55 



3.1.2.1 August 1992 Survey 



REMOTS® photographs detected recently deposited dredged material extending 

 400 m south, and 500 m southeast of the survey center (Figure 3-10). The majority of the 

 material deposited in close proximity to the D/S buoy was composed of black silty sand 

 with a varying silt-clay fraction. Dredged material layers with chaotic sedimentary fabrics, 

 anomalous grain size distributions, and low optical reflectance were presumed to be 

 recently deposited or "fresh" (1991-1992 disposal season) dredged material. Boundaries 

 for the distribution of the fresh dredged material were determined by mapping the spread 

 of the darker NDA-91 and D/S material relative to the lighter and biologically re- worked, 

 historic dredged material of the inactive NL-III, NL-88, and NL-85 mounds (Figure 3-11). 



Differentiation between unsuitable dredged material and cap material through 

 REMOTS® photography was difficult due to the similar lithology of the Dow Chemical 

 sediments. However, a layer of high optical reflectance fine sand originating from the 

 material deposited at the NDA-91 buoy was visible at stations extending to 100 m north, 

 400 m south, 400 m west, and 500 m east of the survey center (Figure 3-12). The depth 

 of the overlying sand varied from 1.27 cm to 7.03 cm at stations 100N and the grid center, 

 respectively. 



At peripheral portions of the survey, there was a noticeable lack of fine sand at 

 stations 300SE through 500SE and all the ESE stations, as well as stations 200N, 400N, 

 500S, 500SSE, 600E, 200NE, and 100NE (Figure 3-10). The sediment profiles of these 

 stations consisted of thin layers of reworked dredged material over black silt (Figure 3-13). 

 The majority of REMOTS® survey stations had layers of fresh or historic dredged material 

 thicker than the penetrating depth of the REMOTS® camera. The detection of ambient 

 sediments was not anticipated based upon the location of the REMOTS® grid relative to the 

 historic NLDS disposal mounds. 



The major modal grain size over the disposal site ranged from granule/coarse sand 

 (-1.0 phi) to very fine silt and clay sized particles (phi sizes >4; Figure 3-14). The 

 coarsest sediment, consisting of very coarse and coarse sands, was located at the survey 

 center, and stations within 300 m south and 100 m east (Table 3-1). As expected, 

 REMOTS® camera prism penetration depth was lowest at those stations with a surface 

 sediment layer consisting of coarser grained sands, granules, and shell. 



Silt-clay (>4 phi) was the dominant grain size major mode at 17 of the 41 

 REMOTS® stations occupied. These stations typically showed a distinct stratigraphy in 

 which a surface layer of medium and fine sand (1-2 phi) was overlying very fine silts and 

 clay (>4 phi; Figure 3-14). The most frequently observed sediment was very fine sand 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



