103 



» Injection of the effluent plume into the mixed layer together with prevailing southwest winds 

 would tend to push the plume offshore toward Stellwagon Basin (18 km) and Bank (26 km), 

 Such distances are relatively small given that wind forcing can transpon fluid and particles tens of 

 kilometers in only a few days. 



• The wine} forcing used in the USGS model was for two years. Interannual variations in wind 

 patterns are common and have been shown to be very important in determining the degree of 

 offshore transpon of buoyant plumes. Selected scenarios of wind forcing (direction and 

 magnitude) should be modeled to examine the effect on effluent transport. In particular, southwest 

 wind forcing of a surface trapped effluent plume should be examined for possible transpon to 

 faifield habitats. 



• It was suggested that strong offshore forcing due to storm events could lead to shoreward 

 transpon of the effluent. This only would be true if the effluent remained in the bottom layer 

 below the thermocline. If the plume penetrated into the surface mixed layer in the summer or is 

 mixed throughout the water column in winter, the effluent could be transponed seaward of the 

 proposed site. By contrast, effluent at the current discharge site is likely to be diluted due to 

 nearshore upwclling and is unlikely to be transponed seaward to the extent that an offshore plume 

 would be. 



• Storm events would Increase the volume of discharged effluent, reduce the degree of secondary 

 treatment, and increase transport. The combination of these effects should be modeled especially 

 since such wet weather/storm conditions can occur frequently (e.g. bi-weekly) throughout the 

 year. 



• Changes in circulation panems in the Gulf of Maine could result in altered inflow and outflow 

 patterns in the Bays. Such variability could be due to wind patterns, freshwater buoyancy plumes 

 entering the region or internal wave fields propagating across the Gulf. Such variability should be 

 examined using the USGS model because it could affect the flow field within the Bays region and 

 transport of the sewage effluent. 



Monitoring: 



I agree with NMFS that long-term deposition of plume borne particulates are not modeled 

 effectively, and that it is therefore important to monitor such deposition. Since the senling regions 

 are not in the vicinity of the proposed outfall Stellwagon Basin and Cape Cod Bay may sen'c as 

 repository sites. During the first four years, a total of 197,000 tons (135 tons/d) of POC will be 

 discharged. This discharge will also contain considerable amounts of toxic contaminants (200 tons 

 of copper, 18 tons of lead, 2 tons of PCBs), the fate of which is largely undetermined. Although ii 

 is stated that most of the currently discharged particulates are flushed into the Bays, this level is not 

 certain, and enhanced monitoring in farfield sites is needed to quantify the loading. In particular, 

 Stellwagon Basin, due to its relatively close proximity to the proposed outfall site, could act as a 

 catch basin for outfall particulates, especially if the offshore transpon is more important that 

 present models predict Contaminants in mammals and chronic effects on mammals also should 

 be monitored. 



It is not clear whether chlorination will be extensive enough to kill all pathogens in the 

 effluent. Monitoring transpon of these disease vectors is therefore important. 



Attraction of right whales to the outfall site is only a remote possibility. The generation time of 

 the zooplankton (Calanus) in February/March (when the right whales are present) is about two 

 months which is much longer than their residence time in the vicinity of the outfall (days at most). 

 Thus it is not possible for a population growth response to occur at that time. Dense Calanus 

 patches are caused by swimming behaviors of the copepods interacting with physical convergence. 



