# FINAL Engineering Site Visit Report for Tennessee Valley Authority’s Widows Creek Fossil Plant Stevenson, AL

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

July 18, 2007

EPA Contract No. 68-C02-095 Work Assignment 4-22i TABLE OF CONTENTS
Page

1.0 S ITE V ISITED AND D ATE .......................................................................................... 1

2.0 A TTENDEES .............................................................................................................. 1

3.0 B ACKGROUND AND O BJECTIVES .............................................................................. 1

4.0 P LANT D ESCRIPTION ................................................................................................ 2

5.0 P LANT O PERATIONS ................................................................................................. 3 5.1 Coal Preparation.......................................................................................... 3 5.2 Boiler Operation.......................................................................................... 4 5.3 Selective Catalytic Re duction Operation.................................................... 4 5.4 Particulate Control ...................................................................................... 6 5.5 FGD System................................................................................................ 7 5.6 Biofouling Control...................................................................................... 8 5.7 Metal Cleaning Operation........................................................................... 8

6.0 W ASTEWATER M ANAGEMENT ................................................................................. 9 6.1 Intake Water................................................................................................ 9 6.2 Coal Pile Runoff ....................................................................................... 11 6.3 Low-Volume Waste.................................................................................. 11 6.4 Metal Cleaning Waste............................................................................... 11 6.5 Cooling Water........................................................................................... 12 6.6 Ash Handling Water ................................................................................. 12 6.7 FGD System Wastewater.......................................................................... 14

7.0 R EFERENCES .......................................................................................................... 15
Appendix A LIST OF ATTENDEES Appendix B PICTURES FROM SITE VISITii LIST OF TABLES
Page

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

6-1 Wastewater Flow Di agram for Widows Creek......................................................10

B-1 Coal Pile Runoff Pond at Widows Creek ............................................................B-1

B-2 Ash Pond Dike at Widows Creek ........................................................................B-2

B-3 Ash Pond at Widows Creek .................................................................................B-3
B-4 Cenospheres Collected from the Ash Pond at Widows Creek.............................B-4
B-5 Pumping Basin at Widows Creek ........................................................................B-5

B-6 Constructed Wetland Cells for the Ol d Ash Pond Runoff at Widows Creek ......B-6
B-7 Gypsum Pond at Widows Creek..........................................................................B-7
B-8 Gypsum Pond Discharge to Widows Creek.........................................................B-81 1.0 S ITE V ISITED AND D ATE

Tennessee Valley Authority’s (TVA’s) Widows Creek Fossil Plant County Road 96 Stevenson, AL 35772
December 12, 2006

2.0 A TTENDEES

Appendix A lists the attendees.

3.0 B ACKGROUND AND O BJECTIVES

Section 304(m) of the Clean Water Ac t (CWA) requires EPA to develop and publish a biennial plan that esta blishes a schedule for the annual review and revision of national effluent limitations guidelines and standards (E LGs) 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 to xic-weighted loadings are predominantly driven by metals present in wastewater discharges, and that the wastestreams contributing the majority of the metals are associated with air pollution co ntrols. Other potential s ources 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 fu rther review of these discharges during the 2007/2008 ELG planning cycle is warra nted. 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 t echnologies/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 ope rations and better un derstand the various wastewater sources present at steam electric plants . This review is expected to largely focus on ash handling wastes, wet flue gas desulfurizati on (FGD) wastes, coal p ile runoff, and final
effluent.

EPA and its contractor, Eastern Resear ch Group, Inc. (ERG), conducted a site visit to TVA’s Widows Creek Fossil Plant (W idows Creek) on December 12, 2006. 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 pr actices used to control the discharges; and 2) determine the feasibility of collecting and anal yzing wastewater samples from steam electric power plants.

4.0 P LANT D ESCRIPTION

TVA’s Widows Creek plant began operation in July 1952, when Unit 1 came on line. Units 2 through 6 were also completed in the early 1950’s. The plant added Units 7 and 8 in the early 1960’s, with Unit 8 beginning operati on in February 1965. At the time Unit 8 began operation, the Widows Creek plant wa s the largest power plant in the world. All eight of the generating units have coal-fired boilers, with a combined total capacity of 1,630 megawatts (MW); however, Units 7 and 8 account for approximate ly 55 percent of the capacity at the plant. On a yearly average, the plant generates appr oximately 65 percent of its available capacity. Widows Creek is located on approximately 1,300 acr es of land in Stevenson, Alabama, beside
the Guntersville Reservoir on the Tennessee River.

In 1970, Widows Creek retrofitted Unit 8 and in 1981 Unit 7 with FGD scrubbers
to control the sulfur dioxide releases from the plant. In 2003/2004, the plant also retrofitted Units 7 and 8 with selective catalytic reducti on (SCR) operations to control nitrogen oxide releases from the plant. The installation of th ese air pollution control devices not only reduces the sulfur dioxide and nitrogen oxide emissions, but it also reduces the mercury emissions from the plant. According to the EPRI representative , Widows Creek has some of the lowest mercury air emissions of any power plant in the country.3 Units 1 through 6 at Widows Creek use a low-sulfur coal, which produces less sulfur dioxide emissions than a high-sulfur coal . In addition, Units 1 through 6 are also equipped with boiler optimization controls, which limit the production of nitrogen oxides.

5.0 P LANT O PERATIONS

Each of the eight generating units at Wi dows Creek has a coal-fired boiler. The plant uses approximately 15,000 tons of coal per day for the eight units. Each of the units generates wastewater; however, the quantity and characterization of the waste streams varies depending on the unit ch aracteristics.

The Widows Creek site visit focused on the generating units and the wastewaters associated with these units. For a general de scription of the steam electric power generation process, see Section 3.2.1 of the Interim Detailed Study Report for the Steam Electric Power Generating Point Source Category . The remainder of this sec tion describes the following seven operations at Widows Creek:

y Coal preparation;

y Boiler operation;

y SCR operation;

y Particulate control (inclu des wet fly ash handling);

y FGD system operation;

y Biofouling control; and

y Metal cleaning operations.

5.1 Coal Preparation

The Widows Creek plant uses two different types of coal; a low-sulfur coal in Units 1 through 6 from the 20 Mile and Bowie mi nes in Colorado and a higher-sulfur coal in Units 7 and 8 from the Warrior, Pattiki, and Galatia mines in the Illinois Basin area. Because the plant uses two different types of coal, the plant manages two coal piles situated within the same area. Although there are two sepa rate coal piles, all of the st orm water runoff that contacts the coal is collected in a single pond.4 For each unit, the plant tran sports the coal from the co al pile to individual unit bunkers by conveyor belts, which are covered. Fr om the bunkers, the coal is sent to the pulverizers, where it is ground into a fine powder that is blown into the boiler using air. Some of the coal entering the pulverizers is too hard to be pulverized; these pyrites (rock-like coal pieces) are collected in a reject bin. The plant breaks the pyrites into smaller piec es, sluices them with a water stream, and transpor ts it to the ash pond.

5.2 Boiler Operation

As the pulverized coal is blown into the bo iler, it is combusted and gives off heat. The heat produced in the boiler is used to convert water into high-pressure st eam. 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 boiler are referred to as bottom ash. The finer particles that are light enough to be transfer red out of the boiler with the flue gas exhaust are referred to as fly ash. At Widows Creek, a continuous stream of sl uice water collects and removes the bottom ash and other slag from the bottom of the boiler. The fly ash is also sluiced from the particulate control devices, as desc ribed in Section 5.4. In addition, the plant periodically generates wastewater from washi ng the fire-side of the boiler. Wastewater associated with boiler cleaning is discussed in greater detail in Sections 5.7 and 6.4.

The plant uses purified water in the bo iler, which is converted by the heat of combustion into high-pressure steam. Widows Cr eek employs a contractor-operated portable reverse osmosis (RO) system to produce this pur ified water, using fresh intake water from the Tennessee River. The pure water is stored on-site . The contractor hauls the RO resin bed from the system off site for regeneration; therefore, there is no wastewater from reverse osmosis regeneration processes discharg ed on site. RO reject water goes to the Unit 1-6 intake.

5.3 Selective Catalytic Reduction Operation

During the coal combustion that occurs in the boiler, the nitrogen in the air reacts with the oxygen at the elevated temper atures to produce nitrogen oxides (NO x ). SCR is a widely used practice for the removal of n itrogen oxide from flue gases. For a general description of the5 SCR process, see Section 3.2.1.6 of the Interim Detailed Study Report for the Steam Electric Power Generating Point Source Category

.

Widows Creek has SCR systems installed for Units 7 and 8. For Unit 7, the SCR system is located downstream of the boiler and upstream of th e air preheater, electrostatic precipitator (ESP), and the FGD system. For Unit 8, the SCR system is located upstream of the air preheater and the FGD system; however, ther e is no ESP for Unit 8. Because there is no ESP for Unit 8, the FGD system removes the fly ash and other particulates from the flue gas. The SCR uses ammonia to facilitate converting the NO x in the flue gas to nitrogen and water. Excess unreacted ammonia from the SCR system is known as “ammonia slip.” The plant can monitor for ammonia slip by analyzing the ash removed from the ESPs because at least part of the
ammonia will collect on the ash. Widows Creek collects ash samples on a weekly basis during ozone season and analyzes them in a laborator y for ammonia to determine the amount of “slip” that has occurred. According to the plant, if ammonia slip begins to occur, it may be a sign that the catalysts are running out of useful life and may need to be replaced.

As the flue gas passes over the catalyst in the SCR process, some of the sulfur
dioxide is oxidized to sulfur tr ioxide. Emissions of this sulf ur trioxide contribute to the
formation of acid rain in the environment. To control the formation of sulfur trioxide, Widows Creek injects sodium sulfite into the flue gas to remove the sulfur trioxide; however, this addition
of sodium sulfite can lead to plugging issues in th e air preheater. Widows Creek injects the sodium sulfite upstream of the air pre-heaters in Unit 7. Widows Creek injects lime into Unit 8.

There are no wastewater discharges dire ctly associated with the SCR systems at the plant; however, the presence of an SCR can affect the characteristics of the fly ash sluice water discharge from the ESP downstream of the S CR. For example, if ammonia slip does occur in the system, it is transported with the fly as h to the ash pond. In addition, at Widows Creek, ammonia slip can also affect the gypsum slurry discharges from Unit 8, because the FGD system acts as the fly ash removal system. Ammonia may al so be present in wash water discharges from cleaning air preheaters, since am monia can deposit on preheater surfaces. Most of the fly ash sluice water at Widows Creek is recycled after se ttling, either to the Units 7 and 8 intake and/or the FGD makeup water system, discussed later in Section 6.6. Gypsum slurry discharges are6 ultimately discharged to the Tennessee River fr om the gypsum ponds, as discussed in Section
6.7. Sodium bisulfate/sodium sulfite injection is used in Unit 7 as needed for opacity control. These chemicals may be ultimately discharged via the ash pond.

5.4 Particulate Control

As described in Section 5.2, ash is gene rated during the coal combustion process and fly ash is transported out of the boiler with the flue gas. Widows Creek utilizes ESPs to remove the fly ash from the flue gas emitted from Units 1 through 7. The ESP systems use high voltage to generate an electric charge on the part icles contained in the flue gas. The charged particles then collect on a metal plate with an oppos ite electric charge. As the particles begin to layer on the metal plates, the plates are tapped/rapped to loosen th e particles, which fall into a collection hopper. The ESPs are the only emi ssion controls on Units 1 through 6; however lowNO x boiler optimization is used to control for NO x emissions and low sulfur coal is burned for
SO 2 emission control. The ESP for Unit 7 is lo cated downstream of the SCR and upstream of
the FGD scrubber.

Widows Creek uses a wet fly ash handling system. The fly ash that is collected
from the ESP is sluiced from the collection hoppers with some of the intake water and transported to the ash pond. The intake water used for sluicing is screen ed prior to its use; however, the plant does not require the water to meet any speci fic characteristics to be used in the sluicing process.

Unit 8 does not have a dedicated partic ulate control system, instead, the FGD scrubber system, discussed in Sect ion 5.5, controls the particulates in the flue gas for the unit in addition to the sulfur dioxide. The plant is curr ently investigating the use of an agglomerator for additional particulate control on Unit 8. In an aggl omerator, some of the particles in the flue gas are given a positive charge and some are given a negative charge. The positive and negative particles are then attracte d to each other, and they clump together forming a larger particle that is more easily removed in a particulate cont rol devices (e.g., ESP, FGD scrubber). The agglomerator itself does not remove the large pa rticles from the system; however, these larger particles can be easily removed from the flue gas using an E SP or other air pollution control7 devices, such as the Unit 8 wet FGD scrubber. Plant personnel do not expect any wastewater generated from the operation of the agglomerat or. In May 2007, Widows Creek began operating an agglomerator on one of the Unit 8 FGD modules . Widows Creek is testing and evaluating the performance of the agglomerator to determine whether to install it on the other Unit 8 FGD
modules.

5.5 FGD System

The Widows Creek plant operates FGD sy stems on Units 7 and 8 to control the
emission of sulfur dioxide from the units. Unit 7 has a spray tower FGD system and Unit 8 has a spray tower FGD system using double contact fountai n sprays. For a general description of the FGD process and the chemical reacti ons involved, see Section 3.2.1.6 of the Interim Detailed Study Report for the Steam Electric Power Generating Point Source Category

.

The spray tower on Unit 7 utilizes an open vessel, where the absorbent liquid (limestone-in-water slurry) is pressurized and sprayed into the vessel through spray nozzles at
various levels. As the absorben t liquid is sprayed dow nward into the vessel, and the flue gas flows counter-currently to the sp ray, the absorption of the flue gas sulfur dioxide occurs on the droplets of the absorbent. The spray tower F GD system on Unit 7 achieve s an 85 to 90 percent removal of sulfur dioxide from the flue gas.

The spray tower on Unit 8 utilizes an open vessel, where the absorbent liquid (limestone-water-slurry) is pressurized and spra yed into the vessel through spray nozzles at the bottom of the spray tower at one level. The spray nozzles create a fountain spray. This fountain spray tower design creates double co ntact between the flue gas and droplets of the absorbent. This spray tower design achieves 94 to 96 percen t removal of sulfur dioxide. In addition to removing sulfur dioxide from the flue gas, the sc rubber system also removes the fly ash from the flue gas in lieu of a precipitator.

Both of the FGD systems at Widows Creek use ash pond discharge water or
Tennessee River water as the water source fo r the FGD scrubbers. Widows Creek does not require the water used in the FGD system to meet any specific characteristics for its use in the8 process. In addition, both systems are once-thro ugh FGD systems, wherein the gypsum slurry at the bottom of the scrubber system is not recycled within the F GD system, but instead is pumped directly to the plant’s gypsum ponds.

Both of the FGD systems at Widows Creek introduce an air stream to oxidize the sulfite product into gyps um, a more useful by-product. Beca use the FGD system on Unit 8 also removes the fly ash from the flue gas, the gypsum slurry discharged from the system contains fly ash particulates, as does the resultant gypsum byp roduct. Plant personnel noted that because the gypsum by-product is not a pure product, it inhib its the sale of the gyps um from Widows Creek.

5.6 Biofouling Control

Each of the eight units at Widows Cr eek uses a once-through cooling system. The plant uses water from the Tennessee River a nd sends it through each of the unit condensers. From the condensers, the plant tr ansports the cooling water to a canal that discharges to the Tennessee River. The cooling water is screened prior to its use; howev er, the plant does not require the water to meet any specific charact eristics to be used in the once-through cooling system.

The Widows Creek plant does not currently use chlorine or other biocides for biofouling control. Instead, the plant has two wa ter boxes for each of the condensers. The plant has the capability to backwash one water box while the other is ope rating. In addition, approximately two times a year, the plant uses ny lon brushes to clean the condenser tubes. The wastewater generated during thes e cleaning operations is reintr oduced into the cooling water waste stream and subsequently discharged.

5.7 Metal Cleaning Operation

Widows Creek has routine outages du ring the year, during which the plant performs maintenance and cleani ng of the process equipment. During these scheduled outages, the plant may clean the water-side of the boilers with ethylenediaminetetr aacetic acid (EDTA) to remove scale and deposits from the boiler tubes. The wastewater cont aining EDTA from the9 cleaned boiler tubes is collected in storage tanks. The wastewater is then evaporated in the boiler of another operating unit.

Widows Creek does not regular ly clean the fire-side of the boiler tubes; however, when they are cleaned, the plant uses raw river wate r. After the cleaning process is complete, the plant pumps the wastewater to the ash pond.

6.0 W ASTEWATER M ANAGEMENT

Widows Creek generates ma ny different types of wastew ater during the operation of the coal-fired units. Figure 6-1 presents the wastewater flow di agram for Widows Creek. Each of the following wastewaters and their treatment are described in this section of the report:

y Intake water;

y Coal pile runoff;

y Low-volume wastes;

y Metal cleaning waste;

y Cooling water;

y Ash handling water; and

y FGD system wastewater.

6.1 Intake Water

Widows Creek uses water from the Tennessee River as the fresh makeup water to the plant. The plant has two se parate intake structures, one fo r Units 1 through 6 and another for Units 7 and 8. The intake for Units 1 through 6 is located on a small channel. The intake for
Units 7 and 8 is located on the river. The inta ke for Units 7 and 8 includes the recycled ash pond effluent, described in Section 6.6; however, the recycle accounts for only 27 MGD of the 725
MGD withdrawn from the river at th is intake. The intake water is screened prior to its use in the process. The periodic backwash of the intake screens is collected and discharged to the condenser cooling water discharge canal.10 Figure 6-1. Wastewater Flow Diagram for Widows Creek11 6.2 Coal Pile Runoff

As discussed in Section 5.1, Widows Creek has two separate coal piles, but only one coal pile runoff pond. As rain falls on the coal piles, the runoff from the area becomes contaminated with pollutants th at are found in the coal. This contaminated wastewater is collected in the coal pile runoff pond. Figure B-1, in Appendix B, presents a picture of the coal pile runoff pond. The coal pile runoff is allowed to settle and is genera lly held in these ponds until increased rainfall causes the pond to reach overflow levels. At this point, the plant will pump some of the coal pile r unoff wastewater to the ash pond.

6.3 Low-Volume Waste

Widows Creek has several low-volume wa ste streams generated by the plant. The low-volume non-contact cooling water used in so me of the plant’s heat exchangers and the intake screen backwash are discharged to th e condenser cooling water discharge canal, which flows directly to the Tennessee River without tr eatment. Most of the other low-volume wastes are collected in the ash pond, which include , but are not limited to, the following:

y Boiler blowdown;

y Non-chemical metal cleaning wastewater;

y Roof and switchyard drainage;

y Floor wash water; and

y Miscellaneous cooling water.

6.4 Metal Cleaning Waste

The wastewater generated during the fi re-side cleaning of the boiler tubes is pumped to the ash pond. Wate r-side boiler tube cleaning wast ewater containing EDTA is evaporated in the boiler of an operating unit. The condenser tubes ar e cleaned using nylon brushes, as described in Secti on 5.6, and the water used in the ope ration is discharged from the plant.12 6.5 Cooling Water

As discussed in Section 5.6, each of the units at Widows Creek has a oncethrough cooling system. The plant transports the cooling water from the condensers to a discharge canal that discharges to the Tenne ssee River. The once-through cooling water represents the largest discharge from the plant. As mentioned in Secti on 5.6, the plant does not use chlorine or other biocides for biofouling control. Instead, the plant backwashes the condensers and additionally uses nylon brushes to clean the scale on the condenser tubes. The wastewater generated from the condenser backwashing is pumped to the ash pond, but the wastewaters generated during the nylon brush cleaning is introduced into the once-through cooling water stream and subsequently discharged.

6.6 Ash Handling Water

As discussed in Sections 5.2 and 5.4, sluice water is used to collect the bottom ash and slag from the bottom of the boiler and the fly ash from the ESP collection hoppers. Widows
Creek uses water from the Tennessee River as the source of the sluice water. These wastewaters are transported to the ash pond; however, the ash sluice water associated with Units 1 through 6 is transported to a different part of the ash pond than the ash sluice water from Units 7 and 8.
Because Units 7 and 8 were constructed near th e bilge and station sump collection area, which discharges to the ash pond, the pl ant routes the ash sl uice from Units 7 and 8 through the bilge and station sump collection area. Ultimately, the ash sluice water from Units 1 through 6 is
combined with the ash sluice water from Units 7 and 8 within the ash pond.

The ash pond at Widows Creek covers approximately 340 acres. The wastewater that enters the ash pond flows through a long, wi nding dike created with ash that has been dredged from the pond. Figure B-2, in Appendix B, presents a pi cture of the ash pond dike at
Widows Creek. As the wastewater flows thr ough the dike, some of the metals and other particulates settle to the botto m. The plant continuously remove s ash from the pond and stacks it in the area surrounding the pond to increase the hei ght of the pond and dike embankments. The plant uses a bulldozer to remove the settled as h. The bulldozer operator repeatedly backs into the pond and bulldozes the ash out of the pond. Af ter the wastewater travels through the diked13 channels, it enters a large open area of the pond. Figure B-3, in Appendix B, presents a picture of this open area of the ash pond.

During the flow of the wastewater th rough the diked channels of the ash pond,
some of this ash water leaches through the embankment of the di ke. In addition, some of the wastewater in the open area of the ash pond leaches through the banks of the pond. This leachate, referred to as “red water” because of its red appearance, is collected by another dike surrounding the area and recycled back to the ash pond.

Within the open area of the ash pond, the pl ant uses a series of booms to collect floating solids off the top of the wastewater. The floating solids in the water are cenospheres, which are formed in the boiler during the coal combustion process. Cenospheres are small, lightweight, hollow spheres, and are a naturally-occurri ng by-product of the combustion process. Figure B-4, in Appendix B, presents a picture of the floating cenos pheres collected at the bank of the ash pond. The hollow portion of these cenospheres is typically filled with air or an inert gas,
which causes them to float on the water. A c ontractor periodically comes to the plant and removes them from the pond bank and transports them off site for beneficial use.

The ash pond wastewater eventually fl ows to the middle stilling pond, which is separated from the ash pond by a dike. At this point, the plant inject s carbon dioxide into the water to control the pH of the discharge. Because carbon dioxide react s with water to form carbonic acid, the addition of carbon dioxide redu ces the pH of the alkaline water. The wastewater from this portion of the pond flows into the pumping basin. The pH of the ash pond wastewater is typically in th e range of 7.0 to 8.5. Widows Creek has a limit of 6.0 to 9.0 for Outfall 001 (discharge to the river); therefore, if the pH of the ash pond water is above 9.0, the plant injects CO 2 to reduce the pH to approximately 7. If Widows Creek is recycling the water back to the Unit 7 and 8 intake, there is no upper pH limit for the discharge.

Widows Creek has two different outfalls for the ash pond effluent. Typically, the plant recycles the ash pond effluent by pumping it to the intake canal fo r Units 7 and 8, via the pumping basin. Figure B-5, in A ppendix B, presents a picture of this pumping basin. The recycled ash pond effluent typical ly accounts for only 3.5 percent of the intake water for Units 714 and 8. During excessive rainfall events, the plant may alternativel y discharge the ash pond effluent directly to the Tennessee River. If the pumping basin begins filling too rapidly, the overflow discharge pipes discharge some of th e ash pond effluent directly to the Tennessee River. According to the plant, the facility uses this outfall one or two times during the year.

In addition to the current ash pond desc ribed above, Widows Creek originally discharged its ash handling wastewater to anot her pond located on the site. This pond has since been filled to capacity with th e ash and essentially dried up. This area now has vegetation growing over this ash fill. The leachate and the st orm water that contacts this area is treated by the plant in a constructed we tland. Figure B-6, in Appendix B, presents a picture of the
constructed wetland cells. The wa stewater from the constructed wetland is discharged to the
Tennessee River.

6.7 FGD System Wastewater

As mentioned in the Section 5.5, Widows Creek uses once-through FGD systems; therefore, the resulting gypsum slurry from both systems is tran sported directly to the gypsum ponds. Gypsum is a by-product of the FGD pro cess, and is contained in the wastewater discharged from the process. For a descripti on of the chemical reactions involved in the FGD process, see Section 3.2.1.6 of the Interim Detailed Study Report for the Steam Electric Power Generating Point Source Category

.

The wastewater from this process flows through three gypsum ponds, each one fed to the next by gravity. Because the gypsum po nd water does not require the pH control that the ash pond effluent receives, the wastewater fro m the final gypsum pond is discharged directly to Widows Creek, which flows into the Tennessee Ri ver. Figure B-8, in Appendix B, presents a picture of the gypsum pond water discharge to Widows Creek. The plant tested the FGD wastewater for several metals during the permit re newal process. The metals with the highest measured concentrations were magnesium and boron, with concentratio ns of 360 and 19 mg/L, respectively. Selenium was measured at a co ncentration of 131 ug/L an d arsenic was measured at 19 ug/L. Mercury was not detected above th e detection limit, 0.1 ug/L. The total suspended solids long term average concentration was 9.7 mg/L and the daily maximum was 15.4 mg/L.15 The flow rate of the FGD slurry into th e gypsum ponds was 3.525 MGD and the long term average dischare flow was 3.88 MGD, with a daily maximum discharge of 9.09 MGD.

As mentioned in Secti on 5.5, the gypsum slurry generated by the Unit 8 FGD system contains fly ash particulat e that is removed from the flue gas. The fly ash in the slurry also settles to the bottom of the gypsum ponds a nd is stacked and dewatered with the gypsum. The addition of the fly ash to the gypsum give s the gypsum a gray appearance instead of the more typical white color. Because the gypsum generated at Widows Creek is essentially contaminated with some amount of fly ash, it is not easily marketable. Consequently, the plant plans to continue storing the gypsum on site, as described above, unt il they reach capacity. They estimate this onsite storage capacity to last approximately 10 years.

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.Appendix A

LIST OF ATTENDEESA-1Table A-1. List of AttendeesNameOrganization (Representing)TelephoneE-mailStanley Bramlett Tennessee Valley AuthorityJohn Cook Tennessee Valley AuthorityGerald Hemmer Tennessee Valley AuthorityJoe Jiles Tennessee Valley AuthorityLindy Johnson Tennessee Valley Authority (423) 751-3361 lpjohnson@tva.govMike Stiefel Tennessee Valley AuthorityDonna Hill Southern Company (205) 257-5234 dbhill@southernco.comPaul Chu Electric Power Research InstituteLiz AldridgeHunton & Williams(804) 788-8549 ealdridge@hunton.comKristy Bulleit Hunton & Williams (202) 955-1547 kbulleit@hunton.comJosh Hall EPA/Office of Water (202) 566-1002 hall.josh@epa.govRon Jordan EPA/Office of Water(202) 566-1003 jordan.ronald@epa.govKarrie-Jo Robinson-Shell EPA/Region 4(404) 562-9308 shell.karrie-jo@epa.govLeslie Churilla ERG (Contractor to EPA) (404) 634-0038 leslie.churilla@erg.comT.J. Finseth ERG (Contractor to EPA) (703) 633-1698 thomas.finseth@erg.comAppendix B

PICTURES FROM SITE VISITB-1 Figure B-1. Coal Pile Runoff Pond at Widows CreekB-2 Figure B-2. Ash Pond Dike at Widows CreekB-3 Figure B-3. Ash Pond at Widows CreekB-4 Figure B-4. Cenospheres Collected fr om the Ash Pond at Widows CreekB-5 Figure B-5. Pumping Basin at Widows CreekB-6 Figure B-6. Constructed Wetland Cells for the Old Ash Pond Runoff at Widows CreekB-7 Figure B-7. Gypsum Pond at Widows CreekB-8 Figure B-8. Gypsum Pond Discharge to Widows Creek