COLLOIDAL TRANSPORT OF NANOSCALE TO MICROSCALE GRAINS IN THE CENTRAL OKLAHOMA AQUIFER
The first investigation involved the collection of 50 sediment samples from the USGS/EPA Norman Test Hole Core spanning the productive zones of the aquifer. These samples were analyzed for BET surface area, micromorphology with SEM, color, texture, and grain size with optical microscopy, and whole-rock trace element geochemistry. Initial results demonstrated anomalously high surface areas in many samples, ranging up to ~60 m2/g. High surface area values were obtained in both clay-rich and clay-poor intervals. SEM imaging of samples from these intervals revealed the presence of abundant microscale hematite rosettes assembled from nanoscale platelets, in addition to clay minerals and other nanoscale iron oxides. Trace element concentrations followed a general power-law relationship with surface area, with much scatter.
In the second investigation TEM grids were deployed in monitoring wells associated with a City of Norman municipal drinking water supply well using an in-house designed subsurface nanoparticle collector. After exposure to groundwater for one week, TEM analysis of the grids revealed abundant iron oxides, quartz with or without surface-bound iron oxides, gypsum, and other trace phases.