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DAMOS Contribution #97 - Executive Summary |
Science
Applications International Corporation (SAIC) conducted a monitoring survey
at the Central Long Island Sound (CLIS) Disposal Site from 18 to 23 JUNE 1991
as part of the DAMOS (Disposal Area Monitoring System) Program. The
objectives of the June 1991 field operations were to map the distribution and
thickness of the dredged material in the areas that received project
materials after the 1990 DAMOS survey (CLIS-90 and CS-90-1) and to evaluate
the status of inactive mounds: MQR, NHAV-74, CLIS-88, CLIS-89, CS-1 and FVP.
Surveying and monitoring techniques included precision bathymetry, REMOTS
sediment-profile photography, CTD and dissolved oxygen information, and
sediment grab samples. In
September 1990, the CLIS disposal buoy was deployed at 41°9.212’N,
72°53.25’W. Barges released approximately 59,000 m3 of dredged material at
this location between September 1990 and May 1991. It was predicted that a
new disposal mound would form at this location. During the 1989/1990 disposal
season, barges released 8,730 m3 of additional dredged material at CS-90-1 to
increase cap thickness. The
precision bathymetric survey detected a small, newly formed disposal mound at
the CLIS-90 buoy location. The addition of 8,730 m3 of material to the
CS-90-1 was detectable in the bathymetric survey as two 20cm thick areas of
accumulation. REMOTS sediment-profile photography detected the presence of
dredged material at all stations within the survey area. “Fresh” or recent
dredged material, identified by sedimentary fabric and shallow apparent RPD
(Redox Potential) depths, was several hundred meters away from the active
mounds. The limit of the dredged material mound, as mapped acoustically, was
within a 100 m radius of the CLIS-90 buoy location. Benthic
recolonization was deterimed from analysis of REMOTS photographs obtained at
CLIS and at three outlying reference areas. Recolonization predictions from
the DAMOS tiered monitoring and management protocol were that the active
mounds should be in a Stage I sere while Stage III sere should colonize the
inactive mounds: MQR, NHAV-74, CLIS-88, CLIS-89,CS-1, and FVP. The 1991
REMOTS data supported these predictions. Water
column profiles of temperature, salinity, sigma-t, and dissolved oxygen were
determined on June 18th at the CLIS-90 buoy and three reference areas. The
water column at these four sampling stations was stratified with respect to
both temperature and salinity. Dissolved oxygen (DO) concentrations below the
pycnocline were 6 to 7 ppm, 2 to 3 ppm lower than near surface values. DO
values were similar between the CLIS-90 buoy location and the three reference
locations. Sediment
samples collected from the CLIS reference areas contained metals in similar
low concentrations as measured during previous CLIS surveys. Polyaromactic
hydrocarbons (PAH’s) were also analyzed to provide a baseline for future
sampling. PAH’s were measured at all three reference areas in concentrations
generally within ranges present in regional Long Island Sound. |
Dated March 6, 1997