Tunnel, shaft, or mine A constructed subsurface open space large enough to accommodate a human that is not substantially open to the atmosphere and is not a well. The excavation may have been for minerals, transportation, or other purposes. See also: Excavation. Groundwater Sites Adapted from USGS Site Types. http://wdr.water.usgs.gov/nwisgmap/help/sitetype.html ODM2 SiteType Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of a data collection Site. To some extent, these types represent the ultimate feature of interest that the site was established to measure. For example, a Stream Site was established to measure properties of a Stream.