84 



site. The water available in the upper 20 m is, because of a seasonal density gradi- 

 ent (pycnocline), the vertical limit to most waste mixing. Although that water is 

 available, wastes cannot mix into it immediately. At the 106-mile site enough water 

 exists to dilute each million gallons of daily waste input by a factor of about 2 mil- 

 lion. Any site north of Cape Hatteras and at about the same distance from the con- 

 tinental shelf as the 106-mile site would have similar dispersive characteristics. This 

 includes the two sites indicated in question 5. 



We see no compelling reason to use different sites in an attempt to segregate in- 

 dustrial waste from sewage sludge. To address this point, it is necessary to consider 

 the physical dimensions of waste plumes, the amount of anticipated dumping, and 

 the dumping strategy. Diluting waste by factors of 5000 (initial mixing), 50,000 and 

 500,000 requires 5-, 50-, and 500-billion gallons of seawater, respectively, for each 

 million gallons of waste. During summer when mixing is limited to the upper 20 m, 

 the areas required to accommodate those volumes of water are 1, 10, and 100 km^, 

 respectively. Since the 106-mile site encompasses 1500 km^ patches of waste diluted 

 50,000 fold or less would be relatively small features while areas containing waste 

 diluted by about a million-fold might cover up to about 10 percent of the total site. 



If sewage sludge were dumped at the 106-mile site in one million gallon incre- 

 ments, five dumps per day would be required to dispose of the 2 billion gallons now 

 annually dumped in the New York Bight. On a comparative basis, the annual indus- 

 trial waste input to the site is now about 60 million gallons (or a little more than 

 one dump per week). If industrial and sewage wastes were both dumped at the 106- 

 mile site, provisions would presumably be made for them not to enter the same 

 quadrant of the site simultaneously. When more then one industrial dumper used 

 the site, each permittee was assigned a quadrant for a three-month period. Over a 

 year's time each permittee used the entire site. It would be beneficial to use most or 

 all of the site for sewage sludge dumping during a year, because a small fraction of 

 the solids in sludge might sink quickly enough so that it does not receive much dis- 

 persion in the water column. Using the whole site over a year would ensure that 

 those particles are spread over at least 1500 km^ which should be sufficient to avoid 

 affecting benthic organisms. Most sludge particles will, however, fall very slowly 

 and be widely dispersed before reaching the seafloor. 



Sludge dumped into one quadrant of the 106-mile site probably will not undergo a 

 million-fold dilution before impinging on other quadrants of the site. Industrial 

 waste plumes containing waste diluted by only a factor of about 50,000 are small- 

 scale (i.e., compressed) features which move with the current, and have been ob- 

 served to migrate from the quadrant in which they originated. Nevertheless, these 

 are finite features which most likely would remain separate from another patch of 

 waste created in any other quadrant. 



The residence time of water and waste within the 106-mile site is about four days. 

 The projected dumping of five barge loads of sludge per day would therefore produce 

 twenty patches of sludge at various stages of dilution within the site whenever a 

 dump of industrial waste was to occur (in a quadrant not used for sludge over the 

 prior few days). If the weather was calm over those few days prior to the industrial 

 dump, the sludge patches would be small-scale features covering, in total, about half 

 the site (one can assume that sludge patches will intermingle since they will be cre- 

 ated near one another). Some of that sludge is likely to be in the industrially used 

 quadrant, but it will not cover it completely. The industrial waste plume, over its 

 first day, will grow to only about 10 km ^ and will most likely remain in sludge-free 

 water. 



If, on the few days preceding an industrial dump, a storm occurs, the sludge 

 within the site will become well mixed and be diluted extensively to a factor of 

 about one million. At that point, the industrial dump will certainly occur in water 

 containing diluted sludge. However, essentially the same consequence would result 

 from dumping sludge at either of the two alternate sites north of 106-mile site. 

 Sludge reaching the 106-mile site would be diluted by a factor of about one million 

 (in the absence of a storm), and an industrial dump would be made into this water 

 mass. 



The short-term monitoring of industrial waste in the water column would there- 

 fore not benefit from sludge being dumped elsewhere. Monitoring would not be af- 

 fected by industrial waste entering water already containing extensively-diluted 

 sludge. If the 106-mile site were used for both waste types, there would be occasions 

 when the industrial waste entered sludge-free water even though small-scale patch- 

 es of sludge existed within the same quadrant. It is only when industrial wastes 

 remain on small scales at dilution of less that 50,000-fold that they have been ob- 

 served to affect marine organisms. Since industrial wastes presently discharged at 



