This study describes the removal of arsenic species in groundwater by nano zero-valent iron process, including As(III) and As(V). Since the background species may inhibit or promote arsenic removal. The influence of several common ions such as phosphate (PO43−), bicarbonate (HCO3−), sulfate (SO42−), calcium (Ca2+), chloride (Cl−), and humic acid (HA) were selected to evaluate their effects on arsenic removal. In particular, a 26−2 fractional factorial design (FFD) was employed to identify major or interacting factors, which affect arsenic removal in a significant way. As a result of FFD evaluation, PO43− and HA play the role of inhibiting arsenic removal, while Ca2+ was observed to play the promoting one. As for HCO3− and Cl−, the former one inhibits As(III) removal, whereas the later one enhances its removal; on the other hand, As(V) removal was affected only slightly in the presence of HCO3− or Cl−. Hence, it was suggested that the arsenic removal by the nanoiron process can be improved through pretreatment of PO43− and HA. In addition, for the groundwater with high hardness, the nanoiron process can be an advantageous option because of enhancing characteristics of Ca2+.