EPA's Vessel General Permit and Small Vessel General

Table 19. Estimated Graywater Pollutant Concentrations used in EPAs Biological
Evaluation.
Pollutant
Point
Estimate
Used in BE
Detection
Frequency Mean (range) 50th /75 th /90 th
Percentiles c
Ammonia as Nitrogen (NH3-N,
mg/L)
1.3 (2.1) a 8/8 1.3 (0.19-4.5) 0.75/1.8/4.5
Total Phosphorus (mg/L) 1.4 (10) 8/8 1.4 (0.42-3.4) 1.2/2.2/3.4
Total Residual Chlorine (mg/L) 0.12 6/8 0.12 (nd b -0.11) 0.02/nc d /0.11
Total Suspended Solids (TSS)
(mg/L)
52 8/8 52 (14-81) 58/69/81
Hexane Extractable Material
(HEM) (mg/L)
39 (149) 8/8 39 (9.4-100) 29/68/100
Silica Gel Treated HEM (SGT-HEM)
(mg/L)
8.1 (36.6) 6/8 8.1 (nd-35) 1.5/9.4/35
Aluminum (total, μg/L ) 380 8/8 380 (50-910) 420/540/910
Arsenic (total, μg/L ) 2 2/8 2 (-2.9) /1.5/2.93
Copper (dissolved, μg/L) 55 8/8 55 (5.3-280) 17/60/280
Lead (dissolved, μg/L) 2.5 4/8 2.5 (nd-6) 1.1/4.2/6
Zinc (dissolved, μg/L) 400 8/8 400 (70-1500) 240/610/1500
a
Values in parentheses are for large cruise ships.
b
Nondetect (censored) concentrations were replaced with ½ of the reporting limit for calculating
average concentrations.
c
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.
d
Distribution statistics were only calculated when analytes were detected at a sufficient frequency.
Stern Tube Packing Gland Effluent and Other Oil/Water Interfaces. A stuffing box packed
with greased flax rings is designed to leak a few drops per minute of ambient water (EPA
estimate, 4 to 8 gallons per day (USEPA 2010b) to cool the gland when a vessel is underway.
Stuffing boxes are also used to seal rudder stocks that penetrate the hull below the waterline. The
packing gland effluent water is often collected in a segregated section of the bilge that contains
an automatic bilge pump.
To estimate stern tube effluent discharge rates for the other vessel types requiring detailed
analysis for the BE, EPA used the size of a utility vessel (measured as gross tons), compared this
vessel size to the other vessel types, and applied an average stern tube packing gland discharge
rate of 6 gallons per day as shown in the example calculation below.
Example: 25 gross tons (fishing vessel)/80 gross tons (utility vessel) x 6 g/day = 2 g/day
Pollutants in the stern tube packing gland effluent include metals, oil and grease, suspended
solids, organics, and phthalates. Oil to sea interfaces include any mechanical or other equipment
where seals or surfaces may release small quantities of oil and grease into the sea. Examples
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