Estimations of Aquifer Characteristics Using Drillers' Logs

Abstract

In an effort to utilize the lithologic information contained within the thousands of drillers' logs on file with the Arizona Department of Water Resources (DWR), a computer program was developed to analyze the logs for basic aquifer characteristics. These characteristics, estimations of specific yield, hydraulic conductivity and transmissivity, are calculated for each well log by comparing drillers' descriptions of alluvial sediments to standardized drillers' terms for which predetermined specific yield values have been assigned. These values approximate conditions in alluvial basins in Arizona. This information and identified hydrostratigraphic units are then coded for computer input. The computer program then calculates estimated aquifer characteristics for the total depth of the saturated sediments and hydrostratigraphic units. When a sufficient density of acceptable drillers' logs exist in the area being studied, the logs are used to approximate the extent and depth of the hydrostratigraphic units present. Thus the gross morphology of features, such as large clay bodies, which can have a significant effect on a hydrologic system, can be evaluated. This program has proven to be valuable by providing a preliminary overview of the geohydrologic systems of alluvial basins and for calculating initial estimates of aquifer characteristics for use in DWR computer modeling studies.