64 



The CLIS-REF and 4500E reference areas were very similar in average metals 

 concentrations as well as the range of variability for individual metals between stations 

 (Appendix C, Table 9). All reference areas exhibited die same trends in individual average 

 metals concentrations in that Fe was the most abundant metal within each reference area, 

 followed hierarchically by Al, Zn, Cr, Cu, Pb, Ni, As, Cd, and Hg. 



3.4 Data Comparisons 



The July 1994 survey at CLIS provided SAIC and NED the opportunity to acquire a 

 wealth of physical, chemical, and biological data by utilizing a wide variety of 

 oceanographic equipment. The performance of six separate survey operations (precision 

 bathymetry, REMOTS® sediment-profile photography, sediment grab sampling, remote 

 surface sediment characterization, subbottom-profiling, and geotechnical coring) within the 

 confines of a single monitoring cruise allowed for comparisons between the various elements 

 verifying, reinforcing, or ground-truthing overlapping data sets. These overlaps provided a 

 unique opportunity to use the data regularly collected on a standard DAMOS disposal site 

 monitoring cruise (bathymetry, REMOTS®, and grab sampling) to evaluate the newer 

 technology utilized during the July 1994 survey at CLIS. 



3.4.1 Sequential Bathymetric Surveys, X-Star Subbottom Profiler, Geotechnical Core 

 Comparison 



Since the inception of the DAMOS Program in 1977, precision bathymetry has been 

 used to monitor the development of dredged material mounds on the seafloor at each 

 disposal site (NUSC 1979). Comparisons between sequential bathymetric surveys 

 determined the size and shape of dredged material deposits, thickness of cap material layers, 

 and rates of mound consolidation. Although this is an accurate and reliable approach, the 

 results are directly dependent upon consistency in the timing of disposal and survey 

 operations, as demonstrated during the New Haven Capping Project (Morris et al. 1996). 



Due to the timing of the precap survey over the NHAV 93 mound, approximately 

 76,000 m' of CDM was left undetectable through conventional batiiymetric data processing. 

 An X-Star subbottom profiler used during the July 1994 survey was successful in discerning 

 the capping material over the northern flanks of the NHAV 93 mound. In addition, the 

 subbottom profiler was capable of quantifying UDM and total dredged material thicknesses 

 over ambient bottom. Slight differences in acoustic signamre between the various dredged 

 material layers were detected and mapped, providing a representation of the NHAV 93 

 mound morphology similar to the bathymetric data products. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1994 



