We present a theoretical study of Auger recombination processes in a GaInNAs/GaAs quantum well structure designed for 1.3 mum laser emission. The calculations are based on a 10x10 k.p model, incorporating valence, conduction, and nitrogen-induced bands. The Auger transition matrix elements are calculated explicitly, without introducing any further approximations into the Hamiltonian used. We consider two main Auger recombination channels: the process when the energy released from the electron-hole recombination causes electron excitation (CHCC process) and the process with hole excitation to the split-off valence band (CHHS process). The CHHS process is shown to be dominant. Good agreement is found when comparing the calculated Auger rates with experimental values of the Auger contribution to the threshold current of GaInNAs quantum well lasers.