MEMORANDUM 

TO: Steam Electric Rulemaking Record 

FROM: TJ Finseth, ERG 

Danielle Lewis, ERG 

DATE: April 19, 2013 

SUBJECT: Analysis of Differences Between the 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 (EAD) for development of effluent limitations 

guidelines and standards (ELGs) for the Steam Electric Power Generating Industry. As part of 

this technical support, ERG developed baseline 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 monitoring activities, and 

industry provided sampling data1

 to characterize wastewater at specific plants operating 

candidate best-available technology (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 pollutant loadings calculations 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 included in the pollutant loadings calculations. EPA 

statisticians used criteria described 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 set used for limitations development and the data 

set used to calculate pollutant loadings. ERG identified 14 data points excluded by EPA for 

limitations development that ERG had not excluded for the pollutant loadings calculations. All 

14 data points are for FGD wastewater and represent 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 precipitation system at Hatfield’s Ferry 

Power Station. Therefore, the 14 data points affect 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 Analytical Database Memorandum (DCN SE02120) 
Memorandum 

April 19, 2013 

Page 2 

chemical precipitation system and the one-stage chemical precipitation with biological treatment 

system loadings. 

To assess the significance of the pollutant loadings 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 precipitation, the original concentration 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 original concentration used to calculate 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 the pollutant loadings data set would result in a 

decrease in the mercury loadings in the treated effluent for both the one-stage chemical 

precipitation and the one-stage chemical precipitation with biological treatment. 

 

If ERG were to recalculate loadings using these lower concentrations, the resulting pollutant 

loadings for both chemical precipitation 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 effluent loadings would be an increase in pollutant removals for both 

treatment options. Therefore, the current pollutant removal calculations slightly underestimate 

the pollutant reductions achieved by the treatment 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 treatment 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 data points and recalculate pollutant loadings and removals for 

both the chemical precipitation and chemical precipitation with biological treatment technology 

options for the final rule2

. 

 

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 Database, which could affect postcompliance biological treatment effluent concentrations. These data entry changes are discussed in the Steam 

Electric Analytical Database Memorandum (DCN SE02120).