A COMPARISON OF SPATIAL DISTRIBUTION OF ARSENIC IN GROUNDWATER, SOIL AND SEDIMENT IN CONTINENTAL US

Elevated arsenic (As) concentration (> 10 ug/L) is commonly found in groundwater. It has been estimated that approximately 51 million person-years are subject to higher risks of bladder, kidney, liver, lung and skin diseases and cancers over the past 50 years in the US. The western US displays more frequent occurrence of elevated groundwater As. This study compares As spatial distribution in soil and stream sediment with that of the groundwater at national, regional and local scales. This is because chemical composition of soil and stream sediment has been shown to be a promising indicator of As concentrations in underlying bedrock aquifers in New England. This work investigates to what extent and at what scales that the soil and stream sediment As concentrations can be used as an indicator of groundwater As distribution in continental US.

Groundwater As data (n=46,119) were combined from National Water-Quality Assessment program (NAWQA) and National Uranium Resource Evaluation Hydrogeochemical and Stream Sediment Reconnaissance program (NURE-HSSR) databases with a sampling density of 1 per 150 km². Soil As data (n=12,705) were from a recently updated PLUTO database with a sampling density of 1 per 600 km². Sediment As data (n=49,764) were combined from the PLUTO and NURE-HSSR databases with a sampling density of 1 per 150 km². All data show highly skewed distributions and thus log transformed before interpolation. Interpolated distributions indicate higher As occurrence in western states than eastern states in groundwater, soil and sediment. The distributions display similarity spatially at national scale. However, discrepancy in several regions may be due to low sampling density.

At regional scale, analyses of this correlation in New England, Florida, and northern Nevada suggest that spatial variation of soil and stream sediment As could be an indicator of groundwater As distribution if the sampling density is higher than 1 per 100-200 km².

At local scale, high density sampling (1 per few or tens of km²) shows very similar spatial patterns of soil and groundwater As distribution in greater Augusta area, Maine. Logistic regression models confirm that soil As is significant among other geological and chemical parameters that affect groundwater As in fractured bedrock aquifers.