1



### MEMORANDUM
**TO:** Steam Electric Rulemaking Record **FROM:** Dan
- Tam Nguye n **DATE:** September 30 , 2015 **SUBJECT: Comparison of Once**  **- Through FGD System**  **s to Recirculating FGD Systems**  ERG is providing technical support to the U.S. Environmental Protection Agency’s Office of Water, Engineering and Analys is Division (EAD) for development of effluent limitations guidelines and standards (ELGs) for the Steam Electric Power Generating Indust ry . This memorandum describes ERG’s review of once
- through FGD s ys tems and how they compare to recirculating FGD s ys tems. **1. INTRODUCTION**  During the public comment period, EPA received comments from the Utility Water Act Group (UWAG) and the Tennessee Vall ey Authority (TVA) claiming that the operation of once
through FGD s ys tems differs significantl y enough from the operation of recirculating FGD systems that implementing a uniform BAT requirement is impractical due to the differences in the resulting waste water characteristics. The se commenters also argued that differences between the two systems related to materials of construction needed to accommodate high chloride levels can obviate the ability

of facilities with once
- through FGD s ys tems to employ the f low minimization scheme that EPA used in its cost estimates . Both UWAG and TVA argue that this difference warrants a subcategorization for once
- through FGD s ys tems. ERG compared the wastewater characteristics, the FGD blowdown flow rates, the operating chloride levels, and the materials of construction reported for once
- through and recirculating FGD s ys tems to evaluate the validity of these claims
. No additional data were provided b y UWAG or TVA or other commenters on once
- through FGD s ystems. Details of ERG’s comparison are included in a separate spreadsheet titled “CBI_ Once Through FGD Analysis ” (DCN SE05360). **2. D**  **ATA S**  **OURCES FOR O**  **NCE -**  **T HROUGH**  **FGD S**  **YSTEMS** This section discusses the available data used to evaluate wastewater and operational characteristi cs of once
- through FGD s ys tems.2

**2.1 Wastewater**  **C haracteristics**  To represent the once
- through FGD blowdown wastewater characteristics, ERG used the one - day grab sampling data from the Widow’s Creek Plant collected b y EP A in 2007 1 (DCN SE02105 ). Analy

tical data for FGD blowdown included total and dissolved metals and classical anal yt es. As part of the Widow’s Creek sampling episode, EPA anal yz ed some anal yt es using both EPA Method 200.8 and EPA Method 1638 and anal yz ed for both total and dissolved fractions . For this comparison, where ERG had data from two different analy tical methods, ERG used the average of the two results. ERG used the J
- values as they were reported by the laboratory

for values measured between the method detection limit (MDL) and the reporting limit (RL) and used the MDLfor non
- detect ed value s below the MDL. Where appropriate, ERG calculated the average result as an arithmetic average of the two results. **2.2 FGD Blowdown Flow Rates**  ERG used industry

responses from Question B5
- 2 of the Questionnaire for the Steam Electric Power Generating Effluent Guidelines (Steam Electric Survey) (DCN SE05903) for plants reporting blowdown flow rates for once
- through s ys tems (termed “single
-pass” in the survey responses). The reported flow s rang e from 3,000 to 2,600,000 gallons per day
. **2.3 Operating Chlorides**  **and Materials of Construction** ERG used industry

responses from Questions B4
- 2 and B4
- 3 of the Steam Electric Survey for once
- through FGD systems reporting the minimum and maximum operating chlorides in the absorber and for plants reporting the materials of construction for their absorbers. The range of operating chloride concentrations in the absorber reported in the survey is 15 to 50,000 ppm. The materials of construction are CBI and included in the spreadsheet (SE05360). **3. D**  **ATA S**  **OURCES FOR R** **ECIRCULATING FGD**  **S YSTEMS**  This section discusses the available data used to evaluate wastewater and operational characteristics of recirculating FGD s ys tems. **3.1 Wastewater**  **C haracteristics**  ERG accessed data for FGD blowdown from recirculating FGD s ys tems using monitoring data from the Steam Electric Survey (Part B, Section 6) and from the EPA Sampling data.

 Monitoring Data
- The minimum and maximum values for each anal yt e were

tabulated to provide a con centration range b y analyte and grouped b y total metals, dissolved metals, and classicals.

1 At this time, ERG does not have any other data from once
- through FGD systems. No data were provided as part of the comments. All of the data submitted in Part B Section 6 of the Steam Electric Survey is qualified as "clarified or settled" in Table B
- 9 and do not represent FGD blowdown (for once
- through FGD systems)
.3

 EPA Sampling Data

– ERG evaluated FGD purge data from the EPA Sampling and CWA 308 Monitoring Programs f or the following plants: Belews Creek, Allen, Miami Fort, Ke ys ton e , Pleasant Prairie, Hatfield ’ s Ferry , and Dickerson. The minimum and maximum values for each analy te were tabulated to provide a concentration range b y analy te and grouped b y total metals, dissolved metals, and classicals. 2 **3.2 FGD Blowdown Flow Rates**  ERG used industry

responses from Question B5
- 2 of the Steam Electric Survey for plants reporting blowdown flow rates for recirculating s ystems. The reported flow s range from 1,500 to 4,400,000 gallons per day. **3.3 Operating Chlorides and Materials of Constr**  **uction** ERG used industry

responses from Questions B4
- 2 and B4
- 3 of the Steam Electric Survey for recirculating FGD plants reporting the minimum and maximum operating chlorides in the absorber and for plants reporting the materials of construction for their absorbers. The range of operating chloride concentrations in the absorber reported in the survey is 10 to 60,000 ppm. The materials of construction are CBI and included in the spreadsheet (SE05360). **4. C**  **OMPARISON AND C**  **ONCLUSIONS** This section provides a summary of ERG’s comparison of FGD once
- through and recirculating s ys tems. **4.1 Wastewater**  **C haracteristics**  ERG compared the concentrations from the detailed sampling data for once
- through systems to concentration ranges from both the monitoring data and sampling data for recirculating s ys tems. Table 1 summarizes the number of analy tes from the data for once
- through systems where the concentrations fell within, above, or below the range of concentrations from the EPA sampling and monitoring data for recirculating FGD s ys tems. Based on this analysis, ERG determined that most of the data for once
- through FGD s ys tems were within the range of concentrations for recirculating FGD s ys tems. When comparing the total metals concentrations, ERG found that only two anal yt es in once - through FGD scrubber wastewater were outside the concentration range of the EPA sampling data for recirculating systems (i.e., the metals concentrations were less than one percent lower than the minimum concentration for recirculating s ys tems). N one of the anal yt es were

2 In this comparison, ERG used the same methodology for handling J
- values and non
- detects below the MDL as wa s used for the Widows Creek data; ERG used the J
- values as they were reported by the laboratory for values measured between the MDL and RL and used the MDL for non
- detects below the MDL.4

above the range from either dataset. For total metals, a majority of the analy

tes appear on the lower end of the concentration range for recirculating FGD s ys tems. When comparing the dissolv ed metals concentrations, ERG found that Widow’s C reek concentrations for two analy tes (arsenic and chromium) were slightl y greater than EPA sampling data and one anal yt e (moly bdenum) was four times greater than the monitoring data. Dissolved metals concentrations were somewhat lower in once
- through FGD s ys tems (or generall y on the lower end of the concentration range for recirculating s ys tems ). Seven anal ytes were below the concentration ranges in both data sets. Classical analy te concentrations were gene rall y comparable between the two ty pes of s ys tems with nitrate/nitrite levels slightl y lower in once
through s ys tems. The data for recirculating s ys tems did not contain all classical anal yt es collected for once
- through systems during the detailed study ; th erefore, concentrations for several classical analy

tes were not compared. **4.2 FGD Blowdown Flow Rates**  Compared to FGD blowdown flow rates for recirculating s ys tems, the flow rates for once - through FGD s ys tems fell within the range of flow rates for recirculating s ys tems , with an average flow rate that is also comparable to recirculating s ys tems . See Table 2 for a summary of flow rates for once
- through and recirculating s ys tems. **4.3 Operating Chlorides and Materials of Construction**  The range of operating chlori de concentrations for once
- through FGD systems falls within the range of operating chloride concentrations for recirculating FGD systems, as reported in the Steam Electric Survey . Although onl y a few plants reported maximum operating chloride levels greater than 10,000 ppm for once
- through FGD s ys tems, those plants report us ing materials of construction similar to what is used for recirculating s ys tems. See Table 2 for a summary of operating chloride concentrations for once
- through and recirculating s ys tem s. In formation on the m aterials of construction is CBI in the Steam Electric Survey and presented in the accompanying CBI spreadsheet (DCN SE05360).5

**Table 1. Comparison of**  **Analyte -**  **Specific Concentrations between Once**  **- Through and Recirculating FGD Systems**  **Recirculating Systems:**  **Monitoring Data Recirculating Systems:**  **EPA Sampling Data**  **Once -**  **Through Systems: Sampling Data**  **Number of Analytes**  **Analytes Outside Range or No Data Number of**  **Analytes Analytes Outside Range or No Data**  **Total Metals**

Above 0 0 Within 26 24 Below 0 2 Magnesium, Manganese No Analyte Data 1 Yttrium 1 Yttrium **Total Analytes 27**  **27 Dissolved Metals** 

Above 1 Moly bdenum 2 Arsenic, Chromium Within 16 14 Below 9 Boron, Cadmium, Cobalt, Copper, Magnesium, Manganese, Silver, Titanium,

Zinc 11 Hexavalent Chromium , Cobalt, Iron, Lead, Magnesium, Manganese, Nickel, Silver, Tin,

Titanium, Zinc No Analyte Data 2 Yttrium, Hexavalent Chromium 1 Yttrium **Total Analytes 28**  **28 Classicals**  Above 1 Sulfate 1 Biochemical Oxygen Demand (BOD)

Within 4 6 Below 2 Nitrate/Nitrite, TDS 2 Nitrate/Nitrite, TDS
No Analyte Data 5 Hexane Extractable Material (HEM), Silica Gel Treated HEM (SGT
- HEM), Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), Total Suspended

Solids (TSS) 3 Hexane Extractable Material ( HEM), Silica Gel Treated HEM (SGT
- HEM), Chemical Oxygen

Demand (COD) **Total Analytes 12**  **12**6

**Table 2**  **. Summary of Purge Flow Rates**  **and Operating Chlorides for Once**  **- Through and**  **Recirculating Systems FGD System**  **Type Purge Flow Rate (gpd)**  **Range of Operating Concentration of**  **Chlorides in Absorber (ppm)**  **Minim um**  **Average Maximum**  **Min im** **um Max** **im um**  Once
- Through 3,300 239,395 2,607,000 14 50,000 Recirculating 1,520 228,078 4,413,600 6 58,000