As the world warms and ice sheets melt, the ocean continually rises. The greater Boston area can expect to see between one and six feet of sea level rise by 2100, according to recent estimates. To find out what this rise might mean for freshwater supplies, a team of hydrogeologists developed an innovative new model that can not only predict saltwater intrusion over the next 75 years, but also pinpoint the main sources of salt contamination today — road salt and human development.