EPA's Vessel General Permit and Small Vessel General

analyzed due to a lack of resources. EPA therefore does not know the types of PPCPs
and the extent to which they are discharged by vessels.
� While the Report to Congress included data for nonylphenols, EPA did not acknowledge
this data in the body of the BE.
The breadth of the extrapolations and the omissions made by EPA when characterizing the
discharges authorized by the VGPs indicate substantial gaps and uncertainty in EPA’s
knowledge of the pollutant discharges authorized by the VGPs. While the Services acknowledge
that uncertainty exists in all risk analyses, the magnitude of uncertainty introduced into the BE
analysis due to EPA’s lack of knowledge regarding authorized discharges is substantial. This
further emphasizes the need for EPA to monitor discharges to gather additional information to
more accurately identify stressors and determine which may be problematic. The EPA will
monitor discharges from the following vessel systems: ballast water treatment systems, exhaust
gas scrubbers, oily water separator, cruise ship graywater, and copper-based anti-fouling hull
coatings.
(3) Exposure to potentially harmful impacts
In this section, we ask whether EPA has reliably estimated whether and to what degree listed
resources are likely to be exposed to potentially harmful impacts of discharges authorized by the
permit. EPA identified uncertainties in their effects analysis that could potentially limit the
interpretation of results and conclusions. In order to address whether EPA has demonstrated
sufficient knowledge of the exposures resulting from discharges authorized by the VGP, we must
first review these uncertainties acknowledged by EPA for the BE’s assessment.
Uncertainties in Exposure Estimates Identified by EPA
The EPA used simple screening models to represent the estuarine and river water bodies and to
estimate the exposure concentrations evaluated in the risk analysis of all U.S. waters navigable
by vessels covered under the VGP and sVGP. They acknowledged that the use of such
screening-level models is typically limited to identifying major water quality issues and to
identify data gaps, not to perform risk analyses as they were used in the BE.
EPA acknowledged that uncertainty was added to the analysis by the extrapolations needed to fill
data gaps for the various combinations of vessel types, discharges, pollutants, and vessel
populations. These extrapolations were required to develop the pollutant loads used in the
modeling analysis. EPA also assumed that the background concentration for all pollutants in the
harbor scenarios was zero. Therefore, the model output used to inform the effects analysis does
not directly evaluate the potential for vessels to contribute to pollutant impairments or quantify if
vessel pollutant loads serve as the “tipping point” between exceeding and not exceeding a given
effect threshold. Rather than assess pollutant load contribution to existing baseline levels in the
RAAs it modeled, EPA relied on the magnitude of risk quotients to provide a sense as to whether
incidental vessel discharges covered under the VGP and sVGP would make notable or sizable
contributions to existing harbor pollutant levels.
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