Figures 7a,b.  Ternary diagrams of the major cations and anions in groundwater according to land use. Based on previous studies conducted on Long Island (deLaguna, 1964; SCDHS, 1987; Leamond et al., 1992; Pearsall, 1996). Residential and agricultural waters plot in distinct fields with little overlap.
Figures 7c,d.  Ternary diagrams of the major cations and anions in monitoring-well samples. Symbol size reflects nitrate concentration. Samples were collected from monitoring wells in residential neighborhoods except for one obtained from an agricultural area (Ag) and one collected downgradient from a landfill (LF). Most samples plot within the residential field except that liming of turf grass tends to blur the distinction between the agricultural and the residential field on the cation plot.
Figures 7e,f.  Ternary diagrams of the major cations and anions in public supply wells. Symbol size reflects nitrate concentration. The only wells that show the enrichment in both calcium and sulfate characteristic of agricultural land use are those at Gun Club Road. PResent land use in the vicinity of these wells is agricultural.