Septic system A site within or in close proximity to a subsurface sewage disposal system that generally consists of: (1) a septic tank where settling of solid material occurs, (2) a distribution system that transfers fluid from the tank to (3) a leaching system that disperses the effluent into the ground. Water Infrastructure 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.