Assessing the Risks to Public Health from Contamination in Potable Wells Using the Geographic Information System (GIS)

Bob Vincent

 

The Well Surveillance Program at the Florida Department of Health (DOH) locates risk sources of anthropogenic contamination and surrounding potable wells using global positioning system (GPS) equipment.  Potable wells identified in a GPS survey are sampled and the water analyzed by the DOH's Jacksonville Laboratory for volatile organic compounds, pesticides, nitrates, arsenic and other potential groundwater contaminants. Since 1998, the DOH has located over 20,000 contaminated sites and completed GPS surveys to identify and sample 90,000 private and public drinking water wells. The primary mission of the Well Surveillance Program is to identify contaminated wells and assist the owner in obtaining an alternative source of drinking water or filters for the well if the maximum contamination level (MCL) is exceeded. A secondary objective is to assist the Department of Environmental Protection (DEP) in assessing the priority for contaminated site cleanups. 

 

The DOH manages a sophisticated Geographic Information System (GIS) database that is used to generate high-resolution well survey maps, conduct spatial analysis for specific contaminants, and provide planning tools for groundwater investigations, remediation and risk-based assessments. Well demographics from GPS records and sample results from the laboratory are stored in a geodatabase and shared by a network of users using desktop GIS or internet map servers (IMS). Spatial analysis involves sorting the potable well data by chemical groups, relative concentration, sample date and location relative to known contamination sites. Unique symbology is assigned to these well attributes and when plotted on a map can show patterns indicative of contamination plumes in the groundwater. Integrating spatial data from a regional, large scale distribution of potable wells with data from monitoring wells at the local site assessment scale can help to define migration pathways, depth of contamination and potential volume of impacted groundwater. Cleanup contractors have used the spatial analysis results of potable well data to successfully design monitoring well networks including rapidly deployed direct push wells.

 

In summary, spatial analysis of water quality from a database of potable wells is proven to be a useful GIS tool to safeguard drinking water supplies, enhance site specific contamination assessments, design remedial action plans and conduct health risk assessments. The ultimate purpose of our work is to protect the health and welfare of all people in the State of Florida by ensuring a safe drinking water supply.