EPA's Vessel General Permit and Small Vessel General

waters of the U.S. and may contain selenium, nutrients, oils, polycyclic aromatic hydrocarbons
(PAHs) and metals, and may have a different pH than receiving waters.
For vessels covered under the VGP, EPA prohibits the discharge of exhaust gas scrubber
washwater containing oil, including oily mixtures, in quantities that may be harmful as
determined in accordance with 40 CFR Part 110. They prohibit the discharge of sludge or
residues generated in treating exhaust gas scrubber washwater discharge and require these
discharges to be delivered ashore to adequate reception facilities. In addition, vessel
owners/operators with exhaust gas cleaning systems that result in washwater discharges must
meet the numeric effluent limits and the monitoring requirements below:
� The discharge washwater from the exhaust gas scrubber treatment system must have a pH
of no less than 6.5 measured at the ship’s overboard discharge, with the exception that
during maneuvering and transit, the maximum difference between inlet and outlet of 2.0
pH units is allowed.
� The maximum continuous PAH (Polycyclic Aromatic Hydrocarbons) concentration in
the washwater must not be greater than 50 μg/L PAHphe (phenanthrene equivalence)
above the inlet water PAH concentration for washwater flow rates normalized to 45
t/MWh. MWh refers to the maximum continuous rating (MCR) or 80 percent of the
power rating of the fuel oil combustion unit. For the purposes of this criterion, the PAH
concentration in the washwater must be measured downstream of the water treatment
equipment, but upstream of any washwater dilution or other reactant dosing unit, if used,
prior to discharge. The 50-μg/L limit is adjusted upward for lower washwater flow rates
per MWh, and vice-versa, and the specific permit limits are listed in the VGP.
� The washwater treatment system must be designed to minimize suspended particulate
matter, including heavy metals and ash. The maximum turbidity (monitored
continuously) in washwater must not be greater than 25 FNU (formazin nephelometric
units) or 25 NTU (nephelometric turbidity units) or equivalent units, above the inlet water
turbidity. However, during periods of high inlet turbidity, the precision of the
measurement device and the time lapse between inlet measurement and outlet
measurement are such that the use of a difference limit is unreliable. Therefore, all
turbidity difference readings must be a rolling average over a 15-minute period to a
maximum of 25 FNU or NTU. For the purposes of this criterion, the turbidity in the
washwater must be measured downstream of the water treatment equipment but upstream
of washwater dilution (or other reactant dosing) prior to discharge. For a maximum of
one 15-minute period within any 12-hour period, the continuous turbidity discharge limit
may be exceeded by 20 percent.
� The washwater treatment system must prevent the discharge of nitrates, plus nitrites
beyond that associated with a 12 percent removal of NOx from the exhaust, or beyond 60
mg/l normalized for washwater discharge rate of 45 tons/MWh, whichever is greater.
MWh refers to the MCR or 80 percent of the power rating of the fuel oil combustion unit.
For the purposes of this criterion, the nitrate concentration in the washwater must be
measured downstream of the water treatment equipment, but upstream of any washwater
dilution or other reactant dosing unit, if used, prior to discharge. The 60-mg/L limit is
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