Report Number: 12
Year: 1980

Water Quality Monitoring Program, Palau Airport Project, Ngurusar Bay, Toagel Mid Channel, Babeldaob and Koror Islands, Palau District, Trust Territory of the Pacific Islands, Part A, Pre-Construction

No abstract was published. The report's Executive Summary follows.

The Palau Airport, located at Babelthuap Island, Palau District, Trust Territory of the Pacific Islands (TTPI), is being improved and developed. The project will require the dredging of coral fill material from a 30-acre site located at Ngurusar Bay, Airai Village, on Babelthuap Island. Approximately 300,000 cubic yards of coral fill will be dredged using dragline methods.

It is required that the dredging activity be controlled and that protection be provided so that water outside of the Water Quality Boundary, defined as 200 feet outside of the dragline limits, are not degraded below the water quality standards of the TTPI.

To satisfy this requirement (in accordance with U.S. Navy Contract No. N-62742-80-C-0002), eight water quality monitoring stations were established along the outside perimeter of the WQB. A sampling program was set up to determine baseline water quality prior to the start of dredging operations. For this objective, water samples were collected daily from December 20, 1979 to January 11, 1980 (December 24 and 25 excepted) and analyzed for turbidity (NTU), suspended solids, dissolved oxygen, temperature, salinity, and pH. One time measurements were made for total nitrogen, total phosphorus, and the following metals: arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc.

During the sampling period, turbidity ranged from 1.1 to 3.9 NTU at the water quality monitoring stations. Statistical analyses of the data showed that turbidity levels at Stations 1 through 7 were essentially the same. Station 8 had higher turbidities, most likely due to its shallow location on the reef flat. Based on the turbidity data collected, a turbidity standard of 5 NTU is recommended for the waters outside the Water Quality Boundary.

Water temperatures at the stations ranged from 26.6 to 31.9 ºC. pH values ranged from 7.45 to 8.01 with a study mean of 7.85. Salinity ranged from 28.8 to 35.5 parts per thousand (o/oo) with a mean of 31.4 o/oo.

Total phosphorous ranged from 0.003 to 0.011 mg/L. Total nitrogen ranged from 0.011 to 0.257 mg/L. Both total phosphorous and total nitrogen concentrations fall within the TTPI Water Quality Standards for these waters.

Dissolved oxygen concentrations ranged from 3.82 to 10.73 mg/L with a mean of 5.91 mg/L. Suspended solids ranged from < 0.1 to 12.6 mg/L with an overall mean of 2.4 mg/L. The ratio of turbidity (NTU) to suspended solids was from 0.41 to 0.62.

Concentrations of arsenic, cadmium, copper and zinc were below detectable limits and/or the TTPI Water Quality Standards. Nickel concentrations ranged from 0.2 to 5.8 μg/L. Mercury concentrations ranged from < 0.1 to 1.7 μg/L. A few of the higher mercury and nickel concentrations measured were in excess of the TTPI Water Quality Standards for these metals. Chromium concentrations ranged from 46 to 67 μg/L with an average (56 μg/L) above the 50 μg/L water quality standard for chromium. Lead concentrations ranged from 160 to 375 μg/L, well exceeding the 10 μg/L water quality standard for lead. An earlier sampling and analysis (by a different laboratory) for these metals also reported lead concentrations in excess of 200 μg/L.

Charles J. Romeo
William J. Zolan
Stephen J. Winter