Data were collected to support the ongoing Installation Restoration Program (IRP) Remedial Investigation and Feasibility Study (RI/FS) at Vandenberg AFB, CA. These data were used to illustrate how the determination of inorganic background populations can affect the selection of chemicals of concern for risk assessment and, ultimately, risk management decisions. Four population determination approaches are discussed: 1) single population, 2) subunits, 3) pure statistics and 4) statistics plus project requirements. The same data set was used to determine background populations following each approach. Background threshold values that represent the upper limit of naturally occurring background were then calculated for each population. Background threshold values varied greatly depending on the approach used. Thus, chemicals of concern selected for risk assessment and risk management decisions could potentially differ depending on the approach. For the Vandenberg project, the best approach utilized a combination of statistics plus project requirements.