WRRCSR No.7:05:91 Leachate Evaluation and Monitoring Project, Kapaa Sanitary Landfill, Kawainui, Oahu, Hawaii

Abstract

The operation of the City and County of Honolulu Kapaa Sanitary Landfill, located next to Kawainui Marsh in Kawainui, Oahu, Hawaii, raised concern over the possibility that landfill leachate could have adverse effects on the marsh. Thus, an intensive 2-yr baseline study (1979-1980) was conducted in which six sampling sites each were established for surface water and groundwater; this was followed by an ongoing, low-level monitoring program begun in 1981 and reported herein through 1990. Analyses were conducted for typical surface-water and leachate parameters. 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 level. The outstanding characteristic of leachate, chemical oxygen demand (COD), which was typically reported at a concentration of 18,000 mg/l, was found at only a fraction of this value at the sample stations - the highest annual median COD value of the 12-yr study being only 85 mg/l for one of the sampling wells, and 325 mg/l at a surface-water sampling station. No consistent correlation could be found between individual constituent concentrations of the surface-water stations or monitoring wells and groundwater levels, rainfall, or seasonal and/or annual changes. It is concluded that any correlation between leachate production and the underlying groundwater quality would have to be considered minor at best.