5.2 Plume Tracers–Minor and Trace Constituents–Boron

Boron (B) is present in laundry detergents, is mobile in groundwater flow systems, and has been used as a tracer to identify septic system and municipal wastewater impacts in groundwater (LeBlanc, 1984; Vengosh et al., 1994; Bassett et al., 1995). However, Boron concentrations in domestic wastewater (ranging from 0.1 to 1 mg/L, Table 1) are elevated by a relatively small factor (e.g., about 5, Bassett et al., 1995) compared to background values, and some natural waters, such as brackish and irrigation-impacted groundwater, can have B values equally as high as wastewater. Consequently, boron is only modestly robust as a wastewater tracer, but is useful at some sites. In a municipal wastewater plume on Cape Cod, Massachusetts, B was used as one of the principal tracers because it occurred throughout the 3 km length of the plume, at consistent concentrations of 0.2-0.4 mg/L, which was about five times higher than background values (LeBlanc et al., 1984; Barbaro et al., 2013).