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2007 Ground Water Summit |
Monday, April 30, 2007 : 1:40 p.m.
Development of Aquifer Properties Based on Relationships Involving Deposition Facies, Percent Sand, and Depth for the Construction of a Ground Water Flow Model
A stratigraphic study of the Chicot and Evangeline Aquifers was undertaken near the Texas Gulf Coast to help construct a detailed groundwater model for assessing the impacts of a well field that extends across several counties. The model covers approximately 9800 square miles. The study involved the analysis of 322 geophysical well logs to establish formational boundaries through incorporation of micropaleontologic data in the offshore area, chronostratigraphically based log correlations from the offshore area through the sand-dominated aquifers landward to the outcrop, and ties to mapped outcrop formation boundaries. Percent sand class was calculated from each log and used to map sand distribution and depositional facies. Study results were combined with pumping test results from the study area to develop algorithms for generating values for horizontal hydraulic conductivity, vertical hydraulic conductivity, and specific storage. For each grid cell, these algorithms estimate the aquifer properties base on the grid cell’s estimated depositional facie, percentage of sand, and depth. The model was calibrated to historical conditions from 1900 to 1997 to reproduce over 800 hydrographs that included 37,000 hydraulic head measurements. Results of the model calibration are compared to recently completed groundwater models that cover the study region but were developed without the benefit of a detailed geophysical study.
John Waugh, San Antonio Water System John Waugh is director of SAWS, San Antonio Water System.