EPA's Vessel General Permit and Small Vessel General

addition of chlorine also produces hypobromous acid (HOBr), hypobromous ion (OBr-), and
bromamines (USEPA 2010a). These products are referred to as chlorine produced oxidants.
Total residual chlorine was detected in bilgewater, deck washdown, and graywater discharges.
Eighty eight to nearly 100% of the total residual chlorine load from vessels is discharged in
graywater at concentrations ranging from 13 mg/day from utility vessels to nearly 2 kg per day
from large Cruise ships (USEPA 2010b).
The post permit TRC concentrations in EPA’s estuarine harbor model averaged 0.1 ug/L and
ranged from 0.002 ug/L to 0.0007 mg/L, suggesting an approximately 25 to 70 percent reduction
in TRC discharged. For the river harbor model, EPA's average post permit TRC was 0.0014
mg/L and ranged from 0.0144 ug/Lto 0.0032 mg/L, suggesting a 3 to 15 percent reduction the
amount of TRC discharged. These post permit TRC estimates fell below the response thresholds
selected by EPA for evaluating risks of exposure to TRC. These thresholds ranged from 3.7 to
50 mg/L for freshwater organisms and from 7.5 ml/L to 46.5 ml/L for estuarine/marine
organisms. The threshold values EPA selected for freshwater and estuarine/marine vertebrates
and for freshwater vertebrates were derived from NOECs and LOECs. The vertebrate NOECs
were 6 ml/L and 40 ml/L for freshwater and estuarine/marine organisms, respectively. The
NOEC for freshwater invertebrates was 2 ug/L.
Chlorine is not expected to bioaccumulate in plants or animals since it reacts with the moist
tissues of living systems (Compton, 1987; Schreuder and Brewer, 2001; Schmittinger et al.,
2006). Also, chlorine is toxic to microbial communities; therefore, biodegradation is not
considered to be a relevant fate process (Vetrano, 2001). In general, the hypochlorous acid
formed during the dissolution of chlorine in natural waters reacts with organic and inorganic
materials, ultimately forming chloride ion, oxidized inorganics, chloramines, trihalomethanes,
oxygen, and nitrogen. Consequently, chlorine does not persist in the aquatic environment in the
form in which it was discharged. As such, listed species and their critical habitat are not
expected to be exposed to total residual chlorine at levels which could cause adverse effects.
Total Suspended Solids
EPA’s estimated post permit TSS concentrations in the estuarine harbor model averaged 0.0281
mg/L and ranged from 0.0015 to 0.13 mg/L, suggesting a 35 to 55 percent reduction in TSS
discharges. For the river harbor model, EPA's post permit TSS averaged 0.72 mg/L and ranged
from 0.00764 to 1.62 mg/L, suggesting a 35 to 40 percent reduction in TSS discharges. Post
permit TSS estimates fell below the response threshold of 3.33 mg/L selected by EPA for
evaluating risks of exposure to TSS. This threshold is based on EPAs existing ambient water
quality criteria converted into TSS equivalents.
Direct effects of suspended materials on invertebrates and fish are complex, ranging from
behavioral to physiological to toxicological. Suspended sediments have been documented to
have a negative effect on the survival of fish, freshwater mussels, and other benthic organisms.
In a frequently cited review paper prepared by Newcombe and Jensen (1996), sublethal effects
(e.g. increased respiration rate) were observed in eggs and larvae of salmonids and
nonsalmonids, as well as in adult estuarine and freshwater non-salmonids, when exposed to Total
Suspended Solids concentrations as low as 55 mg/L for one hour. Mussels compensate for
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