New Wales Sinkhole Remediation

This paper presents the Florida Department of Environmental Protection’s (FDEP) investigation of a sinkhole at the<br>IMC-Agrico Company (IMC) New Wales chemical plant, in Polk County, Florida.<br>In June 1994, a catastrophic condition occurred at the New Wales chemical plant. A sinkhole had opened under<br>their industrial waste storage area (phosphogypsum stack) creating a depression within it. The depression was<br>observed to be 185 feet deep and 120 feet wide, within the 200 foot tall phosphogypsum stack. Further investigation<br>revealed the existence of a 480 foot long conduit that extended from the top of the stack to the upper Floridan<br>aquifer system. Remedial alternatives for a sinkhole of such magnitude and potential harm to the potable water<br>source could not be determined without a thorough understanding of the extent of the sinkhole formation.<br>Exploratory work involved cross-hole seismic surveys together with the drilling of boreholes at strategic locations.<br>Remediation consisted of an extensive grouting program using angle drilling to gain safe access into the erosion<br>cavity. The Phosphate Management Program (PM) of FDEP was responsible for review, evaluation, and approval of<br>every technical aspect of the proposed exploratory and remedial activities, to ensure that an effective long term<br>solution was implemented. The Program also received valuable comments concerning this project from an<br>interdisciplinary technical advisory committee representing local, State, and Federal agencies.<br>IMC expended approximately $7 million toward sinkhole exploration and remediation, and is required to continue a<br>monitoring program to verify success of the remedial effort. The event made national headlines and was broadcast<br>over television networks such as CNN News. Inquiries were received from other countries on the technical aspects<br>of the remediation.