15 stations were resurveyed. Ten additional stations along the southern boundary of the 

 dredged material deposit were surveyed at this time to map further the extent of the fine- 

 grained dredged material documented in the May survey (Figure 2-2). Three replicates were 

 taken at all stations. Analysis of the REMOTS® sediment-profile photographs was limited to 

 grain size measurement, average penetration, and documentation of the presence of dredged 

 material. 



2.3 Sediment Density 



REMOTS ® photographs from the May 1992 survey at CSDS showed the presence of 

 two sediment types with sharply different densities: sand and fine-grained mud (Wiley 1994). 

 The 24 kHz acoustic survey conducted at CSDS on August 10, 1992 was designed to 

 determine if the system could identify the different sediment densities that were observed in 

 the REMOTS® photographs. The sediment density survey interfaced the 24 kHz sound 

 source with the Acoustic Core System® (model CE-IB-100; Caulfield Engineering Group, 

 Oyama, BC, Canada). The Acoustic Core System® is a combination hardware/software 

 package designed to provide quality control during shallow seismic data acquisition. It 

 provided acoustic impedance and density predictions based on signal amplitude in the shallow 

 seismic field. The system calculated impedance values relative to seawater and generated 

 density estimates based on the work of Hamilton (1970, 1971). The survey covered the same 

 area as the first 25 lanes of the bathymetric survey and collected data every 50 m along the 

 survey track. Subsurface density information was collected every 15 cm below the seafloor. 



Data output from the Acoustic Core System® included amplitude and acoustic 

 impedance values. Acoustic impedances have been reliably assigned to different sediment 

 types; therefore, they can be used to detect changes between sediments with dissimilar 

 impedance characteristics (Hamilton 1970, 1971). Impedance values were converted to 

 density values and mapped to quantify changes in sediment type. The densities of surface 

 sediment samples taken from the site were used to verify the densities calculated from the 

 impedance values. For a more detailed discussion of the analysis procedure, see Caulfield 

 and Yim (1983) and Caulfield (1984). 



Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992 



