WRRCTR No.175 Modeling of trace organic (DBCP) transport in Pearl Harbor aquifer, Oahu, Hawaii: Method of characteristics, phase II

Orr, Shlomo
Lau, L. Stephen
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Water Resources Research Center, University of Hawaii at Manoa
A numerical model, based on the method of characteristics (MOC), is used to simulate the transport of DBCP through the basaltic aquifer in Mililani and vicinity and to predict the potential downstream contamination including Waipio Heights Wells II. The Phase II modeling is intended to improve upon the Phase I mixing-cell model. For the two-dimensional solute transport model and the large scale used, the aquifer is considered as homogeneous and isotropic, the solute transport as occurring in the upper irrigation-return lens, and the dispersion as Fickian. The lowest and the most abundant concentration detected in the deep core samples was assumed to be the input concentration at the water table, deep below the pineapple fields. This rather optimistic assumption would render a rather optimistic recovery of the aquifer. The results suggest that predicted DBCP levels will decline to below 20 ppt for the Mililani wells around the year 2000. Waipio Heights Wells II would experience DBCP increase up to 22 ppt around the year2000, then decline slowly. Increased pumpage from Mililani Wells II would hasten aquifer recovery. The mutual relationship between the calibration of the solute transport and the groundwater flow models emphasizes the need for a more precise flow model that more precisely predicts dynamic changes in pumping stresses and recharge. The two models show a general similarity in the prediction of aquifer recovery, which is, however, slightly faster in the mixing-cell model. The mixing-cell model tends to overestimate dispersion, the lateral in particular. Both models show that leachate concentrations as low as 0.1 ppb below the top few feet of soil can contaminate a deep aquifer.
Office of Environment Quality Control, Department of Health Grant/Contract No. T-377
groundwater contamination, organic pesticides, mathematical models, sensitivity analysis, solute transport, groundwater movement, vadose, DBCP, method of characteristics, basaltic aquifer, Mililani wells, Waipio wells, Pearl Harbor aquifer, Oahu
Orr S, Lau LS. 1988. WRRCTR No.175 Modeling of trace organic (DBCP) transport in Pearl Harbor aquifer, Oahu, Hawaii: method of characteristics, phase II. Honolulu (HI): Water Resources Research Center, University of Hawaii at Manoa. WRRC technical report, 175.
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