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.