EPA's Vessel General Permit and Small Vessel General

Table 23. Decision Process for those Vessel Discharges Not Evaluated in EPA's BE.
Vessel Discharge Description Number of
Vessels
Discharging
Machinery
Wastewater
Refrigeration and
Air Condensate
Discharge
Coal Ash from
Coal Fired
Propulsion
Systems on
Ferries
Seawater Cooling
Overboard
Dischargenn
Distillation and
Reverse Osmosis
Brine
such as distilling plants start-up discharge, chilled water condensate drains,
fresh-and saltwater pump drains, and potable water tank overflows. These
flows are generally low in volume and are not expected to contain significant
amounts of pollutants.
Condensation from cold refrigeration or evaporator coils of air conditioning
systems drips from the coils and collects in drip troughs which typically empty
to a drainage system. Large numbers of vessels are equipped with refrigeration
systems to keep food and other perishable items from spoiling. Air
conditioning systems are also used for passenger and crew comfort.
Condensates may contain very small amounts of pollutants such as metals
derived from vessel piping systems.
Combusting coal in boilers produces a residue of combustible flue constituents
known as ash. Some of the ash consists of very fine particles that are entrained
in the flue gas and carries out of the furnace (fly ash), while heavier ash settles
at the bottom of the boiler (bottom ash). Bottom ash may be hydraulically
conveyed (i.e., sluiced with water). The discharge of coal ash slurry from coal
fired propulsion systems on a ferry is authorized by the 2008 VGP until
December 19, 2012.
Seawater cooling systems use ambient water to absorb the heat from heat
exchangers, propulsion systems, and mechanical auxiliary systems. The water
is typically circulated through an enclosed system that does not come in direct
contact with machinery, but still may contain sediment from water intake,
traces of hydraulic or lubricating oils, and trace metals leached or eroded from
the piping within the system. Additionally, because it is used for cooling, the
effluent will have an increased temperature.
Discharges of brine can occur on vessels that do not bunker potable water but
instead use onboard plants to distill seawater or desalinate seawater using
reverse osmosis (RO) to generate fresh water. Distillation units generate brine
Discharge
Volume
and
Frequency
High Low Low
Amount and
Types of
Pollutants
Present in the
Discharge
Low High Potentially
High
High Low Low
Low High Low
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