COMPARISON OF INVERTED ELECTRICAL RESISTIVITY DATA COLLECTED BY AERIAL ELECTROMAGNETICS AND SURFACE ELECTRICAL RESISTIVITY SURVEYS FROM THE MISSISSIPPI RIVER VALLEY ALLUVIUM AND UNDERLYING EOCENE STRATA AT PRESIDENT'S ISLAND, SHELBY COUNTY, TENNESSEE

Defining hydrogeologic layers using inversion of electrical resistivity (ER) or airborne electromagnetic (AEM) data is an ill-posed problem. Previous studies have suggested resistivity varies based on geomorphic location and depositional environments, as well as with changing data collection methods. Understanding the similarity or dissimilarity of ER and AEM data will aid in identifying sediment types within a layer to define a hydrogeologic unit. Thus, this study compares the inverted ER and AEM properties of the Mississippi River Valley Alluvial (MRVA) and the upper Claiborne confining unit (UCCU) to understand their characteristic electrical properties and identify sandy intervals in the UCCU that may provide hydraulic connectivity to the underlying Memphis aquifer. The data for comparison ranges from the depth of 10m to 40m for MRVA, and 45m to 70m for the UCCU in an area with borehole control. The intervals for MRVA and UCCU were chosen with the help of borehole, ER, and AEM data to ensure constituent lithologic characteristics of both layers.

A preliminary statistical analysis shows that ER has higher resistivity ranges for both MRVA and UCCU than AEM. Moreover, the mean and the standard deviation is greater for ER than for AEM. P-values of <0.05 from different statistical hypothesis test (t-test, Welch t-test, and Mann Whitney U Test) suggest inequality in the mean resistivity of AEM and ER for both layers. The ER data show a greater range of resistivity for MRVA and UCCU than AEM likely due to the difference in the input current flow to the subsurface.