### MEMORANDUM

TO: Steam Electric Rulemaking Record

FROM: TJ Finseth, ERG Danielle Lewis, ERG

DATE: April 19, 2013

SUBJECT: Analysis of Differences Between th e Data Set Used for Limitations Development and the Data Set Used for Loadings

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 (ELGs) for the Steam El ectric Power Generating I ndustry. As part of this technical support, ERG developed baseli ne and post-compliance pollutant loadings associated with technology options to estimate the impacts of the proposed ELG on the industry. ERG used analytical data from EPA sampling activities, CWA 308 mon itoring activities, and industry provided sampling data 1 to characterize wastewater at specific plants operating

candidate best-available tec hnology (BAT) treatment technologies . This memorandum describes specific differences between the data set used by ERG to estimate pollutant loadings and industry impacts and the data set used by EPA to calculate effluent limitations and standards (hereafter referred to as “limitations”) based on the technology options.

ERG completed baseline and post-compliance pollu tant loadings calcul ations prior to EPA finalizing the data set used for calculating limitations. ERG followed the criteria in Quality Assurance Project Plan for the Steam Electric Effluent Guidelines Rulemaking (Revision 4) to identify the analytical data that were incl uded in the pollutant loadings calculations. EPA

statisticians used criteria de scribed in Section 13 of the Technical Development Document for the Proposed Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category to identify the analytical data that were of sufficient quality for developing limitations.

There are slight differences between the data se t used for limitations development and the data set used to calculate pollutant loadings. ER G identified 14 data points excluded by EPA for limitations development that ERG had not excluded for the pollutant load ings calculations. All 14 data points are for FGD wastewater and represen t treatment system effluent samples. Thirteen of these data points are industry-provided data for mercury at the effluent from a biological treatment system at the Allen Steam Station and the Belews Creek Steam Station. The remaining data point is for mercury at the effluent of the chemical precipita tion system at Hatfield’s Ferry Power Station. Therefore, the 14 data points aff ect only the mercury loadings for the one-stage

1 All analytical data, including data from EPA sampling activities, CWA 308 monitoring, and industry provided data is described in the Steam Electric Analy tical Database Memorandum (DCN SE02120)Memorandum April 19, 2013 Page 2

chemical precipitation system and the one-stage ch emical precipitation with biological treatment system loadings.

To assess the significance of the pollutant loadin gs calculations including certain values that

EPA determined should be excluded from the limitations development, ERG removed the 14 data points and recalculated the average mercury concentrations for the waste streams. For onestage chemical precipitati on, the original concentra tion used to calculate pollutant loadings was 0.17 ug/L. After excluding the single data point, ERG calculated a concentration of 0.12 ug/L. For biological treatment, the orig inal concentration used to calc ulate pollutant loadings was 0.07 ug/L. After excluding the thirteen mercury data points, ERG calculated a concentration of 0.06 ug/L. Thus, removing the 14 data points from th e pollutant loadings data set would result in a decrease in the mercury loadings in the trea ted effluent for both the one-stage chemical precipitation and the one-stage chemical precipitation with biological treatment.

If ERG were to recalculate load ings using these lower concentr ations, the resulting pollutant loadings for both chemical precip itation and biological treatment would be lower for all plants.

Because the baseline concentrations will remain unchanged, the ultimate effect of removing the 14 data points to adjust the efflue nt loadings would be an increas e in pollutant removals for both treatment options. Therefore, th e current pollutant removal calcu lations slightly underestimate the pollutant reductions achieved by the treatmen t technologies. For the FGD one-stage chemical precipitation technology option, updating the loadings calculations to exclude the one data point would increase pollutant removals by less than 0.000001% (0.08% increase in toxic-weighted pollutant equivalent (TWPE) removals). For the FGD biological treatm ent option, updating the loadings calculations to exclude the 13 data points would increase pollutant removals by less than 0.00000003% (0.04% increase in TWPE). For Regulatory Options 3 and 4, the TWPE removed would increase by less than 0.0003%.

ERG plans to exclude these 14 da ta points and recalculate polluta nt loadings and removals for both the chemical precipitation and chemical prec ipitation with biologic al treatment technology options for the final rule 2

.

2 ERG and EPA plan to revise other sampling data used to calculate the post-compliance biological treatment

effluent concentrations in addition to those described in this memorandum. EPA identified several data entry errors associated with sample results contained in the Steam Electric Analytical Databa se, which could affect postcompliance biological treatment effluent concentrations. These data entry changes are discussed in the Steam Electric Analytical Database Memorandum (DCN SE02120).