### MEMORANDUM

TO: Steam Electric Rulemaking Record

FROM: TJ Finseth, ERG

DATE: April 19, 2013

SUBJECT: Sensitivity Analysis Evaluating the E ffect of Nondetect Results in the Ash Loadings Model

ERG is providing technical support to the U.S. Environmental Protection Agency’s Office of Water, Engineering and Analysis Division (E AD) for development of effluent limitations guidelines and standards (ELG) for the Steam El ectric Power Generating Industry. EPA, with the support of ERG, evaluated wa stewater flow rates and pollut ant concentration data from survey responses, site visits, sampling episodes, trade associations, and previous rulemakings to estimate pollutant discharge loadings associated with the discharge of fly ash and/or bottom ash transport water. In addition, EPA estimated th e corresponding pollutant removals associated with installing and operating dry or closed-l oop ash handling technolog ies and practices. ERG developed a computerized loadings model to calcu late plant-specific pollut ant discharge loadings for all power plants reported to be discharging fly ash and/or bottom ash transport water.

The purpose of this memorandum is to describe th e sensitivity analysis that ERG performed to

evaluate the effect of nonde tect results used in the ash loadings model.

1.0 A SH L OADINGS D ATA S OURCES

As described in Section 10.2.2 of EPA’s Incremental Costs and Pollutant Removals for Proposed Effluent Limitation Guidelines and Sta ndards for the Steam Electric Generating Point Source Category (DCN SE01957 and SE03581), EPA used the following data sources to

characterize the effluent stream from ash impoundments at steam electric power plants:

 EPA ash impoundment sampling data from the detailed study (DCN SE00003);

 Electric Power Research Institute (EPRI) Po wer Plant Integrated Systems-Chemical Emissions Study (PISCES) Re ports (DCNs SE01818-SE01823);

 Permit application data, as provided by memb er companies of the Utility Water Act Group (UWAG) (DCNs SE02918 and SE02918A1);

 Development Document for Final Effluent Limitations Guidelines, New Source Performance Standards, and Pretreatment St andards for the St eam Electric Point Source Category , EPA 440-1-82-029, November 1982 (1982 TDD) (DCN SE02933);

and

 The Steam Electric Technical Questionna ire Database (DCN SE01958 and SE03580).Memorandum April 19, 2013 Page 2

Additional details regarding each of these five da ta sources are included in Section 3 of EPA’s Incremental Costs and Pollutant Removals fo r Proposed Effluent Limitation Guidelines and Standards for the Steam Electric Generating Point Source Category

.

As stated in Section 10.2.2 of EPA’s Incremental Costs and Pollutant Removals for Proposed Effluent Limitation Guidelines and Standards fo r the Steam Electric Generating Point Source Category , EPA reviewed the data representing ash pond effluent streams and, as appropriate,

made some substitutions to the data sets. Fo r data collected during the detailed study, EPA set

nondetected values 1 equal to one-half the quantitation lim it (EPA required their analytical laboratories to report the sample-s pecific quantitation limit). For th e other data sets (i.e., EPRI, 1982 TDD, and Form 2C), EPA could not confir m whether the results for nondetected values were presented as less than the quantitation lim it or less than the detection limit (or some other value); therefore, EPA set nondetected values equa l to the value provided in the data source (e.g., <2 μg/L became 2 μg/L).

ERG performed a sensitivity analysis to evaluate how the baseline ash loadings would change if EPA handled nondetected values reported in the EPRI, 1982 TDD, and Form 2C data differently. ERG did not evaluate changes to the ash load ings based on the treatment of the nondetected

values in the dataset associ ated with EPA’s ash impoundment detailed study sampling data

2.0 M ETHODOLOGY FOR S ENSITIVITY A NALYSIS

To evaluate the change in the baseline ash lo adings based on the treat ment of the nondetected values reported in the EPRI, 1982 TDD, and Form 2C data, ERG calculated the baseline loadings based on the following three scenarios:

 Use the reported value for all nondetect ed values (i.e., methodology used for proposed rule);

 Use one-half the reported value for all nondetected values; and

 Use zero for all nondetected values.

To perform these calculations, ERG created two new versions of the Steam Electric Pollutant Loadings Model for Ash Transport Water (D CN SE02899). In one version Steam Electric Pollutant Loadings Model for Ash Transport Wate r Sensitivity Analysis – One-Half Nondetected Values (DCN SE03882.A2), ERG changed all the nonde tected values associated with the EPRI, 1982 TDD, and Form 2C data equal to one-half th e reported value. In the second version Steam Electric Pollutant Loadings Model for Ash Tr ansport Water Sensitivity Analysis – Zero Nondetected Values (DCN SE03882.A3), ERG cha nged all the nondetected values associated with the EPRI, 1982 TDD, and Form 2C data equal to zero. These sensitivity analysis models

are included as Attachments 2 and 3 to this memorandum. After updating the nondetected values, ERG ran the loadings models to calculate the base line pollutant loadings a ssociated with fly ash and bottom ash transport water. Other than the changes to the nondetected pollutant concentrations, no other changes were made to the models.

1 To simplify the discussion, for the purpose of this memora ndum, the term “non-detected value” is used to refer to both values measured below the quantitation limit and those values measured below the detection limit.Memorandum April 19, 2013 Page 3

3.0 S ENSITIVITY A NALYSIS R ESULTS

Table 1 presents the results of the sensitivity analys is. The results of the sensitivity analysis at the pollutant level can be found in Attachment 1 to this memorandum. As part of this sensitivity analysis, ERG also looked at th e change to the baseline ash lo adings if sulfide was excluded from the ash loadings. Table 2 presents the results of the sensitivity analysis if sulfide was excluded from the ash loadings.MemorandumApril 19, 2013Page 4Table 1. Fly Ash and Bottom Ash Baseline Loadings Sensitivity Analysis Results (Including Sulfide)Waste StreamProposal Methodology:Nondetected Values Treated asReported ValueNondetected Values Treated as One-Half ReportedValueNondetected Values Treated as ZeroLoading(Pounds/yr)TWPE/yrLoading(Pounds/yr)TWPE/yrPercent Changein TWPECompared toProposalLoading(Pounds/yr)TWPE/yrPercent Changein TWPECompared toProposalAnalysis Including SulfideFly Ash 927,079,982 2,521,986 925,164,080 1,729,929 -31% 923,248,177 937,871 -63%Bottom Ash 2,997,297,020 2,716,0592,993,891,100 1,721,910 -37%2,990,485,179 727,762 -73%Table 2. Fly Ash and Bottom Ash Baseline Loadings Sensitivity Analysis Results (Excluding Sulfide)Waste StreamProposal Methodology:Nondetected Values Treated asReported ValueNondetected Values Treated as One-Half ReportedValueNondetected Values Treated as ZeroLoading(Pounds/yr)TWPE/yrLoading(Pounds/yr)TWPE/yrPercent Changein TWPECompared toProposalLoading(Pounds/yr)TWPE/yrPercent Changein TWPECompared toProposalAnalysis Excluding SulfideFly Ash 926,531,845 986,408 924,857,563 871,238 -12% 923,183,281 756,067 -23%Bottom Ash 2,996,730,172 1,128,065 2,993,602,350 912,993 -19%2,990,474,527 697,920 -38%