56 



4.0 DISCUSSION 



The 1992 survey at WLIS was designed to achieve the following: first, to monitor the 

 physical and biological effects of dredged material distribution at the site; second, to evaluate 

 the benthic status of specific stations at the WLIS "D" and "A" mounds; and third, to 

 determine suitable replacement reference areas for WLIS-REF and SOUTH. 



4.1 Dredged Material Distribution and Effects 



A combination of bathymetric survey and REMOTS® data was used to delineate the 

 boundaries of recent deposition. Recent dredged material can be distinguished from older 

 deposits with these methods to accurately define the footprint of the new mound (Figure 3-7). 

 The recently deposited material was located in a central area of the site which has received 

 materials at six distinct locations from 1982 to 1992 (mounds "A" to "F"). The six WLIS 

 mounds are positioned within a 400 m radius, and the dredged material footprints created 

 during the formation of these mounds overlap. Sediment profiles from several stations in the 

 WLIS "F" grid (stations F200W, F300W, and F400W) revealed mixtures of old and new 

 dredged material deposits. 



Based on the depth difference analysis between the 1991 and 1992 bathymetric 

 surveys, the WLIS "F" mound was approximately 200 m in diameter and 1.9 m in height. 

 The results of the REMOTS® survey showed that thin layers of the newly deposited 

 sediments extended further to cover a circular region with a rough diameter of about 350 m. 

 Dredged material was not apparent at stations F200E and F400E. Although these stations 

 had apparent RPD layers > 2.0 cm, sediment-profile photographs showed no evidence of past 

 disposal activity. Interestingly, one of three photographs from Station F300E did reveal a 

 patchy, dark subsurface sediment. This is potentially remnant of historical dredged material, 

 or the result of historic anoxic events. 



i 

 Tabulation of the recorded disposal barge volumes showed that 39,700 m 3 of 



sediments were disposed at the taut- wire moored buoy from November 2, 1991 to May 4, 



1993 (Table 1-1). The depth difference analysis determined that 21,340 m 3 of dredged 



sediments had accumulated in the vicinity of the WLIS "F" mound. The depth difference 



analysis accounted for 54% of the reported barge disposal volume. 



Processes of consolidation of dredged materials and the ambient base material, 

 erosion, and errors in barge disposal volume estimates are known to contribute to the 

 discrepancy in reported versus calculated dredged material volume. In a mass balance study 

 in the New York Bight, Tavolaro (1984) determined an apparent decrease in volume of 

 approximately 41% when comparing the disposal barge log volume and the volume 

 calculated through depth differencing analyses. Based only on Tavolaro 's 41% correction 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1992 



