Final Notes from Site Visit at Midwest Generation’s EME Homer City Generation Plant on 

August 22, 2012

EPA conducted a site visit at Midwest Generation’s EME Homer City Generation Plant (Homer 

City) located in Homer City, Pennsylvania on Wednesday, August 22, 2012 to learn about operations at 

the plant and discuss recent upgrades to the FGD and bottom ash systems. These notes describe the 

information collected during the site visit. Table 2 identifies the site visit participants.

Plant Overview

• Homer City operates three electric generating units, all of which are baseload coal-fired units. 

The plant’s net generating capacity is 1,884 MW. The table below contains some general 

information on the current operation of each steam electric generating unit.

Table 1. Steam Electric Generating Unit Operations

SE Unit Fuel

Net 

Capacity 

(MW) Fly Ash Bottom Ash FGD

Flue Gas Mercury 

Control

1

Coal: 

Bituminous 620

Dry Ash Handling –

Combined 

Vacuum/Pressure System Wet Sluiced None None1

2

Coal: 

Bituminous 614

Dry Ash Handling –

Combined 

Vacuum/Pressure System Wet Sluiced None None1

3

Coal: 

Bituminous 650

Dry Ash Handling –

Pressure System Wet Sluiced

Wet 

System None

1 – A dry activated carbon injection system, located upstream of the electrostatic precipitator (ESP), was installed in January 

2010 to service units 1 and 2. Plant personnel indicate that this system has not been operated since installation.

• Homer City is in the process of upgrading the wet-bottom ash handling system on all three 

generating units to a tank-based system (i.e., no discharge of bottom ash transport water). This 

upgrade is currently under construction and is planned to be completed by November 2012.

• Homer City is also in the process of installing two dry lime scrubber systems, one each on units 1 

and 2. These systems are being installed in anticipation of the pending Mercury and Air Toxics 

Standard (MATS) Rule. These systems are currently under construction with a planned start-up 

date in 2014.

Fly Ash Handling System

• Homer City operates dry fly ash handling systems on all three of its generating units. Units 1 and 

2 utilize a combined Vacuum/Pressure system while Unit 3 uses a pressure system.

• Each unit transfers ash to one of three silos, each generating unit has a dedicated silo. The plant 

maintains a one-unit-per-silo method for ash collection to allow for the shortest transport time and 

simplicity. Each silo has the capacity to store roughly two to three days worth of fly ash.

• Fly ash from each silo is transferred to trucks using a pugmill to moisten the ash to approximately 

12 percent moisture. Homer City unloads the fly ash from Units 1, 2, and 3 approximately five to 

six days per week.

• Homer City beneficially uses (placement) fly ash at the ‘Coal Refuse Site’ or disposes of fly ash 

at the ‘Ash Disposal Site.’ Homer City collects weekly samples of the ash, using a combination 

of fly ash from all three units. Provided that the material meet beneficial use criteria (which 
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include Synthetic Precipitation Leaching Procedure [SLPL] analysis) the plant has the option to 

manage the material in either the ‘Coal Refuse Site’ or the ‘Ash Disposal Site.’ If the material 

does not meet beneficial use criteria, the plant manages the material in the ‘Ash Disposal Site.’

• Homer City personnel stated that the loss of ignition (LOI) in the fly ash is too high for the ash to 

be used by the concrete industry; however, it can be used as structural fill, flowable fill, and for 

road construction. 

• Homer City does not transport any of the fly ash using dry unloaders (i.e., without moistening the 

ash using a pugmill).

Bottom Ash Handling System

• Currently the bottom ash from all three units is wet sluiced to dewatering bins. The dewatered 

non-pyritic solids are sold as anti-skid material. The pyritic bottom ash is managed in either the 

coal refuse of the ash disposal sites. Overflow from the dewatering bins is transferred to a series 

of settling ponds. The effluent from these ponds is either reused in the bottom ash sluice system, 

used to moisten fly ash, or discharged.

• Homer City evaluated several options for achieving zero discharge of bottom ash sluice,

including a mechanical drag system. The plant determined that the closed-loop tank-based 

system currently being installed provided the best solution for managing all of the various plant 

interferences associated with the bottom ash system.

• The new bottom ash system is planned to be operating by November 2012. The new system will 

continue to use water to sluice the bottom ash from the boiler. The sluice will continue to be 

collected in the dewatering bins where the majority of the bottom ash will settle out and be sold 

as anti-skid material or landfilled. The overflow from the dewatering bins will then be transferred 

to a set of settling tanks operating in series with each settling tank. The underflow from the 

settling tanks will be sent back to the dewatering bins to remove the solids with the majority of 

the bottom ash. The overflow will be routed to a set of surge tanks operated in parallel. Similar 

to the settling tanks, the underflow from the surge tanks will be sent back to the dewatering bins 

to remove the solids with the majority of the bottom ash. The overflow from the surge tanks will 

be transferred to a clearwell and from there it will be recycled back as sluice water or used to 

moisten the fly ash. A process flow diagram of the new bottom ash system is included as 

Attachment 1 of this memorandum. 

• The set of settling tanks and surge tanks are open topped tanks and were sized by United 

Conveyor Corporation (UCC) to include 100 percent redundancy (i.e., one settling tank and one 

surge tank would have been sufficient to handle the dewatering bin overflow for all three units). 

Once construction on the tanks is complete the plant will operate both the tank based system and 

the pond system until the new system can achieve equilibrium. At which point the bottom ash 

system is designed to require no discharge of wastewater and the bottom ash sluice discharge to 

Outfall 005 will be sealed.

• Homer City expects that make-up water will need to be added to the system to account for the 

water remaining in the bottom ash solid, evaporation, and water used to moisten the fly ash.

Homer City is planning to use stormwater from the area around the bottom ash system as part of 

the make-up water for the system.

• Homer City does not anticipate any build up of constituents or scaling issues within the system

and therefore, has no plans to add any chemicals to the system.

• Homer City made no other changes to the bottom ash sluicing system itself (e.g., no changes to 

the sluice pumps). 

• Once the new bottom ash system is operating and the settling ponds are no longer needed, the 

ponds will be closed. The space currently occupied by these ponds will be used for the new dry 

FGD systems.
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Flue Gas Desulfurization (FGD) Systems

• Homer City is in the process of installing dry FGD scrubbers on Units 1 and 2. Both units are 

expected to be operating by 2014. These systems will be dry lime scrubbers and will include the 

addition of activated carbon for increased mercury removal. The plant plans to landfill solids 

produced by the dry FGD systems. These solids will undergo an evaluation to determine which 

disposal site can be used for management of this material. Homer City personnel believe that the 

dry FGD solids could potentially be used as a soil amendment because of its elevated pH.

• Homer City is currently operating a limestone forced oxidation FGD system on Unit 3. 

• Homer City personnel indicated that dibasic acid (DBA) and formic acid were previously added 

to the wet FGD system to increase the sulfur dioxide removal of the system. Homer City 

determined that these additives were resulting in some of the selenium to be organically bound, 

which is more difficult to remove in the downstream wastewater treatment system. Homer City is 

no longer using DBA or formic acid in the wet FGD system.

• The chloride level in the wet FGD system is typically between 14,000 to 18,000 ppm. 

• Blowdown from the FGD system is transferred to the primary hydrocyclones for initial solids 

separation. The overflow can be transferred to the secondary hydrocyclones or recycled back to 

the absorber. The underflow is transferred to the vacuum belt filters.

• From the secondary hydrocyclone, the overflow (i.e., FGD purge) is transferred to the FGD 

wastewater treatment system, while the underflow is transferred to the vacuum belt filters. The 

flow rate of the FGD purge stream is estimated to occur for 5 to 9 hours twice per day at a rate of 

220 gpm. The typical solids concentration of the FGD purge is two percent (but it ranges from 

one to four percent). Underflow from the secondary hydrocyclone is transferred to the vacuum 

belt filter along with the underflow from the primary hydrocyclone.

• Homer City uses a vacuum belt filter to dewater the gypsum. The filtrate from the vacuum belt is 

transferred back to the absorber.

• Dewatered gypsum from the vacuum belt filter is either transferred to the ’Coal Refuse Site’ or

the ’Ash Disposal Site.’ Provided that the material meet beneficial use criteria (which include 

SPLP analysis) the plant has the option to manage the material in either the ‘Coal Refuse Site’ or 

the ‘Ash Disposal Site.’ If the material does not meet beneficial use criteria, the plant manages 

the material in the ‘Ash Disposal Site.’ Prior to 2008, Homer City was able to sell 100 percent of 

the gypsum to the wallboard industry. The influx of scrubbers and slow housing market has 

caused the demand for gypsum to decrease and the plant has been unable to sell gypsum recently.

• Homer City has not conducted any studies on the oxidation reduction potential (ORP) within the 

scrubber and its effects on the FGD wastewater characteristics.

FGD Wastewater Treatment System

• The FGD purge is transferred to the wastewater treatment feed tank. The water from the feed 

tank is then transferred to the first stage neutralization tank where 40 ppm ferric chloride and lime 

slurry are added to adjust the pH to between 6.8 and 6.9 S.U. Homer City noted that historically 

it sees better selenium removal at a lower pH.

• From the first stage neutralization tank, the wastewater is sent to the first stage clarifier. A

cationic polymer is injected inline as a coagulant, while an anionic polymer is added to the 1st

stage clarifier center well as a flocculent. Overflow from the clarifier, which the plant adds 15 to 

20 ppm of ferric chloride, is sent to the second stage neutralization tank, while the underflow is 

transferred to a thickener. 

• In the second stage neutralization tank more lime slurry is added to adjust the pH to 7.0 S.U. 

From the second stage neutralization the wastewater is sent to the second stage clarifier, where 

more polymer is added. 
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• Homer City personnel noted that the second stage clarifier is operating with an effluent turbidity 

of 20 to 30 NTU, which is slightly higher than the normal level of 5 to 15 NTU. The plant 

speculates the increased solids are due to chemicals (i.e., dispersants) used to treat the cooling 

water to allow for additional cycling within the cooling towers. Cooling water is used as FGD 

make-up and slurry and reagent preparation water.

• Homer City maintains a sludge blanket of roughly 5 feet in the second stage clarifier to help 

remove the smaller finer particles. During the site visit the sludge blanket was approximately 2.5 

feet thick. Homer City personnel attributed the smaller sludge blanket to it being an older sludge.

• The underflow from the second stage clarifier is combined with the underflow from the first stage 

clarifier and sent to the thickener. The overflow from the thickener is transferred back to the first 

stage neutralization tank. The thickened solids are dewatered by a vacuum drum filter and the 

solids are hauled to the ‘Ash Disposal Site.’ The vacuum drum filtrate is transferred to the first 

stage neutralization tank.

• The overflow from the second stage clarifier is sent to a pH adjustment tank, which was 

previously used to adjust the pH prior to the downstream biological treatment system. Homer 

City no longer operates the biological treatment system as the system was designed and therefore, 

Homer City no longer adds any chemicals to the pH adjustment tank. 

• The wastewater is then bypassed around the existing heat exchanger and sent to the biological 

system, which consists of an aerobic biological reactor. This system was operated to remove the 

organic content in the wastewater added from the organic acids (i.e., DBA/formic acid) as well as 

the biochemical oxygen demand (BOD) present. Because Homer City no longer adds organic 

acid to the FGD system, the biological system is not needed. Homer City still transfers the 

wastewater to the reactor and aerates the system. Solids accumulated in the biological reactor are 

transferred to the thickener and handled with the clarifier solids.

• Effluent from the biological reactor is transferred to sand filters and then onto the effluent tank 

and discharged. Filter backwash from the sand filters is recycled back to the initial wastewater 

feed tank.

• Using the two stage chemical precipitation system, Homer City indicated that they are able to 

achieve over 90% removal of selenium (from 7 ppm to 0.5 ppm). For the most part, only soluble 

selenium remains in the treated effluent. 

• Homer City indicated that the mercury concentration in the treated FGD wastewater effluent is 

normally at non-detect levels using EPA Method 245.1.

• Homer City has not yet evaluated whether the treated FGD wastewater could be used as make up 

for the dry FGD systems to eliminate the FGD discharge; however, Homer City personnel stated 

that there are concerns regarding times when Unit 3 is operating (which generates FGD 

wastewater) and Unit 1 and/or Unit 2 are not operating, in which case some or all of the FGD 

wastewater would need to be discharged because one or both of the dry FGD systems would not 

be operating. 

Flue Gas Mercury Control (FGMC) Systems

• In January 2010, Homer City installed a dry upstream activated carbon injection system on Units 

1 and 2 to comply with the Pennsylvania Mercury Rule. The plant has never operated either of 

these systems because the Pennsylvania Mercury Rule requirement was not upheld.

• Homer City indicated that no changes were made to the ash handling system as a result of the 

added FGMC systems. The added solids resulting from the FGMC system would have been 

minimal, resulting in no need for added storage space in the silos.

• Homer City had expected that the fly ash samples including the FGMC solids would have still 

passed the toxicity characteristic leaching procedure (TCLP) analysis and therefore, could have 

been disposed of at the ‘Ash Disposal Site.’
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• The dry lime scrubbers being installed on Units 1 and 2 will include the injection of activated 

carbon to control mercury.

Landfills and Leachate Treatment Systems

• Homer City operates three landfills. Two active landfills and one retired landfill. The active 

landfills are referred to as the ‘Ash Disposal Site’ and the ‘Coal Refuse Site.’ The retired landfill 

is known as the ‘Strike Pile.’

• The ‘Ash Disposal Site’ receives fly ash, bottom ash, and calcium sulfate (synthetic gypsum), in

addition to other plant solids. The ‘Coal Refuse Site’ receives fly ash, bottom ash, and calcium 

sulfate (synthetic gypsum), as well as coal refuse. The State of Pennsylvania maintains programs 

that regulates what type of material can be beneficially used in the ‘Coal Refuse Site.’ Provided 

that the material meet beneficial use criteria (which include synthetic precipitation leaching 

procedure (SPLP) analysis) the plant has the option to manage the material in either the ‘Coal 

Refuse Site’ or the ‘Ash Disposal Site.’ If the material does not meet beneficial use criteria, the 

plant manages the material in the ‘Ash Disposal Site.’

• The ‘Ash Disposal Site’ has an underdrain system to collect leachate. The leachate and a portion 

of the storm water is sent to a leachate treatment system. Landfill runoff from the ‘Ash Disposal 

Site’ is either sent to the leachate treatment system or discharges to the ash landfill’s stormwater 

outfalls. 

• Leachate from the ‘Ash Disposal Site’ is piped directly to the leachate treatment system at a rate 

of roughly 180 gpm. There is no leachate collection pond or tank prior to the treatment system. 

In the first step of the treatment system, caustic is used to raise the pH to 8.9 S.U. The amount of 

caustic added is based on pH monitoring that occurs at the treatment system influent and effluent. 

In the second step of the treatment system, the leachate is transferred to a flocculation tank where

a gel polymer is added. The treated effluent is sent to one of two settling ponds. Both settling 

ponds discharge to a single polishing pond. Treated leachate from the polishing pond is 

discharged via plant Outfall 004. 

• The treatment system for leachate from the ‘Ash Disposal Site’ targets iron and manganese. 

Recent permit amendments added new constituents to the limits to include arsenic, boron, nickel, 

and thallium. These additional limits are water quality based limits. Homer City expects that 

additional treatment will be needed to meet the limits; however, the plant is currently evaluating 

options to meet these limits from the permit amendment.

• The ‘Coal Refuse Site’ is lined and includes a leachate collection system. Leachate from the Coal 

Refuse Site is sent to a separate leachate treatment system (Wastewater Recycle [WWR]). WWR

also treats stormwater from the ‘Coal Refuse Site.’ Homer City personnel stated that coal pile 

runoff is not treated in WWR; the ‘Coal Refuse Site’ and coal pile are separate entities.

• Leachate from the ‘Coal Refuse Site’ is collected in a series of six ponds prior to entering the 

treatment systems. Leachate feeds by gravity from one pond to the next and is then pumped to 

the leachate treatment system (WWR).

• The commingled leachate and stormwater from the ‘Coal Refuse Site’ are mixed with lime slurry. 

The target pH of the system is 8.5 S.U. Air is added to the system to encourage iron to oxidize 

and convert from the ferrous oxidation state (Fe2+) to the ferric oxidation state (Fe3+). The aerated 

stream is sent to a clarifier where it is mixed with raw intake water. The oxidized iron, along 

with coagulants, help to precipitate and settle any sediments out of the intake water. The clear 

combined effluent is then used throughout the plant as make-up water. 

• Homer City cited the final destination of each stream as the reason for the different treatment 

methods. Leachate from the ‘Coal Refuse Site’ is used to help treat the plant intake and then used 

as make-up water for various processes within the plant, while leachate from the ‘Ash Disposal 
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Site’ is discharged. Additionally, the ‘Coal Refuse Site’ is larger than the ‘Ash Disposal Site’ and 

produces roughly twice as much leachate.

• The permit for the ‘Ash Disposal Site’ expires in 2013. On October 1, 2012, Homer City 

received a permit to expand the site both horizontally and vertically. The State of Pennsylvania 

requires that the expansion include a synthetic liner.

• The ‘Strike Pile’ is the plant’s retired landfill. This landfill was only used for a 108-day period 

during a labor strike at the plant. No new waste is being added to this landfill.
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Table 2. Site Visit Attendees

Name Organization (Representing) Telephone E-mail

Tom Wilson Homer City Power Plant (724) 479-6140 twilson@mwgen.com

Gary Cline Homer City Station (724) 479-6255 gcline@mwgen.com

Tom Suda Homer City Station (724) 479-6123 tsuda@mwgen.com

Joe Stanek Homer City Station (724) 479-6256 jstanek@mwgen.com

John DeMarines Homer City Station (724) 479-6237 jdemarines@mwgen.com

Bob Duey Homer City Station (724) 479-6145 bduey@mwgen.com

Jeff Lellock Homer City Station (724) 479-6247 jlellock@mwgen.com

Jim Beninati HDR Engineering (724) 497-6237 james.beninati@hdrinc.com

John VanGehuchten HDR Engineering (724) 497-6236 John.vangehuchten@hrdinc.com

Cassandra Shaw GE EFS (508) 596-9140 Cassandra1.shaw@ge.com

Donna Hill Southern Company (205) 257-5234 dbhill@southernco.com

Ron Jordan EPA/Office of Water (202) 566-1003 Jordan.ronald@epa.gov

Cuc Schroeder EPA/Office of Water (202) 566-2397 Schroeder.cuc@epa.gov

James Covington EPA/Office of Water (202) 566-1034 Covington.james@epa.gov

T.J. Finseth ERG (Contractor to EPA) (703) 633-1698 Thomas.finseth@erg.com

Danielle Lewis ERG (Contractor to EPA) (703) 633-1703 Danielle.lewis@erg.com