WRRCTR No.140 Environmental Aspects of Kapaa Landfill, Kawainui, Oahu, Hawaii

Abstract

The operation of the City and County of Honolulu, Kapaa Sanitary Landfill, located next to Kawainui marsh on Windward Oahu, Hawaii, raised concern over the possibility that landfill leachate could have adverse effects on the marsh. Thus, this study established six sampling sites each for surface water, groundwater, and combustible gas. Analyses were conducted for typical surface water and leachate parameters. The combustible gas monitoring was primarily for methane. There was obvious interchange of the marsh water and groundwater, with the higher mineral constituents of seawater intrusion being more evident in the monitoring wells with lower water levels. The outstanding characteristic of leachate, COD, with a reported typical concentration of 18,000 mg/l, was only found at a maximum median value of 38 mg/l in one of the six monitoring wells, while its surface water sampling station counterpart was nearly the same, 39 mg/l. No particular consistent correlation could be found to relate individual constituent concentrations of the surface water stations or monitoring wells to groundwater levels, rainfall, or seasonal and/or annual changes. If leachate is indeed entering the underlying groundwater its effect at this time would have to be considered minor. It was determined that no methane was detected in the gas monitoring wells.