Modeling of virus transport in the subsurface, southern Oahu, Hawaii

Abstract

In this study, the potential is evaluated for viral contamination of groundwater in the southern Oahu aquifer, Hawaii, due to irrigation of sugarcane with effluent from secondary treatment plants. An EPA numerical model, CANVAS, has been modified and applied to simulate virus transport and its distribution in the subsurface of several sugarcane fields near the Pearl Harbor area. By incorporating the model with Monte Carlo simulations, the uncertainties and heterogeneity of the subsurface could be accounted for to some degree. The simulations show that due to natural disinfection provided by the geological and hydrological conditions in the testing fields, there is very low probability that viruses transported from irrigated fields by recharge water will reach drinking-water wells, although the virus concentration at the water table beneath the sugarcane fields is higher than a given criterion, 2 × 10-7 PFU/I. This is mainly due to the large backup distance between the wells and the virus sources, which allows viruses to die off before they reach the wells. The study suggests that a reasonably long setback distance is necessary for the areas where the thickness of soil is not large enough to allow all viruses to die off before they reach the water table or drinking water wells. In addition, care must be taken when the temperature in the subsurface is not high enough to assist the disinfection process