82 



dumping activities? If not, please provide your own best estimate, and indicate the 

 basis for this estimate. 



Answer. Initial dilution of one million-fold cannot be achieved. Such dilution 

 would be achieved, in time, due to oceanic mixing, so long as there was an adequate 

 rate of water renewal at the site. Sludge dumped at the 106-mile site would be dilut- 

 ed one million-fold about one week after dumping (unless a storm occurs and has- 

 tens the mixing process). 



If the criterion for sufficient dilution is to decrease chemical concentrations below 

 water quality standards, it would be necessary to dilute sludge containing 0.5 parts 

 per million PCB on a wet weight basis (a high estimate) by 17,000-fold to meet the 

 30 parts per trillion criteria. At that dilution, other components of sludge for which 

 there are criteria would be diluted to below those criteria. The two elements which 

 would be closest to their criteria levels would be copper at 3 parts per billion (with 

 the criterion at 4 parts per billion) and mercury (at the criterion level of 25 parts 

 per trillion). If the criterion for sufficient dilution were based on sludge concentra- 

 tions being 1% of measured LD50 levels (a criterion within the ocean dumping regu- 

 lations), the necessary dilution would be 30,000-fold (based on results of toxicity tests 

 required of dumping permittees). 



Both of these dilution factors are relatively small. They would be achieved within 

 less than 10 hours after dumping and would require a sludge distribution over a 

 very small part of the site. Biological responses in the water column on those small 

 scales would be of little consequence because they would occur among planktonic 

 organisms which, at the population level, recover quickly as waste plumes are fur- 

 ther diluted by mixing with surrounding waters. The monitoring program previous- 

 ly outlined is concerned with sludge distributions and effects over large scales in the 

 water and on the seafloor. We estimate that sludge will be dispersed sufficiently to 

 avoid any large-scale effects. 



Question 5. The suggestion was made at the May 25th hearing that the 106-mile 

 deepwater industrial waste dumpsite is sufficiently large that a large separation be- 

 tween industrial wastes and sewage sludge could be achieved within the boundaries 

 of this site (e.g., by requiring the two types of wastes to be dumped at opposite 

 corners and minimum (i.e., worst-case) initial dilutions (i.e., within 1 hour) that 

 could be anticipated in the course of a year (or longer) for wastes dumped at various 

 locations within the 106-mile site. How confident can we really be that sludge con- 

 taining 1 ppm of PCBs, if dumped in one quadrant of the 106-site, will undergo a 

 millionfold (or other required degree of) dilution within an hour, or before imping- 

 ing on other quadrants of the dumpsite? 



Answer. We are confident that sludge will impinge on other quadrants of the site 

 before being diluted a million-fold. On occasion, sludge plumes diluted about 50,000- 

 fold will migrate from their original quadrant undergoing further dilution. As dis- 

 cussed previously, this in itself would not be a compelling reason for dumping 

 sludge at a deepwater site other than the 106-mile site. 



Question 6. At least 2 other deepwater ocean dumpsites located to the north of the 

 106-mile site have been historically used for explosive and/or chemical wastes (see 

 attachments). As you know, the 106-mile site is itself a former explosives dumping 

 site. For each of the indicated alternative sites, please indicate if there is any basis 

 for believing, by virtue of prevailing current patterns or the distribution of fishery 

 or other biotic resources, that that site would be a less suitable repository for ocean- 

 dumped sewage sludge than the 106-site? Also, for each such site, would locating 

 sludge dumping there likely increase or decrease the possibility of interaction with 

 industrial wastes dumped at the 106-site, in comparison with having both types of 

 wastes dumped within the 106-mile site? 



Answer. Many sites north of Cape Hatteras and seaward of the continental shelf 

 reflect dispersive characteristics and resources-at-risk similar to the 106-mile site. If 

 another site were chosen, it should, however, be of comparable dimension to the 106- 

 mile site to enhance dispersion of the fast-settling component of sewage sludge par- 

 ticles. 



The 106-mile site is "special" only in an historic sense. There is no technical 

 reason to favor the 106-mile site over other deepwater sites. Segregation of industri- 

 al wastes from sewage sludge is not a reason to dump sludge at one of the alterna- 

 tive sites indicated in the question. 



On average, sludge, or any other waste which remains primarily in the upper 

 water column and which is dumped at any site off the northeast continental shelf, 

 will move with currents paralleling the shelf contour and become entrained within 



