Spatial analysis of groundwater chloride anomalies, earthquake sand-blows, and surface soils in the Mississippi River Valley alluvium in southeastern Arkansas


Groundwater samples from the Mississippi River Valley Alluvial (alluvial) aquifer in Desha County, Arkansas (AR) have historically yielded elevated chloride concentrations (> 100 mg/L). Overlapping spatial relationships between earthquake liquefaction sand-blows, soils derived from backswamp deposits, and chloride anomalies in the alluvial aquifer suggest the water quality conditions specific to southeast (SE) AR could be related to the tectonic and geomorphic features. Spatial analysis and statistical techniques are used to determine whether the chloride anomalies in the alluvial aquifer are more closely related to the spatial distribution of liquefaction sand-blows or surface soil types in Desha County. Pattern analysis suggests an underlying process is controlling the distribution of chloride concentrations in the alluvial aquifer. Cluster analyses show the chloride concentrations are more closely related to sand-blow densities than surface soil types, with high chloride concentrations associated with high sand-blow densities and low chloride concentrations associated with low sand-blow densities. Least squares regression analysis does not show a statistically significant spatial relationship between sand-blow densities, surface soil types, and chloride anomalies. However, the statistical relationship between sand-blow densities and chloride anomalies is stronger than surface soil types and chloride anomalies. The results from the spatial and statistical analyses are robust enough to conclude elevated chloride concentrations in the alluvial aquifer are more closely related to tectonic features than surface soil types in the study area. The chloride anomalies in the alluvial aquifer are interpreted to be from the intrusion of saline fluids from depth along faults during past earthquakes.

Publication Title

Groundwater for Sustainable Development