equipment such as coal storage and transferring, coal pulverizing, lime handling operations, and dry ash handling operations.

On February 20, 2015, EPA received an application fo r a NSR permit from SRP for the construction and operation of a Coal Treatment System (CTS) withinthe plant boundaries on pr e-disturbed land at NGS (See Attachment 3). SRP has an exis ting coal conveyor belt system th at transfers untreated coal from railcar unloading piles, to the pulverizers for crushing, and then fed in to one of three existing boilers for combustion in order to generate steam and produce electricity. SRP is proposi ng to construct a CTS,

which adds calcium bromide and cement kiln dust to the coal prior to being pulverized and combusted. The new equipment is being installed in order to reduce oxid es of nitrogen (“NO x ”) and mercury

emissions. This CTS will consist of two new coal f eed belt conveyors that would divert coal from the existing conveyor system to two new mixing pugmills where the coal is mixed with the additives. The treated coal is then fed back into the existing conv eyor system to be pulverized and finally combusted.

The belt conveyors will be controlled by two high effi ciency dust collectors. Cement kiln dust will be delivered by truck and stored in three 150 ton silos and two 20 ton day bins, which will be controlled by baghouses. Some emissions increases from existing dirt roads can be expected because of the increased truck delivery traffic.

The project will result in emissions increases in PM, PM 10 , and PM 2.5 . The construction and operation of the CTS will be within the existing footprint of NGS and the increase in emissions from the changes will not exceed the Prevention of Significant Deteriorati on (PSD) thresholds. Therefore, the changes do not trigger PSD, but the increase in emissions are above the Tribal NSR minor source thresholds.

Proposed Area of Potential Effects The construction and operation of the NGS CTS Project is consider ed a minor modification under the Tribal NSR program and will be incorporating the coal treatment system into the existing coal handling operation. The effects of the proposed construction and operation will occur only within the existing footprint of the NGS. As such, the proposed area of potential effects (APE ) includes the existing footprint of the NGS power plant as seen in Attachment 2. In addition, the increases in emissions due to this project do not exceed Significant Impact Le vels (SILs) beyond the ex isting facility boundary. Therefore, EPA expects no effects due to this modi fication on any historic properties or cultural resources which may exist outside the NGS facility footprint.

Effects on Historic Properties within the APE EPA was advised by the Navajo Nati on Tribal Historic Preservation O fficer (THPO) that the NGS itself is eligible for inclusion in the National Register of Historic Places. The NGS has been in existence since the early 1970’s and has been an integral part of the economy and community of Navajo Nation since
that time.

The area in which the construction of the NGS CTS Pr oject and associated infrastructure, such as the cement kiln dust storage silos and new coal feed belt conveyors, is within the built-up environment of the power plant. The area shown in Figure 2 has been mechanically excavated and leveled and contains an established complex of structures, roads, parking areas, and electrical lines to the degree that the area no longer resembles natural conditions.