Five sets of water samples were collected over a three-month period and analyzed for dissolved metals, and in some sets, suspended metals. The 13 metals investigated were arsenic, barium, cadmium, chromium, copper, iron, lead, manganese, mercury, nickel, selenium, silver and zinc.

Concentrations (in μg/L range) of these metals were generally lower than observed in other U.S. communities. Runoff samples collected from commercially developed areas were generally much higher in metals than runoff from residential areas. Likewise, the metal concentrations were usually much higher as suspended metal as opposed to dissolved metal.

Concentrations of arsenic, barium, selenium and silver were very low and most likely are not affecting groundwater or coastal receiving-water quality. Concentrations of mercury, cadmium and lead in urban runoff at times or at specific sampling locations approached or exceeded drinking and surface water quality standards. Measurements of pH, total solids, hardness, and other parameters indicate that urban runoff has not changed appreciably in the past four years in comparison to previous testing.

Guam's urban runoff is of relatively high quality with respect to metals and, with the possible exception of mercury, lead and cadmium, environmental degradation by metals is probably minimal. Further analyses of receiving waters, sediments and biota and additional limestone percolation studies are needed to determine the distribution of metals in Guam's environment.