USING GEOPHYSICS AND DYE TRACING TO DETERMINE A SOURCE FOR A CONTAMINATED SPRING IN SPRINGFIELD, MISSOURI

Springfield Missouri, like many urban cities, has been remediating older industrial and urban sites under the USEPA’s Brownfield’s program. However, Springfield is located on the Springfield Plateau which consists mostly of Paleozoic carbonates, including the Mississippian Burlington Limestone. The Burlington Limestone is heavily fractured and contains numerous karst features including sinkholes and caves. At a site in Springfield, excavation of contaminated soil uncovered a new groundwater spring, and the spring was found to be contaminated with hydrocarbons from an unknown source area. In an effort to locate the source of groundwater area, a combination of geophysical and dye tracing investigative tools was used. The geophysical investigation was planned as the first activity, to search for possible linear trends or conduits in the Burlington Limestone feeding the spring. Twelve electrical resistivity profiles were conducted using the Schlumberger array with a 1 to 1.5 meter electrode spacing using a 64 electrode imaging system. The resistivity data interpreted using 2-D inversion methods, imaged three to four potential linear low resistivity zones, which were interpreted as high angle joints or fractures. To confirm the electrical resistivity results, an electromagnetic survey using a horizontal dipole system and frequencies of 1000, 2000 and 3000 Hz was performed. These results were consistent with the electrical resistivity results, though less definitive. Based on the geophysical surveys, the joint trends identified were extrapolated offsite to determine if any sinkholes could be identified along those trends. Multiple sinkholes were identified in the approximate trends suggested by the geophysical studies and a dye trace is ongoing from one of those sinkholes. Results of the dye trace and the geophysical studies leading to the trace will be presented.