Draft Notes from Site Visit at Duke Ener gy's Allen Steam Station on October 22, 2009

EPA conducted a site visit at Duke Energy’s Alle n Steam Station (Allen) located in Belmont, NC on Thursday, October 22, 2009 to learn about the operations at the plant, specifically the FGD system and the FGD wastewater treatment sy stem. Table 1, located at the end of this memorandum, identifies the site vi sit participants. The presentati on that the Allen personnel gave during the site visit is provided as Attachment 1 to this memorandum. An overall plant water balance diagram and process flow diagrams of the FGD wastewater treatment system are
included within Attachment 1.

This memorandum describes the information collected during the site visit and the pre-site visit phone call, which was held on October 13, 2009.

Plant Overview

 Allen operates five steam electric units and each has a coal-fired boiler. Units 1 and 2, which both came on line in 1957, each have a capacity of 165 megawatts (MW). Units 3, 4, and 5 came on line in 1959, 1060 and 1961, respectively, and each has a capacity of 275 MW. All five generating units burn bituminous coal. The sulfur content of the coal is 1 to 1.2 pounds SO 2 /MBTU and the chlorine content of the coal is 50 to 1,500 ppm.

 The electric generating units at Allen ar e operated on a cycling basis and are not
baseload units. The table below contains some general information for the five generating units.

Unit Installation

Date Gross Capacity

(MW) Particulate
Control NOx Control SO 2 Control

1 1957 165 Electrostatic Precipitator (ESP) (cold-side) Selective noncatalytic reduction (SNCR) Wet FGD installed
in Feb 2009 (common FGD for Units 1, 2, and 5)

2 1957 165 ESP (cold-side) SNCR Wet FGD installed
in Feb 2009 (common FGD for Units 1, 2, and 5)

3 1959 275 ESP (cold-side) SNCR Wet FGD installed in May 2009 (common FGD for Units 3 and 4)

4 1960 275 ESP (cold-side) SNCR Wet FGD installed in May 2009 (common FGD for Units 3 and 4)

5 1961 275 ESP (cold-side) SNCR Wet FGD installed
in Feb 2009 (common FGD for Units 1, 2, and 5)Page 2

 Allen recently retrofitted a ll five units with two we t FGD scrubber systems to control the sulfur dioxide (SO 2 ) releases from the plant. Units 1, 2 and 5 exhaust to FGD Absorber 1, and Units 3 and 4 exhaust to FGD Absorber 3. The FGD systems were installed in February 2009 (Absorber 1) and May 2009 (Absorber 3). The wet FGD scrubbers are designed to achieve greate r than 95 percent
removal of SO 2

. [QUESTION FOR ALLEN: What SO 2 percent removal do the FGD scrubbers actually achieve?] The SO2 percent removal from the
scrubbers varies with load and sulf ur concentration of the coal being burned. During the official perfor mance testing of the scrubbers in 2009, when 2.4 pounds SO 2 per mmBtu coal was burned at full load, the scrubbers performed at 96.95% removal with no additives. Allen has also installed an FGD wastewater treatment system to cont rol the discharges of the wastewater generated during the operati on of the FGD scrubbers.

 Allen operates ESPs to control fly ash a nd particulate emissions from the plant. Allen also operates SNCR system s to control nitrogen oxide (NO

x ) emissions from the plant. The SNCRs operate year-round. Additionally, the boilers are operated with low-NO

x burners and a separated overfire air system.

 The ESPs at Allen are particulate contro l devices that remove the fly ash and other particulates from the flue gas. A llen utilizes ESPs to remove the fly ash from all five units. The ESPs are designed to remove greater than 99.9 percent of the fly ash from the flue gas. The fly ash and other particulates are collected in hoppers and usually pneumatically transfe rred to fly ash silos. However, Allen also has the capability to handle the fly ash wet, by sluicing the fly ash in the hoppers and transferring the fly ash tr ansport water to the ash basin.

 All five generating units have the following configuration:

 Boiler (SNCR system contained in boiler);

 Air preheater;

 ESP; and

 Wet FGD scrubber system.

 Allen operates a once-through cooling system . The cooling system has a flow rate of approximately 780 MGD. The source of the cooling water is the South Fork
River.

 The Allen plant is located on 1,000 acres adjacent to the Catawba River.

 [QUESTION FOR ALLEN: How many em ployees work at the plant?] As of December 7, 2010, there are 167 employees working at Allen Steam Station.

Ash Handling

 Allen stated that they previously sent all bottom and fly ash to an impoundment/basin; however, Allen converted to dry fly ash handling systems in April of 2009 to extend the life of the as h basin. Allen is still sending all the bottom ash and pyrites to the ash basin.Page 3

 Allen stated that another reason the pl ant decided to conve rt to dry fly ash handling was because of the selenium limit on the effluent from the ash basin (Outfall 002).

 The dry fly ash handling system retrofit was completed in June 2009. The total capital cost of the dry fly ash handling system was $39 million.

 Installation of the dry fly ash handling retr ofit consisted of installing the following pieces of equipment: dry handling valves, vacuum filter separators, Nuva feeders, compressors, high pressure piping, and ash silos. The tie-ins for the equipment were installed during regularly scheduled unit outages. [QUESTION FOR ALLEN: Approximately how long (days, week s?) did it take to complete the tiein?] Approximately seven days was taken to complete the tie in of the dry ash handling system. The following is a description of the dry fly ash handling
system components:

 Between the hoppers (which collect ES P and economizer fly ash) and the existing wet ash handling hydroveyor equi pment, the plant installed a dry handling valve. The dry handling valv e allows Allen to switch between operating the dry and wet fly ash handling systems.

 The vacuum filter system consists of vacuum pumps and filter separators. The vacuum pumps use 350 psi air pressure to create a vacuum, pulling dry ash collected in the hoppers to th e filter separators. Allen has eight filter separators (two for Units 1 and 2 combined and two for each of Units 3, 4, and 5). The filter separator allows the air to separate from the dry fly ash. The air is vented from the top of the filter separator after passing through filter bags, which are like mi ni baghouses. The filter bags are 84 inches long and there are 84 bags per f ilter separator. The filters remove any fly ash and other particulates from the vented air and the filters are pulsed with air occasionally (based on the pressure drop across the filters) to remove the fly ash that accumulates on the bags.

 The ash then falls by gravity from the filter separator into the Nuva
feeders. There are two Nuva feeders fo r each filter separator for a total of 16 Nuva feeders for the plant. Beca use the dry fly ash is blown to the silos under pressure, the Nuva feeder s are required to transition between the vacuum system (i.e., the filter separators) and the pressure system. Therefore, Allen’s dry ash handling sy stem is considered a combination vacuum/pressure system.

 The Nuva feeders allow the ash handling system to transition from the vacuum system to the pressure system . While the first of the set of two Nuva feeders is receiving ash from the filter separator, the second is transferring ash out the bottom so the compressor can blow the ash to the storage silo. Once the first Nuva feed er is full and the second is empty, the plant switches the valves so the first Nuva feeder can begin transferring ash and the sec ond can begin receiving ash.

 The fly ash is blown a distance of 1,8 00 feet to one of two ash storage silos. Allen stated that the pre ssurized pipe is significantly more expensive than the pipe used to tran sfer the sluiced bottom ash to the ashPage 4

basin. Additionally, the pre ssurized pipe is more prone to leaks than the wet ash pipe . [QUESTION FOR ALLEN: What is the relative difference in cost between the piping?]

The vacuum system is tied into pr essurized piping that is provided specifically by United Conveyor (Nuva lloy) and the ash sluice line is highdensity polyethylene (HDPE) for the gravity fed system. The cost of the pressurized piping is approximately 3 to 5 times more (depending on the diameter of the pipe) than the HDPE pi ping on a linear foot basis. Actual cost estimates will be provided to Eastern Research Group (ERG) as confidential business information (CBI ) as part of this submittal.

 The silos have a storage capacity of approximately three days of fly ash when operating at full load (between the two silos).

 The silos have a dry air system that bl ows air into the bottom of the silo to fluidize the fly ash. The silos also have filters at the top of the silos to collect any fly ash from the air that is vented.

 Ash from the silos is trucked away for beneficial reuse. Allen stated that the ash is collected by trucks at a frequency of 110 times per day. Each truck collects approxima tely 1,700 tons of ash.

 Allen has the capability of loading the trucks completely dry (sealed trucks) or conditioning the ash with wa ter for loading (open trucks).

 When fly ash is loaded dry, the ash is transferred from the silos to the trucks pneumatically with a double a nnular spout. A vacuum is pulled through the outer annulus of the spout, creating a tight seal with the truck. Ash is delivered through th e inner annulus of the s pout into the truck. The vacuum captures any fugitive dust and pulls it through the loading silo to the baghouse. It takes about 1 to 2 mi nutes for the ash to settle in the trucks before the spout is pulled away.

 When the fly ash is loaded in a wet form, the fly ash is fed to a pug mill
where it is mixed with service water to 17 percent moisture content, for optimal compaction. The fly ash is then dumped into the open trucks through a spout.

 The area surrounding the silos has sloped concrete and drains to collect rainfall or other water that may have become contaminated with fly ash.
This water is transferred to the stor mwater basin and then pumped to the
ash basin.

 Allen stated that the dr y fly ash is currently 

## sold used for a beneficial reuse application. The plant is waiting on a pe rmit to be approved which will allow Allen to landfill the dry fly ash. [QUESTION FOR ALLEN: Fo r what beneficial reuse application is the fly ash being used?] The dry fly ash was used as
structural fill for the constructed landfill.

 Allen stated that they reta ined the capability of sl uicing the fly ash with the existing wet system. When the fly ash is ha ndled wet, the ash sluice is transferred to the ash basin at a flow rate of 1,200 gpm. [QUESTION FOR ALLEN: When does the plant use the wet fly ash handling system?]Page 5

The fly ash system is operated on wet mode during all unit start ups (i.e. when fuel oil is being burned in the boiler). When the operating load increases, the fly ash system is switched to dry mode. In addition, the wet fly ash handling system is operated during any dry ash handling system
malfunction.

 Allen handles all bottom ash and pyrites we t. The bottom ash sluice flow rate is 13,700 gpm.

 Both fly and bottom ash are conveyed (pneumatically pumped or sluiced) at a frequency of two times pe r shift (2 shifts/day  4 times/day) for a duration approximately one hour.

Ash Basins and Landfill

 Allen has a retired ash basin, an active ash basin, and an ash pond (polishing pond).

 The retired basin has a total area of 180 

## 68 acres and stopped receiving wastes in 1974. At the time of the visit, Allen was constructing a landfill over the retired ash basin. Allen stated that the plant has been permitted to store the dry fly ash and other coal combustion byproducts in the landfill.

 The landfill has a total area of 68 acres. It will be constructed with a double-liner, a leachate collection system and a leak detection system. The double-liner will
cover ash stored in the inactive ash basin’ s cells and is comprised of the following layers (from bottom to top): an 18 inch clay liner, a geosynthetic liner, a rubber liner (the secondary liner), a drainage net, a drainage layer consisting of two feet of soil (clay), a second drainage net, a nd a rubber liner (the primary liner). The drainage nets and drainage layer comp rise the leak detection system, which detects leaks from the primary liner.

 Allen stated that the permeab ility of the clay liner is 10 -5 cm/sec. The addition of the geosynthetic liner was necessary to obtain a permeability of 10 -7 cm/sec.

 Allen indicated that the collected leacha te will be transferred to the active ash
basin.

 Allen expects that the total cost for the landfill will be approximately $ XX

. [QUESTION FOR ALLEN: Please confir m the cost and provide a breakout .] The breakout of the capital cost of the landfill is CBI. These costs will be provided to ERG as part of this submittal.

 The lifetime of the landfill is expected to be 2.5 million cubic yards, which is expected to last for five years. [QUESTION FOR ALLEN: Please confirm the expected landfill capacity.] The landfill capacity, as noted in the landfill permit to operate, is 2,080,500 cubic yards (cu. yds.) for Phase 1, cells 1 and 2 plus 3,958,200 cu. yds for Phase 2, cells 3 and 4.Page 6

 The active ash basin began receiving botto m ash and fly ash (when handled wet) in 1974 when the inactive ash basin stopped receiving wastes.

 The fly ash (when handled wet) and botto m ash enter the active ash basin, where the solids settle and the water flows through a series of three cells. The plant can direct the ash to any of the three cells. The effluent from the third cell overflows
to a channel that flows towards the back of the ash basin (i.e., away from the Catawba River). Along this channel, the plant has the capability of adding ferric sulfate to aid in settling. The channel th en flows into the main ash pond. The ash pond discharges to the Catawba River. A llen has the capability to add sulfuric acid or sodium hydroxide at the effluent of the pond to adjust the pH between 6
and 9.

 The neither the active ash basin nor the ash pond have a liner.

 Allen stated that the FGD wastewater tr eatment effluent, described later, is transferred to the ash pond. Allen has th e system configured such that the FGD
wastewater treatment effluent enters in to the ash basin channel and does not go through the ash basin cells. Allen stated th at they have the capability to transfer the FGD wastewater through the cells if needed.

 Allen stated that the plant will have the ability to exte nd the lifetime of the active pond by dredging the solids in the active pond and transferring them to the
landfill.

 Allen indicated that the St ate requires them to perfor m leachate monitoring twice a year. Typical chemicals that they test for are boron, magnesium and iron.

 [QUESTIONS FOR ALLEN: How often do you inspect the active basin for structural integrity? When was the la st inspection and what did the inspection consist of?] Inspections are conducted monthly by station personnel or after 2 inches of rainfall in a 24 hour peri od. Annual inspections are conducted by a Professional Engineer (P.E.). The last monthly inspection was conducted on November 19, 2010 by station personnel. No immediate concerns were identified. In addition, an inspect ion was conducted by the North Carolina Department Environment and Natural Resources (NCDENR) Dam Safety,
with no items identified.

 [QUESTION FOR ALLEN: Do you perform gr oundwater monitoring around the landfill and/or ash basins? If so, how often do you perform groundwater monitoring and what parameters are monitored for? Where are th e monitoring wells located? Please provide the groundwater monitoring data for the five most recent samples.] Groundwater monitoring is conducted semi-annually on a voluntary basis. See attached excel spreadsheet (“Allen Ash Basin Groundwat er Data”) for analytical results and parameters. The locations of the wells are provided in the attached PDF file (“Plant – Allen Ash Basin Groundwater Locations”). The voluntary wells were not sampled in November 2010, due to transitioning from the voluntary wells to the newly installed compliance well system.Page 7

FGD Systems

 Allen operates two forced oxidation wet F GD scrubber systems that treat the flue gas from all five electric generati ng units. The FGD systems are located downstream of the ESPs and the flue gas from Units 1, 2, and 5 are combined and transferred to Absorber 1, while the flue from Units 3 and 4 are combined and transferred to Absorber 2. The FGD sy stems control the emission of sulfur dioxide from the units. The plant uses limes tone slurry as the sorbent for sulfur dioxide absorption.

 The FGD systems are designed to achieve a 95 percent removal of sulfur dioxide from the flue gas, based on a design coal of 2.8 lbs SO 2 /MMBTU. Additionally, when Allen built the FGD systems, they inst alled the equipment needed to be able to add dibasic acid (DBA) to the system. At this point, the plant has not used or tested DBA in the system. Allen stated th at they may consider using formic acid
sometime in the future.

 The limestone is delivered to the plant via rail, stored in an outdoor pile, and then transferred to day bins. Allen has ball mills onsite to pulverize the limestone. The limestone is fed to the ball mills, along with service water, and the ball mills pulverize the limestone. From the ball mills, the slurry is transferred to hydroclones to collect limestone particles that are too large for use in the FGD system. The underflow from the hydroclones is transferred to the reject tank and
then sent back to the ball mill for a dditional processing. The overflow from the

hydroclones, which is approximately 50 

## 30 percent solids, is transferred to the reagent tank for storage and then used as fresh limestone slurry in the absorber.

The fresh limestone slurry is fed to the reacti on tank of the FGD system and the recycle pumps pump the slurry to the various le vels of the FGD scrubber. Typi cal solids concentrations in the
absorber are 14-16%. [QUESTION FOR ALLEN: Is make- up water added to the reagent tank or the reaction tank to achieve the 14-16% solids?] Reaction Tank Solids are maintained at 14 to 16% solids by dewatering only (that is sending the primary hydrocyclone underflow to
the filter feed tank and then to the belt fi lter). Make-up water is added to the reaction
tanks for level control due to dewatering (or taking the so lids from 16% down to 14%), purging for chlorides (returning both the primary and secondary hydrocyclone underflow
solids back to the reaction tank while sendi ng the secondary hydrocyclone overflow to WWTS), evaporation or anything else that may cause a change in the level in the reaction

tank.

 Both absorbers have four spray levels; however, the plant typically only operates
three levels at one time. Th e slurry is pressurized a nd sprayed downward into the scrubber vessel through spray nozzles. The flue gas flows counter-current to the falling slurry. As the spray droplets of the slurry contact the flue gas, the
limestone reacts with the sulfur dioxi de and oxygen, producing calcium sulfate (gypsum).

 Allen intermittently pu rges volume of the gypsum slu rry from the reaction tank to

contr ol the solids and/or chlorides concentration in the scrubbers. The process forPage 8

dewatering (maintaining reaction tank solids at 14% to 16%) is different than “purging for chlorides”. The gypsum slurry is removed permanently
from the reaction tank to control solid s. The gypsum slurry is returned to the reaction tank when purging for chlorides. The chlorides concentration in
the scrubbers is maintained betw een 3,000 and 10,000 ppm. The maximum design chlorides concentration is 12,000 ppm in the system. The typical percent of
solids within the absorber is 14 % to 16 %.

 The purge stream from the reaction tank is sent to the gypsum dewatering system.
Allen stated that because of the low

- sulfur coal that they are currently using, they typically have to purge from the FG D system to control the chlorides concentration instead of controlling the solids content in the scrubber. The percent solids are controlled; otherwise, the reaction tank agitators could fail. Dewatering and purging are two different processes within the FGD operation. The gypsum slurry is rem oved permanently from the reaction tank to control solids. The gypsum sl urry is returned to the reaction tank when purging for chlorides.

The purge stream is pumped to the primary hydr ocyclones where the gypsum is separated from the water by centrifugal force. The gypsum is forced outward to the walls of the hydrocyclones and falls downward, while the wa ter exits the top of the hydroc yclones. The gypsum from the primary hydrocyclones is transferred to the filter feed tank, which is then transferred to the
vacuum filter belts. Allen wash es the gypsum with service water as it is applied to the vacuum
belt filter to reduce the chlorides in the gypsum. [QUESTION FOR ALLEN: Where does the plant transfer the gypsum wash water from the vacuum belt filter?] The gypsum wash water is
returned to the reaction tanks.

 Allen stated that the gypsum is shippe d off site by a truck to a wallboard
manufacturer in Mount Holl y, NC. The following are the specifications that the gypsum must meet to be sold to the wallboard manufacturer:

 Less than 10 percent moisture; and

 Less than 120 ppm chlorides.

 Allen stated that the moistu re content in the gypsum is typically 4 percent and the chlorides concentration is typically less than 20 ppm

 The overflow from the primary hydrocyclo nes is transferred to a holding tank, and then pumped to the secondary h ydrocyclones. The underflow from the secondary hydrocyclones is returned to the scrubber. The overflow from the secondary hydrocyclones is sent to the FGD wastewater treatment system. This FGD purge stream contains 0.5 to 0.8 percent of solids.

FGD Wastewater Treatment System

 Prior to the site visit, Allen distribut ed a description of the FGD wastewater treatment system, provided as Atta chment 2 to this memorandum.Page 9

 The FGD wastewater treatment system is designed to receive transfers of FGD wastewater from the FGD system, whic h consists of secondary hydrocyclone overflow, at a flow rate of 400 gpm. The FGD wastewater treatment system consists of chemical precipitation and biological treatm ent technologies.

 The secondary hydrocyclone overflow from the scrubbers is transferred to the equalization tank at the beginning of the wa stewater treatment system. Allen also
has a maintenance tank that is used as e ither a spare equalization tank or a spare sludge holding tank. The equalization tank al so receives water from the filtrate sump (which includes filter press filtrate), gravity filter backwash reject, backflush waste from the biological treatment system, and off-specification biological treatment effluent . The wastewater entering the equalization tank has a pH of 6.7-6.9 and a temperature of 105-115o F. Allen stated that a significant
amount of CO 2 is released during the agitati on of the wastewater in the equalization tank.

 From the equalization tank, the wastewater en ters three reaction tanks in series. In the first reaction tank, lime is added to increase the pH to between 8.6 and 9.2.
The effluent from this tank enters the second reaction tank designed for organosulfide addition; ho wever, the plant does not add organosulfide to the reaction tank because the plant determin ed that organosulfide addition was not necessary to meet its effluent limits.

 After the organosulfide tank, the FGD wast ewater is transferred to the third
reaction tank where ferric chloride is a dded. Allen stated that they are tuning the ferric chloride dosage for the plant and questioning whether ferric chloride is needed in the system to achieve the effluent limits at the plant. According to plant personnel, the plant has dropped the dosag e by 40 percent and has not seen any change in the performance of the system. [QUESTION FOR ALLEN: What parameters are analyzed to assess system performance?] The performance of the system is analyzed by evaluating tota l and dissolved selenium (Se), mercury (Hg) and total suspended solids (TSS) out of the physical/chemical system. Secondary characteristics that may im pact the operation, rather than the performance, of the biochemical system are monitored (i.e. nitrate, phosphate, pH and alkalinity).

Ferric chloride dosing at Allen WWT S has varied from 47 ppm to 20 ppm since the system has been operating. Cu rrent ferric chloride dosing is 30

ppm.

Based on the technology provider’s recommendations for Belews Creek, we started the system at 47 ppm ferric ch loride dosing. Beginning in August 2009, we began reducing this dosing incrementally until we reached 20 ppm in January/February 2010. During this period we did not notice a difference in the performance of the system as measured at the effluent from the physical/chemical and biochemical system s. We did however notice that we needed to use more polymer to mainta in the same performance out of the clarifiers, TSS removal, and that the bio reactor cells required degassing at a significantly increased frequency. The increased gassing of the bioreactorsPage 10

has been attributed with a d ecrease in phosphate removal in physical/chemical. Although there was an increase in TSS in the clarified water, the gravity filters maintain ed a relatively unvaried TSS in the discharge from the physical/chemical system.

Ferric chloride dosing was increased to 30 ppm which has resulted in improved TSS reduction across the clar ifiers and a return to “normal” degassing frequencies in the bioreact ors. Jar testing with various FGD waters and flocculating polymers has sh own that a ferric chloride dosing of between 25 and 50 ppm usually results in optimum clarif ier performance.

Ferric chloride dosing was as follows:

Beginning 3/09 47 ppm 7/30/09 40 ppm 9/17/09 30 ppm 2/15/10 20 ppm 3/22/10 50 ppm 5/14/10 40 ppm 8/6/10 20 ppm 8/10/10 30 ppm

 The overflow from the ferric chloride tank flows through a flow splitter which distributes the flow evenly to two clarif iers. Allen operates the two clarifiers in parallel, each capable of handling 100 % of the waste stream flow. A polymer is added to the wastewater just prior to the clarifiers.

 The sludge collected in the clarifier is transferred to a sl udge holding tank and dewatered with a filter press. The f ilter press uses hydraulic power from compressors to remove water. The solids are transferred to an off-site landfill and the filtrate is recycled to the equalization tank.

 The clarifier overflow is ne utralized by hydrochloric ac id addition (if necessary) and flows through three continuous backwash gravity filters operated in parallel. Each filter is capable of handling 75 % of the wastewater flow. The hydrochloric acid helps prevent scale formation in the filters. The effluent of the gravity filters is approximately 1 to 2 ppm TSS.

 The effluent from the gravity filters is transferred to the biological treatment system feed tank.

 Prior to entering the biologi cal portion of the wastewater treatment system, heat exchangers cool the wastewater to 95 o F, the optimal temperature for the biological treatment system . Allen stated that the heat exchangers were constructed with a titanium alloy which can withstand the high levels of chlorides and suspended solids in the FGD wastew ater entering the biological treatment system. The heat exchanger requires 300 to 350 gpm of cooling water. [ QUESTION FOR ALLEN: Is any make-up water added to dilute or cool thePage 11

influent wastewater to the biological system?] Water is not added to dilute or
cool the influent wastewater to th e biological system. The influent wastewater to the biological system is cooled by using a heat exchanger.

 Allen adds molasses-based nutrients to th e wastewater as it flows from the heat exchanger to the biological treatment syst em. The nutrients provide a source of
carbon to feed the bacteria.

 Allen stated that the biological treatmen t system is nearly identical to the biological treatment system at Belews Creek and consists of two stages. The residence time in each stage is approximately 4 hours.

 Both bioreactor stages cont ain eight biological cells oper ated in parallel. Each of
the bioreactor cells contains beds of ac tivated carbon media 20 feet deep. The wastewater is initially sent into the firs t-stage cells, where the flow into the first cell is evenly distributed to 16 distribution pipes to create an uniform distribution of flow into the top of th e cell. The water level in the cell was designed to be approximately six inches above the activat ed carbon bed; howeve r, at the time of the site visit, the water level was below the top of the carbon bed. Within the activated carbon bed, microbes create a fixed film on the surface of the carbon. Water flows from the top of each cell down through the carbon beds. Water from the first cell is then pumped from the bo ttom of the first cell to the top of the
second cell. The wastewater continues in this fashion through all eight cells that make-up the 1 st stage of the bioreactor.

 The effluent from all first-stage of the bi oreactor is transferred to the first-stage effluent storage area, before being sent to the second-stage bioreactor cells, which are also operated in parallel. Nutrients are added to the wastewater as feed for the
microbes as the wastewater is transferred. As in the first stage, the wastewater is divided evenly among the eight second-stag e cells and each cell has 16 distributor pipes to evenly distribute the flow into the cell.

 Occasionally the bioreactor cells must be backflushed to remove accumulated solids. The plant pumps the effluent fr om the first-stage bioreactor cells backwards through each cell and it overflows in to a spillover area. The plant then
returns the backwash overflow to the e qualization tank at the start of the FGD
wastewater treatment system

.

 Because the first-stage bior eactor cells denitrify the wa ste stream, they produce nitrogen and carbon dioxide gas. To rem ove the gas from the cells, the plant occasionally performs a degassing operat ion where water is sent backwards through the cells, like a backflush, but the flush is only long enough for the gas to “burp” out of the system. The second-sta ge bioreactor cells are primarily anoxic and do not produce as much gas as the firs t-stage cells; therefor e, Allen performs the degassing operation on the second-stage cells less frequently than the firststage cells.Page 12

 Allen stated that the TSS concentra tion within the first and second stage
bioreactor cells is approximately 40 ppm. The solids in the cells are mostly biological materials.

 Allen stated that the system achieves si gnificant reductions in dissolved metals concentrations in the first-stage reactors; therefore, the second stage is primarily a polishing step but it also pr ovides a safety net for high metal loads. Allen stated that arsenic, zinc, nickel and selenium ar e typically below the limit of detection in
the effluent of the biol ogical treatment system.

 Allen stated that the major improvement of the Allen biological treatment system over the Belews Creek system is the in clusion of oxidation- reduction potential (ORP) and pH probes on each individual cell (the Belews Creek system has one ORP probe for each stage). Additionally, the Allen system has sampling points on the effluent from the second stage (B elews Creek has sampling points on the effluent from the second stage recycle) . These improvements have resulted in greater ease of operations for the bi ological treatment system at Allen.

 Allen stated that the effluent from th e FGD wastewater treatment system is transferred to the ash basin. Allen stated that there are no permit limits for the FGD wastewater treatment sy stem effluent (internal Outfall 005); however, Allen stated that they are required to monitor and report the following parameters for the internal outfall: Se, Hg, As, Ni, Zn, Be , Ag, Cr, Cd, sulfates, chlorides, and pH. [Please provide monitoring data for th e FGD wastewater treatment system, including FGD scrubber purge, effluent fr om chemical precipitation/influent to biological treatment, and e ffluent from biological treatment. Include all parameters that are being monitored. Additionally, please indicate the ferric chloride dosage rates at th e time of monitoring (to identify when changes were made to the dosage).] Please refer to the completed Allen Steam Station Questionnaire for the Steam Electric Po wer Generating Effluent Guidelines for untreated FGD scrubber purge monitoring data. Please see attached excel file “Allen Biochem and PhysCh em monitoring.xls” for monitoring
data for the effluent from chemical precipitation/influent to biological treatment, and effluent from the biological treatment.

Please note Method 245.1 was used for the mercury analysis for samples
collected between 6/5/09 to 7/30/09 and Method 1631e was used for the mercury analysis for samples colle cted between 8/5/09 to 6/15/10.

The analysis for the in process data is conducted by the wastewater treatment system (WWTS) operators within the WWTS lab and is intended only to indicate gross operational perf ormance of the system. These results
should not be deemed suitable for compliance purposes.

Detection limits for the nitrate test is 0.1 ppm as N. Results detected below
the detection limits are noted in red and indicated with a less than sign, “<”.

 Allen stated that they are sampling th e effluent from the FGD wastewater treatment system on a weekly basis.Page 13

 The selenium limit from the ash basin effluent (Outfall 002) is 31 ppb. Allen expected the limit to be lowered to 21 ppb when the biological treatment system was designed.

 Allen stated that because the electric generating units are operated on a cycling basis and are not baseload units, there ar e times when the units have been shut down for a few days. During these shut down periods, the wastewater treatment system does not receive any scrubber purge wastewater and th erefore, the plant has to find a way to feed the microbes to keep them alive. Allen stated the following regarding there ope rations during shut downs:

 If the plant knows ahead of time that they will be shut down for a couple days, they can build up additional scrubber purge in the e qualization and maintenance tanks and then operate the FGD wastewater treatment system at a reduced flow rate until they begin operating again.

 If the plant is down for several days without advanced knowledge, the plant can run service water through th e system and feed nutrients to the bioreactors to sustain biological growth.

 During pilot testing, the plant shut off the system for three weeks with the system sitting idle with water in it and when the system started operating again, it was achieving its typical performance after 24 hours.

 Allen stated that the biological treatmen t system is fully operational within 1-2 residence times after a complete shut down of the entire system. Additionally, Allen stated that the biological species in the bioreactor cells will respond to variations in influent chemistry (i.e. retu rn to steady state) within 1-2 residence
times.Page 14Table 1. Site Visit AttendeesNameOrganization (Representing)TelephoneE-mailRobert Wylie Duke Energy (704) 382-4669 Robert.Wylie@duke-energy.comKim Hamm Duke Energy Kimberly.Hamm@duke-energy.comGreg AusbergerDuke/AllenGregory.Augspurger@duke-energy.comBill KennedyDuke EnergyWilliam.Kennedy@duke-energy.comRobynRobbinJollyDuke/Allen(704)829-2412 Robbin.Jolly@duke-energy.comTerry K. HollifieldDuke/AllenTerry.Hollifield@duke-energy.comTed ManesDuke EnergyTed.Manes@duke-energy.comSteve ImmelDuke/AllenSteve.Immel@duke-energy.comDon ScruggsDuke/AllenDon.Scruggs@duke-energy.comDonna HillUWAG/Southern Company(205) 257-5234 dbhill@southernco.comJosh HallEPA(202) 566-1002 hall.josh@epa.govJezebele AliceaVirellaEPA (202) 566-1755 Alicea.jezebele@epa.govKurt Blohm ERG (Contractor to EPA)(703) 633-1675 kurtis.blohm@erg.comTJ Finseth ERG (Contractorto EPA) (703) 633-1698 thomas.finseth@erg.com