h. Low recovery rates of surface and bottom drifters suggested the 

 absence of strong, shore-directed, currents. 



The general conclusion of the interim study was that the sewer 

 sludge is assimilated into the ocean environment as quickly as it is 

 put there, and that no adverse effects on the ocean environment have 

 occurred. It should be emphasized that the quantity of sludge disposed 

 of by Philadelphia in this area, is much less than that disposed of in 

 the New York Bight, and that the practice is rather recent, dating back 

 only to 1961. Furthermore, apparent rapid assimilation of the sludge 

 may be due to the rapid dispersion by surface currents and the low settl- 

 ing rate of the sludge particles. Laboratory tests of the physical char- 

 acteristics of Philadelphia's sewage sludge (Kupferman and Murphy, 1973) 

 showed such slow settling rates. Also, when mixed with sea water, the 

 sludge appeared to "fluff out," 1 milliliter of undiluted sludge bulking 

 up to almost 2 milliliter at the bottom of the settling tube. 



3. Chesapeake Bay 



The gross physical and biological effects of shallow-water disposal 

 of dredge material in the upper Chesapeake Bay were studied by the 

 Chesapeake Biological Laboratory of the University of Maryland (Cronin, 

 et al, 1967). The comprehensive study included a description of the 

 natural loads of suspended sediments in the water, and descriptions of 

 zooplankton, phytoplankton, benthic organisms, fish and larvae popula- 

 tions in the Bay. Furthermore, the direct effects of disposal on all 

 of these characteristics and populations, were assessed. 



It was established that study area was highly productive of animals 

 and plants, that it was intensively used by a variety of useful fish 

 and invertebrates, and therefore was important as a spawning and nursery 

 ground. Although field studies of the type conducted are not considered 

 adequate to evaluate critically the effects of heavy sediment loads, they 

 do provide qualitative data about the presence or absence of massive 

 damage . 



The studies also observed and concluded that; (a) the spoils spread 

 over an area which was at least five times larger than the designated 

 disposal area, and that turbidity increased over a 2-square mile area. 

 However, the turbidity was within the natural range of turbidities found 

 in this area throughout the year; (b) a high concentration of nutrients 

 was in the area; total phosphate and nitrogen were increased by factors 

 of 50 and 1,000 respectively; (c) no gross effect was observed on the 

 microscopic plants and animals in the water, nor on the eggs and larvae 

 of fish, nor on adult fish held in cages near the discharge point or 

 caught near the area; and (d) significant loss of bottom animals occurred 

 as a result of burial, but certain species began repopulation soon after 

 deposition, and 18 months later, the numbers had returned to previous 

 levels. 



The study emphasized the future need for suitable laboratory studies 



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