Figure 2. Showing comparison of helium-4 and neon concentrations for water from monitoring wells in the Portland basin, Oregon, with air-water solubility curve (Weiss, 1971) and excess air curve. Air-water solubility curve and excess air curve calculated for mean sea level; gas concentrations for water samples were adjusted (United States Committee on Extension to the Standard Atmosphere, 1976) to equivalent mean sea level concentrations.