limits were calculated. This calculation simply implies that the 
actual (and unknown) volume difference will occur within the lower 
and upper confidence limits with a probability of 0.95. These 
limits (L, and L,) are defined to be 1.96 standard errors to either 
side of estimated value (V,): 
ie Wat o6 (Sy) esl 7, 0008 11916 (51739) 5754 m, 
17,000 + 1.96(5739) 28250 m°. 
L, 
V, + 1.96(s,) 
Because this 95% confidence interval (L, to L,) does not 
surround zero, the probability that the actual volume difference 
equals zero is very small and, therefore, indicates that a volume 
difference of between 5754 and 28,250 m’ did occur. This apparent 
difference can represent post- depositional consolidation and 
compaction and/or erosion and dispersion. Our analysis does not 
allow separating these two processes. However, if one assumes the 
worst case (100% loss due to erosion and dispersion), the loss of 
17,000 m° spread evenly over the 900 x 900 meter area compared 
(543, 438 m a) in the calculations would mean a change in depth of 
approximately only 3 cm. 
Shi2 Side Scan Sonar Survey 
The results of the side scan survey conducted in August 
1985 revealed two distinct areas of high acoustic reflectance. 
Areas of high reflectance denote areas of bottom where seafloor 
sediments have a high acoustic impedance, such as hard packed sand 
and/or rock. Past experience has shown that high reflectance areas 
are also indicative of recent disturbances in the bottom morphology 
as a result of disposal operations. The side scan sonar survey is 
a useful reconnaissance method to determine the spatial 
distribution of dredged material, but the final determination of 
bottom composition must be accomplished using other techniques. 
The results of the side scan survey (Figure 3-9) indicated high 
acoustic reflectance material in two distinct areas. The area 
labeled "AREA 1" corresponds to the locations of the NL-I, NL-II, 
and NL-III disposal mounds. The NL-RELIC disposal mound was 
dredged by the Corps of Engineers in the spring of 1984, to reduce 
the elevation of the mound, and the impressions: left by the 
dredge's suction head were clearly evident (Figure 3-10). The 
other area of high acoustic reflectance (AREA II in Figure 3-9) was 
noted in the southwest portion of the side scan sonar survey. Data 
collected during the REMOTS® survey (see Section 3.3) suggested 
that this may be dredged material. 
IL7/ 
