CHEMICAL LEACHING NEAR THE WAIAWA SHAFT, OAHU, HAWAII .1. FIELD EXPERIMENTS AND LABORATORY ANALYSIS

This paper is the first paper of a two-part series concerned with asse ssing the potential for organic chemical leaching to a ground-water sk imming tunnel in the Pearl Harbor Basin, Oahu, Hawaii as a direct resu lt of a proposed urban development. The objective of our simulation-ba sed assessment was to provide insight into the potential for chemicals , that may be introduced to the recharge areas of the Waiawa Shaft as a result of the proposed developments, to subsequently leach through t he unsaturated zone to ground water. In this paper field and laborator y results are presented for experiments designed to support the modeli ng effort reported in the second paper of this series. The chemical le aching experiments were conducted at two field locations. The chemical s which were applied and then monitored for their downward movement in the near-surface unsaturated zone are bromide, chlorpyrifos and fenam iphos. We found (1) good mass balance for bromide at both sites, (2) l imited mobility of chlorpyrifos and fenamiphos at the field plots, and (3) good agreement between field and laboratory measured degradation rates.