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Geophysical Surveys over Karst Recharge Features, Illinois, USA
Author(s) -
CARPENTER Philip J.,
AHMED Shawkat,
Xiling Edited By Zhu
Publication year - 2001
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2001.tb00527.x
Subject(s) - bedrock , groundwater recharge , geology , karst , aquifer , ground penetrating radar , electrical resistivity tomography , infiltration (hvac) , hydraulic conductivity , sinkhole , hydrology (agriculture) , groundwater , geomorphology , coring , soil science , soil water , geotechnical engineering , drilling , radar , electrical resistivity and conductivity , computer science , engineering , paleontology , telecommunications , thermodynamics , mechanical engineering , physics , electrical engineering
Karst aquifers supply a significant fraction of the world's drinking water. These types of aquifers are also highly susceptible to pollution from the surface with recharge usually occurring through fractures and solution openings at the bedrock surface. Thickness of the protective soil cover, macropores and openings within the soil cover, and the nature of the weathered bedrock surface all influence infiltration. Recharge openings at the bedrock surface, however, are often covered by unconsolidated sediments, resulting in the inadvertent placement of landfills, unregulated dump sites, tailing piles, waste lagoons and septic systems over recharge zones. In these settings surface geophysical surveys, calibrated by a few soil cores, could be employed to identify these recharge openings, and qualitatively assess the protection afforded by the soil cover. In a test of this hypothesis, geophysical measurements accurately predicted the thickness of unconsolidated deposits overlying karstic dolomite at a site about 100 km south of Chicago, Illinois. Zones of elevated electrical conductivity and high ground‐penetrating radar (GPR) attenuation within the sediments coincided with subcropping solutionally‐enlarged hydraulically active bedrock fractures. These fractures extend to over 12‐m depth, as shown by 2‐D inverted resistivity sections and soil coring. Anomalous electromagnetic (EM) conductivity and GPR response may be due to higher soil moisture above these enlarged fractures. An epikarstal conduit at 2.5‐m depth was directly identified through a GPR survey. These results suggest that surface geophysical surveys are a viable tool for assessing the susceptibility of shallow karst aquifers to contamination.