Engineering Site Visit Report for 

EME Homer City Generation L.P.’s 

 Homer City Power Plant 

Homer City, PA 

Prepared for:

 U.S. Environmental Protection Agency

 Engineering and Analysis Division

Office of Water 

 1200 Pennsylvania Avenue 

 Washington, DC 20004 

Prepared by:

Eastern Research Group, Inc. 

14555 Avion Parkway 

Suite 200 

 Chantilly, VA 20151-1102 

9 August 2007 

EPA Contract No. 68-C02-095 

Work Assignment 4-22 
i

TABLE OF CONTENTS 

Page 

1.0 Site Visited and Date......................................................................................................... 1 

2.0 Attendees ........................................................................................................................... 1 

3.0 Background and Objectives............................................................................................... 1 

4.0 Plant Description ............................................................................................................... 2 

5.0 Plant Operations ................................................................................................................ 3 

5.1 Intake Water............................................................................................................. 4 

5.2 Coal Preparation ...................................................................................................... 4 

5.3 Boiler Operation ...................................................................................................... 6 

5.4 SCR Systems............................................................................................................ 7 

5.5 Particulate Control ................................................................................................... 8 

5.6 FGD System............................................................................................................. 8 

5.7 Biofouling Control................................................................................................. 11 

6.0 Wastewater Treatment..................................................................................................... 11

6.1 Bottom Ash Treatment........................................................................................... 11 

6.2 FGD Wastewater Treatment .................................................................................. 12 

6.3 Industrial Wastewater Treatment (IWT) System................................................... 16 

7.0 References ....................................................................................................................... 16 

Appendix A LIST OF ATTENDEES 

Appendix B PHOTOS FROM SITE VISIT 
ii

LIST OF TABLES 

Page 

A-1 List of Attendees................................................................................................. A-1 
iii

LIST OF FIGURES 

Page 

6-1 FGD Wastewater Treatment System at Homer City............................................. 14 

B-1 FGD Scrubber Spray Tower at Homer City ....................................................... B-1 

B-2 Gypsum Rinse on Vacuum Filter Belt at Homer City ........................................ B-2 

B-3 Gypsum Final Product on Vacuum Filter Belt at Homer City............................ B-3 

B-4 Gypsum Storage Dome at Homer City ............................................................... B-4 

B-5 Bottom of Cooling Tower for Unit 3 at Homer City .......................................... B-5 

B-6 Bottom Ash Settling Ponds at Homer City......................................................... B-6 

B-7 FGD Wastewater Treatment Feed Tank at Homer City ..................................... B-7 

B-8 FGD Wastewater Treatment 1st Stage Clarifier at Homer City ......................... B-8 

B-9 FGD Wastewater Treatment 2nd Stage Clarifier at Homer City ......................... B-9 

B-10 FGD Wastewater Treatment Biological Reactor at Homer City ...................... B-10 

B-11 FGD Wastewater Treatment Clarifiers and Biological Reactor at Homer City B-11 

B-12 FGD Wastewater Treatment Vacuum Filter at Homer City ............................. B-12 
1

1.0 SITE VISITED AND DATE

EME Homer City Generation L.P.’s Homer City Power Plant 

1750 Power Plant Road 

Homer City, PA 15748-9558 

February 6, 2007 

2.0 ATTENDEES

Appendix A lists the attendees. 

3.0 BACKGROUND AND OBJECTIVES

 Section 304(m) of the Clean Water Act (CWA) requires EPA to develop and 

publish a biennial plan that establishes a schedule for the annual review and revision of national 

effluent limitations guidelines and standards (ELGs) required by CWA section 304(b). During 

EPA’s 2005/2006 review of ELGs, EPA determined that the Steam Electric Power Generating 

Point Source Category (40 CFR Part 423) is the second-largest discharger of toxic-weighted 

pollutants. EPA’s analyses indicated that the toxic-weighted loadings are predominantly driven 

by metals present in wastewater discharges, and that the waste streams contributing the majority 

of the metals are associated with air pollution controls. Other potential sources of metals include 

coal pile runoff, metal/chemical cleaning wastes, coal washing, and certain low volume wastes. 

 In presenting the findings of the 2005/2006 study, EPA noted certain data 

limitations affect the Agency’s estimate of the potential hazard posed by discharges from this 

category and, therefore, EPA determined that further review of these discharges during the 

2007/2008 ELG planning cycle is warranted. Due to the limited resources and time available for 

conducting this study, EPA is concentrating its efforts for the 2007/2008 study on better 

characterizing pollutant sources and available pollution control technologies/practices for the 

pollutants responsible for the majority of the toxic-weighted pollutant loadings from steam 

electric facilities. This will focus the review on wastewater discharges from coal-fired power 

plants. 
2

 EPA intends to review overall plant operations and better understand the various 

wastewater sources present at steam electric plants. This review is expected to largely focus on 

ash handling wastes, wet flue gas desulfurization (FGD) wastes, coal pile runoff, and final 

effluent. 

 EPA and its contractor, Eastern Research Group, Inc. (ERG), conducted a site 

visit to EME Homer City Generation L.P.’s Homer City Power Plant (Homer City) on February 

6, 2007. The purpose of the visit was to: 1) gather information about the plant’s operations, the 

wastewater discharges from the plant, and the wastewater management practices used to control 

the discharges; and 2) determine the feasibility of collecting and analyzing wastewater samples 

from steam electric power plants. 

4.0 PLANT DESCRIPTION

 Homer City operates three steam electric units and each has a coal-fired boiler. 

Units 1 and 2, which came on line in 1969, each have a capacity of 650 megawatts (MW). Unit 

3, which came on line in 1977, has a capacity of 700 MW. Typically, Homer City produces 

between 13 and 14 million megawatt hours (MW-hrs) per year. The Homer City plant is located 

on approximately 2,400 acres near Homer City, Pennsylvania, near Two Lick Creek and 

Blacklick Creek. Homer City operates a 1,800-acre reservoir, the Two Lick Reservoir, 

approximately 8 miles upstream of the plant site. The plant employs approximately 260 people. 

 Homer City is part of the Pennsylvania, New Jersey, and Maryland (PJM) 

electricity grid and adjusts its MW output based on the grid’s needs (typical fluctuation may be 

20 to 30 MW). During the summer and winter, Homer City typically operates at maximum or 

close to maximum load 24 hours per day. During the spring and fall, the plant may reduce its 

load at night to 50 percent of its capacity. 

 

 In 2001, Homer City retrofitted Unit 3 with a wet FGD scrubber system to control 

the sulfur dioxide releases from the plant. Unit 3 is subject to New Source Performance 

Standards (NSPS) air regulations. Plant personnel reported that with the installation of the FGD 

scrubber on Unit 3, the total plant sulfur dioxide emissions were reduced by 40 percent to come 
3

into compliance with new permit limits, and the mercury emissions were reduced by 55 percent. 

The mercury reductions are based on the mercury removal across the Unit 3 FGD scrubber as 

tested by the Department of Energy (DOE) during 2001. Plant personnel estimated that Homer 

City’s operating and maintenance cost is $400/ton sulfur dioxide removed. At the time the FGD 

scrubber was installed on Unit 3, Homer City also installed an FGD treatment system to control 

the discharges from the wastewater generated during the operation of the FGD scrubber. Homer 

City plans to install FGD scrubbers on Units 1 and 2. 

 Between 2000 and 2001, Homer City retrofitted Units 1 through 3 with selective 

catalytic reduction (SCR) systems to control nitrogen oxide (NOx) releases from the plant. Plant 

personnel reported that with the installation of the SCR systems, the total plant NOx emissions 

were reduced by 80 percent, compared to limits based on Reasonably Available Control 

Technology (RACT). Plant personnel estimated that Homer City’s operating and maintenance 

cost is $800 - $1,500/ton NOx removed. 

 Homer City has taken steps to reduce air emissions beyond installing FGD and 

SCR systems. Units 1 and 2 use a mid-sulfur coal, which generates less sulfur dioxide emissions 

than a high-sulfur coal. Additionally, the coal used in Units 1 and 2 is cleaned on site in a 

process that reduces the sulfur, which is discussed in Section 5.2. The boilers in Units 1 through 

3 are equipped with low NOx burners and separated overfire air (SOFA) systems, which limit the 

production of NOx. 

 

5.0 PLANT OPERATIONS

 Each of the three generating units at Homer City has a coal-fired, wall-fired 

boiler. Units 1 and 2 have supercritical boilers that burn mid-sulfur coal. Unit 3 has a Babcock 

& Wilcox drum boiler that burns high-sulfur coal. The plant uses approximately five million 

tons of coal per year. 

 The Homer City site visit focused on the generating units and the wastewaters 

associated with these units. For a general description of the steam electric power generation 

process, see Section 3.2.1 of the Interim Detailed Study Report for the Steam Electric Power 

Comment [MSOffice1]: NOTE TO 

EPA: I added this statement because of 

Homer City’s edit in Section 5.7 about 

using cooling tower blowdown for Units 

1 and 2 FGD scrubbers in the future. I 

had also read this on the internet after our 

site visit. As far as I know, we don’t 

know when they plan to install the new 

FGDs. 
4

Generating Point Source Category. A detailed description of the wastewater treatment systems 

is provided in Section 6.0 of this report. The remainder of this section describes the following 

seven plant operations at Homer City: 

• Intake water; 

• Coal cleaning and preparation; 

• Boiler operation (includes wet bottom ash handling); 

• SCR systems; 

• Particulate control (includes dry fly ash handling); 

• FGD system operation; and 

• Biofouling control. 

5.1 Intake Water

 The plant withdraws water from Two Lick Creek for use in the steam electric 

generating process following treatment for metals removal. The pH of the intake water is 

adjusted with lime and cationic polymer at the Makeup Pump House and the water is pumped to 

a sludge contact clarifier. Water from this clarifier is either used as make-up water for all three 

cooling towers or sent to a second sludge contact clarifier. Cooling tower make-up water has the 

following characteristics: pH is 7.5 – 7.8 s.u., total iron (Fe) is 0.85 – 1.33 ppm, and total 

suspended solids (TSS) is 9 – 16 ppm. Water from the second sludge contact clarifier is used for 

potable water as well as the reverse osmosis and demineralizer system, which supplies boiler 

make-up water. Wastewater from the reverse osmosis and demineralizer system is discharged to 

the industrial wastewater treatment (IWT) system described in Section 6.3. The reverse osmosis 

unit rejects approximately 100 to 150 gpm continuously and the demineralizer system is 

regenerated every 30 to 45 days, producing caustic and acidic waste streams. 

5.2 Coal Preparation

 Homer City uses eastern bituminous coal in its boilers. Eighty percent of the coal 

is trucked in from local mines. The remaining 20 percent is delivered to the plant by train. 

Homer City evaluates all available coals relative to heat content, sulfur, ash, and other relevant 

constituents, including washability for raw coals and price. Coals procured for Homer City are 

bituminous, mid to high Vol A rank of Northern Appalachia origin. 
5

 Homer City is one of only a few power plants in the country that cleans coal on 

site. Homer City cleans the coal used in Units 1 and 2, creating a mid-sulfur coal. The coal 

cleaning process removes a portion of the sulfur and ash and other impurities that are not 

organically bound. Homer City stated that cleaning coal on site is economical because it allows 

them to purchase coal from smaller local mines at a competitive price. 

 Homer City cleans its coal using a process that employees both gravimetric and 

flotation processes. Magnetite is combined with water for use in the gravimetric processing of 

the coarser coal size fractions, and specially formulated frother and collector agents are used in 

the flotation processing of the smallest coal size fractions. In the coal cleaning process, the 

heavier particles (impurities) are physically separated from the lighter particles (coal). Frothing 

is used to separate the finest particles. Very little water is lost in the process and it exits the plant 

as moisture on the plant products. Process water is recycled in closed circuit water clarification 

units. All of the clarified water is recycled back to the coal cleaning process and the waste solids 

resulting from the water clarification process are thickened and disposed of in the on-site lined 

refuse disposal area. An on-site un-lined storm and sedimentation pond, which also serves as an 

emergency holding pond for plant process water, is used as a supply of plant make-up water. 

The coal cleaning process is zero discharge. 

 

 The coal cleaning process is part of the front end of raw coal deliveries. Coals 

that are delivered to the station intended for the cleaning cycle go through the coal cleaning 

process before reporting to the station for consumption. Homer City transports coal from the 

coal cleaning plant and coal storage piles to individual unit bunkers by conveyor belt. From the 

bunkers, the coal is transported to pulverizers where it is crushed by rollers into a fine powder. 

The pulverizing process generates no wastewater. The coal storage system is designed to hold 

approximately 1 to 1.5 million tons of coal. 

 Storm water runoff from the coal piles collects in three settling ponds. Two 

ponds are operated in series and one pond is stand-alone. Runoff from the Units 1 and 2 coal 

pile and the Unit 3 coal pile is directed to Coal Pond 3. The excess water from collection and 

pumping (to the IWT plant) is drained into Coal Pond 2. Storm water from the truck scales, 

cleaning plant feed piles, and the train unloading areas is collected in Coal Pond 1. Coal Ponds 1 
6

and 2 are clay lined and Coal Pond 3 is lined with a synthetic liner. All ponds are designed to 

contain 10 year 24 hour rain events. The solids that settle in these ponds are recovered, dumped 

back on the coal piles, and used in the boilers. Water from the coal pile runoff ponds is pumped 

to the IWT system (described in Section 6.3) as needed, depending on the amount of rainfall. 

Plant personnel stated that Homer City sampled the coal pile runoff for permit renewal. 

5.3 Boiler Operation

 As the pulverized coal is blown into the boilers, it is combusted and gives off 

heat. The heat produced in the boilers is used to convert water into high-pressure steam. As the 

coal is combusted, solid, non-combustible constituents of the coal, referred to as ash, are 

generated. The heavy ash particles that collect on the bottom of the boilers are referred to as 

bottom ash. The finer particles that are light enough to be transferred out of the boilers with the 

flue gas exhaust are referred to as fly ash. 

 At Homer City, sluice water removes the bottom ash and other slag from the 

bottom of the boilers. The bottom ash sluice water is piped to hydrobins, which remove 90 to 95 

percent of the solids. The supernatant overflow from the hydrobins drains to ash settling ponds, 

which are described in Section 6.1. The dewatered bottom ash from the hydrobins is either used 

locally for anti-skid and road construction or placed in the on-site, unlined ash landfill. Water 

from the ash settling ponds is recycled back to the boilers for re-use as sluicing water. 

 Homer City does not chemically clean the fire-side of the boilers, but infrequently 

removes ash with a water spray. Homer City cleans the water-side of Unit 3’s boiler every 10 

years using ethylenediaminetetraacetic acid (EDTA). The EDTA used is evaporated in the 

boiler. Homer City last cleaned the Units 1 and 2 boilers during 1988 and 1991, respectively. 

Water-side cleaning of the boilers is only rarely necessary because Homer City uses an 

oxygenated boiler water treatment process, described in Section 5.1. 
7

5.4 SCR Systems

 During the coal combustion that occurs in the boiler, the nitrogen in the air and 

coal reacts with oxygen to produce NOx. The SCR process is widely used for the removal of 

NOx from flue gases. For a general description of the SCR process, see Section 3.2.1.6 of the 

Interim Detailed Study Report for the Steam Electric Power Generating Point Source Category. 

 At Homer City, the SCR systems on Units 1 through 3 remove approximately 60 

to 90 percent of the NOx from the flue gas. Homer City currently operates the SCR systems 

from May 1 through September 30 each year. In 2009, Homer City will operate the SCR 

systems year round due to the Regional Haze Rule. 

 

 In each SCR system, anhydrous ammonia is diluted with air and injected onto 

three layers of ceramic catalyst. The ceramic catalyst operates between 600 and 650 °F. Each of 

the three layers contains 100 tons of catalyst. Catalyst activity levels are adversely affected by 

ash plugage, surface erosion, and chemical poisoning. Homer City attempts to prevent plugging 

issues and extend catalyst life, as the catalyst replacement cost for each layer of catalyst is 

approximately $2 million. According to Homer City, current industry research is focused on 

extending SCR catalyst life by reducing its reaction with metals in the flue gas. 

 The SCR systems for Units 1 through 3 are located downstream of the boiler and 

upstream of the air preheater and electrostatic precipitator (ESP). The plant injects only the 

amount of ammonia needed to convert the NOx in the flue gas to nitrogen and water. Excess 

unreacted ammonia from the SCR system, caused by flue gas fluctuations, is known as 

“ammonia slip.” As the flue gas passes over the catalyst in the SCR process, some of the sulfur 

dioxide is oxidized to sulfur trioxide, which combines with unreacted ammonia to form 

ammonium bisulfate. Ammonium bisulfate can cause fouling and corrosion in air heaters. The 

plant typically operates the SCR systems with less than two percent ammonia slip to avoid 

fouling the air preheater with the ammonium bisulfate byproduct. Typically, without bisulfate 

fouling, air heaters are washed once a year. One thousand gallons per minute (gpm) of ash 

recycle water is used and a typical air heater wash lasts for about 8 to 12 hours. 

 
8

5.5 Particulate Control

 As described in Section 5.2, ash is generated during the coal combustion process 

and fly ash is transported out of the boiler with the flue gas. Homer City utilizes ESPs to remove 

greater than 99.8 percent of the fly ash from the flue gas emitted from Units 1 through 3. Each 

ESP contains three to four separate cells. The ESPs use high voltage to generate an electric 

charge on the particles contained in the flue gas. The charged particles then collect on a metal 

plate with an opposite electric charge. To improve particle collection, the plant injects about 6 to 

12 parts per million (ppm) of anhydrous ammonia into the flue gas stream just upstream of the 

ESPs on Units 1 and 2. The ammonia helps agglomerate the particles, and these larger particles 

are more likely to stick to the charged plates. As the particles begin to layer on the metal plates, 

the plates are tapped/rapped to loosen the particles, which fall into a collection hopper. Units 1 

and 2 generate about 20 to 25 tons per hour (tph) of fly ash and Unit 3 generates about 35 to 40 

tph of fly ash. 

 There is no wastewater generated from the operation of the ESPs or fly ash 

handling system at Homer City. Fly ash is pneumatically transferred to silos where it is stored 

until it is trucked to the on-site unlined ash landfill or beneficially used at the on-site lined coal 

refuse site. Homer City adds water to the fly ash (12 percent moisture) to prevent the fly ash 

from blowing away during transport and to aid in compaction at the landfill. The fly ash cannot 

be used in cement manufacturing because it contains a significant amount of uncombusted coal 

due to the low NOx burners used in the boilers to meet RACT requirements. 

 

5.6 FGD System

 Homer City operates an FGD system on Unit 3, downstream of the ESP, to 

control the emission of sulfur dioxide from the unit. The FGD system is a five-level spray tower 

that uses limestone as the sorbent. For a general description of the FGD process and the 

chemical reactions involved, see Section 3.2.1.6 of the Interim Detailed Study Report for the 

Steam Electric Power Generating Point Source Category. 
9

 The plant has a limestone storage pile on site that contains approximately 30,000 

tons of Pennsylvania limestone. The plant uses a ball mill to crush the limestone on site. The 

limestone is mixed with blowdown water from the Unit 3 cooling tower to create the absorbent 

limestone slurry used in the FGD scrubber. Storm water from the limestone storage and 

handling area drains to a pond and the water is pumped into the FGD make up water tank. 

 The limestone slurry is pumped to the various levels of the scrubber tower 

(typically three or four levels out of the five are operated at one time) and sprayed downward 

into the scrubber. Figure B-1, in Appendix B, presents a photo of the scrubber spray tower. As 

the flue gas flows up through the tower, counter-current to the spray, the absorption of the flue 

gas sulfur dioxide occurs on the droplets of the absorbent slurry. To increase the sulfur dioxide 

removal efficiency of the scrubber, the plant adds formic acid to the system, which buffers the 

solution and aids in dissolution of the calcium carbonate. The plant previously used dibasic acid 

(DBA), but found that it reduced the selenium removal efficiency of the FGD wastewater 

treatment system, as discussed in Section 6.2. According to Homer City personnel, the FGD 

system removes approximately 97 to 99 percent of the sulfur dioxide from the Unit 3 flue gas. 

The addition of the formic acid increases the sulfur dioxide removal by approximately two 

percent and allows the plant to operate the system with one less spray level (i.e., up to four levels 

instead of all five). This reduced operating cost outweighs the additional cost to operate a 

biological reactor to remove the formic acid in the FGD wastewater treatment system, which is 

discussed in Section 6.2. 

 The FGD scrubber system uses about 1,000 gallons per minute (gpm) of water. 

Approximately 80 percent of this water leaves the system through the stack (stack gas is 14 

percent moisture). The majority of the water used in the scrubber system is used to continuously 

remove solids from the mist eliminator at the top of the scrubber. 

 In the FGD scrubber, the slurry that collects at the bottom of the scrubber is 

agitated to keep the solids in suspension. A forced oxidation system is used in which 

compressed air is introduced into the bottom slurry to further oxidize calcium sulfite to calcium 

sulfate (gypsum). The slurry is recycled up to the various spray levels until the chlorides 

concentration in the slurry reaches approximately 15,000 to 20,000 ppm. The spray tower is 
10

constructed of Inconel, a superalloy used in high temperature applications that is resistant to 

oxidation and corrosion. This material can withstand up to 25,000 ppm chlorides. When the 

slurry reaches the maximum allowable solids concentration, the plant blows down some of the 

slurry from the scrubber and adds fresh make-up limestone slurry to the scrubber. Homer City 

personnel estimated that blowdown occurs daily for approximately 12 to 18 hours. During 

blowdown, the solids level of the slurry typically decreases from 15 to 13 percent. 

 During blowdown, the gypsum slurry is sent to hydrocyclones, in which solid 

gypsum is separated from the water by centrifugal force. The solid gypsum is forced outward to 

the walls of the hydrocyclones and falls downward, while the water exits the top of the 

hydrocyclones. The gypsum from the hydrocyclones is transferred to vacuum filter belts. 

Approximately 80 percent of the supernatant overflow from the hydrocyclones is recycled back 

to the scrubber and the remaining 20 percent is transferred to the feed tank for the FGD 

wastewater treatment system, which is discussed in Section 6.2. Homer City has recently 

installed a second set of hydrocyclones to further reduce the solids content of the supernatant 

overflow before it is transferred to the FGD wastewater treatment system. 

 The gypsum is rinsed on the vacuum filter belt to reduce the chloride 

concentration. Blowdown from Unit 3’s cooling tower is used as rinse water. Figure B-2, in 

Appendix B, presents a photo of the gypsum rinse on the vacuum filter belt. As the gypsum is 

rinsed and dried, water that falls through or around the belt is collected and recycled back to the 

absorber. There is an optimal gypsum crystal size range for manufacturing wallboard, and the 

pores of the vacuum filter belts are sized accordingly. If the gypsum crystals are too small, they 

pass through the pores and are recycled back to the scrubber where they continue to grow. The 

gypsum typically contains 30 to 40 percent moisture at the beginning of the vacuum filter belt 

and 10 percent moisture at the end in the final gypsum product. The gypsum falls off the 

vacuum filter belt and is conveyed to a domed structure for storage (see Figures B-3 and B-4). 

Homer City produces gypsum that is light in color and contains less than one percent impurities, 

which is mostly fly ash. Homer City produces about 1,000 tons of gypsum per day and sells it to 

a wallboard manufacturer in Pittsburgh for about $1/ton. 

 
11

5.7 Biofouling Control

 Each of the three generating units at Homer City has a recirculating cooling 

tower. The cooling towers are hyperbolic and are open at the bottom. The intake water for the 

cooling systems is treated using chemical precipitation, as discussed in Section 5.1. The cooling 

tower blowdown from Unit 3’s cooling tower is used as gypsum rinse water, limestone slurry 

makeup water, and mist eliminator spray water. Units 1 and 2 cooling tower blowdown is 

currently directed back to Two Lick Creek via NPDES Outfall #001, but will be utilized as 

makeup for the Units 1 and 2 FGD scrubbers in the future. 

 Homer City uses quaternary amine for biofouling control in the cooling towers for 

Units 1 and 2, and sodium bromide in Unit 3’s cooling tower. Quaternary amine is not used in 

Unit 3’s cooling tower because it would cause foaming in the scrubber. Homer City uses these 

biocides year-round and uses slightly more during summer. Homer City adds the biocides three 

times per week. Typically, the cooling tower blowdown loop is closed for about eight hours 

after addition of the biocide to allow it to degrade to a non-detect level. The plant typically 

discharges cooling tower blowdown approximately 24 hours/day 7 days/week. 

 

6.0 WASTEWATER TREATMENT

 Homer City operates three systems on site for treatment of wastewaters. This 

section discusses these treatment systems: 

• Bottom ash treatment; 

• FGD wastewater treatment; and 

• Industrial Wastewater Treatment. 

6.1 Bottom Ash Treatment

 Homer City operates four ash settling ponds. Two ash settling ponds are typically 

in use at one time and are operated in parallel. Each ash pond has an approximate volume of 

1.76 million gallons. Figure B-6, in Appendix B, presents a photo of the bottom ash settling 

ponds. The ash settling ponds receive overflow from the bottom ash hydrobins (discussed in 

Section 5.3) and storm water runoff. Approximately six acres of storm water drains into the 
12

ponds from the ash handling and precipitator areas. Water is transferred from the ash settling 

ponds to a clear well via weirs, which are on the opposite side of the ponds from the inlet pipes. 

From the clear well, water is recycled for use as bottom ash sluice. There is a periodic discharge 

from the clear well through the NPDES Outfall #005, the frequency of which depends on the 

amount of rainfall that has been received. Ash recycle discharge water is limited to less than 30 

mg/L average TSS and a pH of 6.0 to 9.0 s.u. The ash settling ponds are cleaned every six to 

eight months. The recovered solids are transported to the on-site, unlined fly ash landfill. 

6.2 FGD Wastewater Treatment

 Overflow from the FGD hydrocyclones, discussed in Section 5.6, is transferred to 

the feed tank of the FGD wastewater treatment system. The feed tank is agitated to prevent 

calcium from settling out and scaling the tank. The hydraulic residence time in the 150,000 

gallon feed tank is about 22 hours. Homer City typically maintains the wastewater volume in the 

feed tank at about 40 to 80 percent of the total tank volume. Figure B-7 presents a photo of the 

feed tank. Figure 6-1 presents a flow diagram of Homer City’s FGD wastewater treatment 

system. Water from the feed tank is transferred continuously (24 hours per day) to a 1st stage 

neutralization tank, in which lime is added to adjust pH of the wastewater from 6.0 to 8.1. The 

plant adds the following to the 1st stage neutralization tank: ferric chloride for metals 

precipitation; and cationic polymer and air to further enhance the precipitation/coagulation. 

From the 1st stage neutralization tank, the wastewater is transferred to the 1st stage clarifier, in 

which anionic polymer is added for coagulation. The majority of the heavy solids (mainly 

calcium sulfate and calcium carbonate) are removed in the 1st stage clarifier. Figure B-8 presents 

a photo of the 1st stage clarifier. 

 Homer City personnel indicated that excess solids entering the 1st stage clarifier 

can interfere with metals precipitation and removal. In particular, Homer City is concerned 

about interference with selenium removal, which affects their ability to meet their NPDES permit 

limit. In an attempt to reduce the interference with metals removal in the 1st stage clarifier, 

Homer City recently added a second set of hydrocyclones to the gypsum dewatering system for 

additional gypsum solids removal upstream of the FGD wastewater treatment system, as 

Comment [MSOffice2]: NOTE TO 

EPA: I’m assuming this means ESP areas 

and that this means there could be a bit of 

fly ash in the ash ponds. 

Comment [MSOffice3]: NOTE TO 

EPA: This is how Homer City responded 

to the question about requirements for reuse. I’m assuming they mean that the 

discharge from the clear well is limited to 

less than 30 TSS, and because the recycle 

water originates from the clear well, it 

has the same characteristics. So, Homer 

City has not answered the original 

question, but we can possibly find this 

out when we are on site. 
13

discussed in Section 5.6. The secondary hydrocyclones ensure that less than one percent solids 

enter the FGD wastewater treatment system. 

 Water from the 1st stage clarifier is transferred to the 2nd stage neutralization tank, 

in which lime is added to adjust the wastewater pH to 8.1. The plant adds the following to the 

2nd stage neutralization tank: ferric chloride for metals precipitation; and air and occasionally 

cationic polymer to further enhance the precipitation/coagulation. When the plant initially began 

operating the FGD wastewater treatment system, it also added organosulfide to the 2nd stage 

neutralization tank for mercury removal; however, the plant has since determined that sufficient 

mercury removal can be achieved without the addition of organosulfide. 

 From the 2nd stage neutralization tank, wastewater is transferred to the 2nd stage 

clarifier, in which anionic polymer is added for coagulation. The 1st and 2nd stage clarifiers are 

each approximately 50,000 gallons. The hydraulic residence time across each of the 50,000-

gallon 1st and 2nd stage clarifiers is approximately 7.5 hours. Homer City has observed greater 

metals removal in the 2nd stage clarifier than the 1st stage clarifier, due to a better iron hydroxide 

floc, which plant personnel attribute to the lower solids content in the 2nd stage clarifier. Figure 

B-9 presents a photo of the 2nd stage clarifier. Sludge from the clarifiers is transferred to a 

thickener and then to a vacuum filter. Some sludge from the clarifiers and thickener is recycled 

to the 1st stage neutralization tank to prevent scaling on the tank walls. Recycling the sludge 

introduces crystals into the tank and scaling preferentially occurs on the crystal surfaces. 

 Overflow from the 2nd stage clarifier is transferred to the pH adjustment tank, in 

which micronutrients (typically urea), phosphoric acid, and corn syrup are added to ensure 

growth of microorganisms in the biological reactor. In the past, Homer City has added HCl or 

lime to adjust the pH to 7.5 to 8.0 prior to biological treatment; however, the overflow from the 

2nd stage clarifier is typically at the appropriate pH and therefore adjustment is not necessary. 
14

Overflow 

from 

Hydrocyclones WWT Feed 

Tank

1st Stage 

Neutralization 

Tank

Vacuum 

Filter

Thickener

Sand 

Filters

Heat 

Exchanger

pH 

Adjustment 

Tank

2nd Stage 

Clarifier

2nd Stage 

Neutralizaiton 

Tank

1st Stage 

Clarifier

Outfa

027 

Filter 

Backwash

Sludge to 

On-Site 

Landfill

Biological 

Reactor

Effluent 

Tank

Sludge

Sludge Recycle

Lime

Ferric 

Chloride Air

Nutrients,

Phosphoric Acid,

Polymer Polymer Lime Polymer Corn Syrup

Ferric 

Chloride Air Polymer

Sump

Figure 6-1. FGD Wastewater Treatment System at Homer City
15

 From the pH adjustment tank, water is transferred through a heat exchanger to the 

biological reactor. The microorganisms in the aerobic biological reactor reduce the organic 

content and the associated biochemical oxygen demand (BOD) of the wastewater. BOD in the 

FGD wastewater is a result of the formic acid that is added to the limestone slurry. Figure B-10 

presents a photo of the aeration in the biological reactor. Flow through the biological reactor is 

continuous. The hydraulic residence time in the 350,000 gallon biological reactor is about 2 

days. Sludge from the biological reactor is transferred to the thickener, where it is combined 

with the clarifier sludge and then transferred to the vacuum filter. The vacuum filter reduces the 

sludge moisture content from approximately 60 to 70 percent down to 20 percent. Figure B-12 

presents a photo of the vacuum filter. Homer City generates twenty-five tons per day of filter 

cake (mostly calcium sulfate/gypsum) from the vacuum filters, which the plant tests to ensure 

compliance with leachability requirements and then disposes of in the on-site, unlined fly ash 

landfill. 

 

 Wastewater from the biological reactor is transferred through sand filters. 

Wastewater from the sand filters is transferred continuously to an effluent tank, except when the 

filters are backwashed. Homer City backwashes the sand filters once every 12 hours for about 

15 minutes. The backwash is directed to a sump, which also collects all floor drain wastewater. 

Wastewater from the sump is transferred to the FGD wastewater treatment system feed tank a 

few times per day (about 4,000 gallons per transfer). 

 Wastewater from the effluent tank is discharged through NPDES Outfall #027 to 

Blacklick Creek. Homer City estimates that the hydraulic residence time in the 3,000 gallon, 

agitated effluent tank is approximately 12 to 13 minutes. 

 The flow rate exiting the feed tank of the FGD wastewater treatment system is 

typically about 110 gpm. Homer City typically adds about 10 to 20 gpm of chemical feed to the 

FGD wastewater treatment system; therefore, the flow rate exiting the FGD wastewater 

treatment system averages approximately 120 gpm. The flow rate exiting the effluent tank varies 

from about 70 to 170 gpm due to the operation of the variable frequency drive that maintains a 

constant level in the effluent tank; the average flow rate is approximately 120 gpm. The 
16

hydraulic residence time for the entire FGD wastewater treatment system is approximately 3.5 

days. 

 The original FGD wastewater treatment system equipment and installation cost 

was $1,983,000 in 2001. Approximately 50 percent of the total cost was for equipment and 50 

percent of the total cost was for installation. Since the 2001 FGD wastewater treatment system 

startup, EME Homer City has invested an additional $1,653,000 in plant equipment, process 

upgrades, and selenium removal research. The FGD wastewater treatment system annual 

operation and maintenance costs have averaged approximately $200,000 per year from 2003 to 

2006. Currently, EME Homer City is further studying the selenium removal chemistry across 

the FGD wastewater treatment system in order to optimize plant performance. 

6.3 Industrial Wastewater Treatment (IWT) System

 Homer City operates an industrial wastewater treatment (IWT) system that treats 

wastewaters from the coal pile runoff ponds, the demineralizer regeneration system, plant roof 

and floor drains, and parking lot storm water drains. Homer City operates the treatment ponds of 

the IWT like the bottom ash settling ponds, in which two ponds are in use at one time; however, 

Homer City can isolate each pond to facilitate cleansing. Attached drawings. The IWT ponds 

discharge through the IWT plant and then to NPDES Outfall #005. 

7.0 REFERENCES

1. U.S. EPA. 2006. Interim Detailed Study Report for the Steam Electric Power 

Generating Point Source Category. EPA-821-R-01-015. Washington, DC. 

November. DCN 01923. 

Comment [MSOffice4]: NOTE TO 

EPA: Do you know what this note from 

Homer City refers to? 
Appendix A 

LIST OF ATTENDEES 
A-1 

Table A-1. List of Attendees 

Name Organization (Representing) Telephone E-mail Thomas Hickes EME Homer City Generation L.P. (724) 479-6145 thickes@mwgen.com Gary Cline EME Homer City Generation L.P. (724) 479-6255 gcline@mwgen.com Jeff Bard Midwest Generation EME (312) 583-6105 jbard@mwgen.com Maria Race Midwest Generation EME (312) 583-6062 mrace@mwgen.com Dana Krach Pennsylvania DEP (412) 442-4202 Kristin Margut Pennsylvania DEP (814) 472-1932 Kareen Milcic Pennsylvania DEP (412) 442-4033 Donna Hill Southern Company (205) 257-5234 dbhill@southernco.com Lindy Johnson Tennessee Valley Authority (423) 751-3361 lpjohnson@tva.gov Liz Aldridge Hunton & Williams (804) 788-8549 ealdridge@hunton.com Mindy Gampel EPA/OPEI (202) 564-1213 gampel.mindy@epa.gov Josh Hall EPA/Office of Water (202) 566-1002 hall.josh@epa.gov Ron Jordan EPA/Office of Water (202) 566-1003 jordan.ronald@epa.gov Jan Matuszko EPA/Office of Water (202) 566-1035 matuszko.jan@epa.gov Ahmar Siddiqui EPA/Office of Water (202) 566-1044 siddiqui.ahmar@epa.gov T.J. Finseth ERG (Contractor to EPA) (703) 633-1698 thomas.finseth@erg.com Sarah Holman ERG (Contractor to EPA) (703) 633-1661 sarah.holman@erg.com 
Appendix B 

PHOTOS FROM SITE VISIT
B-1 

Figure B-1. FGD Scrubber Spray Tower at Homer City 
B-2 

Figure B-2. Gypsum Rinse on Vacuum Filter Belt at Homer City 
B-3 

Figure B-3. Gypsum Final Product on Vacuum Filter Belt at Homer City 
B-4 

Figure B-4. Gypsum Storage Dome at Homer City 
B-5 

Figure B-5. Bottom of Cooling Tower for Unit 3 at Homer City 
B-6 

Figure B-6. Bottom Ash Settling Ponds at Homer City 
B-7 

Figure B-7. FGD Wastewater Treatment Feed Tank at Homer City 
B-8 

Figure B-8. FGD Wastewater Treatment 1st Stage Clarifier at Homer City 
B-9 

Figure B-9. FGD Wastewater Treatment 2nd Stage Clarifier at Homer City 
B-10 

Figure B-10. FGD Wastewater Treatment Biological Reactor at Homer City 
B-11 

Figure B-11. FGD Wastewater Treatment Clarifiers and Biological Reactor at Homer City 
B-12 

Figure B-12. FGD Wastewater Treatment Vacuum Filter at Homer City