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