Atmospheric nitrogen deposition is a major threat to biodiversity.  Serpentine grasslands and the Bay checkerspot butterfly have become “poster children” for biodiversity impacts, with non-native grasses overrunning flower-filled fields on nutrient-poor soils.  Atmospheric deposition was a major nexus for the development of The Santa Clara Valley Habitat Plan, a Habitat Conservation Plan/Natural Communities Conservation Plan. Patterns of deposition in space and time have been identified as a critical area for monitoring and research.  Springwater derived from serpentine grasslands downwind of Silicon Valley have highly elevated nitrate levels, up to 5.5 ppm NO₃-N, indicating severe N-saturation.  Low biomass, strong seasonality, shallow soils, and fractured bedrock contribute to high leaching levels.  Nitrate levels follow deposition gradients, with higher levels at low elevations closer to San Jose, and nitrate from relatively clean-air sites are well below 1 ppm NO₃-N.  Residence times for shallow groundwater are on the order of 1-3 years, so it should be possible to track deposition through time as a multi-year average.  After 5 years, a set of sites showed slight increases in NO₃-N, in line with estimates from TDEP.  TDEP provides insights into the forms of deposition – in Silicon Valley, oxidized N has decreased with strong regulation, but reduced N has increased with unregulated vehicular NH₃ emissions.   Sampling about 20 sites at the end of the dry season (Sep.-Oct.) costs less than $10,000, and provides and robust integrated measure of total deposition.