Paul R. Eyre | Geology Reports

USGS1994

Ground-Water Quality Reconnaissance, Tutuila, American Samoa, 1989

In May and July 1989, 19 ground-water samples were collected from 17 of the 35 water-supply wells on the island of Tutuila, American Samoa. Samples were analyzed for temperature, pH, hardness, specific conductance, turbidity, total and fecal coliform bacteria, major ions, major nutrients, 12 common metals, and 66 organic compounds. Chemical analysis of the water samples shows that, after chlorination, sampled ground water was in compliance with U.S. Environmental Protection Agency primary drinking-water regulations. Fourteen of the 19 samples were collected before the water was chlorinated in the water distribution system, and five were collected after chlorination. Seven of the 14 unchlorinated samples contained coliform bacteria and five of the seven contained fecal coliform bacteria, indicating potential contamination from disease-causing pathogens. All five of the chlorinated samples contained trace levels of trihalomethanes, but at concentrations below U.S. Environmental Protection Agency maximum contaminant levels. Trihalomethanes were the only organic constituents detected. Concentrations of total dissolved solids in the 19 samples ranged from about 100 to 2,400 milligrams per liter. Four samples had concentrations of total dissolved solids and chloride that exceeded the U.S. Environmental Protection Agency secondary drinking-water regulations of 500 and 250 milligrams per liter, respectively. For samples with less than 300 milligrams per liter of dissolved solids, sodium, calcium, magnesium, and bicarbonate were the dominant ions, indicating that they were derived from dissolution of minerals and carbon-dioxide enrichment of recharge water. For samples with greater than 300 milligrams per liter of dissolved solids, sodium and chloride were the dominant ions, indicating increased mixing of ground water with seawater.

Water-Resources Investigations Report↗

USGS1986

Hydrology of the leeward aquifers, southeast Oahu, Hawaii

The leeward southeast Oahu ground-water area includes the Waialae and Wailupe-Hawaii Kai aquifers. The Waialae aquifer is separated from the ground water of Kaimuki to the west by Palolo valley fill and the Kaau rift zone, and from the Wailupe-Hawaii Kai aquifer to the east by a line of northeast-trending volcanic dikes. The distinct ground-water head changes across these boundaries indicate that the aquifers are separate, with little or no leakage between them. A water budget of leeward southeast Oahu determined the quantity and spatial distribution of ground-water recharge. These estimates of recharge, 6 million gallons per day over the Waialae area and 9.1 million gallons per day over the Wailupe-Hawaii Kai area, were used as input to a finite-element two-dimensional ground-water flow model. Ground-water heads were simulated in the modeled aquifer for several pumping scenarios. Projected pumpage from the recently drilled wells int he area is predicted to draw the water table down about one foot from its present mean position. The existing ground-water development of 1.4 million gallons per day is small compared to the quantity of ground water that flows through the area and discharges to the sea. Because the Waialae and Wailupe-Hawaii Kai aquifers are isolated from adjacent ground-water bodies, they can be fully developed without affecting ground-water resources outside the area.

Hawaii↗