EPA's Vessel General Permit and Small Vessel General

In querying the database (http://invasions.si.edu/nemesis/browseDB/searchQuery.jsp), we
limited our search criteria to only include hull-fouling ANS documented in a single calendar
year. We performed this search for each year between 2008 and 2011 (years covered under the
previously issued VGP). The annual number of newly documented hull-fouling ANS in waters
of the U.S. ranged from 10 to 20 species, with a mean of 13.5 (95% CI: 11.3 – 15.7).
As described above, the VGPs require few explicitly mandated anti-fouling and hull husbandry
practices or technologies. Therefore, we do not expect to see substantial reductions of hullfouling
ANS under the proposed VGPs, and these invasions are likely to continue at a minimum
rate of 13 species per year. We conclude that there is at least a small likelihood that listed
resources would be exposed to ANS invasions as a result of hull fouling and hull husbandry as
authorized by the VGPs.
Ballast Water
Ballast water is water taken onboard in large volumes to assist with vessel draft, buoyancy, and
stability. It is taken from coastal port areas and transported with the ship to the next port of call,
where the water may be discharged or exchanged. If a ship is receiving or delivering cargo to a
number of ports, it may release or take on a portion of ballast water at each port. Large
commercial vessels (e.g., container ships, bulk carriers, other cargo vessels, tankers, and
passenger vessels) normally have ballast tanks dedicated to this purpose, and some vessels may
also ballast empty cargo holds. The discharge volume varies by vessel type, ballast tank
capacity, and type of deballasting equipment.
According to the BE, the VGP would authorize discharges from approximately 72,000 vessels;
many of these vessels utilize ballast water. The sVGP would authorize discharges from 115,000
to 138,000 vessels; however these vessels (i.e., commercial fishing vessels less than 79 feet,
passenger vessels, and utility vessels) do not have ballast water tanks greater than 8 cubic meters.
Further, the BE notes that according to the U.S. Coast Guard: vessels less than 100 feet
“typically operate in more sheltered environments and do not load and discharge ballast. Their
stability characteristics generally accommodate the amount and type of cargo they carry,
precluding the need to use ballast as a stability enhancer” (USCG 2008).
A National Academy of Science study estimates that ~52 billion gallons (196 million metric
tons) of ballast water are discharged annually (NAS 2011). Ballast water that originated from
outside of North America (i.e., that was taken on from a foreign source port) accounted for 28.5
percent of the total discharge volume, and the remainder came from other ports or locations
within the U.S. and Canada (NAS 2011).
Vessel class estimates of ballast water discharge volumes reported in the BE are based on
median ballast water capacity for those vessels that have ballast tanks (USEPA 2011c). The
median is the middle observation in a dataset or 50 th percentile. It a more robust measure of
central tendency than the mean when the data are not symmetrically distributed around the mean
(i.e., the data are skewed). However, reporting the median alone does not provide much useful
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