Walter, D. A. 1997. Geochemistry and Microbiology of Iron-Related Well-Screen Encrustation and Aquifer Biofouling in Suffolk County, Long Island, New York (WRIR-97-4032). 37 pp., size 8.5" x 11". Description: This report summarizes and interprets geochemical and microbiological data collected from test borings and affected wells to define the geochemical processes that cause well-screen encrustation at specific sites. The report describes the role of iron-related bacteria in the encrustation process and relates their occurrence to chemical conditions in the wells; it also discusses the role of well operation in well-screen encrustation and the effect of well-screen encrustation on well-water quality. A companion report (Walter, 1997) describes the distribution of well-screen encrustation with Suffolk County and the relation of specific-capacity declines to spatial trends in water quality.