# 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 4-22i TABLE OF CONTENTS

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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 Treatmen t (IWT) System................................................... 16

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

Appendix A LIST OF ATTENDEES Appendix B PHOTOS FROM SITE VISITii LIST OF TABLES

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A-1 List of Attendees................................................................................................. A-1iii LIST OF FIGURES

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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 2 nd Stage Clarifier at Homer City ......................... B-9

B-10 FGD Wastewater Treatment Biol ogical 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-121 1.0 S ITE V ISITED AND D ATE

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 A TTENDEES

Appendix A lists the attendees.

3.0 B ACKGROUND AND O BJECTIVES

Section 304(m) of the Clean Water Act (CWA) requires EPA to develop and publish a biennial plan that establishes a schedul e 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 determin ed 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 to xic-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 po llution 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 oper ations 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 P LANT D ESCRIPTION

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-hr s) 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 w ith 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 come3 into compliance with new permit limits, and the me rcury 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 P LANT O PERATIONS

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 desc ription of the steam el ectric 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 th e 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 a nd 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, produc ing 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 stat ed 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 proc ess 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 wher e 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 Co al 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 16 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 wate r 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 proc ess, 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 pois oning. 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 ar e 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 SC R 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 bisu lfate 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 particle s, 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 th e 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 th e 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 is10 constructed of Inconel, a superalloy used in high temperature applications that is resistant to

oxidation and corrosion. This material can wi thstand up to 25,000 ppm chlorides. When the slurry reaches the maximum allowable solids conc entration, 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 crysta l size range for manufacturing wallboard, and the pores of the vacuum filter belts are sized accordingl y. 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 precipita tion, 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 elimin ator 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 W ASTEWATER T REATMENT

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 p onds. 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. Approximate ly six acres of storm water drains into the12 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 1 st 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 1 st stage neutralization tank: ferric chloride for metals precipitation; and cationic polymer and air to fu rther enhance the precipitation/coagulation.

From the 1 st stage neutralization tank, the wastewater is transferred to the 1 st 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 1 st stage clarifier. Figure B-8 presents a photo of the 1 st stage clarifier.

Homer City personnel indicated that excess solids entering the 1 st 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 1 st 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 characte ristics. 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 1 st stage clarifier is transferred to the 2 nd stage neutralization tank, in which lime is added to adjust the wastewater pH to 8.1. The plant adds the following to the

2 nd 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 2 nd 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 2 nd stage neutralization tank, wastewater is transferred to the 2 nd stage clarifier, in which anionic polymer is added for coagulation. The 1 st and 2 nd stage clarifiers are each approximately 50,000 gallons. The hydraulic residence time across each of the 50,000- gallon 1 st and 2 nd stage clarifiers is approximately 7.5 ho urs. Homer City has observed greater

metals removal in the 2 nd stage clarifier than the 1 st stage clarifier, due to a better iron hydroxide floc, which plant personnel attribute to the lower solids content in the 2 nd stage clarifier. Figure B-9 presents a photo of the 2 nd 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 1 st stage neutralization tank to prevent scaling on the tank walls. Recycling the sludge introduces crystals into the tank and scalin g preferentially occurs on the crystal surfaces.

Overflow from the 2 nd 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

2 nd stage clarifier is typically at the appropriate pH and therefore adjustment is not necessary.14OverflowfromHydrocyclonesWWT FeedTank1stStageNeutralizationTankVacuumFilterThickenerSandFiltersHeatExchangerpHAdjustmentTank2ndStageClarifier2ndStageNeutralizaitonTank1stStageClarifierOutfall027FilterBackwashSludge toOn-SiteLandfillBiologicalReactorEffluentTankSludgeSludge RecycleLimeFerricChlorideAirNutrients,Phosphoric Acid,Corn SyrupPolymerPolymerPolymerLimeFerricChlorideAirPolymerSumpFigure 6-1. FGD Wastewater Treatment System at Homer City15 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 th e 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 Ci ty 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 th e hydraulic residence time in the 3,000 gallon, agitated effluent tank is approxi mately 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. The16 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 add itional $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 R EFERENCES

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 ATTENDEESA-1Table A-1. List of AttendeesNameOrganization (Representing)TelephoneE-mailThomas Hickes EME Homer City Generation L.P. (724) 479-6145 thickes@mwgen.comGary Cline EME Homer City Generation L.P. (724) 479-6255 gcline@mwgen.comJeff Bard Midwest Generation EME (312) 583-6105 jbard@mwgen.comMaria Race Midwest Generation EME (312) 583-6062 mrace@mwgen.comDana Krach Pennsylvania DEP (412) 442-4202Kristin Margut Pennsylvania DEP (814) 472-1932Kareen Milcic Pennsylvania DEP (412) 442-4033Donna Hill Southern Company (205) 257-5234 dbhill@southernco.comLindy Johnson Tennessee Valley Authority (423) 751-3361 lpjohnson@tva.govLiz AldridgeHunton & Williams(804) 788-8549 ealdridge@hunton.comMindy Gampel EPA/OPEI (202) 564-1213 gampel.mindy@epa.govJosh Hall EPA/Office of Water (202) 566-1002 hall.josh@epa.govRon Jordan EPA/Office of Water (202) 566-1003 jordan.ronald@epa.govJan MatuszkoEPA/Office of Water(202) 566-1035 matuszko.jan@epa.govAhmar Siddiqui EPA/Office of Water (202) 566-1044 siddiqui.ahmar@epa.govT.J. Finseth ERG (Contractor to EPA) (703) 633-1698 thomas.finseth@erg.comSarah Holman ERG (Contractor to EPA) (703) 633-1661 sarah.holman@erg.comAppendix B

PHOTOS FROM SITE VISITB-1 Figure B-1. FGD Scrubber Spray Tower at Homer CityB-2 Figure B-2. Gypsum Rinse on Vacuum Filter Belt at Homer CityB-3 Figure B-3. Gypsum Final Product on Vacuum Filter Belt at Homer CityB-4 Figure B-4. Gypsum Storage Dome at Homer CityB-5 Figure B-5. Bottom of Cooling Tower for Unit 3 at Homer CityB-6 Figure B-6. Bottom Ash Settling Ponds at Homer CityB-7 Figure B-7. FGD Wastewater Treatment Feed Tank at Homer CityB-8 Figure B-8. FGD Wastewater Treatment 1st Stage Clarifier at Homer CityB-9 Figure B-9. FGD Wastewater Treatment 2 nd Stage Clarifier at Homer CityB-10 Figure B-10. FGD Wastewater Treatment Biological Reactor at Homer CityB-11 Figure B-11. FGD Wastewater Treatment Clarifiers and Biological Reactor at Homer CityB-12 Figure B-12. FGD Wastewater Treatment Vacuum Filter at Homer City