WHAT DOES AN AQUIFER CODE MEAN?

There are many online sources for hydrogeologic data in the United States supporting hydrogeologic research from local to global scales. Often, wells in these databases are assigned aquifer codes to provide hydrostratigraphic context for the data collected from wells. This study aims to assess error sources in the hydrostratigraphic categorization of Dakota Aquifer wells in Kansas and Iowa. The Dakota Aquifer, a generic term, encompasses Cretaceous sandstone units associated with several lithostratigraphic formations. We found that wells in Iowa are assigned aquifer codes based primarily on the stratigraphic unit(s) associated with a well’s screened interval. However, our data assessment shows that few Dakota Aquifer System wells in Iowa have the well construction information required to validate the respective aquifer codes. Although 469 of the 1284 Dakota wells have screen depth information, only 211 of the 469 wells contain filter pack interval depths, critical to understand a well’s hydrostratigraphic context. While 743 of 1284 wells provide information about the Dakota formation and its members, 399 of the 743 wells simply record Dakota without specifying its members. This evaluation required careful analysis of handwritten drillers’ logs since much of the relevant information was not captured in the datasets. A similar synopsis for the Kansas wells is in progress. Furthermore, almost all hydrostratigraphic picks in these databases presume that the hydrostratigraphy follows the lithostratigraphy without confirmation from independent hydraulic data. The next phase of this study involves installing one high-resolution multilevel system (MLS) targeting the Cretaceous strata in each state. The MLSs with numerous short monitoring intervals (<1 m) will avoid blending water from separate hydrostratigraphic units. Head and geochemical profiles from the MLSs integrated with geophysics collected from the boreholes and lithologic data, and geochemical data from the cores will be used to assess changes in hydrogeologic properties and flow path characteristics with depth, indicating distinct hydrostratigraphic units. The results will determine lower cost proxy datasets, most reflective of the hydrostratigraphic units to improve the hydrostratigraphic characterization of all Dakota Aquifer wells.