DATE: 2 3 Nov 2016

MEMO: Review of Sierra Club’s 1

- hour SO 2 SIP modeling evaluation of the NPPD Sheldon

Power Station in Hallam, Nebraska, and NPPD Gerald Gentleman Power Station in Sutherland, NE, conducted by Steven Klafka, P.E., BCEE, Wingra Engineering, S. C.,

Madison WI.

F ROM : Lisa M. Alam

Nebraska Department of Environmental Quality (NDEQ) Air Program Planning and Development Team, Air Quality Division
1200 "N" Street, Lincoln, NE 68508

- 8922

Phone: 402

- 471

- 2925

A t the request of the Sierra Club

, Steven Klafka of Wingra Engineering, in Madison WI completed air dispersion modeling of two power plants identified by the US EPA as first round facilities required to do

air di spersion modeling to support Nebraska area designations of the 1

- hour SO 2 NAAQS. Those two power stations are the NPPD Sheldon Station in Hallam, Nebraska, and the NPPD Gerald Gentleman

Station in Sutherland, NE.

In reviewing Mr. Klafka ’s efforts, I iden tified four issues that stood out and require d comment; emission

rates, receptors, buildings, and the background concentration.

Emission Rates:

To characterize current 1

- hour SO 2 air quality a ttainment, the EPA recommended us ing actual emissions,

to reflect the temporally varying emissions. Mr. Klafka modeled actual emissions, but Mr. Klafka also chose to model the Potential To Emit (PTE) emissions and present both sets of impacts . PTE emissions are produced by the maximum c apacity of a stationary source to emit a pollutant

. A maximum capacity

assum es that the physical and operational design is operating at 100% of it s design capacity , 100% of the

time

. Most consumers know that power plants have peak daily and peak seasonal loads, when the plant is not operating at 100% of its design capacity. The modeling of PTE emissions does not reflect the temporal impact of the two power plant facilities , and the addition of this emission rate to this modeling

demonstration only causes confusion

.

Receptors

There were no fence line receptors in either the Sheldon or the Gerald Gentleman models , and non

ambient air receptors inside the fenceline were included in both air dispersion models . Additionally, there

were receptors covering a large body of water in the Gerald Gentleman model. These receptors should have been excluded, as per EPA ’s 1

- hour SO2 SIP modeling guidance.

Buildings There were no buildings in either model. M r. Klafka claims the lack of buildings is more conservative

. P roof of t his assertion would be helpful

. In my experience, buildings create cavitation and therefore higher impacts.

Background Concentrations

A b ackground concentration was calculated by Mr. Klafka to be 88.9 μ g/m 3 . The monitor used to arrive

at this value was identified only as “2011

- 13 design value for Douglas County, Nebraska.” There are only two SO 2 monitor s in the entire State of Nebraska, and both monitors are located in Douglas County,

in Omaha, NE, pictured below.Both NPPD Gerald Gentleman Power Station and the NPPD Sheldon Power Station in Hallam, NE are

located in sparsely inhabited rural areas, se e figures below. Using a background concentration of SO 2 from an urban area like Omaha, NE would overestimate the background concentration of SO 2 normally found in rural areas like Hallam, NE. In air dispersion modeling, b ackground concentrations are added to the predicted modeled impact to account for natural sources, nearby sources not directly included in the modeling effort, and distant unidentified sources. Using a background concentration from an urban area like Omaha would overestimate these background contributions which is why the background concentration from the rural monitor located at Cedar Bluff Reservoir in Trego County, KS. This monitor is far from any nearby large SO 2 sources, so is representative of background concentrations in rural areas of Nebraska exclusive of nearby major source impacts.To check M r. Klafka’s background concentration calculations, I calculated the concentrations from both

available monitors in Omaha, NE, and came up with the results in the table below. I calculated a three year average for 2011 through 2013, and 2012 through 2014. I don’t know how Mr. Klafka was able to arrive at 88.9 μg/m 3

.

2014

- 12 2011

-

13

99th Percentile 3

- yr

ave 3

- yr

ave

CBSA Address Site ID 2014 2013 2012 2011 ppb ppb

Omaha

- Council Bluffs, NE

- IA Douglas County Hosp 42nd & Woolworth 310550019 21.0 27.0 38.0 37.0 28.7 34.0

Omaha

- Council Bluffs, NE

- IA 1616 Whitmore 310550053 54.0 56.0 73.0 66.0 61.0 65.0

http://www3.epa.gov/airdata/ad_rep_mon.html

2014

- 12 2011

-

13

99th Percentile 3

- yr

ave 3

- yr

ave

CBSA Address Site ID 2014 2013 2012 2011 μ g/m 3 μ g/m 3

Omaha

- Council Bluffs, NE

- IA Douglas County Hosp 42nd & Woolworth 310550019 55.0 70.7 99.5 69.6 75.1 79.9

Omaha

- Council Bluffs, NE

- IA 1616 Whitmore 310550053 141.4 146.7 191.2 124.1 159.7 154.0