CAPPING SURVEY AT THE NEW LONDON DISPOSAL SITE 

 FEBRUARY 3, 1989 



1.0 INTRODUCTION 



The New London Disposal Site covers a one square nautical 

 mile area located approximately two nautical miles south of the 

 mouth of the Thames River, Connecticut. This site, centered at 

 latitude 41 16.1'N and longitude 72 04. 6 'W, has been monitored since 

 1977 by the New England Division (NED) of the Army Corps of 

 Engineers. This study focuses on a subsection of the New London 

 Disposal Site which received an estimated 13,000 cubic meters of 

 contaminated dredged material (at buoy location 41 16. 425 'N and 72 

 04.320'W) from the Thames River Shipyard in October 1988. A 

 precision bathymetric survey and a REMOTS® sediment profile survey 

 were performed at this location after disposal of the contaminated 

 material to document the distribution of dredged material. The 

 results were used to develop a capping plan intended to provide 

 complete coverage of the contaminated sediment with clean material 

 (SAIC, 1988) . 



From October 1988 through January 1989, clean sediment 

 was deposited at six disposal points over the observed distribution 

 of contaminated dredged material (Table 1) . The number of scow 

 loads of cap material to be deposited at each disposal point was 

 planned to achieve a desired cap thickness of 50-100 cm over the 

 contaminated material. After completion of the capping operation, 

 on February 3, 1989 a bathymetric survey was performed to delimit 

 the distribution and thickness of capping material over the 

 previously disposed contaminated dredged material. From the results 

 of this survey, the capping operation and the potential need for 

 additional cap material at the location were assessed. 



2 . METHODS 



On February 3, 1989, a precision bathymetric survey was 

 conducted at 25 m lane spacing over an 800 X 800 m area centered at 

 the coordinates of the disposal buoy. The precision navigation 

 required for the survey was provided by the SAIC Integrated 

 Navigation and Data Acquisition System (INDAS) . This system uses 

 a Hewlett-Packard 9920 series computer to collect position, depth, 

 time, and date information for subsequent analysis as well as for 

 providing real-time navigation for the helmsman. Positions were 

 determined to an accuracy of + 3 m from ranges provided by a Del 

 Norte Trisponder System. Shore stations for this system were 

 established in Connecticut at known benchmarks at Millstone Point 



