Dr. Walker’s research supports exposure assessment as a part of risk assessment associated with human health protection. I have conducted studies of exposure and potential for exposure to: Arsenic in private water supplies; E. coli, as an indicator of fecal contamination in water; Leptospira, as a result of changes in land use in Hawaii; and Cryptosporidium.  His extension work provides technical support and information through: Water supply operators throughout Nevada; using an innovative partnership and distance learning technologies; Web sites that help interpret water quality and have served as models for at least two national efforts; Peer-reviewed fact sheets and special publications and newsletters; and small grants programs for Extension Educators.