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 have done our best, 

given the amount of information provided and the relatively short turnaround time, to thoroughly 

review the data. These comments should be considered preliminary, as we may, upon further 

consideration of the data, have additional comments.

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 discussion 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 associated 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 explain 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 information 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 Methods Descriptions

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 digestion (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 parameters 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 biphasic solids samples digested and analyzed for metals and Hg?