75 



3.0 RESULTS 



3.1 Bathymetry 



The Portland Disposal Site varies in depth from 42 to 64 m (Figure 3-1). The higher 

 elevations are hard rock ridges with steep slopes that enclose more gently sloping sandy 

 valleys. The ridges are located in the southwest corner of the site (minimum water depth of 

 43 m), at the northern border of the site (minimum water depth of 45 m), and to the east 

 (minimum water depth of 49 m). These ridges enclose two main valleys. One, centered at 

 approximately 43°34.167' N, 70°02.167' W, trends northwest to southeast and has a 

 maximum depth of 60 m. The other valley trends north to south in the center of the site and 

 slopes to a maximum water depth of 64 m. 



The July 1992 bathymetric survey identified a well-defined mound just south of the 

 buoy location. The mound is approximately 100 m in diameter and 7 m in height (minimum 

 water depth 49 m; Figure 3-1). The location and shape of the mound appear to have 

 remained unchanged since 1989 (Figure 3-2). 



A depth difference comparison between the January 1989 and the July 1992 

 bathymetric surveys shows extensive areas of accumulation (Figure 3-3) and isolated areas of 

 loss (Figure 3-4). Accumulations of 0.75 m and 1.0 m are located within a 300 m radius of 

 the buoy location. Below 43°34.083' N, another broad area of accumulation with similar 

 values is seen. Large ( > 1 m) positive differences in depth between 1989 and 1992 occur in 

 very localized areas and are marked by dense contour lines. Most areas of negative depth 

 differences are localized around areas of steeply sloping ridges. Two areas of negative depth 

 difference (southeast of 43°34.250' N, 72°02.250' W and northeast of 43°34.000' N, 

 70°01.750' W) are located on the southwest slopes of ridges. 



3.2 REMOTS® 



The REMOTS® photographs from the 42 stations were analyzed for the presence of 

 dredged material and a variety of parameters indicative of the health of the benthic 

 environment. Previous REMOTS® surveys at PDS have been hampered by the hard rock 

 bottom which can inhibit data collection (SAIC 1990). Because the general location of the 

 dredged material was known in July, more usable images were collected from the disposal 

 site than in January. Due to the rocky bottom, there were still difficulties in collecting data 

 from the reference areas, and no data was obtained at 16 out of 39 stations. 



The January 1992 PDS REMOTS® survey outlined the dredged material boundary 

 within 250 m of the disposal location (Figure 2-2). The REMOTS® stations in the present 

 survey were chosen to repeat some of the dredged material stations surveyed in January and 

 to further define the dredged material footprint by expanding the survey into ambient bottom. 



Monitoring Cruise at the Portland Disposal Site, July 1992 



