that accumulates at the bottom of the furnace. The bottom ash consists
of the heavier ash particles that could not be entrained in the flue
gas and fall to the bottom of the furnace. In most furnaces, the hot
bottom ash is quenched in a water-filled hopper. Ash from the hopper is
then fed into a conveying line where it is diluted into slurry and
pumped to an impoundment or dewatering bins. The ash sent to a
dewatering bin is separated from the transport water and then disposed.
For both of these systems, the water used to transport the bottom ash
to the impoundment or dewatering bins is usually discharged to surface
water as overflow from the systems, after the bottom ash has settled.
Alternatively, some furnaces are fitted with mechanical drag systems
where the bottom ash drops into a water-filled trough, but the ash is
removed using a submerged mechanical drag conveyor that drags the
bottom ash out of the furnace. At the end of the trough, the drag chain
reaches an incline, which dewaters the bottom ash by gravity, draining
the water back to the trough as the ash moves up the conveyor. The
bottom ash is often dumped into a nearby bunker for temporary storage.
As the bottom ash continues dewatering in the nearby bunker, water that
drains from the system may be discharged; however, EPA does not
consider this water from the bunker to be bottom ash transport water
because the mechanical conveyor, and not the water, is the transport
mechanism that moves the ash away from the boiler. Instead, the
wastewater draining from the bunker would be low volume wastes. Over 65
percent of the units generating bottom ash operate wet bottom ash
transport systems, approximately 30 percent operate systems that
eliminate the use of transport water, and approximately 5 percent
operate both. Plants that have both wet and dry handling operations
typically use the wet handling system as a backup to the dry system.
Some plants that have wet bottom ash systems operate them in a manner
that does not discharge to surface water.
    Bottom ash transport water is an intermittent stream from steam
electric units. The bottom ash transport water flow rates are typically
not as large as the fly ash transport water flow rates; however, bottom
ash transport water is still one of the larger volume flows for steam
electric plants. Based on responses to the industry survey, the average
bottom ash transport water flow rate is 1.8 MGD. EPA estimates that the
steam electric industry discharged a total of 157 billion gallons of
bottom ash transport water in 2009.
    Power plants that generate fly ash and bottom ash can either
dispose of it in landfills or surface impoundments, or can use it in
applications such as cement or concrete manufacturing. Power plants
have used the ash in many applications that preclude the need to
dispose of the ash in landfills/impoundments.
2. FGD Systems
    FGD systems remove sulfur dioxide from the flue gas so that it is
not emitted into the air. There are both wet and dry FGD systems. Dry
FGD systems generally inject an aqueous sorbent (e.g., lime) into a
spray dryer such that the water present evaporates as it contacts the
hot flue gas. The sulfur dioxide in the flue gas reacts with the lime
as it dries and results in a dry particulate product that is captured
in a downstream fabric filter; no wastewater is generated from the dry
FGD process. In wet FGD systems, the flue gas stream comes in contact
with a liquid stream containing a sorbent, typically lime or limestone,
which is used to effect the mass transfer of pollutants from the flue
gas to the liquid stream. This process not only transfers the sulfur
dioxide from the flue gas to the liquid stream, but other pollutants
(e.g., metals) as well. During this process, the lime/limestone and
sulfur dioxide react to form calcium sulfite or calcium sulfate (i.e.,
gypsum), depending on the oxidation level of the FGD system. Gypsum is
a marketable product, and as such, plants that generate gypsum
generally sell (or give away) the material for use in building
materials (e.g., wallboard). Plants that do not generate gypsum, or
only partially oxidize the calcium sulfite, generally dispose of their
FGD solids in landfills or surface impoundments. Those plants that
produce a saleable product, such as gypsum, may rinse the product cake
to reduce the level of chlorides in the final product. This wash water
may be reused or discharged to a receiving water or POTW. Additionally,
both calcium sulfite and gypsum typically require dewatering prior to
sale/disposal and this dewatering process also generates a wastewater
stream that may be reused or discharged. The FGD system generally
requires a blowdown stream to purge chlorides to prevent scaling and
corrosion of the FGD equipment.
    FGD wastewater is typically an intermittent stream generated by
coal-fired power plants operating wet FGD systems. Based on responses
to the industry survey, the average FGD wastewater flow rate is 559,000
gallons per day (gpd). EPA estimates that the steam electric industry
discharged a total of 23.7 billion gallons of FGD wastewater in 2009.
    Based on the responses to the industry survey, there are
approximately 401 FGD systems either currently operating or that will
be installed by January 1, 2014.\9\ Approximately 90 of the currently
operating FGD systems are dry systems that do not generate any
wastewater streams, while 311 systems are wet FGD systems.\10\
---------------------------------------------------------------------------

    \9\ Because EPA expects to take final action on this rule in
2014, EPA used 2014 as the baseline year for its analysis. EPA is
considering using alternative dates, such as 2022 which may better
reflect the implementation timeframe for the ELG, for the baseline
year for its analyses for the final rule.
    \10\ This is not the number of steam electric power plants with
wet FGD systems. An individual steam electric power plant may
operate one or more FGD systems.
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3. Flue Gas Mercury Control (FGMC) Systems
    FGMC systems remove mercury from the flue gas, so that it is not
emitted into the air. According to the responses to the industry
survey, two main types of

systems are currently in use in the industry: (1) Addition of oxidizers
to the coal prior to combustion, whereby the oxidized mercury is
removed in the wet FGD system; and (2) injection of activated carbon
into the flue gas which adsorbs the mercury and is captured in a
downstream particulate removal system.
    The use of the oxidizers does not generate a new wastewater stream;
however, it may increase the concentration of mercury in the FGD
wastewater because the oxidized mercury is more easily removed by the
FGD system. The activated carbon injection system does have the
potential to generate a new wastestream at a plant, depending on the
location of the injection. If the injection occurs upstream of the
primary particulate removal system, then the mercury-containing carbon
(i.e., FGMC waste) is collected and handled the same way as the fly
ash. Therefore, if the fly ash is wet sluiced, then the FGMC wastes are
also wet sluiced and likely sent to the same surface impoundment. In
this case, adding the FGMC wastes to the fly ash can increase the
amount of mercury in the fly ash transport water. If the injection
occurs downstream of the primary particulate removal system, then the
plant will need a secondary particulate removal system (typically a
fabric filter) to capture the FGMC wastes. Plants typically inject the
carbon downstream of the primary particulate collection system if they
plan to market the fly ash because the carbon in FGMC wastes can make
the fly ash unmarketable. In this situation, the FGMC wastes, which
would be collected with some carry-over fly ash, could be handled
either wet or dry.
    Based on the responses to the industry survey, in 2009 there were
approximately 120 operating FGMC systems, with an additional 40 planned
for installation by 2020. Approximately 90 percent of the currently
operating FGMC systems are dry systems that do not generate or affect
any wastewater streams. Approximately six percent of the currently
operating systems are wet systems. For the remaining 4 percent of the
systems, the type of handling system (e.g., wet or dry handling) is
unknown.
4. Combustion Residual Leachate From Surface Impoundments and Landfills
    Combustion residuals comprise a variety of wastes from the
combustion process, including fly ash, bottom ash (which includes
boiler slag), and FGD solids (e.g., gypsum and calcium sulfite), which
are generally collected by or generated from the air pollution control
technologies. These combustion residuals may be stored at the plant in
on-site landfills or surface impoundments (i.e., ponds). Based on
industry survey results, there are approximately 228 plants that
operate combustion residual landfills and 264 plants that operate
combustion residual surface impoundments. Some plants operate both
landfills and impoundments, while other plants may operate only one or
the other, or neither type of disposal unit.
    Leachate is the liquid that drains or leaches from a landfill or
surface impoundment. Most landfills have a system to collect the
leachate and some impoundments have leachate collection systems. The
two sources of leachate are precipitation that percolates through the
waste deposited in the landfill/impoundment and the liquids produced
from the combustion residuals placed in the landfill/impoundment. In
addition to leachate, stormwater that enters the impoundment or
contacts and flows over the landfill would be contaminated with
combustion residual pollutants. Leachate and contaminated stormwater
contain heavy metals and other contaminants through the contact with
the combustion residuals.
    Some landfills and surface impoundments are lined. In a lined
landfill/impoundment, the leachate collected in the liner typically
flows through a collection system consisting of ditches and/or
underground pipes. From the collection system, the leachate is
transported to an impoundment (e.g., collection pond). The stormwater
collection systems typically consist of one or more small impoundments
or collection ponds. The leachate and stormwater may be treated in
separate impoundments or combined together. Some plants discharge the
effluent from these leachate impoundments, while other plants send the
leachate impoundment effluent to another impoundment handling the ash
transport water or other treatment system (e.g., constructed wetlands).
Unlined impoundments and landfills usually do not collect leachate
thereby leaving the leachate to potentially migrate to nearby ground
waters, drinking water wells, or surface waters.
    Based on responses to the industry survey, approximately 100 plants
collect landfill leachate from approximately 110 existing (i.e., active
or inactive) landfills containing CCR, while approximately 50 plants
collect leachate from existing CCR surface impoundments. Another 40
plants collect leachate from both types of systems.
    Leachate is an intermittent stream whose flow rate, frequency, and
duration are generally determined by weather conditions. For this
reason, leachate flow rates can vary greatly for a plant, as well as
varying from one plant to another. Additionally, there are differences
in flow rates depending on whether the landfill or surface impoundment
is active/inactive or retired. Retired landfills or surface
impoundments tend to have lower flow rates because they have been
capped or closed and, therefore, are not open to the atmospheric
rainfall. Based on the industry survey, the average active/inactive
landfill leachate flow rate was approximately 60,000 gpd. EPA estimates
that the steam electric industry discharged approximately 6.2 billion
gallons of leachate in 2009.
5. Gasification Processes
    As described above, IGCC plants uses a carbon-based feedstock
(e.g., coal or petroleum coke) and subject it to high temperature and
pressure to produce a synthetic gas (``syngas'') which is used as the
fuel for a combined cycle generating unit. In these IGCC plants, after
the syngas is produced, it undergoes cleaning prior to combustion. The
cleaning processes can involve any number of the following processes:
     Water scrubbing;
     Carbonyl-sulfide hydrolysis;
     Acid gas removal (stripping); and
     Sulfur recovery.
    The wastewater generated by these processes, along with any
condensate generated in flash tanks, slag handling water, or wastewater
generated from the production of sulfuric acid, are referred to as
``grey water'' or ``sour water,'' and require treatment prior to reuse
or discharge.
    EPA identified two plants currently operating IGCC units, and a
third IGCC unit is scheduled to begin operation this year. A fourth
IGCC power plant is under construction and is scheduled to begin
commercial operation in 2014.
    The gasification processes generally operate continuously and,
therefore, generate most of the individual gasification wastestreams
continuously. Based on the information collected during EPA's sampling
program, EPA determined the gasification wastewater transferred to the
treatment system ranged from 6,000 to 109,000 gpd, with an average flow
of 66,000 gpd.
6. Metal Cleaning Wastes
    The ELGs define metal cleaning waste as ``any wastewater resulting
from cleaning [with or without chemical cleaning compounds] any metal
process equipment, including, but not limited to, boiler tube cleaning,
boiler fireside cleaning, and air preheater cleaning.'' 40

CFR 423.11. Plants use chemicals to remove scale and corrosion products
that accumulate on the boiler tubes and retard heat transfer. The major
constituents of boiler cleaning wastes are the metals of which the
boiler is constructed, typically iron, copper, nickel, and zinc. Boiler
firesides are commonly washed with a high-pressure water spray against
the boiler tubes while they are still hot. Fossil fuels with
significant sulfur content will produce sulfur oxides that adsorb on
air preheaters. Water with alkaline reagents is often used in air
preheater cleaning to neutralize the acidity due to the sulfur oxides,
maintain an alkaline pH, and prevent corrosion. The types of alkaline
reagents used include soda ash, caustic soda, phosphates, and
detergent.
    The frequency of metal cleaning activities can vary depending on
the type of cleaning operation and individual plant practices. Some
operations occur as often as several times a day, while others occur
once every several years. Soot blowing, the process of blowing away the
soot deposits on furnace tubes, generally occurs once a day, but some
units do this as often as several hundred times a day. While 83 percent
of units responding to the industry survey use steam or service air to
blow soot, some plants may generate wastewater streams. Air heater
cleaning is another frequent cleaning activity. Sixty-six percent of
the units perform this operation at least once every two years, while
other units perform this cleaning task very infrequently, only once
every 40 years. Generally, plants use raw or potable water to clean the
air heater.
    The following types of metal cleaning wastes were reported in
responses to the industry survey:
     Air compressor cleaning;
     Air-cooled condenser cleaning;
     Air heater cleaning;
     Boiler fireside cleaning;
     Boiler tube cleaning;
     Combustion turbine cleaning (combustion portion and/or
compressor portion);
     Condenser cleaning;
     Draft fan cleaning;
     Economizer wash;
     FGD equipment cleaning;
     Heat recovery steam generator cleaning;
     Mechanical dust collector cleaning;
     Nuclear steam generator cleaning;
     Precipitator wash;
     SCR catalyst soot blowing;
     Sludge lancing;
     Soot blowing;
     Steam turbine cleaning; and
     Superheater cleaning.
7. Carbon Capture and Storage Systems
    The industry is investigating carbon capture and storage systems to
remove carbon dioxide (CO2) from the flue gas. Many steam
electric power plants are considering alternatives available for
reducing CO2 emissions; however, according to the industry
survey responses, there are no full-scale carbon capture systems
currently operating. EPA obtained information about two pilot-scale
systems that operated in recent years; however, neither of these
systems is currently operating. Additionally, several plants reported
in their survey responses that they are planning to install a pilot-
scale carbon capture system and some plants reported plans to install
full-scale systems by 2020.\11\
---------------------------------------------------------------------------

    \11\ In order to protect CBI claims, EPA cannot provide specific
numbers.
---------------------------------------------------------------------------

    There are three main approaches for capturing the CO2
associated with generating electricity: Post-combustion, pre-
combustion, and oxyfuel combustion.
     In post-combustion capture, the CO2 is removed
after combustion of the fossil fuel.
     In pre-combustion capture, the fossil fuel is partially
oxidized, such as in a gasifier. The resulting syngas (CO and
H2) is processed to create CO2 and more
H2, and the resulting CO2 can be captured from a
relatively pure exhaust stream before combustion takes place.
     In oxy-fuel combustion, also known as oxy-combustion, the
fuel is burned in oxygen instead of air. The flue gas consists of
mainly CO2 and water vapor; the latter condenses through
cooling. The result is an almost pure CO2 stream that can be
transported to the sequestration site and stored.
    Based on preliminary information regarding these technologies, EPA
believes they may result in new wastewaters at steam electric power
plants. However, as these technologies are currently in the early
stages of research and development and/or pilot testing, the industry
has little information on the potential wastewaters generated from
carbon capture processes. As part of its sampling program, EPA obtained
analytical data associated with two wastestreams generated from a post-
combustion carbon capture system. Because of the small size of the
pilot-scale system, the plant transferred the wastewater off site for
treatment.

C. Control and Treatment Technologies

    EPA evaluated the technologies available to control and treat
wastewater generated by the steam electric industry. Individual plants
may use one or more processes that generate wastewater streams. They
may treat these wastestreams separately or in various combinations. For
this reason, EPA evaluated available technologies for each major
wastestream separately.
1. FGD Wastewater
    EPA identified 145 steam electric power plants that generate FGD
wastewater. Of these, 117 plants (81 percent) discharge FGD wastewater
after treatment using one or more of the following technologies:
     Surface Impoundments: Surface impoundments (e.g., settling
ponds), designed to remove particulates from wastewater by means of
gravity, may be configured as one impoundment or a series of
impoundments. Impoundments are typically sized to allow for a certain
residence time to enable the suspended solids to settle to the bottom.
The impoundments are also designed to have sufficient capacity to allow
for temporary storage or permanent disposal of the settled solids.
Surface impoundments are not designed to remove dissolved metals.
Plants may add treatment chemicals to the impoundment, typically to
adjust pH before final discharge.
    There are 63 plants (54 percent of the discharging plants) that use
surface impoundments as the only type of treatment for FGD wastewaters.
Most (49) of these plants also combine their FGD wastewater with other
plant wastewater while the remainder (14) use impoundments to treat FGD
wastewater alone. Additional plants (above and beyond the 63 plants
described in the preceding sentences) also use surface impoundments to
remove suspended solids prior to a more advanced treatment process,
such as chemical precipitation or biological treatment.
     Chemical Precipitation: Some plants use chemical
precipitation systems instead of or in addition to surface
impoundments. Chemical precipitation treatment is a tank-based system
in which chemicals are added to enhance the removal of suspended solids
and dissolved solids, particularly certain dissolved metals. The
dissolved metals amenable to chemical precipitation treatment are
removed from aqueous solutions by converting soluble metal ions to
insoluble metal hydroxides or sulfides. The precipitated solids are
then removed from solution by coagulation/flocculation followed by
clarification and/or filtration. Chemical reagents such as lime
(calcium hydroxide), sodium hydroxide, and ferric chloride are used to
adjust the pH

of the water to reduce the solubility of the metal(s) targeted for
removal.
    Some plants also use sulfide chemicals (e.g., organosulfides or
sodium sulfide) to precipitate and remove heavy metals, including
mercury. Sulfide precipitation is more effective than hydroxide
precipitation in removing mercury because mercury sulfides have lower
solubilities than mercury hydroxides. Other metal sulfide compounds
also typically have lower solubilities than metal hydroxide compounds.
Because sulfide precipitation is more expensive than hydroxide
precipitation, plants usually use hydroxide precipitation first to
remove most of the metals, and then sulfide precipitation to remove the
remaining low solubility metals. This configuration overall requires
less sulfide, thereby reducing the expense for the sulfide treatment
chemicals.
    EPA identified 40 plants (34 percent of the discharging plants)
that treat their FGD wastewater using chemical precipitation (in some
cases, also employing additional treatment steps such as biological
treatment). Lime is the most commonly used treatment chemical to
perform the pH adjustment needed for these systems. Sulfide
precipitation, alone or in combination with hydroxide precipitation, is
used by 33 plants (28 percent of the discharging plants). Most plants
operating chemical precipitation treatment systems for FGD wastewater
employ ferric chloride addition (i.e., iron coprecipitation) as part of
the treatment process.
     Biological Treatment: Some steam electric power plants
also treat FGD wastewater using biological treatment systems. An
anoxic/anaerobic biological system being used in the industry is
effective at removing both metals (total and dissolved) and nutrients.
This system is designed to significantly reduce nitrogen compounds and
selenium. These fixed-film bioreactors are designed for plug flow
operation and have zones of differing oxidation potential that allow
for nitrification and denitrification of the wastewater and reduction
of metals, such as selenium. The system alters the form of selenium,
reducing selenate and selenite to elemental selenium, which is then
captured by the biomass and retained in treatment system residuals.
    EPA identified five plants that operate the fixed-film anoxic/
anaerobic biological treatment systems to treat FGD wastewater, and
another plant recently installed a suspended growth biological
treatment system that targets removal of selenium and other metals.\12\
Four of these six plants also operate chemical precipitation systems
prior to the biological treatment system. There are also at least four
other plants that operate aerobic/anaerobic sequencing batch reactors
to treat FGD wastewater that has already undergone chemical
precipitation. These systems are capable of removing organics and
nutrients, but are not operated in a manner to remove selenium or other
metals.
---------------------------------------------------------------------------

    \12\ A seventh plant is scheduled to begin operating a
biological treatment system for selenium removal in 2014. This plant
is not included in this summary of biological treatment systems.
---------------------------------------------------------------------------

     Vapor-Compression Evaporation System: This type of system
uses a falling-film evaporator (or brine concentrator) to produce a
concentrated wastewater stream and a distillate stream. With
pretreatment, such as chemical precipitation and softening, brine
concentrators can reduce wastewater volumes by 80 to 90 percent. Plants
can further process the concentrated wastewater stream in a
crystallizer or spray dryer, which evaporates the remaining water to
generate a solid waste product and potentially a condensate stream. The
distillate and condensate streams may be reused within the plant or
discharged to surface waters. EPA identified two U.S. plants and four
Italian plants that treat FGD wastewater using vapor-compression
evaporation. A third U.S. plant is currently installing a vapor-
compression evaporation treatment system; it is scheduled to be
operational by the end of 2013.
     Constructed Wetlands: Constructed wetlands are engineered
systems that use natural biological processes involving wetland
vegetation, soils, and microbial activity to reduce the concentrations
of metals, nutrients, and TSS in wastewater. High temperature, chemical
oxygen demand (COD), nitrates, sulfates, boron, and chlorides in
wastewater can adversely affect constructed wetlands performance. To
overcome this, plants typically dilute FGD wastewater with service
water (i.e., supply water used widely throughout the plant for a
variety of uses) before it enters a constructed wetland.
    EPA identified three plants that treat their FGD wastewater using
constructed wetlands. The constructed wetlands used to treat FGD
wastewater typically are designed to treat only the FGD wastewater (and
the service water used for dilution); however, because these systems
are open to the environment, they also receive stormwater from the
surrounding areas.
     Other Technologies: EPA identified several other
technologies that have been evaluated for treatment of FGD wastewater,
including iron cementation, reverse osmosis, absorption or adsorption
media, ion exchange, and electro-coagulation. Other technologies under
laboratory-scale study include polymeric chelates, taconite tailings,
and nano-scale iron reagents. Most of these technologies have been
evaluated only as pilot-scale studies; however, two of these
technologies are currently operating at full-scale to treat FGD
wastewater. One plant operates a full-scale ion exchange system that
selectively targets the removal of boron, in conjunction with a
chemical precipitation treatment stage to remove mercury and other
metals, and an anaerobic biological treatment stage to remove selenium.
Another plant treats the FGD wastewater with chemical precipitation,
followed by a full-scale treatment unit that uses cartridge filters in
combination with two sets of adsorbent media specifically designed to
enhance removals of metals. After passing through three sets of
cartridge filters (3-micron, 1-micron, and then 0.2-micron), the FGD
wastewater passes through a carbon-based media that adsorbs mercury,
and then through a ferric hydroxide-based media that adsorbs arsenic,
chromium, and other metals. The adsorbent media reportedly achieves a
maximum effluent concentration of 14 parts per trillion for mercury.
     Design/Operating Practices Achieving Zero Discharge: EPA
identified four design/operating practices available enabling plants to
eliminate the discharge of wastewater from wet FGD systems: 1) Several
variations of complete recycle, 2) evaporation ponds, 3) conditioning
dry fly ash, and 4) underground injection. Of the 145 plants that
generate wastewater from FGD processes, 28 plants (19 percent) operate
in such a manner that they do not discharge wastewater to surface
waters or POTWs. Many of the plants in the southwestern United States
that generate FGD wastewater use evaporation ponds that do not
discharge.
2. Fly Ash Transport Water
    Fly ash separated from boiler exhaust by electrostatic
precipitators (ESPs) or fabric filters is collected in hoppers located
underneath the equipment. From the collection hoppers, the fly ash is
either transferred as dry ash to silos for temporary storage or
transported (sluiced) with water to a surface impoundment (i.e., ash
settling pond). Plants that generate fly ash transport

water use surface impoundments to manage the wastewater. EPA has not
identified any facilities using more advanced treatment, such as
chemical precipitation or biological treatment, to treat fly ash
transport water. EPA identified 393 generating units (at 144 plants)
that wet sluice at least a portion of fly ash. Wet sluicing systems use
water-powered hydraulic vacuums to withdraw fly ash from the hoppers.
The ash is pulled to a separator/transfer tank, combined with sluicing
water, and pumped to the surface impoundment to remove particulates
from the wastewater by means of gravity, before discharge to a
receiving stream.
    Many coal and oil-fired power plants design their fly ash handling
systems to minimize or eliminate the discharge of fly ash handling
transport water. Such approaches include:
     Wet Vacuum Pneumatic System: These systems use water-
powered hydraulic vacuums for the initial withdrawal of fly ash from
the hoppers, similar to wet sluicing systems. Instead of sluicing the
ash to a surface impoundment, these systems capture the ash in a
filter-receiver (bag filter with a receiving tank) and then deposit the
dry ash in a silo.
     Dry Vacuum Pneumatic System: These systems use a
mechanical exhauster to move air, below atmospheric pressure, to pull
the fly ash from the hoppers and convey it directly to a silo. The fly
ash empties from the hoppers in to the conveying system via a material
handling valve.
     Pressure System: These systems use air produced by a
positive displacement blower to convey ash directly from the hopper to
a silo. Each ash collection hopper is equipped with airlock valves that
transfer the fly ash from low pressure to high pressure in the
conveying line. The airlock valves are installed at the bottom of the
hoppers and require a significant amount of space. Retrofit
installations of pressure ash handling systems may require raising the
bottom of the hopper.
     Combined Vacuum/Pressure System: These systems use a dry
vacuum system to pull ash from the hoppers to a transfer station, where
the ash is transferred from the vacuum (low pressure) to ambient
pressure. From the transfer station, the fly ash is transferred via
airlock valves to a high pressure conveying line. A positive
displacement blower conveys the ash to a silo. Because the airlocks are
not located under the hopper, combination vacuum/pressure systems have
the space advantages of dry vacuum systems.
     Mechanical System: Oil-fired units or other units that
generate a low volume of fly ash may use manual or systematic
approaches to remove fly ash (e.g., scraping the sides of the boilers
with sprayers or shovels, then collecting and removing the fly ash to
an intermediate storage destination or disposal).
    The following identifies the number of units (and plants) in the
steam electric industry operating each of the different technologies
available to eliminate the discharge of fly ash transport water:
     Wet vacuum pneumatic system--51 units (22 plants);
     Dry vacuum pneumatic system--485 units (220 plants);
     Pressure system--188 units (91 plants);
     Combined vacuum/pressure system--223 units (102 plants);
     Mechanical system--16 units (13 plants); and
     Other dry systems--5 units (3 plants).
3. Bottom Ash Transport Water
    Bottom ash (at times also referred to as boiler slag) is produced
as fuel is burned in a boiler and collected in hoppers or other types
of collection equipment directly below the boiler. Generally, boilers
are sloped inward, with an opening at the bottom to allow the bottom
ash to feed by gravity into collection hoppers. The hoppers contain
water to quench the hot ash. Once the hoppers are full, gates at the
bottom of the hoppers open, releasing the bottom ash and quench water
to a conveying line, where the ash is diluted with water to
approximately 20 percent solids (by weight) and pumped to a surface
impoundment or a dewatering bin for solids removal. Conveying bottom
ash in a water slurry is called wet sluicing. EPA identified 870 units
(345 plants) that wet sluice at least a portion of their bottom ash.
For further information, see Section 4.3.2 of the Technical Development
Document for Proposed Effluent Limitations Guidelines and Standards for
the Steam Electric Power Generating Point Source Category (TDD)--EPA
821-R-13-002.
    Many coal and oil-fired power plants design their bottom ash
handling systems to reduce or eliminate the discharge of bottom ash
handling transport water. Available technologies include:
     Mechanical Drag System: In these systems, the ash
collection hopper is replaced with a transition chute that routes the
bottom ash to a water-filled trough. In the trough, a drag chain
continuously moves the ash to an incline where it is dewatered and then
conveyed to a nearby ash collection area. Excess quench water collected
in the dewatering system is recycled to the quench water bath.
    Although mechanical drag systems require little space under the
boiler they may not be suitable for all boiler configurations.
    In the steam electric industry, 99 coal-fired units use mechanical
drag systems for bottom ash handling. Operators have announced plans to
retrofit mechanical drag systems on additional units by 2020. EPA
estimates that these announced retrofits include approximately 10-30
generating units. (Note: the precise value has been withheld to prevent
disclosing CBI.)
     Remote Mechanical Drag System: These systems collect
bottom ash in water-filled hoppers and wet sluice the ash to a
mechanical drag system located away from the boilers. Sluice water
collected from the dewatered bottom ash is collected and reused in the
bottom ash handling system. Plants can use remote mechanical drag
systems to convert existing bottom ash handling systems with limited
space or other configuration limitations. One U.S. plant has installed
and is currently operating a remote mechanical drag system to handle
bottom ash. At least one additional plant is currently installing a
remote mechanical drag systems to handle bottom ash. Additionally, a
large U.S. power company has been evaluating installing remote
mechanical drag systems for several of its plants.
     Dry Vacuum or Pressure System: These systems transport
bottom ash from the boiler to a dry hopper without using any water. The
system percolates air through the ash to cool it and combust unburned
carbon. Cooled ash then drops to a crusher and is conveyed via vacuum
or pressure to an intermediate storage destination.
     Complete Recycle System: Complete recycle systems
transport bottom ash using the same processes as wet sluicing systems.
Plants can install complete recycle on existing wet sluicing units.
Instead of transporting it to an impoundment, the ash is sluiced to
dewatering bins, where it is dewatered and moved to storage. The
transport (sluice) water is treated to remove solids in a settling tank
and is recycled to the bottom ash collection system. Prior to reusing
the treated transport water, plants may add treatment chemicals to the
water to adjust pH and prevent equipment corrosion.
     Vibratory Belt System: Bottom ash deposits on a vibratory
conveyor trough, where the plant cools the ash by air and ultimately
moves it through the

conveyor deck to an intermediate storage destination.
     Mechanical System: Oil-fired units or other units that
generate a low volume of bottom ash, may use manual or systematic
approaches to removing ash that accumulates in the boiler (e.g.,
scraping the sides of the boilers with sprayers or shovels, then
collecting and removing the bottom ash to an intermediate storage
destination or disposal).
    The following identifies the number of units (and plants) in the
steam electric industry operating each of the different technology
options available to eliminate or minimize the amount of bottom ash
transport water:
     Mechanical drag system--99 units (74 plants);
     Remote mechanical drag system--at least 2 units (2 plants)
installing systems since 2009;
     Dry vacuum system--111 units (68 plants);
     Dry pressure system--13 units (11 plants);
     Complete recycle systems--at least 20 plants; and
     Mechanical systems--38 units (19 plants).
4. Combustion Residuals Leachate From Landfills and Surface
Impoundments
    Plants often treat combustion residual landfill leachate with some
of the same technologies used to treat FGD wastewater as described in
Section VI.C.1. EPA identified 102 coal-fired power plants that
generate and discharge leachate. Based on the responses to the industry
survey, 29 of these plants treat the leachate prior to discharge using
surface impoundments, constructed wetlands, or biological treatment. In
some cases, plants co-treat the leachate with FGD wastewaters and, in
some cases, treat the leachate independently.
    Based on information from the industry survey and site visits,
surface impoundments are the most common type of system used to treat
combustion residual leachate from landfills and impoundments.
Constructed wetlands are the next most commonly used treatment system.
The anoxic/anaerobic biological treatment system used as the basis for
FGD wastewater effluent limits in this proposed rule is also being used
by one plant to treat leachate, with the leachate mixing with FGD
wastewater immediately prior to the bioreactor stage.
    Some plants mix the leachate with fly ash prior to disposing the
ash in a landfill to control fugitive dust emissions and to improve the
handling characteristics of the dry fly ash. Leachate is also used at
some plants for dust control around ash loading areas and landfills.
Many plants will collect the leachate from a surface impoundment and
pump it directly back to the impoundment from which it originated.
    Physical/chemical treatment systems are capable of achieving low
effluent concentrations of various metals and are effective at removing
many of the pollutants of concern present in leachate discharges to
surface waters. The pollutants of concern in leachate have also been
identified as pollutants of concern for FGD wastewater, fly ash
transport wastewater, bottom ash transport water, and other combustion
residuals. This is to be expected since the leachate itself comes from
landfills and surface impoundments containing the combustion residuals
and those wastes are the source for the pollutants entrained in the
leachate. Given the similarities present among the different types of
wastewaters associated with combustion residuals, combustion residual
leachate will be similarly amenable to chemical precipitation
treatment. The treatability of pollutants such as arsenic and mercury
using chemical precipitation technology is also demonstrated by
technical information compiled for ELGs promulgated for other industry
sectors. See, e.g., the TDDs supporting the ELGs for the Landfills
point source category (EPA-821-R-99-019) and the ELGs for the Metal
Products and Machinery point source category (EPA-821-B-03-001).
5. Gasification Wastewater
    The treatment technologies in use at steam electric power plants
for gasification wastewater include:
     Vapor-Compression Evaporation System: This type of system
is identical to the vapor-compression evaporation system described for
FGD wastewater. It uses a falling-film evaporator (or brine
concentrator) to produce a concentrated wastewater stream and a
distillate stream. The concentrated wastewater stream may be further
processed in a crystallizer or spray dryer, which evaporates the
remaining water to generate a solid waste product and potentially a
condensate stream. Facilities may reuse the distillate and condensate
streams within the plant or discharge them to surface waters.
     Cyanide Destruction System: This system adds sodium
hypochlorite (i.e., bleach) to the wastewater in mixing tanks to
destroy the cyanide. The cyanide system treats the condensate and
distillate streams from both the brine concentrator and crystallizer
just prior to discharge.
    EPA is aware of two plants that currently operate integrated
gasification combined cycle (IGCC) units in the United States, and a
third plant is scheduled to begin operating an IGCC unit this year. All
three of these plants currently treat or plan to treat the IGCC
wastewaters with vapor-compression evaporation systems. The IGCC plant
scheduled to begin operating this year is installing both a vapor-
compression evaporation system and a cyanide destruction system to
treat the gasification wastewater.
6. Flue Gas Mercury Control (FGMC) Wastewater
    FGMC wastewater originates from activated carbon injection systems.
The system can be configured either upstream or downstream of the
primary particulate collection system. EPA identified 73 plants with
current or planned activated carbon injection systems. Of these, 58
plants operate upstream injection systems while the remaining 15 plants
inject the carbon downstream.
    In cases where the injection occurs upstream of the primary
particulate collection system, plants collect and handle the mercury-
containing carbon with the fly ash. In cases where the injection occurs
downstream of the primary particulate collection system, plants collect
the mercury-containing carbon in a secondary particulate control system
(e.g., a fabric filter). As with fly ash systems, plants collect the
mercury-containing carbon in hoppers located underneath the equipment.
From the collection hoppers, plants either transfer the mercury-
containing carbon as dry ash to silos for temporary storage (67 plants;
92 percent) or transport (sluice) it with water to an ash impoundment
(6 plants; 8 percent). Water transport can result in a wastewater
discharge, typically an overflow from the impoundment. However, five of
the six plants that use water to transport the FGMC waste to a surface
impoundment do not discharge any FGMC wastewater and the remaining
plant has the capability to handle the FGMC waste using a dry system
but sometimes uses a wet system instead.
    Coal-fired power plants can minimize or eliminate the discharge of
FGMC particulate handling transport water by using the same solids
handling technologies that are available for fly ash. These
technologies include:
     Wet Vacuum Pneumatic System: These systems use water-
powered hydraulic vacuums to withdraw dry FGMC waste from the hoppers,
similar to wet sluicing systems. Instead of

sluicing the FGMC waste to a surface impoundment, these systems capture
the FGMC waste in a filter--receiver (bag filter with a receiving tank)
and then deposit it in a silo.
     Dry Vacuum Pneumatic System: These systems use a
mechanical exhauster to move air, below atmospheric pressure, to pull
the FGMC waste from the hoppers and convey it directly to a silo. The
collected FGMC waste empties from the hoppers into the conveying system
via a material handling valve.
     Pressure System: These systems use air produced by a
positive displacement blower to convey FGMC waste directly from the
hopper to a silo.
     Combined Vacuum/Pressure System: These systems first
utilize a dry vacuum system to pull FGMC waste from the hoppers to a
transfer station, and then use a positive displacement blower to convey
it to a silo.
7. Metal Cleaning Wastes
    As described in Section VI.B.6, metal cleaning wastes are generated
from cleaning any metal process equipment. Because there are many
different processes at plants that use metal equipment, there are a
variety of metal cleaning wastes that are generated. The treatment
methods used for each of the different types of metal cleaning wastes
vary to some degree depending on the specific cleaning operations.
    Based on information from the industry survey, surface impoundments
and chemical precipitation systems are two of the most common types of
systems used to treat metal cleaning wastes. Other types of treatment
systems include constructed wetlands, filtration, reverse osmosis,
clarification, oil/water separation, and brine concentrators.
    In addition to the treatment systems used to control the discharges
of metal cleaning wastes, some plants also employ other handling
approaches to control or eliminate the discharge of metal cleaning
wastes. For example, some plants immediately recycle the metal cleaning
wastes back to other plant operations, while other plants evaporate the
metal cleaning wastes in the boiler to evaporate the wastewater and
eliminate the discharge. Other handling operations reported in the
industry survey include offsite treatment, hazardous waste disposal,
third-party disposal, mixing with fly ash and landfilling, and deep
well injection.
    Physical/chemical treatment systems are capable of reducing the
concentration of pollutants, including metals, in the wastewater.

VII. Selection of Regulated Pollutants

A. Identifying the Pollutants of Concern

    The following paragraphs discuss the pollutants of concern
identified for each of the wastestreams considered for regulation in
this proposal. For the purpose of this rulemaking, pollutants of
concern are those pollutants that have been quantified in a wastestream
at sufficient frequency at treatable levels (i.e., concentrations). EPA
used the following sources of wastewater characterization data to
identify pollutants of concern in wastewater from steam electric power
plants: EPA's field sampling program, industry-supplied data including
data provided in responses to the industry survey, and various
literature sources. EPA relied primarily on its field sampling program
data because the data were collected using consistent methods and
analytical techniques for a broad range of pollutants. Therefore, where
EPA had data from its field sampling program, it preferentially used
that data. Where EPA did not collect field sampling data for a
wastestream and industry-supplied data was available, EPA used that
data. In the absence of either EPA field sampling data or industry-
supplied data, EPA used literature data.
    After reviewing the available sources of data for each of the
wastestreams addressed by this rulemaking, EPA first combined the
pollutant data to create consolidated datasets representing the
concentrations of pollutants present in each wastestream prior to
treatment. EPA then eliminated all pollutants that were not detected in
any wastewater samples--any pollutants falling into this category are
not considered pollutants of concern. Finally, for the remaining
pollutants for each wastestream, EPA then identified each pollutant
that was detected at a concentration greater than or equal to ten times
the baseline value (see Section 6 of the TDD) in at least 10 percent of
all untreated process wastewater samples.\13\
---------------------------------------------------------------------------

    \13\ This is consistent with the process EPA used to identify
pollutants of concern for many categories. EPA takes this approach
to ensure the pollutants are present in treatable levels.
---------------------------------------------------------------------------

    EPA identified the following 34 pollutants of concern for FGD
wastewater using EPA field sampling data: one conventional pollutant
(TSS); \14\ 13 toxic pollutants, including arsenic, cyanide, mercury,
and selenium; 12 nonconventional metals; and 8 other nonconventional
pollutants (e.g., ammonia, nitrate/nitrite, and total phosphorus).
---------------------------------------------------------------------------

    \14\ EPA did not analyze its field sampling data for oil and
grease. Rather, since the existing steam electric ELG currently
contains BPT limitations applicable to FGD wastewater for oil and
grease, EPA already has data from the existing rulemaking
demonstrating oil and grease is also a pollutant of concern in FGD
wastewater.
---------------------------------------------------------------------------

    EPA identified the following 24 pollutants of concern for fly ash
transport water using EPA field sampling data: one conventional
pollutant (TSS); \15\ 9 toxic pollutants (metals including arsenic,
lead, mercury, and selenium); 11 nonconventional pollutant metals; and
3 other nonconventional pollutants (i.e., TDS, chloride, and nitrate/
nitrite).
---------------------------------------------------------------------------

    \15\ EPA did not analyze its field sampling data for oil and
grease. Rather, since the existing steam electric ELG currently
contains BPT limitations applicable to fly ash transport wastewater
for oil and grease, EPA already has data from the existing
rulemaking demonstrating oil and grease is also a pollutant of
concern in fly ash wastewater.
---------------------------------------------------------------------------

    EPA was unable to obtain readily available data for untreated
bottom ash transport water for use in identifying the pollutants of
concern using the methodology described above. However, because the
pollutants found in bottom ash are constituents that are present in the
coal (or petroleum coke or oil), as is the case for fly ash, EPA
concluded that the pollutants of concern for bottom ash transport water
are identical to the pollutants of concern identified for fly ash
transport water.
    EPA was also unable to obtain readily available data for
identifying the pollutants of concern in FGMC wastewater. Nevertheless,
based on process knowledge and engineering judgment, EPA concluded that
the pollutants of concern for FGMC wastewater are likely to be
identical to the pollutants of concern identified for fly ash transport
water. This is due to the fact that, when activated carbon is injected
into the flue gases, the carbon intermixes with the fly ash particles,
and then the commingled mixture of activated carbon (which adsorbs
mercury and other pollutants from the flue gases) and fly ash particles
is captured together and transferred to the FGMC wastewater.
    EPA evaluated the pollutants of concern for combustion residual
leachate using industry sampling data for untreated leachate submitted
under Part G of the industry survey. EPA evaluated the landfill
leachate separately from the surface impoundment leachate. The
pollutants of concern for landfill leachate include the following: one
conventional pollutant (TSS); \16\ 3 toxic pollutants

(arsenic, mercury, and selenium); 9 nonconventional pollutant metals;
and 3 other nonconventional pollutants (i.e., chloride, sulfate and
TDS). The pollutants of concern for impoundment leachate include: \17\
2 toxic pollutants (i.e., arsenic and mercury), 7 nonconventional
pollutant metals, and 3 other nonconventional pollutants (i.e.,
chloride, sulfate, and TDS).
---------------------------------------------------------------------------

    \16\ The landfill leachate samples were not analyzed for oil and
grease. Rather, since the existing steam electric ELG currently
contains BPT limitations applicable to combustion residual leachate
for oil and grease, EPA already has data from the existing
rulemaking demonstrating oil and grease is also a pollutant of
concern in combustion residual leachate.
    \17\ The surface impoundment leachate samples were not analyzed
for oil and grease. Rather, since the existing steam electric ELG
currently contains BPT limitations applicable to combustion residual
leachate for oil and grease, EPA already has data from the existing
rulemaking demonstrating oil and grease is also a pollutant of
concern in combustion residual leachate.
---------------------------------------------------------------------------

    EPA identified 19 pollutants of concern for gasification wastewater
using EPA field sampling data, including: 1 conventional pollutant
(BOD); 7 toxic pollutants (including arsenic, cyanide, mercury, and
selenium); 5 nonconventional pollutant metals; and 6 other
nonconventional pollutants.
    As part of the 1974 rulemaking, EPA collected characterization data
associated with chemical and nonchemical metal cleaning wastes. Based
on the data collected during that rulemaking, EPA determined that TSS,
oil and grease, copper, and iron were pollutants of concern for this
wastestream warranting regulation and established BPT limitations for
these four pollutants in discharges of metal cleaning wastes, including
both nonchemical and chemical metal cleaning wastes. (EPA has also
established BAT, NSPS, PSES, and PSNS for chemical metal cleaning
wastes.) For additional information regarding the pollutants that may
be present in nonchemical metal cleaning wastes, see the 1974
Development Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Steam Electric Power Generating Point
Source Category. Based on the information developed for the previous
rulemakings for the steam electric power generating ELGs and the data
from the industry survey, EPA identified 4 pollutants of concern for
nonchemical metal cleaning wastes, including: 2 conventional pollutants
(TSS and oil and grease); 1 toxic pollutant (copper); and 1
nonconventional pollutant (iron).
    See Section 6 of the Technical Development Document for Proposed
Effluent Limitations Guidelines and Standards for the Steam Electric
Power Generating Point Source Category (TDD)--EPA 821-R-13-002 for more
detailed information regarding pollutants of concern.

B. Selection of Pollutants for Regulation Under BAT/NSPS

    The pollutants of concern identified for each wastestream
represents those pollutants that are present at treatable
concentrations in a significant percentage of untreated wastewater
samples from that wastestream. Effluent limits and monitoring for all
pollutants of concern is not necessary to ensure that the pollutants
are adequately controlled because many of the pollutants originate from
similar sources, have similar treatabilities, and are removed by
similar mechanisms. Because of this, it may be sufficient to establish
effluent limits for one pollutant as a surrogate or indicator pollutant
that ensures the removal of other pollutants of concern. In addition,
establishing effluent limits may not be appropriate for certain
pollutants of concern when the technology used as the basis for the
effluent limits is not reliably effective at removing the pollutant(s).
    From the list of pollutants of concern identified for each
wastestream, EPA selected a subset of pollutants for establishing
numeric effluent limitations. EPA considered the following factors in
selecting regulated pollutants from the list of pollutants of concern:
     The pollutant was detected in the untreated wastewater at
treatable levels in a significant number of samples.
     The pollutant is not used as a treatment chemical in the
treatment technology that serves as a basis for the proposed regulatory
option. EPA eliminated pollutants associated with treatment system
additives because regulating these pollutants could interfere with
efforts to optimize treatment system operation.
     The pollutant is effectively treated by the treatment
technology that serves as the basis for the proposed regulatory option.
EPA excluded all pollutants for which the treatment technology was
ineffective (e.g., pollutant concentrations remained approximately
unchanged or increased across the treatment system).
     The pollutant is not adequately controlled through the
regulation of another pollutant.
    Because the criteria for identifying regulated pollutants from the
list of pollutants of concern depends on the treatment technology that
serves as the basis for a proposed regulatory option, EPA may regulate
a different subset of pollutants for a single wastestream under
different regulatory options.
    For the proposed options for this rulemaking (described below in
Section VIII), EPA identified six pollutants for potential regulation
for FGD wastewater: oil and grease, TSS, arsenic, mercury, nitrate/
nitrite, and selenium. For leachate, EPA identified four potential
pollutants for regulation: oil and grease, TSS, arsenic and mercury.
    For fly ash discharges, bottom ash, and FGMC wastewater, under some
proposed options, EPA is proposing to establish zero discharge
limitations, which in effect directly control all pollutants of
concern. For other proposed options that would not require zero
pollutant discharge, EPA identified two potential pollutants for
regulation: oil and grease and TSS for nonchemical metal cleaning
wastes, EPA identified four pollutants for potential regulation (TSS,
oil and grease, copper, and iron). EPA identified four pollutants for
regulation for gasification wastewater: arsenic, mercury, selenium, and
TDS.
    See Section 6.7 of the Technical Development Document for Proposed
Effluent Limitations Guidelines and Standards for the Steam Electric
Power Generating Point Source Category (TDD)--EPA 821-R-13-002 for more
information about the pollutants of concern and EPA's rationale for
selecting the pollutants proposed for regulation.

C. Methodology for the POTW Pass Through Analysis (PSES/PSNS)

    Section 307(b) and (c) of the CWA requires EPA to promulgate
pretreatment standards for pollutants that are not susceptible to
treatment by POTWs or which would interfere with the operation of
POTWs. EPA looks at a number of factors in selecting the technology
basis for pretreatment standards for existing and new sources. These
factors are generally the same as those considered in establishing BAT
and NSPS, respectively. However, unlike direct dischargers whose
wastewater will receive no further treatment once it leaves the
facility, indirect dischargers send their wastewater to POTWs for
further treatment. As such, EPA must also determine that a pollutant is
not susceptible to treatment at a POTW or would interfere with POTW
operations.
    Before establishing PSES/PSNS for a pollutant, EPA examines whether
the pollutant ``passes through'' a POTW to waters of the U.S. or
interferes with the POTW operation or sludge disposal practices. In
determining whether a pollutant would pass through POTWs, EPA generally
compares the percentage of a pollutant removed by well-operated POTWs
performing secondary treatment

to the percentage removed by BAT/NSPS treatment systems. A pollutant is
determined to pass through POTWs when the median percentage removed
nationwide by well-operated POTWs is less than the median percentage
removed by direct dischargers complying with BAT/NSPS effluent
limitations and standards. Pretreatment standards are established for
those pollutants regulated under BAT/NSPS that pass through POTWs to
waters of the U.S. or interfere with POTW operations or sludge disposal
practices. This approach to the definition of pass-through satisfies
two competing objectives set by Congress: (1) That standards for
indirect dischargers be equivalent to standards for direct dischargers,
and (2) that the treatment capability and performance of POTWs be
recognized and taken into account in regulating the discharge of
pollutants from indirect dischargers.
    For this proposed rule, EPA conducted a pass through analysis for
the technology basis for each wastestream for each regulatory option
presented below in Section VII.C. For those wastestreams and regulatory
options for which EPA is proposing zero discharge of pollutants, EPA
set the percentage removed by the technology basis at 100 percent. EPA
did not conduct its traditional pass-through analysis for these
wastestreams (e.g., fly ash transport water, bottom ash transport
water, and flue gas mercury control wastewater) because limitations for
these wastestreams for direct dischargers would consist of no discharge
of process wastewater pollutants to waters of the U.S., and therefore,
all pollutants would ``pass through'' the POTW for these wastestreams.
    During the 1976 development of pretreatment standards for chemical
metal cleaning wastes, EPA selected pollutants for regulation based on
two criteria:
     The pollutant has the potential to harm the POTW (e.g.,
impair the activity of the biological treatment system); or
     The pollutant has the potential to harm the receiving
water (i.e., if the pollutant is not removed or is removed inadequately
by the POTW).
Using these criteria, the Agency determined it was appropriate to
establish pretreatment standards for the discharge of copper in
chemical metal cleaning wastes. For this rulemaking, EPA believes that,
as is the case for copper in chemical metal cleaning wastes, the copper
present in nonchemical metal cleaning wastes would pass through the
POTW.
    For FGD wastewater, leachate, and gasification wastewater, EPA
determined the percentage removed for the pollutants by the technology
basis using the same data sources used to determine the long-term
averages for each set of limitations (see Section 13 of the TDD).\18\
As it has done for other rulemakings, EPA determined the percentage
removed by well-operated POTWs performing secondary treatment from one
of two data sources:
---------------------------------------------------------------------------

    \18\ For FGD wastewater and leachate, this discussion applies to
those regulatory options that would provide additional control for
discharges of toxics like arsenic, mercury and selenium.
---------------------------------------------------------------------------

     Fate of Priority Pollutants in Publicly Owned Treatment
Works, September 1982, EPA 440/1-82/303 (50 POTW Study); and
     National Risk Management Research Laboratory (NRMRL)
Treatability Database, Version 5.0, February 2004 (formerly called the
Risk Reduction Engineering Laboratory (RREL) database).
    The 50 POTW study presents data on the performance of 50 POTWs
achieving secondary treatment in removing toxic pollutants. When data
for a pollutant were available from the 50 POTW Study, EPA used that
data. When data for pollutants were not available from the 50 POTW
Study, EPA used NRMRL data. The NRMRL treatability database provides
information on removals obtained by various treatment technologies for
a variety of wastewater sources. Therefore, where EPA used data from
the NRMRL treatability database, it used only data from the treatment
of domestic and industrial wastewater using technologies representative
of secondary treatment. For a more detailed discussion of how EPA
performed its removal analysis, see Section 11 of the TDD.
    With a few exceptions, EPA performs a POTW pass-through analysis
for pollutants selected for regulation for BAT/NSPS for each
wastestream of concern and for each regulatory option. The exception is
for conventional pollutants such as BOD5, TSS, and oil and
grease. POTWs are designed to treat these conventional pollutants;
therefore, they are not considered to pass through.
    Section VIII below summarizes the results of the pass through
analysis. All of the pollutants proposed for regulation under BAT/NSPS
(except for conventional pollutants and iron found in nonchemical metal
cleaning wastes) were found to pass through and, therefore, were
selected for regulation under PSES/PSNS.

VIII. Proposed Regulation

A. Regulatory Options

1. BPT/BCT
    EPA is not proposing to revise the BPT effluent guidelines or
establish BCT effluent guidelines in this notice because the same
wastestreams would be controlled at the proposed BAT/BADCT (NSPS) level
of control. EPA is proposing to remove FGD wastewater, FGMC wastewater,
gasification wastewater, and leachate from the definition of low-volume
wastes. As a result, EPA is making a structural adjustment to the text
of the regulation at 40 CFR part 423 to add paragraphs that list these
four wastestreams by name, along with their applicable effluent
limitations. The reformatted regulatory text for these four
wastestreams includes BPT effluent limits, which are the same as the
current BPT effluent limits for low volume wastes.
2. Description of the BAT/NSPS/PSES/PSNS Options
    EPA is proposing to revise or establish BAT, BADCT (NSPS), PSES,
and PSNS that may apply to discharges of seven wastestreams: FGD
wastewater, fly ash transport water, bottom ash transport water,
combustion residual leachate, nonchemical metal cleaning wastes, and
wastewater from FGMC systems and gasification systems. In Section VI of
this preamble and in the TDD, EPA describes the treatment technologies
and operational practices that it reviewed during the development of
this proposed rule. From these, EPA identified a subset of technologies
(treatment processes and operational practices) that were most
promising as candidate BAT/BADCT options. In this proposal, EPA is
presenting eight main regulatory options (i.e., Option 1, Option 3a,
Option 2, Option 3b, Option 3, Option 4a, Option 4, and Option 5) that
represent different levels of pollutant removal associated with
different wastewater streams (i.e., each succeeding option from Option
1 to Option 5 would achieve more reduction in discharges of pollutants
to waters of the U.S). Table VIII-1 summarizes the eight main
regulatory options, which are described in the paragraphs below.
    As discussed further below, EPA is also proposing to add provisions
to the ELGs that would prevent facilities from circumventing applicable
ELGs. The proposed provisions would clarify the acceptable conditions
for discharge of reused process wastewater and establish effluent
monitoring requirements.

    EPA is considering establishing BMPs that would apply to surface
impoundments (i.e., ponds) that receive, store, dispose of, or are
otherwise used to manage coal combustion residuals including FGD
wastes, fly ash, bottom ash (which includes boiler slag), leachate, and
other residuals associated with the combustion of coal to prevent
uncontrolled discharges from these impoundments as described below in
the paragraph titled, ``BMPs for CCR Surface Impoundments.''
    As part of its consideration of technological availability and
economic achievability for all regulatory options, EPA considered the
magnitude and complexity of process changes and new equipment
installations that would be required at facilities to meet the
requirements of the rule. As described further below, EPA proposes that
certain limitations and standards being proposed today for existing
sources would not apply until July 1, 2017 (approximately three years
from the effective date of this rule).
    EPA is also considering establishing, as part of the BAT for
existing sources, a voluntary incentive program that would provide more
time for plants to implement the proposed BAT requirements if they
adopt additional process changes and controls that would provide
significant environmental protections beyond those achieved by the
preferred options in this proposed rule. As described further below,
power plants would be granted two additional years (beyond the time
described above in the preceding paragraph) if they also dewater, close
and cap all CCR surface impoundments at the facility (except combustion
residual leachate impoundments), including those surface impoundments
located on non-adjoining property that receive CCRs from the facility.
A power plant participating in the voluntary incentive program could
continue to operate surface impoundments for which combustion residual
leachate was the only type of CCR solids or wastewater contained in the
impoundment. Power plants would be granted five additional years
(beyond the time described above in the preceding paragraph) if they
eliminate discharges of all process wastewater to surface waters, with
the exception of cooling water discharges.

                                                                      Table VIII-1--Steam Electric Main Regulatory Options
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Technology basis for the main BAT/NSPS/PSES/PSNS regulatory options
          Wastestreams           ---------------------------------------------------------------------------------------------------------------------------------------------------------------
                                           1                  3a                   2                  3b                   3                  4a                   4                   5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
FGD Wastewater..................  Chemical            BPJ Determination.  Chemical            Chemical            Chemical            Chemical            Chemical            Chemical
                                   Precipitation.                          Precipitation +     Precipitation +     Precipitation +     Precipitation +     Precipitation +     Precipitation +
                                                                           Biological          Biological          Biological          Biological          Biological          Evaporation
                                                                           Treatment.          Treatment for       Treatment.          Treatment.          Treatment.
                                                                                units at a
                                                                                facility with a
                                                                                total wet-
                                                                                scrubbed capacity
                                                                                of 2,000 MW and
                                                                                more; BPJ
                                                                                determination for
                                                                                <2,000 MW.
Fly Ash Transport Water.........  Impoundment (Equal  Dry handling......  Impoundment (Equal  Dry handling......  Dry handling......  Dry handling......  Dry handling......  Dry handling
                                   to BPT).                                to BPT).
Bottom Ash Transport Water......  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Dry handling/       Dry handling/       Dry handling/
                                   to BPT).            to BPT).            to BPT).            to BPT).            to BPT).            Closed loop (for    Closed loop.        Closed loop
                                                                                units >400 MW);
                                                                                Impoundment
                                                                                (Equal to
                                                                                BPT)(for units
                                                                                <=400 MW).
Combustion Residual Leachate....  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Impoundment (Equal  Chemical            Chemical
                                   to BPT).            to BPT).            to BPT).            to BPT).            to BPT).            to BPT).            Precipitation.      Precipitation
FGMC Wastewater.................  Impoundment (Equal  Dry handling......  Impoundment (Equal  Dry handling......  Dry handling......  Dry handling......  Dry handling......  Dry handling
                                   to BPT).                                to BPT).
Gasification Wastewater.........  Evaporation.......  Evaporation.......  Evaporation.......  Evaporation.......  Evaporation.......  Evaporation.......  Evaporation.......  Evaporation
Nonchemical Metal Cleaning        Chemical            Chemical            Chemical            Chemical            Chemical            Chemical            Chemical            Chemical
 Wastes \19\.                      Precipitation.      Precipitation.      Precipitation.      Precipitation.      Precipitation.      Precipitation.      Precipitation.      Precipitation
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------

    \19\ As described in Section VIII, EPA is proposing to exempt
from new copper and iron BAT limitations any existing discharges of
nonchemical metal cleaning wastes that are currently authorized
without iron and copper limits.
---------------------------------------------------------------------------

    FGD Wastewater. Addressing the variety of pollutants present in FGD
wastewater typically requires several stages of treatment to remove the
suspended solids, particulate and dissolved metals, and other
pollutants present. Historically, power plants have relied on surface
impoundments to treat FGD wastewater because NPDES permits generally
focused on controlling suspended solids for this wastestream. Surface
impoundments are the technology basis for the current BPT effluent
limits (last revised in 1982) for steam electric power plants. In
recent years, physical/chemical treatment systems and other more
advanced systems have become more widely used as effluent limits for
metals and other pollutants have been included in permits, in nearly
all cases driven by the need to utilize such technologies to meet water
quality-based effluent limits (WQBELs) established to meet applicable
water quality standards in

the receiving waters. At present, a number of steam electric plants
either use chemical precipitation or chemical precipitation and
biological treatment to control discharges of FGD wastes. However,
surface impoundments continue to be the predominant technology used to
treat FGD wastewater, with 54 percent of plants that discharge FGD
wastewater relying on this technology alone (i.e., not including the
plants that use surface impoundments as pretreatment for more advanced
treatment). In addition, it is common for plants to commingle the
surface impoundment FGD effluent with wastestreams of significantly
higher flows (e.g., ash transport water and cooling water) because the
higher-flow wastestreams dilute the FGD wastewater so that the
resulting pollutant concentrations in the combined wastestream do not
exceed the applicable water quality-based effluent limitations.
    Surface impoundments use gravity to remove solid particles (i.e.,
suspended solids) from the wastewater. Metals in FGD wastewater are
present in both soluble (i.e., dissolved) and particulate form. Some
metals, such as arsenic, are often present mostly in particulate form;
these usually can be removed to a substantial degree by a well-operated
settling process that has a sufficiently long residence time. However,
other pollutants, such as selenium, boron, and magnesium, are present
mostly in soluble form and are not effectively and reliably removed by
wastewater surface impoundments. For metals present in both soluble and
particulate forms (such as mercury), surface impoundments will not
effectively remove the dissolved fraction. Furthermore, the conditions
present in some surface impoundments can create chemical conditions
(e.g., low pH) that convert particulate forms of metals to soluble
forms, which would not be removed by the gravity settling process in
the surface impoundment. Additionally, EPRI (a technical research
organization funded by the electric power industry) has reported that
adding FGD wastewater to surface impoundments used to treat ash
transport water (i.e., ash ponds) may reduce the settling efficiency in
the impoundments due to gypsum particle dissolution, thus increasing
the effluent TSS concentrations. EPRI has also reported that the FGD
wastewater includes high loadings of volatile metals, which can
increase the solubility of metals in surface impoundments, thereby
leading to increased levels of dissolved metals and resulting in higher
concentrations of metals in the discharge from surface impoundments.
    During the summer, some surface impoundments become thermally
stratified. When this occurs, the top layer of the impoundment is
warmer and contains higher levels of dissolved oxygen, whereas the
bottom layer of the impoundment is colder and can have significantly
lower levels of oxygen and may develop anoxic conditions. Typically,
during fall, as the air temperature decreases, the upper layer of the
impoundment becomes cooler and denser, thereby sinking and causing the
entire volume of the impoundment to circulate. Solids that have
collected at the bottom of the impoundment may become resuspended due
to such mixing, increasing the concentrations of pollutants discharged
during the turnover period. Seasonal turnover effects largely depend
upon the size and configuration of the surface impoundment. Smaller,
and especially shallow, surface impoundments likely do not experience
turnover because they do not have physical characteristics that promote
thermal stratification. However, some surface impoundments are large
(e.g., greater than 300 acres) and deep (e.g., greater than 10 meters
deep) and likely experience some degree of turnover.
    Technologies more advanced than surface impoundments exist and that
are more effective at removing both soluble (i.e., dissolved) and
particulate forms of metals, as well as other pollutants such as
nitrogen compounds and TDS. Because many of the pollutants of concern
for FGD wastewater are present in dissolved form and would not be
removed by surface impoundments, and because of the relatively large
mass loads of these pollutants (e.g., selenium, dissolved mercury)
discharged by the FGD wastestream, EPA explored other technologies that
would be more effective at removing these pollutants of concern and is
co-proposing three options that would include such technologies.
However, for reasons discussed in Section VII.A.3, EPA is also co-
proposing options under which some or all facilities would continue,
for the purposes of the ELGs, to be subject to the BPT requirements
based on surface impoundments for treatment of FGD wastewater. Under
these options, BAT would be left to a site-specific determination. For
the reasons discussed above and in Section VIII.A.3, EPA also does not
believe that surface impoundments represent best available demonstrated
control technology for controlling pollutants in FGD wastewater.
Therefore, none of the regulatory options for NSPS presented in this
proposal are based on the performance of surface impoundments for FGD
wastewater.
    The technology basis for the effluent limitations and standards for
FGD wastewater in Option 1 is physical/chemical treatment consisting of
the following: Chemical precipitation/coprecipitation (employing the
combination of hydroxide precipitation, iron coprecipitation, and
sulfide precipitation). Option 1 also incorporates the use of flow
minimization for plants with high FGD discharge flow rates (i.e.,
greater than 1,000 gpm) and FGD system metallurgy and operating
practices that can accommodate an increase in chlorides (e.g., scrubber
systems constructed of non-metallic materials or corrosion-resistant
metal alloys, or systems operating with absorber chloride
concentrations substantially below the design chloride limit). The flow
minimization at these plants would be achieved by either reducing the
FGD purge rate or recycling a portion of their FGD wastewater.
    Physical/chemical treatment (i.e., chemical precipitation) is used
to remove metals and other pollutants from wastewater. Chemicals are
added to the wastewater in a series of reaction tanks to convert
soluble metals to insoluble metal hydroxide or metal sulfide compounds,
which precipitate from solution and are removed along with other
suspended solids. An alkali, such as hydrated lime, is typically added
to adjust the pH of the wastewater to the point where metals
precipitate out as metal hydroxides (typically referred to as hydroxide
precipitation). Chemicals such as ferric chloride are often added to
the system to increase the removal of certain metals through iron
coprecipitation. The ferric chloride also acts as a coagulant, forming
a dense floc that enhances settling of the metal precipitate in the
downstream clarification stage. Coagulants and flocculants are often
added to facilitate the settling and removal of the newly formed
solids. Plants trying to increase removals of mercury and other metals
will also include sulfide addition (e.g., organosulfide) as part of the
process. Adding sulfide chemicals in addition to hydroxide
precipitation provides even greater reductions of heavy metals due to
the very low solubility of metal sulfide compounds, relative to metal
hydroxides. Sulfide precipitation is widely used in Europe and multiple
locations in the United States have installed this technology. Forty
U.S. power plants (34 percent of plants

discharging FGD wastewater) include physical/chemical treatment as part
of the FGD wastewater treatment system; more than half of these plants
(28 percent of plants discharging FGD wastewater) use both hydroxide
and sulfide precipitation in the process.
    The technology basis for the effluent limitations and standards for
FGD wastewater in Options 2, 3b (for units located at facilities with a
total wet-scrubbed capacity of 2,000 MW or more) \20\, 3, 4a, and 4 is
chemical precipitation/coprecipitation (the same technology basis under
Option 1) used in combination with anoxic/anaerobic biological
treatment designed to optimize removal of selenium. As is the case for
Option 1, these BAT options also incorporate the use of flow
minimization for plants with high FGD discharge flow rates (i.e.,
greater than 1,000 gpm) and FGD system metallurgy and operating
practices that can accommodate an increase in chlorides. The flow
minimization at these plants would be achieved by either reducing the
FGD purge rate or recycling a portion of their FGD wastewater.
---------------------------------------------------------------------------

    \20\ This value is calculated by summing the nameplate capacity
for all of the units that are serviced by wet FGD systems.
---------------------------------------------------------------------------

    Physical/chemical treatment systems are capable of achieving low
effluent concentrations of various metals and the sulfide addition is
particularly important for removing mercury; however, this technology
is not effective at removing selenium, nitrogen compounds, and certain
metals that contribute to high concentrations of TDS in FGD wastewater
(e.g., bromides, boron). Six power plants in the U.S. are operating FGD
treatment systems that include a biological treatment stage designed to
substantially reduce nitrogen compounds and selenium.\21\ Other
industries have also used this technology to remove selenium and other
pollutants. These systems use anoxic/anaerobic bioreactors optimized to
remove selenium from the wastewater. The bioreactor alters the form of
selenium, reducing selenate and selenite to elemental selenium, which
is then captured by the biomass and retained in treatment system
residuals. The conditions in the bioreactor are also conducive to
forming metal sulfide complexes to facilitate additional removals of
mercury, arsenic, and other metals. The information in the record for
this proposed rule demonstrates that the amount of mercury and other
pollutants removed by the biological treatment stage of the treatment
system, above and beyond the amount of pollutants removed in the
chemical precipitation treatment stage preceding the bioreactor, can be
substantial. In addition, the anoxic conditions in the bioreactor
remove nitrates by denitrification and, if necessary, the biological
processes can be modified to include a step to nitrify and remove
ammonia. Four of these six plants precede the biological treatment
stage with physical/chemical treatment; thus, the entire system is
designed to remove suspended solids, particulate and dissolved metals,
soluble and insoluble forms of selenium, and nitrate and nitrite forms
of nitrogen. The other two plants operating anoxic/anaerobic
bioreactors to remove selenium precede the biological treatment stage
with surface impoundments instead of chemical precipitation. While the
treatment systems at these two plants would be less effective at
removing metals (including many dissolved metals) than the plants
utilizing chemical pretreatment, they nevertheless show the efficacy of
biological treatment for removing selenium and nitrate/nitrite from FGD
wastewater. Three percent of the plants discharging FGD wastewater use
chemical precipitation followed by anaerobic biological treatment to
treat this wastewater, which is the technology basis for Options 2, 3b
(for units located at facilities with a total wet-scrubbed capacity of
2,000 MW or more), 3, 4a, and 4.
---------------------------------------------------------------------------

    \21\ A seventh plant is scheduled to begin operating a
biological treatment system for selenium removal next year. Another
plant is installing a similar treatment system to remove selenium in
discharges of combustion residual leachate.
---------------------------------------------------------------------------

    The technology basis for the effluent limitations and standards for
FGD wastewater in Option 5 is chemical precipitation/coprecipitation
used in combination with vapor compression evaporation. Physical/
chemical treatment systems can achieve low effluent concentrations for
a number of pollutants, and reduce concentrations even further when
combined with biological treatment systems, as described above and in
the TDD. However, these technologies have not been effective at
removing substantial amounts of boron and pollutants such as sodium and
bromides that contribute to high concentrations of TDS. Another FGD
wastewater treatment technology that can address these more
recalcitrant pollutants, as well as removing the pollutants treated by
physical/chemical and biological technologies, is vapor-compression
evaporation. This technology uses an evaporator to produce a
concentrated wastewater stream and a reusable distillate stream. The
concentrated wastewater stream is either disposed of or further
processed to produce a solid by-product and additional distillate. The
plant can reuse the distillate stream as makeup water. Two U.S. plants
and four Italian plants are operating this technology to treat FGD
wastewater from their coal-fired generating units.\22\
---------------------------------------------------------------------------

    \22\ A third U.S. plant is currently installing a vapor-
compression evaporation system to treat the FGD wastewater.
---------------------------------------------------------------------------

    For Option 3a and Option 3b (for units located at facilities with a
total wet-scrubbed capacity of less than 2,000 MW), EPA is proposing
not to characterize a technology basis for effluent limitations and
standards applicable to discharges of pollutants in FGD wastewater at
this time. As illustrated above, there is a wide range of technologies
currently in use for reducing pollutant discharges associated with FGD
wastewater, and research continues in the development of additional
technologies to treat FGD wastewater (see Section 7.1.7 of the TDD for
more information on emerging technologies). The more advanced
technologies (those that reduce the most pollutants) reflect recent
innovations in the area of treatment of FGD wastewater. EPA expects
this trend to continue and, therefore, under Option 3a and Option 3b
(for units located at facilities with a total wet-scrubbed capacity of
less than 2,000 MW), effluent limitations representing BAT for
discharges of FGD wastewater would be determined on a site-specific BPJ
basis. Under Options 3a and Option 3b (for units located at facilities
with a total wet-scrubbed capacity of less than 2,000 MW), pretreatment
program control authorities would need to develop local limits to
address the introduction of pollutants in FGD wastewater by steam
electric plants to the POTWs that cause pass through or interference,
as specified in 40 CFR 403.5(c)(2).
    As described below in this section of the preamble, EPA is
proposing that certain limitations and standards being proposed today
for existing sources would apply to discharges of FGD wastewater
generated on or after the date established by the permitting authority
that is as soon as possible within the next permit cycle after July 1,
2017. FGD wastewater generated prior to that date (i.e., ``legacy''
wastewater) from existing direct dischargers would remain subject to
the existing BPT effluent limits. For indirect dischargers, EPA is
proposing that PSES for FGD wastewater would apply to FGD wastewater
generated after a date determined by the control authority that is as
soon as possible beginning July 1,

2017. EPA considered subjecting legacy FGD wastewater to the proposed
BAT and PSES requirements. However, as explained above, FGD wastewater
and its associated pollutants are typically sent to surface
impoundments for treatment prior to discharge. These surface
impoundments often contain other plant wastewaters, such as fly ash or
bottom ash transport water, coal pile runoff, and/or low volume wastes.
According to data provided by the industry survey, 78 percent of
surface impoundments that receive FGD wastewater also receive fly ash
and/or bottom ash transport water. EPA does not have the data to
demonstrate that the technologies identified above represent BAT for
legacy FGD wastewater. As such, EPA is not proposing BAT requirements
associated with discharges of legacy FGD wastewater generated prior to
the date established by the permitting authority (for direct
dischargers) or control authority (for indirect dischargers). As
proposed today, discharges of legacy FGD wastewater by existing direct
dischargers would remain subject to the existing BPT effluent limits;
however, under some of the proposed options, EPA is also considering
setting the BAT effluent limitations for legacy FGD wastewater that has
not been mixed with non-legacy wastes equal to the existing BPT
effluent limits. See Section XVI for additional information.
    Fly Ash Transport Water. Under Options 1 and 2, BAT effluent
limitations for fly ash transport water would be set equal to the
current BPT effluent limitations, based on the technology of gravity
settling in surface impoundments to remove suspended solids. The
current effluent guidelines for existing sources include BPT effluent
limits for the allowable levels of TSS and oil and grease in discharges
of fly ash transport water. The BPT effluent limits are based on the
performance of surface impoundments, which when well-designed and well-
operated can effectively remove suspended solids, including pollutants
such as particulate forms of certain metals when associated with the
suspended solids.
    Under Options 3a, 3b, 3, 4a, 4, and 5, EPA would establish ``zero
discharge'' effluent limitations and standards for discharges of
pollutants in fly ash transport water, based on the use of dry fly ash
handling technologies. The dry handling technologies for fly ash are
described above in Section VI of this preamble and in the TDD for the
proposed rule. Although surface impoundments can be effective at
removing particulate forms of certain metals and other pollutants, they
are not designed for, nor are they effective at, removing other
pollutants of concern such as dissolved metals and nutrients. The
concentrations of pollutants that remain in the ash impoundment
effluent following gravity settling, in combination with the large
volumes of fly ash transport water discharged to surface waters (2.4
MGD on average per discharging plant), results in a large mass loading
of pollutants of concern being discharged from surface impoundments.
Furthermore, as described in Section VI, surface impoundments can be
susceptible to seasonal turnover that degrades pollutant removal
efficacy, and co-managing FGD and ash wastes in the same impoundments
can lead to increased pollutant discharges.
    Dry handling technologies are the technology basis for the current
fly ash NSPS/PSNS requirements, which were promulgated in 1982. All
generating units built since then have been subject to a ``zero
discharge'' standard. Some existing units have also converted to dry
handling technologies. Due to the NSPS discharge standard or economic
or operational factors, approximately 66 percent of coal- and petroleum
coke-fired generating units that produce fly ash currently operate dry
fly ash transport systems, while another 15 percent operate both wet
and dry fly ash transport systems. The remaining 19 percent operate
only wet fly ash transport systems. In cases where a unit has both wet
and dry handling operations, the wet handling system is typically used
as a backup to the dry system. Effluent limitations and standards based
on dry ash handling would completely eliminate the discharge of
pollutants in fly ash transport water.
    EPA considered basing one or more regulatory options for fly ash
transport water on chemical precipitation treatment technology, with
numeric effluent limits for discharges of the wastestream to surface
waters. EPA has not identified any facilities using this treatment
technology to treat fly ash transport water, although EPA has reviewed
two literature sources that describe laboratory- or pilot-scale tests
using the technology. Upon reviewing the discharge flow rates for fly
ash transport water, however, EPA determined that the costs associated
with treatment using chemical precipitation were higher than the cost
of the dry handling technology upon which Options 3a, 3b, 3, 4a, 4, and
5 are based, despite being less effective at removing pollutants. Since
the costs for chemical precipitation treatment are higher than the cost
for converting to dry handling technologies, and chemical precipitation
removes fewer pollutants, EPA did not include chemical precipitation
treatment as part of the regulatory options for fly ash in this
proposed rule. See DCN SE03869.
    As described below in this section of the preamble, EPA is
proposing that the limitations for existing sources based on Options
3a, 3b, 3, 4a, 4, or 5 would apply to discharges of fly ash transport
water generated after the date established by the permitting authority
that is as soon as possible within the next permit cycle after July 1,
2017. For indirect dischargers, EPA is proposing that PSES for fly ash
would apply to the fly ash transport water generated after a date
determined by the control authority that is as soon as possible
beginning July 1, 2017. Fly ash transport water generated by existing
direct dischargers prior to that date (i.e., ``legacy'' wastewater)
would remain subject to the existing BPT effluent limits. EPA
considered subjecting legacy fly ash transport water (i.e., the fly ash
transport water generated prior to the date established by the
permitting authority, as described above) to the proposed BAT zero
discharge requirement. As explained above, currently fly ash transport
wastewater and the associated pollutants are sent to surface
impoundments for treatment prior to discharge. The technology basis
identified above for the proposed zero discharge requirement eliminates
the generation of the fly ash wastewater but does not eliminate fly ash
transport wastewater that has already been transferred to a surface
impoundment. Furthermore, the technologies identified as the basis for
fly ash transport water discharge requirements have not been
demonstrated for the legacy fly ash transport wastewater that has
already been generated. As such, EPA is not proposing BAT or PSES
requirements for discharges of legacy fly ash transport water generated
prior to the date established by the permitting authority or control
authority. As proposed today, discharges of legacy fly ash transport
water by existing direct dischargers would remain subject to the
existing BPT effluent limits; however, EPA is also considering whether
to set the BAT effluent limitations for legacy fly ash transport water
equal to the existing BPT effluent limits. See Section XVI for
additional information.
    Bottom Ash Transport Water. Under Options 1, 3a, 2, 3b, 3, and 4a
(for units less than or equal to 400 MW), effluent limitations and
standards for bottom ash transport water would be set equal to the
current BPT effluent limitations,

based on the technology of gravity settling in surface impoundments to
remove suspended solids. The 1982 effluent guidelines for existing
sources include BPT effluent limits for the allowable levels of TSS and
oil and grease in discharges of bottom ash transport water. The BPT
effluent limits are based on the performance of surface impoundments,
which when well-designed and well-operated can effectively remove
suspended solids, including pollutants such as particulate forms of
certain metals when associated with the suspended solids.
    Although surface impoundments can be effective at removing
particulate forms of metals and other pollutants, they are not designed
for nor are they effective at removing other pollutants of concern such
as dissolved metals and nutrients. The concentrations of pollutants
that remain in the wastestream at the ash impoundment effluent, in
combination with the large volumes of bottom ash transport water
discharged to surface waters, results in a large mass loading of
pollutants of concern being discharged from surface impoundments.
Effluent limitations and standards based on the technologies used as
the basis for Options 4a (for units more than 400 MW), 4, and 5 would
completely eliminate the discharge of pollutants in bottom ash
transport water.
    Under Options 4a (for units more than 400 MW), 4, and 5, EPA would
establish ``zero discharge'' effluent limitations and standards for
discharges of pollutants in bottom ash transport water, based on either
using bottom ash handling technologies that do not require transport
water or managing a wet-sluicing bottom ash handling system so that it
does not discharge bottom ash transport water or pollutants associated
with the bottom ash transport water. These technologies for handling
bottom ash are described above in section VI of this preamble and in
the TDD for the proposed rule. About 80 percent of coal- and petroleum
coke-fired units generating bottom ash operate wet bottom ash transport
systems, while approximately 20 percent operate systems that eliminate
the use of transport water. Most, but not all, of the wet bottom ash
transport systems discharge to surface waters. In cases where a plant
has both wet and dry handling operations, the wet handling system is
typically used as a backup to the dry system. In the case of bottom ash
handling systems, the term ``dry'' is typically used to refer to a
process that does not use water as the transport medium to sluice the
bottom ash to a CCR impoundment. In some cases, a ``dry'' bottom ash
system may be entirely dry and avoid all use of water. Many dry bottom
ash systems, however, include a water bath at the bottom of a boiler in
which the bottom ash is dropped and cooled, and then the bottom ash is
mechanically dragged out of the boiler along a conveyor belt and
deposited in a pile adjacent to the building housing the boiler. The
bottom ash conveyed out of the water bath will be damp because the ash
particles retain some moisture from the water bath and small volumes of
water will typically drain from the standing bottom ash pile. The water
draining from the pile is usually collected in a sump and either
returned to the water bath below the boiler or managed as low volume
waste. Such mechanical drag systems are considered as one available
technology that may be used to achieve proposed limitations and
standards under Options 4a (for units >400 MW), 4, and 5. Other
technologies serving as the basis for limitations and standards
proposed under Options 4a (for units >400 MW), 4, and 5 are completely
dry bottom ash systems, remote mechanical drag systems, and
impoundment-based systems that are managed to eliminate the discharge
of all bottom ash transport water and the associated pollutants.
    In developing the technologies that serve as the basis for the
regulatory options with respect to bottom ash transport water, EPA
considered basing one or more options on chemical precipitation
treatment technology, with numeric effluent limitations or standards
for discharges of the wastestream to surface waters. Upon reviewing the
discharge flow rates for bottom ash transport water, however, EPA
determined that the costs associated with treatment were comparable to
the cost of the technologies upon which Options 4a (for units more than
400 MW), 4, and 5 are based, despite being less effective at removing
pollutants. Since the costs for chemical precipitation treatment were
found to be higher than the cost for converting to dry handling or
closed loop technologies, and the treatment technology removes fewer
pollutants, EPA did not include chemical precipitation treatment as
part of the regulatory options for bottom ash in this proposed rule.
See DCN SE03869.
    As described below in this section of the preamble, EPA is
proposing that certain BAT limitations for existing sources under
Options 4a (for units more than 400 MW), 4, or 5 would apply to
discharges of bottom ash transport water generated after the date
established by the permitting authority or control authority that is as
soon as possible within the next permit cycle after July 1, 2017. For
indirect dischargers, EPA is proposing that PSES for bottom ash
transport water would apply to bottom ash transport water generated
after a date determined by the control authority that is as soon as
possible beginning July 1, 2017. Bottom ash transport water generated
by existing direct dischargers prior to that date (i.e., ``legacy''
wastewater) would remain subject to the existing BPT effluent limits.
EPA considered subjecting legacy bottom ash transport water (i.e., the
bottom ash transport water generated prior to the date established by
the permitting authority or control authority, as described above), to
the BAT and PSES zero discharge requirement considered under Options 4a
(for units more than 400 MW), 4, and 5. As explained above, currently,
bottom ash transport wastewater and the associated pollutants are sent
to surface impoundments for treatment prior to discharge. The
technology bases identified above for Options 4a (for units more than
400 MW), 4, and 5 eliminate the generation of the bottom ash wastewater
but do not eliminate bottom ash transport wastewater that has already
been transferred to a surface impoundment. The technologies identified
as the basis for bottom ash transport water discharge requirements
under Options 4a (for units more than 400 MW), 4, and 5 have not been
demonstrated for the legacy bottom ash transport wastewater that has
already been generated and do not represent BAT/PSES with respect to
legacy bottom ash wastewater. As such, under Options 4a (for units more
than 400 MW), 4, and 5 EPA would not establish BAT or PSES requirements
for discharges of legacy bottom ash transport water generated prior to
the date established by the permitting authority. As proposed today,
discharges of legacy bottom ash transport water by existing direct
dischargers would remain subject to the existing BPT effluent limits;
however, EPA is also considering whether to set the BAT effluent
limitations for legacy bottom ash transport water equal to the existing
BPT effluent limits. See Section XVI for additional information.
    Combustion Residual Leachate. Under Options 1, 3a, 2, 3b, 3, and
4a, effluent limitations and standards for leachate from surface
impoundments and landfills containing combustion residuals would be set
equal to the current BPT effluent limitations, based on the technology
of gravity settling in surface impoundments to remove

suspended solids. Leachate is currently included under the definition
of low volume wastes, which are regulated by effluent limits for TSS
and oil and grease based on surface impoundments designed to remove
suspended solids. EPA is proposing that under Options 1, 3a, 2, 3b, 3,
and 4a, the rule would remove leachate from the definition of low
volume wastes at 40 CFR 423.11(b) and would set BAT effluent limits for
leachate equal to BPT limits for TSS and oil and grease (i.e., the
current effluent limits for low volume wastes).
    The technology basis for effluent limitations and standards for
leachate under Options 4 and 5 is chemical precipitation/
coprecipitation. This same technology is the basis for BAT Option 1 for
FGD wastewater. Properly designed and operated surface impoundments can
effectively remove suspended solids, including pollutants such as
particulate forms of certain metals when associated with the suspended
solids. However, since surface impoundments are not designed for, nor
are they effective at, removing other pollutants of concern such as
dissolved metals, EPA used chemical precipitation/coprecipitation as
the technology basis for Options 4 and 5. Physical/chemical treatment
systems are capable of achieving low effluent concentrations of various
metals and are effective at removing many of the pollutants of concern
present in leachate discharges to surface waters. The pollutants of
concern in leachate are the same pollutants that are present in, and in
many cases are also pollutants of concern for, FGD wastewater, fly ash
transport wastewater, bottom ash transport water, and other combustion
residuals. This is to be expected since the leachate itself comes from
landfills and surface impoundments containing the combustion residuals
and those wastes are the source for the pollutants entrained in the
leachate. Given the similarities present among the different types of
wastewaters associated with combustion residuals, combustion residual
leachate will be similarly amenable to chemical precipitation
treatment. The treatability of pollutants such as arsenic and mercury
using chemical precipitation technology is also demonstrated by
technical information compiled for ELGs promulgated for other industry
sectors. See, e.g., the TDDs supporting the ELGs for the Landfills
Point Source Category (EPA-821-R-99-019) and the ELGs for the Metal
Products and Machinery Point Source Category (EPA-821-B-03-001).
However, as is the case when treating FGD wastewater, this technology
is not effective at removing selenium, boron and certain other
parameters that contribute to total dissolved solids (e.g., magnesium,
sodium).
    EPA also considered developing a regulatory option that, for
leachate, would be based on the technology of chemical precipitation/
coprecipitation used in conjunction with anoxic/anaerobic biological
treatment. This is the same technology used as the basis for effluent
limitations and standards for FGD wastewater under Options 2, 3b (for
units at facilities with a total wet-scrubbed capacity of 2,000 MW or
more), 3, 4a, and 4. EPA has reviewed this technology as a potential
basis for effluent limitations and standards for leachate and the TDD
presents information about the compliance costs and pollutant removals
associated with this technology. The microorganisms used in the
bioreactors for the biological treatment technology for FGD wastewater
are resilient and have shown that they operate effectively under
varying conditions that occur in FGD system and the FGD wastewater
treatment system. However, leachate flows can be more variable than FGD
wastewater and, more importantly, may be too intermittent to facilitate
reliable and consistent biological treatment. Such variations are
easily accommodated in a chemical precipitation treatment system, but
may be difficult to manage in a biological treatment system reliant on
healthy and sustainable populations of microorganisms.
    If EPA did finalize BAT effluent limits developed under Options 4
or 5 would (although it is not proposing such limits as a preferred
option today), EPA's intent is that these limits would apply to
discharges of leachate generated after the date established by the
permitting authority that is as soon as possible within the next permit
cycle after July 1, 2017. For indirect dischargers, PSES for leachate
would apply to leachate generated after a date determined by the
control authority that is as soon as possible beginning July 1, 2017.
Leachate generated by existing direct dischargers prior to that date
(i.e., ``legacy'' leachate wastewater) would remain subject to the
existing BPT effluent limits. EPA considered subjecting legacy leachate
wastewater to the proposed BAT and PSES limitations and standards.
However, although some plants use relatively small surface impoundments
to treat leachate and these impoundments would contain relatively small
volumes of legacy leachate wastewater, other plants send leachate to
relatively large surface impoundments that also contain other plant
wastewaters, such as fly ash or bottom ash transport water, cooling
water, and/or other low volume wastes. EPA does not have the data to
demonstrate that the technologies identified above represent BAT for
legacy combustion residual leachate. As such, EPA would not expect to
finalize BAT requirements associated with discharges of legacy
combustion residual leachate (i.e., the leachate generated prior to the
date established by the permitting authority or control authority). As
proposed today, discharges of legacy combustion residual leachate by
existing direct dischargers would remain subject to the existing BPT
effluent limits; however, EPA is also considering whether to set the
BAT effluent limitations for legacy combustion residual leachate that
has not been mixed with non-legacy wastes equal to the existing BPT
effluent limits. See Section XVI for additional information.
    FGMC Wastewater. Under Options 1 and 2, effluent limitations and
standards for FGMC wastewater would be set equal to the current BPT
effluent limitations, based on the technology of gravity settling in
surface impoundments to remove suspended solids. Like leachate, FGMC
wastewater is currently included under the definition of low volume
wastes, with effluent limits for TSS and oil and grease based on
surface impoundments designed to remove suspended solids. EPA is
proposing that under all options, FGMC wastewater would be removed from
the definition of low volume wastes at 40 CFR 423.11(b). Under Options
1 and 2, BAT effluent limits for FGMC wastewater would be set equal to
BPT limits for TSS and oil and grease (i.e., the current effluent
limits for low volume wastes).
    As discussed above in Section VI of this preamble, some plants
inject dry sorbents (e.g., activated carbon) into the flue gas stream
to reduce mercury emissions from the flue gas. Mercury adsorbs to the
sorbent particles, and these mercury-enriched sorbents are then removed
from the flue gas using a fabric filter or ESP. The sorbent can be
injected upstream of the primary particulate collector, in which case
the mercury-enriched sorbent is collected with the majority of the fly
ash. Alternatively, the sorbent can be injected downstream of the
primary particulate collector and collected with a much smaller amount
of fly ash (i.e., the fly ash that passed through the primary
collector) in a smaller, dedicated secondary particulate collector such
as a fabric filter. In either case, the plant collects the mercury-

enriched sorbents along with fly ash. Because of this, the BAT
technology basis for FGMC wastewater in this proposal is identical to
the BAT technology basis for fly ash.
    Under Options 3a, 3b, 3, 4a, 4, and 5, EPA would establish ``zero
discharge'' effluent limitations and standards for discharges of
pollutants in FGMC wastewater based on using dry handling technologies
to store and dispose of fly ash without utilizing transport water. The
dry handling technologies that would be used for FGMC wastes are
identical to the dry fly ash handling technologies described above in
section VI of this preamble and in the TDD for the proposed rule.
Although surface impoundments can effectively remove particulate forms
of metals and other pollutants, they are not designed for nor are they
effective at removing other pollutants of concern such as dissolved
metals and nutrients. Effluent limits based on dry handling would
completely eliminate the discharge of pollutants in FGMC wastewater.
    EPA is also aware of some plants that add oxidizers to the coal
prior to burning the coal in the boiler. This chemical addition
oxidizes the mercury present in the flue gas, which allows the plant to
remove mercury more readily from the flue gas in the wet FGD system.
EPA did not evaluate separate treatment technologies for the use of
oxidizers to control flue gas mercury emissions because using oxidizers
does not generate a separate FGMC wastewater.
    To the extent that a power plant generates FGMC wastewater before
any BAT zero discharge limitation were to apply, the proposed BAT
limitations under Options 3a, 3b, 3, 4a, 4, and 5 would apply to
discharges of FGMC wastewater generated after the date established by
the permitting authority that is as soon as possible within the next
permit cycle after July 1, 2017. For indirect dischargers, EPA is
proposing that PSES for FGMC wastewater would apply to FGMC wastewater
generated after a date determined by the control authority that is as
soon as possible beginning July 1, 2017. As proposed today, legacy FGMC
wastewater generated by existing direct dischargers prior to that date
would remain subject to the existing BPT effluent limits; however, EPA
is also considering whether to set the BAT effluent limitations for
legacy FGMC wastewater equal to the existing BPT effluent limits. EPA
considered subjecting legacy FGMC wastewater to the proposed BAT/PSES
zero discharge requirements. As explained above, although most FGMC
wastes are managed using dry handling systems, EPA has identified six
plants that manage their FGMC waste with systems that use water to
transport the waste to surface impoundments. The technology basis
identified above for the proposed zero discharge requirement eliminates
the generation of the FGMC wastewater by implementing certain process
changes that do not use water to transport the FGMC waste; however, it
does not eliminate the already-generated FGMC wastewater that has
already been transferred to and stored in a surface impoundment. The
technologies that underlie regulatory Options 3a, 3b, 3, 4a, 4, and 5
do not represent BAT or PSES for the control of pollutants from legacy
FGMC wastewater and would not allow FGMC wastewater that has already
been generated to comply with a zero discharge requirement. As such,
EPA is not proposing BAT or PSES requirements associated with
discharges of legacy FGMC wastewater generated prior to the date
established by the permitting authority or control authority. However,
EPA is considering whether to set the BAT effluent limitations for
legacy FGMC wastewater equal to the existing BPT effluent limits. See
Section XVI for additional information.
    Gasification Wastewater. The technology basis for the effluent
limitations for all eight regulatory options for gasification
wastewater is vapor-compression evaporation. Two operating IGCC plants
in the U.S. currently use this technology, and a third IGCC plant that
is scheduled to begin commercial operation soon will also use it to
treat gasification wastewater. Like leachate and FGMC wastewater,
gasification wastewater is currently included under the definition of
low volume wastes, with effluent limits for TSS and oil and grease
based on surface impoundments designed to remove suspended solids. EPA
considered using surface impoundments as the technology basis for one
or more of the regulatory options for gasification wastewater. However,
surface impoundments are not effective at removing the pollutants of
concern present in gasification wastewater. In addition, one of the
currently operating IGCC plants formerly used a surface impoundment to
treat its gasification wastewater and the impoundment effluent
repeatedly exceeded NPDES permit limits established to protect water
quality. Because of the demonstrated inability of surface impoundments
to remove the pollutants of concern and the current industry practice
of operating vapor-compression evaporation to treat the gasification
wastewater at all U.S. IGCC plants, EPA determined that surface
impoundments do not represent BAT level of control.
    In addition to the vapor-compression evaporation technology that is
the basis for all BAT and BADCT/NSPS options for gasification
wastewater, EPA considered also including cyanide treatment as part of
the technology basis for one or more options. EPA notes that the
Edwardsport IGCC plant that is scheduled to soon begin commercial
operation includes cyanide destruction as one step in the treatment
process for gasification wastewater. However, EPA currently does not
have sufficient gasification wastewater data with which to calculate
effluent limits based on the performance of cyanide treatment as part
of a BAT/BADCT (NSPS) regulatory option. A possible approach to resolve
this would be to transfer effluent limits for cyanide from an ELG for
another industry sector. Alternatively, EPA may obtain effluent data
from the gasification wastewater treatment system for the Edwardsport
IGCC unit once it begins commercial operation and use these data to
calculate effluent limitations for cyanide. EPA solicits data on the
concentrations of cyanide present in gasification wastewater and
solicits comment on whether EPA should establish BAT or BADCT (NSPS)
control on the discharge of cyanide.
    Nonchemical Metal Cleaning Wastes. The technology basis for the
effluent limitations for all eight regulatory options for nonchemical
metal cleaning wastes is chemical precipitation. Separation processes
in the physical/chemical treatment, along with chemical addition when
needed to facilitate coagulation and settling of suspended solids,
would effectively remove TSS and oil and grease to effluent
concentrations below the limitations included in the proposed rule. In
addition, treatment chemicals added to adjust pH to precipitate
dissolved metals or to facilitate flocculation/coagulation are
effective at removing copper and iron to effluent concentrations below
the proposed limitations, in addition to reducing the concentrations of
other pollutants present in nonchemical metal cleaning wastes.
    The current ELG relies on three key terms specific to metal
cleaning waste: ``metal cleaning waste,'' ``chemical metal cleaning
waste,'' and ``nonchemical metal cleaning waste.'' The regulation
includes a definition of the broadest term, ``metal cleaning waste,''
as ``any wastewater resulting from cleaning [with or without chemical
cleaning compounds] any metal process equipment, including, but not
limited to, boiler tube cleaning, boiler fireside

cleaning, and air preheater cleaning.'' 40 CFR 423.11(d). Thus, this
definition includes any wastewater generated from either the chemical
or nonchemical cleaning of metal process equipment. In addition, the
regulation also defines ``chemical metal cleaning waste'' as ``any
wastewater resulting from cleaning of any metal process equipment with
chemical compounds, including, but not limited to, boiler tube
cleaning.'' See 40 CFR 423.11(c). The regulation also includes, but
does not expressly define the term ``nonchemical metal cleaning waste''
when it states that it has ``reserved'' the development of BAT ELGs for
such wastes. See 40 CFR 423.13(f). Although the regulation provides no
definition of ``nonchemical metal cleaning waste,'' it is clear from
the definitions of metal cleaning waste and chemical metal cleaning
waste that nonchemical metal cleaning waste is any wastewater resulting
from the cleaning of metal process equipment without chemical cleaning
compounds.
    The current ELGs include BPT effluent limits for the allowable
levels of TSS, oil and grease, copper and iron in discharges of metal
cleaning waste, which includes both chemical and nonchemical metal
cleaning wastes. Although the current BPT effluent limits apply to
nonchemical metal cleaning wastes, EPA has found that some discharges
of nonchemical metal cleaning waste are authorized pursuant to permits
incorporating limitations based on BPT requirements for low volume
wastes and, therefore, do not have iron and copper limits. The
information EPA has collected to date indicates many facilities are not
discharging nonchemical metal cleaning wastewater or have copper and
iron limits (see Section VIII.A.3 and Section 7.7 of the TDD for more
information).
    The current ELGs do not include BAT/NSPS requirements for the
broadly defined category of metal cleaning wastes; however, they do
include BAT/NSPS for chemical metal cleaning waste. EPA has not
promulgated BAT/NSPS for nonchemical metal cleaning waste. Similarly,
although the current ELGs do not include PSES/PSNS for metal cleaning
waste, they do include PSES/PSNS for chemical metal cleaning waste. EPA
has not promulgated PSES/PSNS for nonchemical metal cleaning waste. An
overview of the existing ELGs for metal cleaning waste, including
chemical and nonchemical metal cleaning waste, is provided below in
Table VIII-2.

                                       Table VIII-2--Parameters Limited by Existing ELGs for Metal Cleaning Waste
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            Wastestream                        BPT                     BAT                    NSPS                   PSES                   PSNS
--------------------------------------------------------------------------------------------------------------------------------------------------------
Chemical Metal Cleaning Waste......  TSS, Oil & Grease,      Copper, Iron..........  TSS, Oil & Grease,     Copper...............  Copper.
                                      Copper, Iron.                                   Copper, Iron.
Nonchemical Metal Cleaning Waste...  ......................  Reserved..............  Reserved.............  Reserved.............  Reserved.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    As described above, EPA found that some discharges of nonchemical
metal cleaning waste are authorized pursuant to permits incorporating
limitations based on BPT requirements for low volume wastes and,
therefore, do not have iron and copper limits. Because the potential
costs for dischargers to comply with iron and copper limits is not
known, EPA is proposing to provide an exemption from new copper and
iron limitations or standards for existing discharges of nonchemical
metal cleaning wastes from generating units that are currently
authorized without iron and copper limits. For these discharges, BAT
limitations for nonchemical metal cleaning waste would be set equal to
BPT limitations for low volume waste, and the regulations would not
specify PSES. EPA solicits comment on the specific generating units
that should be included in the exemption. See Section VIII.A.3 for
additional details regarding the information that EPA is requesting as
part of the comment solicitation.
    EPA is also considering setting BAT for nonchemical metal cleaning
waste equal to the metal cleaning waste BPT for all nonchemical metal
cleaning wastes (i.e., no exemption for discharges of nonchemical metal
cleaning wastes currently authorized without iron and copper limits)
and, for PSES, to establish copper standards for all discharges of
nonchemical cleaning wastes. As part of this approach, EPA is
evaluating whether some plants would incur costs to comply with the
current BPT standards. Therefore, as described later in this preamble,
EPA is also soliciting comments associated with each generating unit
with discharges of nonchemical metal cleaning wastes that are not
currently subject to the BPT copper and iron limits, in order to
understand the nonchemical metal cleaning wastes that are generated,
the characteristics of the wastewater, what actions would be needed to
comply with the proposed copper and iron limits, and estimated costs
associated with those actions. See Section VIII.A.3 for details
regarding the information that EPA is requesting as part of the comment