Modeling Water Balance for a Demonstration-Scale Alternative Landfill Cover in Hawaii

A problem associated with landfills is the production of leachate, caused by water infiltrating into the disposed waste material, and the migration of it from the landfill with various contaminants. The solution to this is to reduce infiltration, which reduces the leachate production. Vegetative covers are an attractive method in the arid regions using evapotranspiration to reduce the amount of water seeping into the landfill. In the tropics, where rainfall exceeds the potential evapotranspiration, runoff enhancing mechanisms can be used to minimize infiltration and leachate generation. An experimental landfill cover site with rain gutters placed as runoff enhancing mechanism had been established at the Marine Corps Base Hawaii in Kaneohe, Hawaii to monitor different components of the water balance in three different treatments — control, 20 % and 40 % coverage with gutters. A rain simulator was also used to augment the natural rain episodes to obtain a wider range of rainfall intensities. While both the 20% and 40% covered areas produced lower amounts of leachates than the control plot, the 40 % covered area did not produce the expected (lesser) amount of leachate. The gutters were more effective in high intensity rainfalls than in low intensity ones. These observations suggest that interception by vegetation overhanging into the gutters might have reduced runoff generation. The Hydrological Evaluation of Landfill Performance (HELP) model was used to study the leachate and the runoff generated. The simulated results overestimated the leachate generation in agreement with the understanding that daily averaging of rainfall should increase the leachate volume. Additional event based modeling are also under progress to look at the process in detail.