MULTI-AQUIFER WELLS PROVIDE LARGE-VOLUME CONTAMINANT TRANSPORT PATHWAYS IN URBAN AREAS
We have used a combination of field and modeling studies to evaluate the contribution of multi-aquifer wells to virus transport. Measurements of vertical borehole flow were collected in five wells, each of which is open to a shallow bedrock aquifer, an underlying shale aquitard, and a deep aquifer. One well located in the regional discharge area showed no measureable flow across the aquitard. The other four wells are located in regional recharge areas. Measured velocities ranged from 1 to 13 meters/minute downward in these wells, and volumetric flux, which depends on well bore diameter, ranged from 190 to over 3,790 liters/minute. Modeling shows that these flow rates are reasonable, and that multi-aquifer wells provide rapid transport from the water table to the deep aquifer. However, model-simulated travel times from these wells to other water-supply wells are not sufficiently fast to explain observed virus transport in this setting.
Both field measurements and modeling confirm that multi-aquifer wells are potential conduits for large volumes of groundwater flow. Their significance with respect to transport of sewer leakage and other contaminants should be considered in managing urban well fields.