling episode 

and samples collected by industry as directed by EPA (i.e., “CWA 308 samples”). 

NRG Energy also submitted self-monitoring data for arsenic (EPA Methods 200.7, 200.8, and 

6020) and mercury (SM 3112B) for effluent from the chemical precipitation treatment system. 

These data were submitted in response to a letter from EPA requesting the company to provide 

existing analytical data for the treatment system. 

3.3.1 Arsenic 

Arsenic by EPA Method 200.7 

NRG Energy provided effluent data for arsenic using Method 200.7, spanning the period 

1/3/2012 through 1/6/2014. As discussed in section 2.2, data collected using Method 200.7 are 

 

7

 10/1/2013 is the last date that samples were collected for mercury prior to the start of the decommissioning period. 

8

 These quantified results below 200 ng/L were measured using EPA Method 245.7, a much more sensitive 

analytical method. 
13 

generally acceptable for use in developing effluent limits or estimating pollutant reductions, 

provided the laboratories achieved a sufficiently sensitive reporting limit, there are no indications 

of analytical interferences, and evaluation of the data does not identify other reasons for 

excluding the data, such as treatment system upsets or other factors. 

Keystone’s NPDES permit does not include effluent limits for arsenic; instead, the permit 

requires the plant to “monitor and report” the arsenic concentrations in the treatment system 

effluent. Because of this, NRG Energy stated that the plant was not concerned with attempting to 

achieve a low reporting limit and their laboratory determined that 20 ug/L was the level they 

could achieve on a routine basis (DCN SE04318). Analyses conducted on EPA-collected 

samples and the CWA 308 samples showed effluent arsenic concentrations of approximately 4 

ug/L. Method 200.8 self-monitoring data provided by NRG Energy show similar effluent 

concentrations, in the range of 1-5 ug/L (see further discussion in the section below). The 

reporting limit for the Method 200.7 data is an order of magnitude higher than these Method 

200.8 effluent concentrations and, as a result, most of the Method 200.7 data are reported as 

nondetects.9

 Because the Method 200.7 data for Keystone do not have a low enough reporting 

limit to reliably measure the arsenic concentrations in the treatment system effluent, these data 

(from 1/3/2012 through 1/6/2014) are not acceptable for calculating effluent limits. 

Arsenic by EPA Method 200.8 

NRG Energy provided effluent data for arsenic using Method 200.8, spanning the period 

1/13/2014 through 4/28/2014. NRG Energy began using this method in January 2014 to analyze 

for arsenic in the treatment system effluent. The ICP-MS instrumentation used for the 200.8 

analysis was operated in collision mode (i.e., using a collision cell). As discussed in section 2.1, 

data collected using Method 200.8 with a collision cell or dynamic reaction cell are generally 

acceptable for use in calculating effluent limits, provided the laboratories achieved a sufficiently 

sensitive reporting limit, there are no indications of analytical interferences, and evaluation of the 

data does not identify other reasons for excluding the data, such as treatment system upsets or 

other factors. The data provided typically had a reporting limit of 1 ug/L, with the highest 

sample-specific reporting limit at 5 ug/L (due to sample dilution). This reporting limit is 

sufficient for the purposes of the ELG rulemaking and Keystone’s Method 200.8 arsenic data 

(from 1/13/2014 through 4/28/2014) are acceptable for calculating effluent limits, subject to the 

additional data evaluations described in section 3.1.10

Arsenic by EPA Method 6020 (SW-846) 

 

9

 Keystone reported only two quantified results using Method 200.7, out of more than 100 observations. In a phone 

conversation, company representatives acknowledged that these two quantified results appear to be outliers. (DCN 

SE04318) 

10 NRG Energy reported that the laboratory’s quantitation limit for arsenic using Method 200.8 is 1 ug/L (DCN 

SE04318). Even after accounting for elevated reporting limits due to sample dilution, much of the effluent data for 

arsenic using this method are reported as nondetect at 4 ug/L. This reporting limit is comparable to the 

concentrations achieved by laboratories during the EPA sampling and 308 sampling episodes, and EPA is not aware 

of any other Part 136-approved methods reliably achieving substantially lower reporting limits for arsenic in FGD 

wastewater. 
14 

NRG Energy provided a single result (nondetect at 5 ug/L) for effluent arsenic using Method 

6020. NRG Energy stated that this sample was collected as part of a sampling event conducted 

by EPA Region 3 related to a hydraulic fracturing study. NRG Energy collected a split sample 

with EPA Region 3 and used Method 6020 in an effort to be consistent with the analyses being 

performed by Region 3.11 NRG Energy analyzed only one sample using this method and the 

company representatives stated that they are not familiar with the method or how the sample was 

analyzed.12 (DCN SE04318) 

Method 6020 is issued by EPA’s Office of Resource Conservation and Recovery (ORCR) as part 

of the SW-846 methods manual. It is an ICP-MS method used to determine metals in acid 

digestates from samples of various matrices, including aqueous and solid samples. Although 

Method 6020 is similar in some respects to EPA Method 200.8, the SW-846 methods manual is 

issued as guidance for monitoring compliance with ORCR solid waste regulations and does not 

contain the degree of quality control requirements that are typically included in analytical 

methods issued for NPDES compliance monitoring. EPA has not approved Method 6020 for 

compliance monitoring under the National Pollutant Discharge Elimination System (NPDES) in 

40 CFR Part 136. Additionally, EPA no longer provides copies of Method 6020 on its website 

because the method has been superseded in the SW-846 methods manual by Method 6020A.13 

Because of this (and because NRG Energy is not familiar with how the sample was analyzed), 

the Method 6020 data for a single day at Keystone are not acceptable for calculating effluent 

limits. 

3.3.2 Mercury 

Mercury by Standard Method 3112B 

NRG Energy provided mercury data using Standard Method 3112B (SM3112B). These data 

were provided in response to a data request from EPA, and span the period 1/3/2012 through 

4/28/2014. This analytical method does not include example detection or reporting limits; 

however, SM 3112B is very similar to EPA Method 245.1 which has a nominal quantitation limit 

of 200 ng/L. Given its similarity to Method 245.1, SM 3112B is generally expected to have 

comparable reporting limits -- three orders of magnitude higher than Method 1631E (quantitation 

limit of 0.5 ng/L). Because of this, SM 3112B is often not sensitive enough to measure the 

mercury present in treatment system effluent and therefore is generally unacceptable for 

calculating pollutant loadings and effluent limitations for FGD wastewater. This is the case for 

the Keystone effluent mercury data, where 99 percent of the nearly 250 observations were 

reported as nondetect at concentrations of 200 ng/L or higher. As discussed in section 2, a more 

sensitive analytical method, such as Method 1631E, likely would have been able to quantify the 

amount of mercury present in the effluent, as demonstrated by the results of the EPA-collected 

 

11 EPA Region 3 actually used EPA Method 6020A to analyze their sample, not Method 6020. 

12 Based on the summary-level data report NRG Energy provided from their contract laboratory in Pennsylvania, 

EPA confirmed that the laboratory’s accreditation through the Pennsylvania Department of Environmental 

Protection is for the older version, Method 6020, and that they do not hold an accreditation for Method 6020A. 

Neither NRG Energy nor their contract laboratory provided any supporting quality control data for the analysis of 

arsenic, reinforcing EPA’s decision that the data are not acceptable for use in calculating effluent limits. 13 See section 2 for a comparison of the quality control requirements in Methods 6020 and 6020A. 
15 

samples and CWA 308 sampling (these observations were all quantified at concentrations below 

200 ng/L). For this reason, the NRG Energy’s SM 3112B data (for 1/3/2012 through 4/28/2014) 

are not acceptable for calculating effluent limits. 

3.4 Miami Fort Station 

Duke Energy’s Miami Fort Station operates a chemical precipitation system to treat the FGD 

wastewater. This facility is one of the BAT plants used by EPA to calculate limits for both the 

proposed and final rules. EPA collected data from Miami Fort during an EPA sampling episode 

and samples collected by industry as directed by EPA (i.e., “CWA 308 samples”). 

In their comments on the proposed rule, UWAG submitted plant self-monitoring data for 

mercury (EPA Method 1631E) in the effluent from the chemical precipitation treatment system. 

Duke Energy submitted effluent self-monitoring data for arsenic (EPA Method 200.8) and 

mercury (EPA Method 1631E) with their comments on the proposed rule. 

Duke Energy also provided additional effluent data for arsenic (EPA Method 200.8) and mercury 

(EPA Method 1631E) in response to a letter from EPA requesting the company to provide 

existing analytical data for the treatment system. 

3.4.1 Arsenic 

Arsenic by EPA Method 200.8 

Duke Energy provided arsenic data using Method 200.8 as part of their comments on the 

proposed rule and in response to a request from EPA. As discussed in section 2.1, data collected 

using Method 200.8 with a collision cell or dynamic reaction cell are generally acceptable for 

rulemaking purposes, provided that the laboratories achieved a sufficiently sensitive reporting 

limit and additional evaluation of the data does not identify other reasons for excluding the data. 

The data submitted with Duke Energy’s comments spans the period 7/13/2009 through 5/8/2013. 

These arsenic data were included again in Duke Energy’s response to EPA’s data request, along 

with additional data, resulting in the arsenic data spanning the period 7/13/2009 through 

12/3/2013. Multiple laboratories were involved in analyzing the Miami Fort arsenic data, and 

important characteristics of these analytical results warrant evaluating their acceptability as four 

different sets of data: (1) split samples from the EPA sampling episode and CWA 308 sampling, 

analyzed by three non-Duke Energy labs (Applied Speciation, Southern Research Institute, and 

Ohio State University); (2) plant self-monitoring data analyzed by Duke Energy’s company 

laboratory; (3) a single analytical result from a commercial laboratory; and (4) round robin 

analyses by four laboratories for samples collected on one day (5/8/2013; Pace Analytical, 

Heritage, TestAmerica, and Duke Energy’s McGuire lab). These four sets of arsenic data are 

discussed below. 

Split Samples from EPA Sampling Episode and CWA 308 Sampling
16 

For the EPA sampling episode and CWA 308 sampling events, Duke Energy collected 

split samples and had them separately analyzed by three different labs. The results from 

these three labs are similar in magnitude to each other, as well as to the results from the 

laboratory that analyzed samples under contract to EPA. These results provided by Duke 

Energy for the three labs are all quantified values at approximately 5 ug/L or lower, and 

therefore the labs achieved a sufficiently sensitive reporting limit (i.e., the quantitation 

limits for these analyses were low enough to measure the concentration of arsenic present 

in the samples). This set of arsenic data for Miami Fort Station is acceptable for 

calculating effluent limits, subject to the additional data evaluations described in section 

3.1. 

Samples Analyzed by Duke Energy’s Company Lab

The samples analyzed by Duke Energy’s company lab span the period 7/13/2009 through 

12/3/2013. All observations in this set of data were reported as nondetect, with reporting 

limits for most observations at 20 ug/L. No sample within this set of data had a reporting 

limit below 10 ug/L. In contrast, multiple independent laboratories analyzing the samples 

from the EPA sampling episode and CWA 308 sampling, which occurred within the time 

period represented by this set of observations, were able to attain much lower reporting 

limits and, as a result, better quantify the concentration of arsenic present in the treatment 

system effluent (all EPA-contracted and industry-contracted lab results for the EPA and 

CWA 308 sampling episodes were quantified at concentrations below 10 ug/L).14 This 

demonstrates that Duke Energy’s company lab did not achieve sufficiently sensitive 

reporting limits and therefore this set of data from Duke Energy’s company lab for Miami 

Fort are not acceptable for use. 

 

Single Sample Analyzed by a Commercial Laboratory

Duke Energy provided the analytical result for arsenic for a sample collected on 

6/28/2011. The sample was analyzed by a commercial laboratory and, according to the 

lab report, the reported value of 4.34 ug/L is above the reporting limit of 2 ug/L. 

There are no indications of analytical interferences and evaluation of the data does not 

identify other reasons for excluding the data, such as treatment system upsets or other 

factors. The lab report stated that the reporting limit for the sample was 2 ug/L. This 

reporting limit is sufficient for the purposes of the ELG rulemaking and Miami Fort’s 

Method 200.8 arsenic data for this day (6/28/2011) are acceptable for calculating effluent 

limits, subject to the additional data evaluations described in section 3.1. 

Round Robin Laboratory Analyses 

 

14 EPA contracted with a commercial laboratory to analyze samples from the EPA sampling episode and the CWA 

308 sampling. In addition, Duke Energy collected split samples during those sampling events, which were then 

analyzed by three labs not affiliated with Duke Energy: Applied Speciation, Southern Research Institute, and Ohio 

State University. 
17 

Duke Energy provided results for round robin analyses conducted by four laboratories for 

samples collected on 5/8/2013.15 The results provided for these four labs were nondetect 

at 5 ug/L (Pace Analytical), nondetect at 5 ug/L (Duke Energy’s McGuire lab), detect at 

46 ug/L (Heritage), and nondetect at 500 ug/L (TestAmerica). The TestAmerica result 

demonstrates an extremely high reporting limit, particularly in comparison to all other 

arsenic data provided by Duke Energy and Method 200.8 arsenic data for other plants. 

The result reported by the Heritage lab is unusually high for effluent from a FGD 

wastewater chemical precipitation treatment system and the results from Pace Analytical 

and Duke Energy’s McGuire lab strongly suggest the Heritage result may be in error. 

Since EPA is unable to confirm the validity of any of the round robin results, the Miami 

Fort arsenic data for 5/8/2013 are not acceptable for use. 

3.4.2 Mercury 

Mercury by EPA Method 1631E 

Both UWAG and Duke Energy provided mercury data using Method 1631E. The data submitted 

by UWAG with their comments on the proposed rule spans the period 7/1/2009 through 5/4/2011 

and is a subset of the data provided by Duke Energy. Duke Energy provided mercury data with 

their comments on the proposed rule for the period 7/1/2009 through 5/8/2013. These mercury 

data were included again in Duke Energy’s response to EPA’s data request, along with additional 

data, resulting in the mercury data spanning the period 7/1/2009 through 12/3/2013. Multiple 

laboratories were involved in analyzing the Miami Fort mercury data, and important 

characteristics of these analytical results warrant evaluating their acceptability as two different 

sets of data: (1) recurring plant self-monitoring data and split samples from the EPA sampling 

episode and CWA 308 sampling episodes; and (2) round robin analyses by four laboratories for 

samples collected on one day (5/8/2013; Pace Analytical, Heritage, TestAmerica, and Duke 

Energy’s McGuire lab). These two sets of mercury data are discussed below. 

Recurring Self-Monitoring and Split Samples from EPA & CWA 308 Sampling 

These mercury effluent data span the period 7/1/2009 through 12/3/2013 (excluding 

round robin data for 5/8/2013). As discussed in section 2.4, data collected using Method 

1631E are generally acceptable for use provided that the laboratories achieved a 

sufficiently sensitive reporting limit and additional evaluation of the data does not 

identify other reasons for excluding the data. The reporting limit for these data is 

sufficiently sensitive for the purposes of the ELG rulemaking (i.e., all analytical results 

for mercury were reported as quantified values) and these Method 1631E mercury data 

(for 7/1/2009 through 12/3/2013) are acceptable for calculating effluent limits, subject to 

the additional data evaluations described in section 3.1. 

 

15 According to Duke Energy’s comments on the proposed rule, samples collected from the treatment system 

effluent were sent to the Duke Energy Environmental Lab, where they were split into four individual samples. Three 

of the samples were sent to commercial labs for analysis, while the fourth sample was analyzed internally at Duke 

Energy’s Environmental Lab. The spreadsheet of data submitted by Duke Energy refers to the internal company lab 

as Duke Energy’s McGuire lab. 
18 

Round Robin Laboratory Analyses 

Duke Energy provided results for round robin analyses conducted by four laboratories for 

samples collected on 5/8/2013.16 As discussed in section 2.4, data collected using 

Method 1631E are generally acceptable for use provided that the laboratories achieved a 

sufficiently sensitive reporting limit and additional evaluation of the data does not 

identify other reasons for excluding the data. The reporting limit for these data is 

sufficiently sensitive for the purposes of the ELG rulemaking (i.e., all round robin 

analytical results for mercury were reported as quantified values) and these Method 

1631E mercury data from the round robin laboratory analyses (for 5/8/2013) are 

acceptable for calculating effluent limits, subject to the additional data evaluations 

described in section 3.1. 

3.5 Pleasant Prairie Power Plant 

We Energies’ Pleasant Prairie Power Plant operates a chemical precipitation system to treat the 

FGD wastewater. This facility was not used by EPA to calculate effluent limits for the proposed 

rule; however, based on public comments and other information in the record EPA may include 

Pleasant Prairie as one of the BAT plants that will be used by EPA to calculate limits for the 

final effluent guidelines. EPA collected data from Pleasant Prairie during an EPA sampling 

episode and samples collected by industry as directed by EPA (i.e., “CWA 308 samples”). 

In their comments on the proposed rule, UWAG submitted plant self-monitoring data for 

mercury (EPA Method 245.7) in the effluent from the chemical precipitation treatment system. 

We Energies submitted self-monitoring data for arsenic (EPA Method 6020A) and mercury 

(EPA Methods 245.7 and 1631E) for chemical precipitation effluent with their comments on the 

proposed rule. 

We Energies also provided additional effluent data for arsenic (Method 6020A) and mercury 

(Method 245.7) in response to a letter from EPA requesting the company to provide existing 

analytical data for the treatment system. 

3.5.1 Arsenic 

Arsenic by EPA Method 6020A 

We Energies provided effluent data for arsenic in its comments to the proposed rule and in 

response to an EPA data request letter. The submitted data spans the period from 11/13/2007 

through 4/17/2013. These data were analyzed using EPA Method 6020A in conjunction with a 

dynamic reaction cell. 

 

16 According to Duke Energy’s comments on the proposed rule, samples collected from the treatment system 

effluent were sent to the Duke Energy Environmental Lab, where they were split into four individual samples. Three 

of the samples were sent to commercial labs for analysis, while the fourth sample was analyzed internally at Duke 

Energy’s Environmental Lab. The spreadsheet of data submitted by Duke Energy refers to the internal company lab 

as Duke Energy’s McGuire lab. 
19 

Method 6020A was issued by EPA’s Office of Resource Conservation and Recovery as part of 

the SW-846 methods manual. It is an ICP-MS method that generally is similar to EPA Method 

200.8; however, EPA has not approved Method 6020A for NPDES compliance monitoring in 40 

CFR Part 136. As discussed in section 2, arsenic concentration data collected using Method 

6020A generally are not considered acceptable for calculating effluent limits unless the 

laboratories achieved a sufficiently sensitive reporting limit and the method was approved for 

compliance monitoring by the permitting authority. Additionally, as is the case with data 

collected using Method 200.8, results generated using Method 6020A without the collision cell 

or dynamic reaction cell are generally not acceptable for calculating effluent limits for the steam 

electric effluent guidelines. 

In the case of Pleasant Prairie, We Energies’ use of Method 6020A, which included use of the 

dynamic reaction cell, was authorized under Wisconsin Administrative Code as part of a blanket 

approval of SW-846 methods that use the same instrumentation as the wastewater methods 

approved at 40 CFR Part 136, and that contain rigorous quality control requirements.17 As noted 

in section 2, Method 6020A does contain more quality control information than the earlier 

version, Method 6020, especially with regard to instrument calibration. Moreover, We Energies 

provided additional information about the quality control operations that were implemented as 

part of the analyses for these data, along with the summary level quality control data associated 

with the analysis results (DCN SE04328A3). These quality control operations are comparable to 

the quality control requirements included in Method 200.8 and the quality control acceptance 

criteria employed by the laboratory are at least as stringent as those in Method 200.8. Because of 

this, consistent with the Method 6020A discussion in section 2, the Method 6020A data for 

Pleasant Prairie (for 11/13/2007 through 4/17/2013) are acceptable for calculating effluent limits, 

subject to the additional data evaluations described in section 3.1. 

3.5.2 Mercury 

Mercury by EPA Method 245.7 

Both UWAG and We Energies provided plant self-monitoring data for mercury using EPA 

Method 245.7. The data submitted by UWAG span the period 1/5/2009 through 5/10/2011 and 

are a subset of the data provided by We Energies. Mercury data submitted by We Energies span 

the period 10/4/2007 through 12/18/2013. As discussed in section 2.5, industry self-monitoring 

data collected using Method 245.7 are generally acceptable for calculating effluent limits 

provided that the laboratories achieved a sufficiently sensitive reporting limit. The reporting 

limits associated with Pleasant Prairie’s mercury data are sufficient for the purposes of the steam 

electric ELG rulemaking (i.e., nearly all results were reported as quantified values above the 

reporting limit). Therefore, the Method 245.7 mercury data (for 10/4/2007 through 12/18/2013) 

are acceptable for calculating effluent limits, subject to the additional data evaluations described 

in section 3.1. 

Mercury by EPA Method 1631E 

 

17 Dinsmore and Weber, Wisconsin Department of Natural Resources, letter to USEPA Region 5, October 14, 1997. 

(DCN SE04328A3) 
20 

We Energies provided mercury data for the effluent from the secondary clarifier using Method 

1631E. The Method 1631E data were submitted with We Energies’ comments on the proposed 

rule and represent a single day (12/15/2010). 

As discussed in section 2.4, data collected using Method 1631E are generally acceptable for use 

provided that the laboratories achieved a sufficiently sensitive reporting limit and additional 

evaluation of the data does not identify other reasons for excluding the data. The reporting limit 

for these data is sufficient for the purposes of the ELG rulemaking (i.e., the result was reported 

as a quantified value above the reporting limit) and We Energies’ Method 1631E mercury data 

(for 12/15/2010) are acceptable for calculating effluent limits, subject to the additional data 

evaluations described in section 3.1. 

3.6 Allen Steam Station 

Duke Energy’s Allen Steam Station operates a FGD wastewater treatment system that includes 

chemical precipitation/iron coprecipitation followed by anoxic/anaerobic biological treatment. 

This facility is one of the BAT plants used by EPA to calculate limits for both the proposed and 

final rules. EPA collected data from Allen during an EPA sampling episode and samples 

collected by industry as directed by EPA (i.e., “CWA 308 samples”).18 

In their comments on the proposed rule, UWAG submitted plant self-monitoring data for 

selenium (EPA Method 200.8) in the effluent from the treatment system. 

Duke Energy provided effluent data for selenium (EPA Method 200.8) and nitrate-nitrite (EPA 

Method 353.2) in response to a letter from EPA requesting the company to provide existing 

analytical data for the treatment system. 

Selenium by EPA Method 200.8 

Both Duke Energy and UWAG provided selenium data analyzed using Method 200.8 in 

conjunction with a collision cell. The data submitted by UWAG with their comments span the 

period 7/15/2009 through 5/23/2011 and are a subset of the plant self-monitoring data EPA 

obtained from Duke Energy prior to proposal (spanning 3/3/2009 through 5/23/2011). The data 

submitted by Duke Energy partially overlaps the data submitted by UWAG, with the Duke 

Energy submittal spanning the period 5/10/2010 through 10/22/2013. 

As discussed in section 2.1, selenium data collected using Method 200.8 with a collision cell or 

dynamic reaction cell are generally acceptable for rulemaking purposes, provided that the 

laboratories achieved a sufficiently sensitive reporting limit and additional evaluation of the data 

does not identify other reasons for excluding the data. The reporting limits for these data are 

sufficient for the purposes of the ELG rulemaking. Many results were reported as quantified 

 

18 Prior to proposing revised effluent guidelines, EPA also obtained self-monitoring data for Allen from Duke 

Energy. These data include effluent concentrations for selenium spanning the period 3/3/2009 – 5/23/2011 and were 

considered when deriving the proposed effluent limits. 
21 

values above the reporting limit. All of the nondetected results were at 10 ug/L or lower, 

comparable to the reporting limits achieved by laboratories during the EPA sampling and 308 

sampling episodes, and EPA is not aware of any other Part 136-approved methods reliably 

achieving substantially lower reporting limits for selenium in FGD wastewater. For these 

reasons, the Allen selenium data (for 3/3/2009 through 10/22/2013) are acceptable for 

calculating effluent limits, subject to the additional data evaluations described in section 3.1.19

Nitrate-Nitrite by EPA Method 353.2 

Duke Energy provided nitrate-nitrite data analyzed using EPA Method 353.2. These data were 

provided in response to a data request from EPA, and span the period 9/29/2011 through 

10/22/2013. As discussed in section 2.8, industry self-monitoring data collected using Method 

353.2 are generally acceptable for effluent limits provided that the laboratories achieved a 

sufficiently sensitive reporting limit. The reporting limits associated with Allen’s nitrate-nitrite 

data are sufficient for the purposes of the steam electric ELG rulemaking because the reporting 

limits for nondetect observations were below 1 mg/L. Therefore, the Method 353.2 nitrate-nitrite 

data from Allen (for 9/29/2011 through 10/22/2013) are acceptable for calculating effluent 

limits, subject to the additional data evaluations described in section 3.1. 

3.7 Belews Creek Steam Station 

Duke Energy’s Belews Creek Steam Station operates a FGD wastewater treatment system that 

includes chemical precipitation/iron coprecipitation followed by anoxic/anaerobic biological 

treatment. This facility is one of the BAT plants used by EPA to calculate limits for both the 

proposed and final rules. EPA collected data from Belews Creek during an EPA sampling 

episode and samples collected by industry as directed by EPA (i.e., “CWA 308 samples”).20 

In their comments on the proposed rule, UWAG submitted plant self-monitoring data for 

selenium (EPA Method 200.8) in the effluent from the treatment system. 

Duke Energy provided effluent data for selenium (EPA Method 200.8) and nitrate-nitrite (EPA 

Method 353.2) in response to a letter from EPA requesting the company to provide existing 

analytical data for the treatment system. 

Selenium by EPA Method 200.8 

Both Duke Energy and UWAG provided selenium data analyzed using Method 200.8 in 

conjunction with a collision cell. The data submitted by UWAG with their comments span the 

period 2/6/2008 through 5/25/2011 and are identical to the plant self-monitoring data EPA 

 

19 Note that the data for 3/3/2009 – 8/26/2009 were collected during the commissioning period for the wastewater 

treatment system and were excluded when calculating effluent limits for the proposed and final rules, as a result of 

data evaluations described in section 3.1. See the Effluent Limitations Memorandum for more information. 

20 Prior to proposing revised effluent guidelines, EPA also obtained self-monitoring data for Belews Creek from 

Duke Energy. These data include effluent concentrations for selenium spanning the period 2/6/2008 – 5/25/2011 

and were considered when deriving the proposed effluent limits. 
22 

obtained from Duke Energy prior to proposal (also spanning 2/6/2008 through 5/25/2011). The 

data submitted by Duke Energy partially overlaps the data submitted by UWAG, with the Duke 

Energy submittal spanning the period 6/9/2010 through 11/28/2013. 

As discussed in section 2.1, selenium data collected using Method 200.8 with a collision cell or 

dynamic reaction cell are generally acceptable for rulemaking purposes, provided that the 

laboratories achieved a sufficiently sensitive reporting limit and additional evaluation of the data 

does not identify other reasons for excluding the data. The reporting limits for these data are 

sufficient for the purposes of the ELG rulemaking. Many results were reported as quantified 

values above the reporting limit. All but one of the nondetected results were at 10 ug/L or lower, 

comparable to the reporting limits achieved by laboratories during the EPA sampling and 308 

sampling episodes, and EPA is not aware of any other Part 136-approved methods reliably 

achieving substantially lower reporting limits for selenium in FGD wastewater. For these 

reasons, the Belews Creek selenium data (for 2/6/2008 through 11/28/2013) are acceptable for 

calculating effluent limits, subject to the additional data evaluations described in section 3.1.21

Nitrate-Nitrite by EPA Method 353.2 

Duke Energy provided nitrate-nitrite data analyzed using EPA Method 353.2. These data were 

provided in response to a data request from EPA, and span the period 5/15/2013 through 

11/28/2013. As discussed in section 2.8, industry self-monitoring data collected using Method 

353.2 are generally acceptable for effluent limits provided that the laboratories achieved a 

sufficiently sensitive reporting limit. The reporting limits associated with Belews Creek’s nitratenitrite data are sufficient for the purposes of the steam electric ELG rulemaking because the 

reporting limits for nondetect observations were below 1 mg/L. Therefore, the Method 353.2 

nitrate-nitrite data from Belews Creek (for 5/15/2013 through 11/28/2013) are acceptable for 

calculating effluent limits, subject to the additional data evaluations described in section 3.1. 

 

 

21 Note that the data for 2/6/2008 – 7/28/2008 were collected during the commissioning period for the wastewater 

treatment system and were excluded when calculating effluent limits for the proposed and final rules, as a result of 

data evaluations described in section 3.1. See the Effluent Limitations Memorandum for more information. 
23 

Table 1.  Summary of initial determinations regarding acceptability of effluent self‐monitoring data,

prior to additional data evaluations described in section 3.1.

Analyte Description   Method Date Acceptable/

Exclude

HATFIELD’S FERRY POWER STATION

Arsenic

Plant Self‐Monitoring

(Allegheny lab)

200.7 06/30/09 – 11/29/11 Acceptable

Plant Self‐Monitoring  

(Beta lab)

200.7 12/6/11 – 10/1/13

10/8/13 – 12/10/13 (decommissioning

period)

Exclude

Plant Self‐Monitoring  

(Beta lab)

200.8 11/29/12, 12/19/12, 12/21/12 Exclude

Mercury

Plant Self‐Monitoring   245.7 6/30/09 – 10/1/13 Acceptable

Plant Self‐Monitoring

Decommissioning period

245.7 10/8/13 – 12/10/13 Exclude

Plant Self‐Monitoring 245.1 11/29/12, 12/19/12, 12/21/12 Exclude

KEYSTONE GENERATING STATION

Arsenic

Plant Self‐Monitoring   200.7 1/3/12 – 1/6/14 Exclude

Plant Self‐Monitoring 200.8 1/13/14 – 4/28/14 Acceptable

Frac study split sample 6020 2/21/13 Exclude

Mercury Plant Self‐Monitoring   SM 3112B 1/3/12 – 4/28/14 Exclude

MIAMI FORT STATION

Arsenic

Split samples from EPA &

CWA 308 sampling episodes  

200.8 7/13/10‐7/16/10, 9/28/10, 11/2/10,

12/7/10, 1/14/11

Acceptable

Plant Self‐Monitoring

(Duke Energy company lab)

200.8 7/13/09 – 12/3/13 Exclude

Commercial lab 200.8 6/28/11 Acceptable

Round robin lab analyses 200.8 5/8/13 Exclude

Mercury

Plant Self‐Monitoring and

split samples from EPA &

CWA 308 sampling episodes

1631E 7/1/09 – 12/3/13 Acceptable

Round robin lab analyses 1631E 5/8/13 Acceptable

PLEASANT PRAIRIE POWER PLANT

Arsenic Plant Self‐Monitoring 6020A 11/13/07‐4/17/13 Acceptable

Mercury

Plant Self‐Monitoring 245.7 10/4/07 – 12/18/13 Acceptable

Plant Self‐Monitoring 1631E 12/15/10 Acceptable

ALLEN STEAM STATION

Nitrate‐

Nitrite

Plant Self‐Monitoring 353.2 9/29/2011 – 10/22/2013   Acceptable

Selenium Plant Self‐Monitoring 200.8 3/3/09 – 10/22/13 Acceptable

BELEWS CREEK STEAM STATION

Nitrate‐

Nitrite

Plant Self‐Monitoring 353.2 5/15/2013 – 11/28/2013 Acceptable

Selenium Plant Self‐Monitoring 200.8 2/6/08 – 11/28/13 Acceptable