Ann Wearmouth 8301 Professional Place, Suite 230

Landover, MD 20785 T (301) 955

- 9028 C (240) 299

- 3378 

## Mid

- Atlantic , LLC

April 30, 2012

Via Electronic Mail

Ronald P. Jordan U. S. EPA Headquarters Engineering & Analysis Division (4303T) Ariel Rios Building 1200 Pennsylvania Avenue, N.W. Washington, DC 20460

RE: Dickerson Data: Monthly Sampling Events

Dear Mr. Jordan:

Thank you for the opportunity to comment on the draft data from the additional samples taken at our facility in September and December 2010, and January 2011. We had asked UWAG to
comment on the draft as well and this response includes their input. We ha ve done our best, given the amount of information provide d and the relatively short turn around time, to thoroughly review the data. These comments should be considered preliminary, as we may, upon further consideration of the data, have additional comment s.

I. General Comments

Data Usability

GenOn agrees with EPA’s efforts to identify and flag potentially erroneous (outlier) data points in the Dickerson data set. However, if a value is an outlier, then it should be discarded from the data set and not used for any purpose. Also, there is no d iscussion of how flagged data points will be used (or excluded) from consideration in calculating the new steam electric effluent guidelines. For example, data points flagged B, Est, F and T indicate potentially significant inaccuracy (bias) in the associ ated data.

GenOn also questions the validity and use of the 3

- set averages EPA calculated using the four monthly data sets (See Tables E5

- 1

- E5

- 4). The use of averages in some cases may obscure important differences among data points. EPA should expl ain how it intends to use the

averages.Left Out 1 Sample Date

Although Dickerson submitted 4 sets of samples as EPA requested, EPA only analyzed the first three sets of samples. The samples collected on February 9, 2011 apparently were never analyzed. GenOn respectfully requests an explanation as to why EPA decided against analyzing the fourth set of samples

.

II. Inadequate Treatment System Design and Operational Descriptions and Data

We noted several instances of inadequate treatment system design and operational descriptions and data in our earlier comments on the draft Sampling Episode Report (SER) for Dickerson. All of those comments also apply to the additional data set.

However, we reiterate here an essential point:

EPA’s study plan should have included a comprehensive study of the coal feed stock during each sampling event. It is clear that coal characteristics have a very significant impact on FGD chemistry and wastewater treatment. While EPA gathered some information about coal constituents during the sampling events, it should have collected
full in formation about levels of sulfur, metals, and chlorides in the coal, as well as the heating value of the coal being burned during the relevant period for the sampling event.

III. Analytical M ethods D escriptions

Also, as we stated in our earlier comments, the analytical descriptions in the SER and the analytical narratives omit some basic information that should be included and would be helpful in making data evaluations and comparisons. We reiterate our request for basic analytical information, as follows:

1. How were the trace metals samples digested? Was a heated strong acid leach digestion patterned after EPA method 200.2 used or some other alternative digestion? Were the metals samples preserved to pH < 2 at least 24 hours prior to digesti on (total recoverable) or analysis (dissolved)?

2. How were the Hg samples digested? Was the bromine monochloride digestion done at room temperature, heated, by method 1631E appendix A, etc.?

3. Were individual grab samples for Hg and some other paramet ers flow

- proportion composited? If so was the compositing done physically prior to analysis or was the “compositing” done arithmetically after the individual analysis of each sample?

4. How were the dissolved Hg samples filtered?

5. How were SP

- 1 biphas ic solids samples digested and analyzed for metals and Hg?