EPA's Vessel General Permit and Small Vessel General

on reproduction and survival would likely to occur. Risk quotients for the alternative exposure
scenarios A and B (where fewer vessels are discharging EGS washwater and the Se effluent
concentrations are lower) were substantially lower. However, even at the lower exposures
predicted under scenarios A and B some of the risk quotients for the San Francisco Bay-Delta
model approached or equaled 1.0 for fish and exceeded 1 for birds. These results suggest that
selenium from vessel discharges could pose a risk to listed species in the future if the number of
vessels utilizing exhaust gas scrubbers increase beyond what is anticipated.
EPA has agreed to develop and implement a monitoring plan for gas-scrubber discharges. With
technical assistance from the Services, EPA will identify metrics for assessing selenium loadings
in waters inhabited by ESA- listed species. EPA will also state which analytical methods should
be used to accurately measure selenium in saline gas-scrubber discharges. They will also
compile NOI and annual report information regarding the number and type of vessels using
exhaust gas scrubbers and discharge monitoring data for selenium. And finally, EPA will
evaluate vessel data, identify ports/locations where the metric has been exceeded and will, as
appropriate, identify and implement additional actions to reduce any unacceptable risk.
Table 30. Generalized steps in ecosystem-scale methodology for translation of a tissue Se
concentration to a water-column Se concentration for protection of fish and aquaticdependent
wildlife. [Adapted from Table 5, Presser and Luoma, 2010b].
Translation of Tissue Criterion to Water-Column Concentration
• Develop a conceptual model of food webs in watershed.
• Choose toxicity guideline for fish or aquatic bird species in estuary.
• Choose fish or bird species to be protected in watershed.
• For fish, choose species-specific TTFfish or use default TTFfish of 1.1; for
birds, choose species-specific TTFibird or use default TTFbird of 2.0.
• Identify appropriate food web(s) for selected fish or bird species based on
species-specific diet.
• Choose site-specific TTFinvertebrate for invertebrates in selected food web(s)
or use default TTFinvertebrate for species of invertebrate (see list in Presser and
Luoma, 2010).
• Choose site-specific Kd or use Kd indicative of a) generalized source of Se
and receiving water conditions or b) site-specific hydrologic type and speciation; or a
default Kd of 1000 (see list in Presser and Luoma, 2010).
• Solve equation(s) for allowable water-column concentration for protection of
fish or birds (i.e., predator)
If assume single invertebrate diet, then
o Cwater = (Cpredator) ÷ (TTFpredator) Kd (TTFinvertebrate)
If assume a mixed diet of invertebrates, then
o Cwater = (Cpredator) ÷ (TTFpredator) (Kd) [(TTFinvertebrate a) (prey
fraction)] + [(TTFinvertebrate b) (prey fraction)] + [(TTFinvertebrate c) (prey fraction)]
If assume sequential bioaccumulation in longer food webs, then
o Cwater = (Cpredator) ÷ (TTFpredator) Kd (TTFinvertebrate a) (TTFforage
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