K1-95-HW: Cruise Report 1995 - Preliminary results.

Phase III: Sediment Chemistry and Biological Sampling Survey

M.E. Torresan, M.A. Hampton, J.H. Barber, Jr., and F.L. Wong

U.S. Geological Survey Open-file Report 95-839

1995

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Any use of trade names is for descriptive purposes only and does not imply endorsement by the USGS.

Summary
Introduction
Study Area
Previous Studies
  Designation
  Monitoring 1, 2
Methods
  Vessel
  Navigation
  Sampling
  Subsampling 1, 2
Results
Acknowledgments References 1, 2

Figures
1 Location
2 Box corer

Tables
1 Stations
2 Samples
3 Analyses
4 Bioassay

Appendices
1 Box Cores
2 Custody: Quanterra
3 Custody: Batelle

PRELIMINARY RESULTS
The 1995 survey, conducted June 14 through 17, resulted in the collection of 39 box cores from 20 different stations. Multiple box cores were composited at 7 stations to provide the material required for the bioassay and bioaccumulation analyses currently underway (Figure 1). Seventeen of the 20 stations occupied provided the biological samples for the benthic infaunal identification and population density study conducted by Dr. Julie Brock of the University of Hawaii, and the sediment chemistry analyses conducted by Quanterra Environmental Laboratories (Figure 1). The sediment chemistry analyses are documented in reports by Quanterra Environmental Services (Quanterra, 1995h-k). Seven of the 20 stations occupied in 1995 were occupied in 1994, and provide the data for direct comparison of sediment chemistry at the same sites from two consecutive years. The sum total of the data collected from all three phases of the monitoring program will provide the U.S. Army Corps of Engineers and the U.S. Environmental Protection Agency with the information required to make informed decisions as to the management of the South Oahu disposal site in Mamala Bay.

The 1995 box core descriptions shown in Appendix 1 corroborate the data collected in 1994, and verify the various acoustic signatures visible in the sonar images shown in Torresan and others (1995) and Figure 1. The high-backscatter material centered over the disposal sites is a heterogeneous mixture of olive-gray to gray-brown mud that acts as a binding matrix for the coarser sand to cobble-size material. The natural sediment, seen as the low back scatter region surrounding the disposal sites and most of the study area, is predominantly a beige-colored muddy carbonate sand. The high-backscatter region that is visible on the west and southwest side of the mosaic shown in Torresan and others (1995) is exposed carbonate reefs and associated sediment.

Chemical analyses completed to date do not yield definitive results, but generally, analyte concentrations are low, and many of the analytes chosen from the list of contaminants of concern are non-detectable. In some instances specific contaminants exhibit higher concentrations in native sediment, relative to dredged material and vice versa. In other instances certain analytes show both high and low concentrations in both native sediment and dredged material. Conclusions regarding the biological analyses are pending completion of those studies.

Suggestions for further studies include deployment of oceanographic instrumentation to evaluate the types of current activity responsible for the array of wavy bedforms observed in the sonar images, subbottom profiles and video and still photographs. This will allow the quantification of the bottom flow that can potentially resuspend and redistribute the dredged material and any associated contaminants.

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