EPA's Vessel General Permit and Small Vessel General

that the sVGP authorizes discharges from between 115,000 and 139,000 vessels, discharge
estimates are based on data from approximately 0.05% of the permitted population. The vessels
sampled for the report were commercial fishing vessels and other non-recreational vessels less
than 79 feet, that is to say, sVGP-authorized vessels. Vessels described in the Report to
Congress volunteered to allow EPA to sample discharges. This “opportunity sampling”
approach likely favored participation of operators who were confident that their vessel
discharges were low impact.
In its report, EPA discussed whether these data could be extrapolated to other vessels, including
larger vessels, such as those authorized to discharge under the VGP. EPA cautioned against
extrapolating bilgewater data to vessels not sampled for the Report to Congress (e.g., cruise
ships, ferries, barges, tankers) because these vessels differ considerably in design, construction,
and operation. The BE also used information from a 2008 report on cruise ship discharges
(USEPA 2008), but this report only provides data for bilgewater volume in these larger vessels,
not data on the pollutants present in bilgewater Ultimately EPA characterized VGP bilgewater
discharges using bilgewater pollutant data from the Report to Congress and bilgewater volume
data from the cruise ship discharges report. EPA also cautioned against extrapolating deckwash
and graywater volume and constituents among vessels because these would differ due to
activities conducted on board. For example, fishing vessels and cruise ships would have very
different graywater and deckwash characterisitcs. Nevertheless, voluntary discharge data from
61 small vessels were used to characterize discharges from VGP vessels.
EPA considered zinc discharges from cathodic protection sacrificial anodes to be of too low
volume and toxicity to be considered in the BE. NMFS calculated zinc load using the discharge
rate reported in BE Table 3-3 and the wetted hull area estimates reported in BE table 3-18.
These calculations indicate that sacrificial anode discharges can actually make up a substantial
portion of the zinc load discharged from some vessels. Sacrificial anodes contribute
approximately 20% to 80% of the zinc discharged from barges, cargo ships and oil tankers at
pierside and approximately 50 to 95% of zinc discharges from these vessels while underway.
Under worst-case conditions (i.e. oil tanker anodes), the inclusion of anode discharges would
result in a five-fold increase in zinc loading while pierside and 17 fold increase while underway.
Fortunately, increasing the modeled zinc estimates by 17 fold does not appreciably change the
risk conclusions of the BE analysis.
While the analyte list examined in the BE was extensive, there were a number of omissions that
should be noted:
� EPA states that mercury was not evaluated because it was not possible to sample away
from sources of metals or sources of airborne mercury such as engines or generators,
which may contaminate the sample. In stating this, EPA indirectly acknowledges that
mercury is a contaminant generated on vessels and that it does not know the relative
sources or extent to which mercury is discharged from vessels.
� EPA acknowledges that pharmaceuticals and personal care products (PPCPs) would
occur in graywater and sewage mixed with graywater but stated that PPCPs were not
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