WRRCTR No.181 Organic Chemical Contamination of Oahu Groundwater

Abstract

An investigative project developed the scientific knowledge needed to respond to the discovery of organic chemical contamination of groundwater in Hawaii. Ethylene dibromide (EDB) and dibromochloropropane (DBCP), both suspected carcinogens to humans and banned shortly after the discovery of contamination, were discovered in the tens of nanograms per liter (ng/l or parts per trillion) in central, southern, and northern Oahu. As a result, eight potable water wells were closed, thereby removing 13 mgd from the drinking water supply during 1982 to 1983. The 3-yr project involved deep boring, laboratory testing, and predictive transport modeling conducted by a University of Hawaii multidisciplinary research team, and was funded by special appropriations from the Hawaii State legislature with supplemental funds from the Office of Environmental Quality Control and the Department of Health. Project results indicate, first, that EDB-contaminated groundwater was of limited extent and mainly located hydraulically downgradient from reported leaks of aviation fuels containing EDB; that DBCP contaminated groundwater was relatively widespread and located beneath and downgradient from pineapple fields on which DBCP had been applied as fumigants for many (17-25 or more) years; and that trichloropropane (TCP), an impurity of the previously used fumigant Shell DD, was found to be the most widespread. Second, the residues of DBCP and EDB which remain in the surface soils do not constitute a significant source of future contamination of the underlying deep groundwater. Third, DBCP in the contaminated groundwater in Mililani is predicted to experience limited migration in the basal groundwater and to drop to below the regulated level by the year 2000 under the present scenario of groundwater management. The project also developed guidelines for the timing of fumigant application to minimize the transport of pesticides below surface soils and for alternative treatment methods of contaminated groundwater for potable use, and addressed water well technology for contaminated aquifers.