Report Number: 95
Year: 2002

Nitrate-Nitrogen Concentrations in the Northern Guam Lens and Potential Nitrogen Sources

Nitrate-nitrogen concentrations in the Northern Guam Lens (NGL) were studied using nitrate-nitrogen data from 147 water wells. Data spanning from January 1978 through December 2000 indicated that concentrations had not neared the United States Environmental Protection Agency's Safe Drinking Water maximum contaminant level of 10 mg/L. However, 39 wells had increasing nitrate-nitrogen trends while nine wells had decreasing trends based on linear regression. Twenty-two wells had maximum nitrate-nitrogen levels between 4 and 4.99 mg/L while six wells had maximum concentrations over 5 mg/L. The Mangilao Subbasin had the highest number of wells with statistically increasing nitrate-nitrogen concentrations. Potential nitrogen sources in northern Guam were identified through aerial and terrestrial investigation. These sources include sewer lines, septic tank/leaching field systems, golf courses, farms, piggeries, fish farms, chicken farms, pastures, and ponding basins.

Mauryn Q. McDonald