Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…mass discharge employ one of three basic approaches: integral pump tests (IPT) [Teutsch et al., 2000; Bockelmann et al., 2001, 2003], multilevel sampling (MLS) [Borden et al., 1997; Einarson and Mackay, 2001], and passive flux meter measurements (PFM) [Hatfield et al., 2004; Annable et al., 2005].
Category: