Charles Roger Whitley
Temporal Analysis of Private Drinking Water Wells to Evaluate Potential Aquifer
Contamination
Abstract
Introduction
This paper describes the development and application of a spatial analysis method to evaluate the
contamination of private drinking wells following the 1994 Tropical Storm Alberto flooding in
southwest Georgia. Large numbers of wells (up to 95% of the private wells in a county) were
sampled for E. coli contamination after periods of up to two years. These wells were located
with Global Positioning Systems (GPS) and combined with the historical sample data to provide
the basis for the analysis. The purpose of this paper is to develop a an initial method for
examining the time dependency of contamination of the private wells through GPS located well
sites and well sampling data. This will allow examination of the extent of contamination and
detect the potential for migration of that contamination over time. Although data collection is
ongoing and more data will be required before final analysis can be completed this paper will
focus on Calhoun County, Georgia as a case study with the larger flooded area to be examined as
the program continues .
Flood Recovery Program
Extremely limited resources were available to meet the immediate and long-term needs that were
created by the flooding during July of 1994. In the aftermath of the rains, 55 Georgia counties
were declared disaster areas (Figure 1). In order to address the public health needs that resulted
and to develop methods for disaster planning in the future, the Flood Recovery Program was
formed with federal assistance through the Centers for Disease Control and Prevention. The
objectives of the two-year program were to (1) Assess and address the public health service
needs generated by the flood disaster related to environmental health, infectious diseases, child
health, chronic conditions, and injury of the 320,000 residents in the 14 counties of the Albany
health district. (2) Undertake environmental health activities to identify the remaining concerns
produced by flood damage and its aftermath related to well and septic contamination, damage
and displacement at known hazardous waste sites, and breeding of disease causing insects
throughout the 55 affected counties, (3) Produce a comprehensive state disaster response field
operations manual and conduct training, and (4) Develop the skill capacity of district and local
level staff in all parts of Georgia to undertake disaster-response activities related to overall crisis
management and emergency response, environmental health concerns, and epidemiological
surveillance as well as provide these staff with both primary data and necessary equipment
needed in such activities.
Figure 1. Extent of 1994 Tropical Storm Alberto Flood
Methodology
Well Samples
For each county within the flooded zones private drinking wells were examined for coliform and
E. coli contamination. In some counties the number of drinking wells examined
approaches 95% of the total private wells within the county. For Calhoun County, Georgia 543
wells were sampled within a county with a total population of 4,945. Within this region an
average of 52.8% of the households use private wells for drinking water. The samples were
carried out over a period of time from 1994 to 1996. Information which was gathered about the
wells included a site number, contamination results, the date taken, the positional location of the
well, and historical well information including well type, construction, pump type, etc. The
wells which sampled for positive for coliform contamination were chlorinated and resampled at a
later date. If the wells demonstrated a positive contamination again the wells were rechlorinated
and this process carried out until the drinking wells were replaced or became contaminate free.
GIS Flood Data
Following the flooding of 1994 a total of 55 Georgia counties were declared disaster areas. The
main areas of the flooding were concentrated along the river basins of the Flint, Chattahoochee,
and Ocmulgee river basins. Flood extents and boundaries were gathered by the United States
Geological Survey (USGS) through examination of aerial photography of the area along with
modeling of the Digital Elevation Models and river levels. The area for Calhoun County lies
entirely within the Flint river basin and so the Flint river flood boundaries were used for the
methodology study.
GIS Methods
The samples for the drinking wells were divided into three groups corresponding to the years in
which the data was gathered - 1994, 1995, and 1996. Although some wells were sampled in
multiple years the number remained negligible. Using ArcView 3.0 the well samples were
brought in as an event theme along with the coverages for the counties and flood boundaries.
The following analysis of the well samples describes the frequency and rate of contamination
broken down into three time periods. For each year views were constructed demonstrating the
geographic locations for the sampled wells within each year along with the flood data. For the
year of the flood 1994 155 wells were sampled of which 73 (47.1%) different wells showed
positive samples of coliform contamination. Of the 73 contaminated wells 21 (28.77%) showed
a resistance to disinfection through the use of chlorination (Figure 2). For the following year of
1995 223 private wells were sampled of which 110 (49.33%) were contaminated. Of these 110
contaminated wells 63 (57.27%) were chlorinated and tested as contaminated again (Figure 3).
In 1996 239 wells were sampled with 84 (35.15%) testing positive for coliform contamination.
Of the 84 wells which tested positive for contaminants 27 (32.14%) tested positive more than
once (Figure 4).
Figure 2. 1994 Well Sampling Survey - Calhoun County, Georgia
Figure 3. 1995 Well Sampling Survey - Calhoun County, Georgia
Figure 4. 1996 Well Sampling Survey - Calhoun County, Georgia
Future Analysis & Methodology
Once data collection of the well samples has been completed for the entire region, the wells will
be examined for a variety of time periods including shorter periods. Also of interest will be the
frequency and change in status of contamination in wells which
are in close contact with potential contamination hazards including landfills, toxic sites, and
different land cover classifications. For an example of a similar analysis which will be
performed for the Flood Recovery Program see Paper #410, Statistical Evaluation of Flooding
and Physical Well Characteristics on Wells Failing Chlorination.
Acknowledgments
This analysis described in this paper was developed and supported 100% by federal funds from
Centers for Disease Control and Prevention grant U1Q/CCU411900-01. Its contents are solely
the responsibility of the authors and do not represent the official views of the CDC.