NGWA Event and Education Recordings Archive

The karst geology that underlies most of Florida and South Georgia can serves as a pathway for surface water migration that can adversely impact the quality of water produced from typical supply wells.  Groundwater supply wells that come under the direct influence of surface water (UDI) can pose a health risk due to harmful microorganisms requiring the effected utilities to cease using the well or provide expensive additional treatment unless the source of UDI can be determined and eliminated. The City of Valdosta had one of their seven production wells declared UDI by the State Environmental Protection Department and three other wells declared at high or moderate risk for UDI.  To address the UDI declarations and avoid expensive modifications of the existing treatment facilities, a comprehensive approach was developed to evaluate, diagnose, and remediate the problem wells.  The program included diagnostic logging and video surveying under high flow conditions, in-situ sampling and water quality profiling, packer testing, evaluation of flow contribution throughout the borehole, and testing and evaluation of well mechanical integrity. 

 Results of the comprehensive testing suggested that the worst well was providing a direct conduit to the surface and likely had become the UDI source for the three other wells.  The UDI well was plugged and abandoned and the remaining wells re-lined to deeper casing set points.  The overall program was highly successful in that the UDI source was eliminated at reasonable cost compared to alternative water treatment or new well construction.  Results of the remediation efforts are that UDI indicators were reduced to essentially zero and the wellfield integrity and capacity were maintained.