GEORGIA POWER

– Addendum to S upplemental Mercury CEMS Data Submittal

Page 1 of 2 Electric Utility Steam Generating Unit (EGU) Hazardous Air Pollutant Emissions (HAPs) Information Collection Request (ICR), OMB Control No. 2060

- 0631 May 3, 2010

In the information collection reque st (“ICR”) sent to Southern Company by the Environmental Protection Agency (“EPA”) on December 24, 2009 , EPA requested in Footnote 46 to Part II, Question 11 that facilities submit available mercury continuous emission monitoring system (“CEMS”) data that follow recognized QA/QC procedures. While EPA did not make the submittal mandatory, Georgia Power wishes to provide available mercury CEMS data to assist the rulemaking process. Georgia Power has installed and operated monitors on certain units that, as closely as possible, follow the QA/QC procedures as written under the vacated Clean Air Mercury Rule (“CAMR”) through 40 CFR Part 75 . However, Georgia Power does not regularly submit reports to a regulatory agency on an ongoing basis. Thus, we required a dditional time to review and prepare the data for submittal to EPA.

For units with wet flue gas desulfurization (FGD) control technology installed, flue gas may exist through either a wet or a dry stack, depending on whether the FGD is in operation. In these cases, the mercury CEMS is installed on the wet stack only. 2009 Mercury CEMS data are available for the following units and stacks:

Bowen Unit 2 FGD Stack Liner

Bowen Unit 3 FGD Stack Liner

Branch Units 3/4 Common Stack Liner

Hammond Units 1

- 4 Co mmon FGD Stack

Scherer Unit 3 Stack Liner Wansley Unit 2 FGD Stack Liner

The mercury CEMS data show that measured mercury emissions are highly variable, even on units operating emission controls. Furthermore, our experience with the mercury

monitors has shown that monitor reliability and performance can also vary greatly unit to

unit or over time . The supplemental mercury monitoring data, along with description of concerns and issues we have experienced with the monitors are included in this submittal.

Mercury CEMS Data Variability The mercury CEMS data provided show that measured mercury emissions exhibit great variability over time. For example, even after removal of invalid data, the hourly CEMS

data from Branch Un i ts 3/4, which operates a cold

- side electrostatic precipitator (ESP), ranges from around 1 lb/TBtu to over 17 lbs/TBtu. Units that are further controlled exhibit wide variability as well. For example, the hourly CEMS data from Bowen Unit 3

, which operates an FGD and SCR as well as the ESP, ranges from close to zero to about 9

lb/TBtu. For a given unit, a particular mercury level may be “achieved” at some point, but may not be “achievable” on a consistent basis. Emission standards set through the rulemaking process must account for this inherent variab ility of mercury emissions.GEORGIA POWER

– Addendum to S upplemental Mercury CEMS Data Submittal

Page 2 of 2 Mercury CEMS Monitor Reliability Based on our experience, mercury m onitors installed on different units may behave very differently in terms of reliability. Even monitors installed on sister units in terms of boiler config uration and controls have not always performed consistently. At this point in time, w e are not able to pinpoint the reasons for th ese differences . We believe further development of the technology is needed to provide for long term consistent and reliable performance. Monitor availability for the six systems being reported range d from 74.5% to 90.9% (with an average of 83.4 % ) for 2009

.

One of the factors affecting monitor availability is the recovery time for the m ercury monitor ing system following cert ain tests, QA procedures, and maintenance. There is

often a n extended period where readings are obviously abnormal and inaccurate and must

be marked invalid

. T h e recovery time before readings return to normal is often 12 hours or longer

. We also experie nce variable performance and life from lamps and calibrators.

CAMR Part 75 QA may reasonably assure consistency of monitored values, but there is still no assurance of the accuracy of monitored values. Part 75 QA procedures were based on the capabiliti es of current monitoring systems and established for known achievable levels of mercury for use in a trading program. Therefore, the allowed

calibration tolerance of Part 75 at very low levels of mercury emissions could result in significant discrepancies

, including negative values or measured emissions that are more

than double actual emissions. However, tightening this tolerance with current monitoring systems would be require more frequent maintenance and calibration which would lead to

more monitor do wntime. Running in speciated mode cause s additional problems including contamination of the analyzer and umbilicals and unreliable mercury readings. Thus, monitors should measure total mercury only for best results.

Mercury CEMS Data Assumptions and Pro cedures The mercury CEMS data are provided to demonstrate mercury variability

. T he QA procedures as proposed in 40 CFR Part 75 were followed with one exception. We a re not currently following the Interim Protocol for NIST traceabl ity for the monitoring sy stem calibrators. Many of these calibrators were included in the NIST traceability study used to develop the Interim Protocol , and d uring the study, they were found to be generally accurate and stable. Since that time, however, we have had to repai r several calibrators ; thus meas ured values may have significant error

. We have, however

, successfully passed

annual RATAs using Method 30B on all of the units.

The submitted data includes valid data only for total mercury . Out

- of

- control and

substitute d data are not included , except in cases where values of 5% are substituted

where measured CO 2 values were below 5%, in accord ance with Part 75 procedures. Negative emission rates are considered invalid data and are not included. Only hourly

data in units of lbs/TBtu are prov ided. Since the spreadsheet template provided by EPA only includes the option for units of lbs/MMBtu, we have inserted an additional column

with the lbs/TBtu data.