As part of a groundwater observation network, the USGS, in cooperation with local water agencies, water districts, the military, and private landowners, has constructed many multiple-well monitoring sites. These sites consist of a cluster of two or more observation wells completed at different depths within a single borehole, each typically screened across a 20-foot interval (Huff and others, 2002). Data from the shallowest well of a multiple-well site were used for the regional water-table maps.