Trace Element Concentrations in Ground Water- Lower Illinois River Basin
Kelly L. Warner and William S. Morrow
Ground water samples from 120 wells in the agricultural Lower Illinois
River Basin were collected to characterize the water quality in three major
hydrogeomorphic areas--the Bloomington Ridged Plain shallow aquifer (BRP),
the Bloomington Ridged Plain deep aquifer in the buried Mahomet valley
(BRPMV), and the shallow Galesburg and Springfield Plain (GSP) aquifer.
The shallow aquifers are fractured till and thin sand layers, and the deep
aquifer is a sand and gravel aquifer. Sixty privately owned wells were
sampled and 60 shallow wells were drilled. The privately owned wells are
in the shallow GSP and the deep BRPMV. The median depth of the shallow
GSP wells is 50 ft below land surface. The median depth of the BRPMV is
256 ft below land surface. The newly drilled wells in the BRP aquifer have
a median depth of approximately 20 ft below land surface. Samples were
analyzed for 18 different trace elements including arsenic, uranium, lead,
copper, radon and others.
Comparison of trace element concentrations from privately-owned wells
indicate a difference between the shallow (GSP) and deep wells (BRPMV).
The deep wells have median arsenic concentrations of 14 ug/L and several
samples that exceed 50 ug/L, whereas the shallow aquifers have median concentrations
of 3 ug/L and no concentrations above 50 ug/L. The shallow wells did have
detections of uranium and radon that were absent in the deeper aquifer.
Other trace elements were detected in concentrations at or near the reporting
limit for the constituent.
U.S. Geological Survey
221 N. Broadway
Urbana, IL 61801
(217) 344-0037
klwarner@usgs.gov, wsmorrow@usgs.gov