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In this paper, the frequency of threshold precipitation events is discussed from the perspective of ground-water recharge in arid and semiarid environments of the Nevada Test Site (NTS). The terminology threshold precipitation refers to precipitation events resulting in the penetration of moisture approximately 1 m into the unsaturated zone at study sites on NTS. While it is not proved that this type of moisture penetration results in ground-water recharge, it is suggested that deep penetration does remove moisture from the atmospheric and surface components of the hydrologic cycle. Estimates of the frequency of episodic recharge events are important from the viewpoint of regional contaminant transport models and provide perspective on the length of precipitation record required to estimate recharge.