EPA's Vessel General Permit and Small Vessel General

Table 21. Estimated Stern Tube Packing Gland Effluent Pollutant Concentrations used in
EPAs Biological Evaluation.
Pollutant
Point
Estimate
Used in
BE
Detection
Frequency Mean (range) 50th /75 th /90 th
Percentiles b
Total Phosphorus (mg/L) 0.13 7/9 0.13 (nd a -0.25) 0.1/0.22/0.25
Total Suspended Solids (TSS, mg/l) 59 9/9 59 (5.6-270) 28/81/270
Hexane Extractable Material (HEM, mg/l) 14 5/9 14 (nd-67) 1.65/23/67
Chromium, (dissolved, μg/L) 13 5/9 19 (nd-110) 3.8/20/110
Silica Gel Treated HEM (SGT-HEM, mg/l) 19 5/9 13 (nd-56) 1.7/19/56
Copper (dissolved, μg/L) 22 4/9 22 (nd-92) nc c /38/92
Nickel (dissolved, μg/L) 210 6/9 210 (nd-1000) 13/370/1000
Nickel (total, μg/L) 610 8/9 610 (nd-3200) 45/970/3200
Bis (2-ethylhexyl)phthalate (μg/L) 4.7 3/9 4.7 (nd-24) nc/4.1/24
Tetrachloroethene (μg/L) 1.4 1/9 1.4 (nd-0.2) nc/nc/0.2
a
Nondetect (censored) concentrations were replaced with ½ of the reporting limit for calculating average
concentrations.
b
Percentiles are the concentrations of each analyte below which at least that percentage of the values fall.
So the 75th percentile is the concentration below which at least 75% of the observations were found.
c
Distribution statistics were only calculated when analytes were detected at a sufficient frequency.
Underwater Ship Husbandry Discharges. Although discharges from underwater ship
husbandry is considered a low volume and low frequency discharge generated by a low number
of vessels, EPA analyzed the risk of this discharge in its BE due to the high potential risk posed
by the concentration and types of pollutant discharged. Underwater husbandry discharge
volumes were not estimated because EPA was unable to find available data to accurately
estimate volume of these discharges. Furthermore, EPA round approached ANS risk
qualitatively, so volume estimates were not necessary. EPA’s Report to Congress did provide
copper release estimates for underwater ship husbandry events (Table 22).
Table 22. Dissolved Copper Release from Vessel AFSs During an Underwater Hull
Cleaning “Event” (Schiff et al. 2003, after USEPA 2010).
AFS Cleaning Method
Epoxy copper
antifouling paint
Hard vinyl/Teflon
copper antifouling
paint
Biocide-free coating
Copper Release
(μg/cm2/event)
Less abrasive management practices 8.6
No management practices 17.4
Less abrasive management practices 3.8
No management practices 4.2
Less abrasive management practices 0.03
No management practices 0.05
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