Draft Notes from Site Visit at Detroit Edison’s Monroe Power Plant on September 23, 2009

EPA conducted a site visit at Detroit Edison’s Monroe Power Plant (Monroe) located in 

Monroe, MI on Wednesday, September 23, 2009 to learn about the operations at the plant. Table 

1, located at the end of this memorandum, identifies the site visit participants. Attachment 1 

provides the presentation that the Monroe personnel gave during the site visit. 

This memorandum describes the information collected during the site visit.

Plant Overview

• Monroe is owned by Detroit Edison Company, a subsidiary of DTE Energy. Detroit Edison 

was founded in 1903. It is the ninth largest electric utility in the United States with 2.1 

million customers and over 11,000 MW of electric power generating capacity, primarily coal 

fired. Detroit Edison owns one nuclear plant (Fermi 2). 

• The Monroe plant covers 1,200 acres and is surrounded by Lake Erie and the Raisin River. 

The Monroe-related property is split into three sections, including the Monroe plant property, 

the dry fly ash loading area, and the fly ash basin, including the 200 acres of land south of the 

fly ash basin. Monroe purchased the 200 acres south of the fly ash basin for possible future 

use if the basin needed to be expanded. An aerial view of the Monroe plant property is 

provided as Attachment 2 to this memorandum.

• Monroe employs more than 400 permanent employees and 100 long term contract 

employees. Monroe also employs about 500-800 temporary construction employees for 

various construction projects, including the Environmental Project.

• Monroe produces about 35 percent of DTE Energy’s electrical power and 44 percent of its 

fossil power. Monroe has a net winter electric generating capacity of 3,135 MW, and the net 

summer capacity is typically about 3,115 MW. The plant’s auxiliary power requirement is 

about 5 percent parasitic load without the flue gas desulfurization (FGD) operation. With the 

added FGD operation, the auxiliary power requirement increases to about 6.2 percent. The 

plant generates about 16 to 18 million MWs per year. The table below contains some general 

information for each electric generating unit. 

Unit Installation 

Date

Capacity 

(MW) a

Fly Ash 

Handling 

System

Particulate 

Control

NOx 

Control

SO2

1

Control

1971 817

Dry and wet 

systems in 

operation

Cold-side 

electrostatic 

precipitator 

(ESP)

Low-NOx 

burners;

SCR

FGD 

scrubber 

planned to 

be installed 

by 2015.

2 1972 823

Wet system in 

operation; 

Dry system 

installed

projected 

operation in 

Cold-side 

ESP

Low-NOx 

burners;

SCR 

planned to 

be installed

FGD 

scrubber 

planned to 

be installed 

by 2015.
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Unit Installation 

Date

Capacity 

(MW) a

Fly Ash 

Handling 

System

Particulate 

Control

NOx 

Control

SO2

Fall 2009.

(UPDATE: 

in operation 

since Sept. 

2009)

Control

3 1973 823

Wet system in 

operation; 

Dry system 

planned to be 

installed in 

2013

Cold-side 

ESP

b

Low-NOx 

burners;

SCR

Limestone 

forced 

oxidation 

(LSFO) 

FGD 

scrubber 

planned to 

be 

operational 

in Nov 2009

4 1974 817

Wet system in 

operation; 

Dry system 

planned to be 

installed in 

2013

Cold-side 

ESP

b

Low-NOx 

burners;

SCR

LSFO FGD 

scrubber 

operational 

in June 

2009

a – Capacities from the 2005 EIA database. These capacities will be updated with further 

information from the facility.

b – Although the company signed an agreement that allows a 3rd party to install a dry system, as 

of this date the company cannot state that there is a likelihood that a dry system will be installed. 

Among other things, such an installation by a 3rd party is predicated on the company not electing 

to burn pet-coke in this unit. As of this date the company has not decided whether it will burn or 

not burn pet coke in this unit.

• Monroe operates low-NOX burners on each of the coal-fired units (Units 1, 2, 3, and 4). 

Additionally, Monroe operates SCRs on Units 1, 3, and 4. Plant personnel stated that they are 

planning to install an SCR on Unit 2 in the future. The SCRs on Units 1, 3, and 4 each have 

four catalyst layers available, but there are typically less than four layers that are loaded. 

When necessary, these catalyst layers are replaced and are not regenerated on site. 

• Monroe’s current plan for reduction of mercury emissions includes the operation of SCR and 

FGD systems. Monroe estimates that an SCR and FGD scrubber installed in series controls

is expected to typically reduce about 80 percent of mercury emissions. 

• DTE Energy/Monroe participated in a DOE-co-funded pilot study for activated carbon 

injection (ACI) at Monroe. All of the equipment was removed once the study was finished. 

Monroe stated that injecting activated carbon upstream of the ESP would preclude the sale of 

fly ash due to high carbon content, and specifically, high activated carbon content. Monroe 

stated that if they implemented ACI downstream of the ESP to keep the dry fly ash 

marketable, a baghouse would have to be installed. [QUESTION FOR MONROE: Have any 

other options, additional to ACI, been considered for mercury control?] Fuel additives and 
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FGD slurry additives would be considered if additional mercury oxidation is required or reemissions from the FGD became an issue. No additives are used currently.

• The plant has three coal piles; one contains low-sulfur Powder River Basin (PRB) coal (0.2 

to 0.5 percent sulfur); one contains mid-sulfur eastern bituminous coal (1.2 to 1.6 percent 

sulfur); and one contains a blend of coal (60 to 70 percent PRB and 30 to 40 percent eastern 

bituminous). Monroe estimated that this year they have burned closer to 70 percent PRB and 

30 percent eastern bituminous coal because recently the total cost for obtaining PRB coal is 

less than that for eastern bituminous coal. All coal arrives by rail or lake vessel. At full load, 

the plant consumes about 32,000 tons of coal per day and on an average year, burns 8-9 

million tons of coal. 

• Monroe’s coal pile runoff is not acidic due to the significant amount of PRB coal burned. 

The runoff is typically between 7 and 8 S.U. (a recent measurement was 7.76 S.U.). Monroe 

sends the coal pile runoff to a small basin and then to the bottom ash basin. 

• Plant personnel estimated that the distribution of ash generated from the generating units, 

calculated based on coal consumption, is approximately 20 percent bottom ash, 80 percent 

fly ash and 1 percent economizer ash. The plant has no means of measuring any of these ash 

steams and the above numbers are estimates based on literature review of comparable units.

Ash Ponds

• Monroe has two ash ponds, the bottom ash basin (Area 15) and the fly ash basin. Originally, 

the plant’s fly ash pond and bottom ash pond were both located in Area 15. These ash ponds 

were filled with all ash produced at the Monroe site since it began operation in 1971. When 

the plant personnel determined that the area/ponds would soon reach its limits, it was 

converted to the bottom ash pond only. Area 15 was only used for fly ash disposal as an 

interim measure in the early 1970’s, while the fly ash basin was being built. Area 15 has 

never reached its limits and continues to be used as a bottom ash pond. There are no 

chemical additions to the ponds. 

• The bottom ash basin receives bottom ash sluice, coal pile runoff, effluent from the FGD 

wastewater treatment system, and low volume wastes. The bottom ash is sluiced to the basin 

and then dredged and sold or used for roadbed. Bottom ash sales are infrequent. Effluent 

from the bottom ash basin is discharged via Outfall 001B to the main discharge cooling 

canal, and then discharged to Lake Erie via Outfall 001.

• The Monroe constructed the 410-acre fly ash basin was constructed in 1974. The ash basin 

has never been expanded and is currently at about 2/3 of its volume capacity. The bottom of 

the basin is about 5 to 10 feet below ground level, and the highest point of the berm is about 

35 feet above ground level. Monroe fills about 5 to 10 acres of the pond each year with fly 

ash. The estimated end of life for the ash basin is about 20 years from the time of the site 

visit. This could be extended if more dry fly ash can be sold or decreased if the plant is no 

longer able to sell ash or gypsum. The fly ash basin is licensed/permitted by the state as a 

landfill under the solid waste program. 
Page 4

• Compacted “Lake Erie” clay, the naturally-occurring clay in the area, was used to construct 

the berm of the fly ash basin. and is the main component of the bottom of the ash basin. The 

basin is not lined. Monroe stated that the permeability of the clay, 10E-8 UNITS, makes it an 

ideal component for the bottom and berm of the ash pond. [QUESTION FOR MONROE: 

Please confirm the clay permeability and provide the measurement units.] Permeability 

coefficient of the ash basin embankment soils strata ranges from 1.30 X 10(-7) to 2.37 X 10(-

8) cm/sec. Permeability coefficient of the ash basin site soils strata ranges from 1.0 to 2.0 

X10(-8) cm/sec. This data is based on soil test results from a 1986 ash basin embankment 

soils investigation and 1995 ash basin site soils investigation. Clay is not the main 

component of the bottom ash basin. Clay was the only component used to build the fly ash 

basin. Permeability verification documents were provided to GZA: the other EPA contractor 

reviewing ash basin construction. 

• The fly ash basin effluent is currently monitored for total suspended solids (TSS), oil and 

grease with grab samples taken at the end of a discharge canal. Flow is also recorded. The 

water from the fly ash basin is discharged with an underflow/overflow weir that is controlled 

by gates. The water flows underground to one of three upwellings and then flows to the 

monitoring point. The fly ash basin effluent is discharged via Outfall 001F to the main 

discharge cooling canal, and then discharged to Lake Erie via Outfall 001. An aerial view of 

the fly ash basin, with monitoring points and discharges identified, and a plant water balance 

are provided as Attachment 3 to this memorandum. 

• There is an air quality monitor located near the ash basin that continually monitors for 

fugitive dust. 

• An engineering study of the fly ash basin was conducted in 2008 (prior to the TVA ash spill), 

during which the structural integrity of the pond was analyzed. The 2008 study was focused 

on the design of a repair plan for the surficial sloughs that have occurred on the exterior of 

the basin. The 2008 plan was not focused on the stability of the core of the dike. After the 

TVA ash spill occurred, Monroe obtained a second opinion, and it was determined that the 

embankment slope needed to be modified. The second opinion was again focused on the 

surficial sloughs and identified a number of remedial options. The company could have 

maintained the existing slopes, but recognized that there would be less maintenance with a 

flatter slope. Ultimately the company chose to modify the embankment slope to both repair 

surficial sloughs and incur less O & M expense in the future. Monroe operators perform 

weekly inspections of the fly ash basin to look for any visual differences concerning the ash 

basin. DTE Surveyors also use inclinometers and dike movement indicators to inspect the fly 

ash basin. Every two years, Monroe hires a private contractor to survey the ash basin and 

observe/record any location and depth changes.

Ash Handling

Overview

• Monroe operates wet fly ash and wet bottom ash handling systems on Units 1, 2, 3, and 4. 

Recently, Headwaters Resources (Headwaters) built a dry fly ash handling system on Units 1 

and 2. The dry fly ash handling system is currently in operation on Unit 1. Monroe stated that 

Unit 2 should be in operation by the end of September 2009. As currently planned, Units 3 

and 4 will have dry fly ash handling systems installed and operated by 2013. Headwaters 
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may build a dry fly ash handling system on one or both of the remaining Units (units 3 & 4), 

but will not build a dry system on any unit burning petroleum (pet) coke. The company is 

currently entertaining a request that it burn pet coke.

• The bottom ash is sluiced to Area 15. Mill rejects are collected and sluiced with the bottom 

ash. The bottom ash is dredged and sometimes used or sold for roadbed.

• Headwaters owns and operates the dry fly ash handling system at Monroe. Headwaters 

markets the ash to the cement/concrete industry for use in ready mix and concrete pipe. 

Headwaters has been in the business of marketing fly ash since the late 1980’s. 

• As the fly ash handling system is currently set up for Units 1 and 2, Monroe has the ability to 

handle fly ash wet or dry. The dry fly ash handling system was not intended to be a complete 

wet-to-dry conversion. The current system lacks redundancy and capacity to handle 100 

percent of the fly ash dry. Monroe was able to install and bring the dry fly ash handling 

system on line without any additional outages, outside of those regularly scheduled. The dry 

fly ash handling system was first installed parallel to the wet fly ash handling system, and 

then connected to the wet fly ash handling system during a regularly scheduled outage.

• Monroe produces a class of dry fly ash that is between “C” and “F”. Plant personnel stated 

that there is high demand for their fly ash. Plant personnel stated that the loss on ignition 

(LOI) of their fly ash is typically 1.5 percent. 

• The piping of the dry fly ash handling system is routed to pneumatically transfer fly ash to a 

Headwaters owned and operated 4,000 ton storage silo, which is 3,100 ft away from the ash 

silos at the Monroe plant.

• Headwaters operates the dry fly ash truck loading area with four on-site employees. Two 

Headwaters employees, Mr. Mike Dunlap and Mr. Lance Staron, spoke with EPA during the 

Monroe site visit. The dry fly ash truck loading area is currently only able to handle/load 

“bone dry” (less than one percent moisture) fly ash for sale. It is not set up to moisturecondition the fly ash, as would be done for landfilling. Headwaters has sold about 4,000 tons 

of Monroe’s fly ash from August 6, 2009 to the time of the site visit; local market demand 

has driven when Unit 1 fly ash has been handled dry. Similarly, market demand will 

determine whether Unit 2 fly ash will be handled dry. The demand for dry fly ash will likely 

increase next summer. Headwaters intends to stock pile the dry fly ash this winter for the 

demand next season.

• Headwaters has a rail network across the country for selling/transporting dry fly ash and they 

network locally by truck. The company strategically placed ash storage silos across the 

country where ash demand is high. Headwaters looks to expand the dry fly ash sales at 

Monroe. Rail would allow Headwaters to market the fly ash where demand is high yearround. Rail loading equipment is already installed at the Monroe plant. To begin operation, 

this rail loading equipment would need to be connected and track would need to be installed. 

Rail loading would increase the staff requirements at the loading facility. 

Detailed Fly Ash Handling Operation
Page 6

• The fly ash from Monroe’s Unit 1 is collected dry in two rows of precipitator hoppers (upper 

and lower). 

• When Monroe operates the wet fly ash handling system, economizer and fly ash are pulled 

dry by a vacuum (using a water ejector/eductor) through a set of pipes that split from the 

pipes used for the dry fly ash handling system. The ash is then introduced to water for 

sluicing in slurry tanks. The ash sluice is then pumped from the slurry tanks to the fly ash 

basin located approximately 3,500 ft from the precipitator. 

• When Monroe operates the dry fly ash handling system, only fly ash (no economizer ash) is 

pulled by vacuum, using mechanical exhausters, from the precipitator hoppers to two 

filter/separators. The filter/separators separate the fly ash from the transfer air, which is 

exhausted. The fly ash is then dropped into a 150-ton, air-locked transfer hopper. The ash is 

then introduced to the compressed air pressure system that pushes it to the storage silo at the 

Headwaters loading site. The timed, air-locked transfer hopper allows the system to switch 

between the negative and positive air pressure used to transport the ash. 

• The dry fly ash is transported 3,100 ft to the Headwaters loading site. With the current 

system at Monroe, 3,100 ft is probably the farthest distance that the ash can be efficiently 

transported pneumatically. Options to improve the system include larger blowers or a booster 

system. With a booster system, bursts of air are strategically placed along the pipe to enhance 

air flow. Headwaters stated that 4,000 ft is about the maximum distance that ash can be 

transferred pneumatically. 

• Headwaters stated that there are two ways to transfer fly ash pneumatically. The first is called 

a dilute system, in which there is a small amount of ash relative to air in the pipe. This 

system, which is operated at Monroe, offers less risk of clogging. The other type of system 

operates with higher amounts of ash relative to air in the pipe. Although the system ideally 

transfers more ash through the pipe than the dilute system, it is usually more expensive, 

slower, less reliable, and not cost effective.

• From the 4,000-ton storage silo, the ash is pneumatically transferred to a 200-ton loading silo 

by an air slide and bucket conveyor. The air slide, located at the bottom of the storage silo, is 

a long piece of fabric membrane, positioned at a specific gradient with air jets underneath 

that float and move the ash “down the slide”. From the slide, the ash is filled into the bucket 

conveyor, which can load the silo at 200 tons per hour if necessary. Both the air slide and 

bucket conveyor are operated under a vacuum system. Any fugitive dust is pulled back into 

either the main storage silo or the loading silo and collected in a baghouse at the top of each 

silo. There are induced air fans that pull air out of the silos through the filter bags. An air 

quality monitor is located in the loading area that continually monitors for fugitive dust.

• According to Headwaters, capacity at storage silo is enough to handle about 4 days of ash 

production at the plant.

• Dry fly ash is transferred from the loading silo to the trucks pneumatically with a double 

annular spout. A vacuum is pulled through the outer annulus of the spout, creating a tight seal 

with the truck. Ash is delivered through the inner annulus of the spout into the truck. The 
Page 7

vacuum captures any fugitive dust and pulls it through the loading silo to the baghouse. It 

takes about 1 or 2 minutes for the ash to settle in the trucks before the spout is pulled away. 

• Headwaters frequently tests the moisture content of the dry fly ash being loaded. Plant 

personnel stated that is the fly ash usually contains less that 1 percent moisture.

• The amount of ash that is transferred to the trucks is determined by weight. Trucks in 

Michigan are permitted to haul up to 50 tons. Headwaters estimated that they can load about 

25 tons of ash into a truck in 10 minutes, and can load 200 tons from the loading silo into 

eight trucks.

• Monroe stated that a complete conversion from the current wet/dry fly ash handling system 

to a moisture-conditioned dry fly ash handling system (suitable for landfilling the dry fly ash) 

would require the following major changes: 

• The 150-ton silos that collect the dry fly ash from the precipitator hoppers 

would need to be converted to 500-ton silos to support a completely dry 

system. 

• Modifying the silo and loading area for moisture-conditioning would also be 

expensive. This modification would include adding an exhaust system and 

doors to the loading area that will provide enclosure to the transfer space. 

Additionally, Monroe stated that because they burn 70 percent PRB coal, any 

moisture conditioning would cause the ash to become cementitious in the 

bottom of the storage silo.

• Transfer of the moisture-conditioned ash to the basin/landfill would be a 

potential issue. Suggested options include truck, pneumatic transfer, or 

conveyors. State and township permits would be developed to control any 

fugitive dust and the infrastructure (new roads or piping) used for transport.

• Monroe would also have to develop another ash handling system specifically 

for economizer ash. The economizer ash cannot be handled with marketable 

fly ash because the larger size of the economizer ash particles would make the 

ash unmarketable to the cement/concrete industry. Economizer ash also 

cannot be handled with bottom ash because the trace metals it contains would 

not allow Monroe’s bottom ash to meet certain state standards. The bottom 

ash is currently considered by the Michigan Department of Environmental 

Quality (MDEQ) to be inert and not a solid waste (i.e., does not leach any 

pollutants above drinking water standards). 

FGD System

• Monroe operates one limestone forced oxidation (LSFO) FGD scrubber system that services 

Unit 4. An identical FGD scrubber system has been installed to service Unit 3 (planned to be 

in operation Nov 2009). (UPDATE: Unit 3 FGD was placed in operation in November 2009.)

[QUESTION FOR MONROE: Is this FGD scrubber system currently operating?] Monroe is 

currently considering constructing/installing two additional LSFO FGD scrubbers that will 

service Units 1 and 2 by 2015, depending on the outcome of the CAIR rule and economic 
Page 8

factors. Plant personnel estimate that it takes about 30 months to construct, install, and bring 

an FGD scrubber system on line. It took about two weeks from the time Monroe began 

operating the Unit 4 FGD system to the time it was at steady state and Monroe could begin 

sending wastewater to the FGD wastewater treatment system. It took about 10 days from 

that point to “fill” the FGD wastewater treatment system with wastewater. 

• The Unit 4 FGD system has four absorber recycle pumps and four sets of spray headers. 

Three of the four are typically operated. The absorber has two trays. Process flow diagrams 

of the Unit 3 and 4 FGD systems are included in Attachment 4 of this memorandum. 

 

• The Unit 4 FGD absorber is constructed of concrete block and lined with Stebbins, semplate 

tile. It is a B&W design. 

• The Unit 4 FGD system achieves a sulfur dioxide removal of greater than 97 percent. After 

passing through the Unit 4 FGD system, flue gas exits through a dual flue chimney stack, 

which will also service the Unit 3 FGD system when it is operational.

• Monroe receives limestone by boat. The limestone is conveyed to a storage pile. Limestone 

for the Units 3 and 4 FGD systems is then conveyed to a silo with an 890 ton capacity.

• Monroe has two ball mills on site to crush limestone to the correct size for use in the 

limestone slurry. At the time of the site visit, one was in operation and the other was being 

prepped for operation. The ball mill crushes 43 tons of limestone per hour. 

• The limestone slurry from the ball mill is transferred to a classifier to remove the large 

limestone particles before the slurry is transferred to the limestone storage tank. The large 

limestone particles are recycled back to the ball mill for additional processing. 

• Monroe has a 600,000 gallon FGD make-up water tank that holds filtered plant service water. 

Plant service water, which is intake water from the surrounding Lake Erie (note that this is 

not Raisin River water due to a reversal of water flow), is filtered through six multimedia 

filters to remove any unwanted debris (e.g., stones, zebra mussel larvae). Backwash from 

these multimedia filters (“FGD pretreatment backwash”) is sent to the bottom ash basin. The 

filtered water is used for the limestone slurry, the FGD absorber mist eliminators, and the 

vacuum belt filter, 

• Monroe maintains a pH of approximately 5 to 6 S.U. in the Unit 4 FGD absorber.

• Monroe does not add any acid additives to the Unit 4 FGD scrubber system.

• Monroe blows down from the Unit 4 FGD absorber when the solids concentration in the 

absorber reaches 21 percent (by weight). This blowdown occurs about three times per day 

for approximately one to one and a half hours. The typical solids concentration in the FGD 

absorber is 19 to 21 percent and the typical chlorides concentration is 9,000 to 12,000 ppm 

(and always maintained below 12,000 ppm). Plant personnel stated that 15,000 ppm is the 

maximum allowable chlorides concentration according to the design specifications of the 

FGD scrubber. 
Page 9

• The blowdown from the FGD system is transferred to the primary hydroclones for initial 

solids separation. Four sets of hydroclones are currently in place that can service all four 

FGD systems, when operational. If the overflow from the primary hydroclones is between 

11,000 and 12,000 ppm chlorides, it is sent to the chloride purge tank. If the overflow from 

the primary hydroclones is between 9,000 and 10,000 ppm chlorides, it is recycled back to 

the reclaim water tank, from which water is recycled back to the absorber. The underflow 

from the primary hydroclones, which is approximately 55 percent solids (by weight), is 

transferred to filter feed tanks and then to the vacuum belt filter. 

• Monroe uses a vacuum belt filter to dewater the gypsum into a saleable byproduct. The 

vacuum used is created with a 500 horsepower pump. Monroe washes the gypsum with 

filtered plant service water as the gypsum is applied to the belt filter to reduce chlorides. The 

moisture content of the dewatered gypsum is about seven to eight percent. The filtrate from 

the vacuum belt filter is transferred to the reclaim tank. 

• Monroe markets the gypsum product and they are currently looking to improve their current 

contract. Monroe anticipates that the gypsum specifications will be less than ten percent 

moisture and less than 100 ppm chlorides in order for the gypsum to be used for wallboard. 

The gypsum produced at Monroe typically contains about 30 ppm chlorides. The gypsum 

from the vacuum belt filter is transferred to a gypsum storage building. The gypsum is either 

sold (Monroe is currently holding some saleable gypsum) or trucked to an offsite landfill at 

the Sibley Quarry, which is owned by Monroe. Typically, Monroe sends about four 

truckloads of gypsum per day to the Sibley Quarry. The Sibley Quarry landfill is not lined. 

Groundwater monitoring wells are located around this landfill. Landfill leachate is collected.

• The water in the chloride purge tank is transferred to the secondary hydroclones for 

additional solids separation. The underflow from the secondary hydroclones is transferred to 

the reclaim tank and the overflow is transferred to the wastewater treatment tank. Monroe 

sends wastewater from the wastewater treatment tank to the FGD wastewater treatment 

system once every three days for approximately two hours. 

• Monroe takes grab samples of the influent to the FGD wastewater treatment system from the 

top of the open wastewater treatment tank using a bucket. 

FGD Wastewater Treatment System

• The FGD wastewater treatment system operated at Monroe was designed by Siemens. 

Monroe monitors the wastewater treatment system at various points (effluent of equalization 

tank, reaction tank #1, effluent of the clarifier, and the final wastewater treatment system 

effluent) to ensure that it is achieving metals removal according to Siemens’ design 

specifications. Monroe sends the FGD wastewater treatment samples to a lab for analysis of 

metals that include, but are not limited to, aluminum, antimony, arsenic, copper, lead, 

mercury, and selenium.

• The two-train FGD wastewater treatment system operated at Monroe was designed to handle 

wastewater from all four FGD systems, when installed/operating. When operating at full 

capacity, Monroe projects that FGD wastewater will be treated 7 days a week and sludge will 

be treated 5 days a week. Currently, Monroe operates the FGD wastewater treatment system 

as a batch process. Each train of the wastewater treatment system was designed to treat 600 
Page 10

gpm of FGD wastewater (each clarifier can handle 1,200 gpm). The current, typical flow 

rate through the wastewater treatment system is 550 gpm. A process flow diagram of the 

FGD wastewater treatment system is included in Attachment 5 of this memorandum.

• The FGD scrubber purge (from the wastewater treatment tank) is transferred to the 

equalization tank of the FGD wastewater treatment system. The equalization tank also 

receives the filtrate from the wastewater treatment filter press, off-spec treated effluent, and 

water collected from the sumps of the wastewater treatment system building. [QUESTION 

FOR MONROE: At what flow rate is the FGD wastewater transferred to the equalization 

tank? What is the residence time of the wastewater in the equalization tank?] The influent

flow rate to the Equalization tank is 1200 gpm. The residence time in the equalization tank 

depends on the flow rate that the WWT plant is processing. At a flow rate of 600 gpm the 

residence time is approximately 12 hours.

• The wastewater treatment system includes a maintenance tank in case the equalization tank 

or sludge holding tank is out of service. 

• The wastewater from the equalization tank is transferred to reaction tank #1 (the wastewater 

treatment system includes two of these tanks) where lime slurry is added to adjust the pH of 

the wastewater. Organosulfide is added to target the removal of certain metals, such as 

mercury. The target pH in reaction tank #1 is between 8 and 9 S.U. 

• The FGD wastewater gravity drains to reaction tank #2 (the wastewater treatment system 

includes two of these tanks) where ferric chloride is added.

• From reaction tank #2, the wastewater gravity drains to the clarifiers (the wastewater 

treatment system includes two clarifiers). As the water is transferred, AcuTreat® 4355

polymer is added. The total retention time in the clarifiers is about 6 hours. 

• From the clarifier, the wastewater gravity drains into one of five sand gravity filters 

(continuous backwash). Hydrochloric acid is used to adjust the pH of the wastewater to 

between 6 and 8 S.U. as the water is transferred to the sand filters. 

• From the sand filters, the water is transferred to the treated wastewater storage tanks (there 

are two of these tanks) and is sent to the bottom ash basin (Area 15). [QUESTION FOR 

MONROE: How often is this treated effluent sent to the bottom ash basin, for how long, and 

at what flow rate?] On average Monroe’s WWT Plant will discharge to the bottom ash basin 

14 hours a day at a flow rate of 275 GPM. This depends upon the pH falling within a range 

of 6.5 to 9.0 and how much waste water is being sent to the WWT Plant from the FGD

system. This effluent is monitored for pH and turbidity. Off-spec treated wastewater is 

recycled to the equalization tank. 

• Monroe takes grab samples of the treated wastewater downstream of the treated wastewater 

storage tank on the suction side of the treated wastewater discharge pumps from a fiberglass 

reinforced plastic (RFP) pipe tap.

• Monroe estimated that the total retention time for the entire wastewater treatment process is 

approximately 12 hours. The residence time of the wastewater depends on the flow rate that 
Page 11

the WWT facility is processing. At a flow rate of 600 gpm the residence time is 

approximately 20 hours.

• Some of the sludge from the clarifiers is recycled to reaction tank #1 for seeding. The rest of 

the sludge is transferred to the sludge holding tank and then to the sludge conditioning tanks. 

Monroe dewaters the sludge from the sludge conditioning tanks using four belt filter presses.

As the sludge is loaded onto the belt press, AcuTreat® 4355 polymer is added. The press 

sandwiches the sludge between two rollers to remove moisture. The filtrate from the belt 

presses is recycled to the equalization tank. The dewatered sludge, which is typically about 

35 percent moisture, is transferred to four sludge hoppers and trucked off site to a landfill.

Metal Cleaning Wastes

• Monroe cleans each of their four boilers about once every ten years. Monroe uses an acid 

wash to clean the boiler tubes. The wastewater from cleaning the boilers is sent to a 6.5 

million gallon, open storage tank. Monroe’s past practice was to send water from the storage 

tank to the Unit 4 boiler, where it was evaporated. There is currently no discharge of metal 

cleaning wastes. [QUESTION FOR MONROE: What type of acid is used to clean the boiler 

tubes? The two acids used to clean the boiler tubes are 4% hydroxyacetic acid and 2% formic 

acid. How much wash water is generated and transferred to the storage tank with each 

cleaning (for each boiler)? The typical boiler volume is approximately 105,500 gallons. 

Unit 3 was cleaned in November 2009 and generated approximately 2.2 million gallons of 

wastewater, including wash water and rinse water. Unit 2 was cleaned in May 2010 and 

generated approximately 1.7 million gallons of wastewater, including wash water and rinse 

water. Exact volumes of metal cleaning wastewaters are not known for earlier cleanings, but 

are likely between about 1.7 million gallons and 2.5 million gallons. How often is water 

transferred from the storage tank to Unit 4 for evaporation? Between 1994 and 2001, the 

plant evaporated chemical metal cleaning wastewater in the Unit 4 boiler. However, Monroe 

will no longer be evaporating metal cleaning wastes, because it will poison the SCR catalyst 

and possibly the FGD. The current practice is to adjust the wastewater to a pH of 10 using 

lime, and then agitating it with oxygen in order to meet the NPDES permit requirements prior 

to discharge under the NPDES permit. EPA noted a significant volume of water in the 

storage tank – are other cleaning waters sent to this tank? Only chemical metal cleaning 

wastes are sent to this tank. Because it is an open tank, storm water may also enter the tank.

• Monroe stated that they only use water to clean the air heaters. No chemicals are added to the 

water during this process. The water is sent to the bottom ash basin (Area 15).
Table 1. Site Visit Attendees

Name Organization (Representing) Telephone E-mail

Mary Hana Environmental Management and 

Resources (313) 235-8704 hanamj@dteenergy.com

Chuck Larlham Environmental Management and 

Resources /Monroe Power Plant (734) 384-2560 larlhamr@dteenergy.com

Claire Jennings Environmental Management and 

Resources /Monroe Power Plant (734) 384-2562 jenningsc@dteenergy.com

Dan Casey Monroe Power Plant (734) 384-2371 caseyd@dteenergy.com

Dennis Leonard Environmental Management and 

Resources (313) 235-8714 leonardd@dteenergy.com

Brett Mac Intyre Environmental Management and 

Resources (313) 235-6922 macintyreb@dteenergy.com

Paul Tracy Monroe Power Plant (734) 384-6812 tracyp@dteenergy.com

Donna Hill UWAG/Southern Co. (205) 257-5234 dbhill@southernco.com

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

Jezebele AliceaVirella EPA/Office of Water (202) 566-1755 alicea.jezebele@epa.gov

Sarah Holman ERG (Contractor to EPA) (703) 633-1661 sarah.holman@erg.com

Elizabeth Sabol ERG (Contractor to EPA) (703) 633-1659 elizabeth.sabol@erg.com