U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Background Aqueous Chemistry and Effects of Carbon Dioxide Variations in Recharge in Shallow Ground Water in a Glacial Outwash Aquifer, Cape Cod, Massachusetts

Abstract

Previous geochemical research at the Otis Air Base Site, Cape Cod, Massachusetts, determined that the principal geochemical process developing background water chemistry of shallow ground water is CO₂-controlled hydrolysis of sodium feldspars. Preliminary geochemical modeling, however, demonstrated that CO₂ sources should vary laterally over the project area. Field analyses of unsaturated zone gases showed variations in available CO₂ for recharge waters. These variations depend on land use and vegetative cover in the area of ground-water recharge. On the basis of measurements of CO₂ concentrations in unsaturated-zone gases at 20 sites, CO₂ dissolved in recharge water can range from about 0.035 to 1.000 millimoles per liter in the project area. The various land-use practices and local surface features in and around Otis Air Base (residential subdivisions, golf courses, large cultivated grass fields, kettle ponds, and woodlands) are associated with variations in the amount of CO₂ in the unsaturated zone.