Geologic and hydrologic data collected by the United States Geological Survey (USGS) are used to evaluate the existing ground water monitoring well network completed in the upper portion of the Snake River Plain aquifer (SRPA) beneath the Idaho Chemical Processing Plant (ICPP). The ICPP is located at the south central end of the Idaho National Engineering Laboratory (INEL), about forty miles west of the city of Idaho Falls. •. Most monitoring wells at the ICPP are open over multiple water-producing zones, with uncased intervals commonly ranging from 100 to as much as 300 feet below the regional water table. The USGS data analyzed and compared in this study include: a) lithologic, geophysical, and stratigraphic information, including the conceptual geologic models developed by Jones (1961) and Anderson (1991), b) intrawell, ground water flow measurements (Tracejector tests) as described by Barraclough et al. (1967), and c) dedicated, submersible, sampling pump elevations as provided by Jensen (USGS, personal / communication). Qualitative evaluation ofthese data indicate that theupper portion oftheSRPA is bothheterogeneous andanisotropic atthescale oftheICPP monitoring wellnetwork. Meaningful spatial correlations ofdistinct hydrostratigraphic units (i.e., aquifers) are extremely difficult toestablish betweenthemajority ofICPP monitoring wells basedon available hydrogeologic data. Basalt flowtopunits, whicharebelieved torepresent the mostpermeable pathways forhorizontal ground waterflow, do notappear tobelaterally continuous basedon caliper, natural-gamma, andlithologic logs. Limited spatial agreement exists betweentheaquifers defined by thehydrostratigraphic conceptual modelofJones (196 I)andthebasalt flowgroups identified by thelithostratigraphic conceptual modelof Anderson(199I). Traccjcctor test results (after Barraclough ctal., 1967a) indicate that thehydraulic interconncction and spatial configuration ofwater-producing zonesisextremely complex this project was made available by the