U.S. GEOLOGICAL SURVEY
Water-Resources
Investigations Report 97-4032
Geochemistry and Microbiology of Iron-Related
Well-Screen Encrustation and Aquifer Biofouling
in Suffolk County, Long Island, New York
By Donald A. Walter
Abstract
Introduction
Purpose and scope
Iron-related well-screen encrustation and aquifer biofouling
Acknowledgments
Hydrogeologic setting
Ground-water flow
Ground-water quality
Data collection and analysis
Water quality
Encrusting material
Sediment cores
Geochemistry
Mineralogy and solid-phase chemistry
Chemical digestions
Energy-dispersion analysis
X-ray diffraction
Results of water-quality sampling
Mineral-saturation indices
Oxidation-reduction conditions
Iron-oxidation kinetics
Effects of lubrication water during well shutdowns
Microbiology
Occurrence of iron-related bacteria
Source of iron-related bacteria
Role of lignite in well-screen encrustation
Role of sulfur-reducing bacteria
Effects of iron-oxidizing bacteria on water quality
Iron and manganese
Dissolved oxygen, pH, and dissolved carbon
Sulfate, nitrate, and phosphate
Summary
References cited
FIGURES
1. Map showing location of Suffolk County, N.Y
2-3. Generalied vertical sections showing:
2. Stratigraphy near the Nassau-Suffolk County border, Long Island, N.Y
3. Hydraulic heads and ground-water flow paths near the Nassau-Suffolk
County border, Long Island, N.Y
4. Map showing location of Suffolk County Water Authority wells and geologic borings used
in iron-encrustation study, Suffolk County, N.Y
5. Histograms showing saturation indices for selected mineral phases in water samples from
wells in Suffolk County, N.Y., as determined by chemical equilibrium model WATEQF.
A. Goethite, hematite. B. Maghemite, magnetite. C. Ferric hydroxide. D. Quartz
6. Eh-pH diagrams showing distribution of Eh values computed from concentrations of ferrous
and ferric iron and dissolved oxygen: A. In water containing only aqueous iron species.
B. In water in equilibrium with solid ferric hydroxide (Fe(OH)3(s))
7. Histograms showing saturation indices calculated by the chemical equilibrium model WATEQF
for iron compounds in treated lubrication water at 16 well sites in Suffolk County, N.Y.:
A. Iron compounds in treated lubrication water (geothite, hematite, maghemite, and magnetite).
B. Ferric hydroxide in well water and treated lubrication water
8. Box plots showing comparison of (A) dissolved-iron and (B) dissolved-oxygen concentrations
in wells in Suffolk County, N.Y., that contained the iron bacteria Gallionella ferruginea and in
wells that did not
9. Lithologic and gamma logs showing concentrations of dissolved organic carbon (DOC) and
oligotrophic bacteria, and location of iron-bacteria biofilm growth at well S99014, Suffolk
County, N.Y
10. Histograms showing changes in concentrations of selected constituents in well water and treated
lubrication water samples from Suffolk County Water Authority wells, Suffolk County, N.Y.,
after removal of encrusting material and iron-bacteria biofilms from well screens: A. Total iron.
B. Dissolved iron. C. Total manganese. D. Dissolved manganese. E. pH. F. Sulfate
TABLES
1. Description of major hydrogeologic and stratigraphic units underlying Suffolk County, N.Y.
2. Depths of Suffolk County Water Authority wells used in biofouling investigation, Suffolk County,
N.Y., and geologic units tapped
3. Iron and trace-element content of screen-encrusting material from selected wells in Suffolk County,
N.Y., as determined by chemical digestion
4. Mineralogy of screen-encrusting well material as identified by x-ray diffraction
5. Ferrous- and ferric-iron concentrations, pH, dissolved-oxygen concentrations, and calculated redox
potentials for water samples from selected wells in Suffolk County, N.Y
6. Iron-oxidation rates in well water and treated water at selected wells, Suffolk County, N.Y.
7. Detection of filamentous iron bacteria in selected Suffolk County Water Authority wells, Suffolk
County, N.Y.
8. Detection of iron-related bacteria in aquifer sediments and in drilling water, Suffolk County, N.Y.
9. Inorganic chemical analyses of ground-water samples collected at Suffolk County Water Authority
wells, Suffolk County, N.Y., between January 1991 and August 1992
10. Inorganic chemical analyses of lubrication-water samples collected at Suffolk County Water Authority
wells, Suffolk County, N.Y., July-August 1992
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