Evaluations of the effects of the Columbia River on the unconfined aquifer beneath the 100-N Area

Abstract

This study continued a previous study characterizing the effects of river stage and waste-water discharges on the unconfined aquifer under the 1301-N facility in the 100-N Area of the Hanford Site. The current study examined the effects of river stage and waste-water discharges under the larger 100-N Area. River levels were statistically correlated with water-level data from 12 wells in the 100-N Area, and the influences of regional water-table changes were evaluated. The study was conducted between April and November 1990. Water-table elevations in the 100-N Area decreased throughout the study, dropping below the depths of some wells. During peak river stage in June the river level rose above water levels in several wells, causing a reversal in the hydraulic gradient and implying flow from the river into the aquifer. Such a reversal of flow could significantly influence travel times and paths of contaminants moving through the aquifer from the waste-water facilities. During high river stage, daily river-level fluctuations correlated with water levels in wells as far as 750 ft from the river shore. Seasonal river fluctuations correlated with water levels in wells approximately 1000 ft from the river shore. 10 refs., 7 figs., 4 tabs.