WRRCTR No.87 Groundwater Pollution from Sanitary Landfill Leachate, Oahu, Hawaii

Abstract

A two-year study was conducted to determine the chemical characteristics of leachate derived from domestic refuse typical of that found for Honolulu, Hawaii, and to determine the removal characteristics of select Oahu soils with respect to the substances found in these leachates. Based on these findings, guidelines for sanitary landfill site selections, in relation to the prevention of groundwater pollution, were developed. Four Oxisol soils (Molokai, Wahiawa, Helemano, and Lahaina), one Mollisol soil (Mamala), and one Marsh soil, were subjected to both saturated and unsaturated flow conditions, using as the percolating liquid, leachate produced by saturating (domestic refuse) with water. The domestic refuse had a composition typical fop that of Honolulu, Hawaii. Leachate and percolate samples were analyzed for various chemical constituents including pH, hardness, alkalinity, nutrients, chemical oxygen demand, particulates, and a number of metallic cations and heavy metals. Ion exchange was responsible for altering the concentration of inorganic substances in the percolating liquid, while microbial degradation appeared to be the primary mechanism for removing organic substances. Under the test conditions, and using the leachate produced from typical Honolulu refuse, the soils examined were found to have relatively low exchange capacities, while at the same time, organic removals were not significant. Thus, migration of inorganic and organic substances to the groundwater table is possible, and these results suggest that a cautious approach to landfill site selection should be taken, although soil depth to water table and dilution characteristics of the underlying groundwater must also be considered. A procedure for evaluating the feasibility of landfill operations in relation to possible groundwater contamination has been suggested. This procedure utilizes the removal characteristics for the various soils as observed in this study.