[en] Until recently, boreholes have been drilled for the Basalt Waste Isolation Project using water-based drilling fluids. Three drilling fluid tracers are used to monitor borehole development for hydrochemical sampling at the Basalt Waste Isolation Project. The tracers used are fluorescein dye, total organic carbon, and tritium. Used in concert, these tracers yield useful information regarding the degree to which a zone has been developed prior to final sample collection. The adequacy of these tracers in assessing borehole development has been examined using data collected from five zones within three boreholes across the Hanford Site. Field data indicate that fluorescein and total organic carbon perform well in helping to assess borehole development. Tritium data from these examples indicate that final samples collected are greater than or equal to 98 percent groundwater. Limited ionic data were available for one field example. These data indicate that certain species are affected by the introduction of drilling fluids. After the removal of about 9.5 x 10⁴ liters of fluid, most species appear to stabilize. However, tracer data indicate that components of drilling fluid were still present in the zone at this time. A field test is in progress to better quantify the relationship between drilling fluid tracer behavior and major chemical and isotopic species dissolved in basaltic groundwaters. 15 references, 9 figures, 5 tables