Sand Island Wastewater Treatment Plant Outfall Assessment

SSFM International, Inc. was contracted by the City and County of Honolulu to conduct planning and design services for the improvement and rehabilitation of the Sand Island Wastewater Treatment Plant (SIWWTP) Ocean Outfall. Sea Engineering, Inc. was subcontracted by SSFM to conduct the offshore inspection of the outfall.

Inspection tasks included the following:

1. High-Resolution Multibeam Survey
2. Sidescan Sonar Survey
3. Exterior Inspection
   1. Inshore Inspection (0-ft Water Depth to 100-ft Water Depth) utilizing SCUBA and engineer-divers,
   2. Offshore Inspection (90-ft Water Depth to Flap Gate Structure) utilizing the Hawaii Undersea Research Laboratory submersible manned by a pilot and project engineer,
   3. Joint Inspection (0-ft Water Depth to 100-ft Water Depth) utilizing SCUBA and engineer-divers.
4. Shoreline Assessment – Significant shoreline erosion has partially exposed the Stop Gate Structure of the outfall at the shoreline. An erosion analysis was completed and shore protection alternatives were evaluated.