The US Geological Survey, in response to a request from the US Department of Energy`s Pittsburgh Naval Reactors Office, Idaho Branch Office, sampled water from 14 wells during 1994--95 as part of a long-term project to monitor water quality of the Snake River Plain aquifer in the vicinity of the Naval Reactors Facility, Idaho National Engineering Laboratory, Idaho. Water samples were analyzed for naturally occurring constituents and manmade contaminants. A total of 111 samples were collected from 10 monitoring wells and 4 production wells. Twelve quality-assurance samples also were collected and analyzed; 1 was a blank sample and 11 were replicate samples. The blank sample contained concentrations of one inorganic constituent, one organic constituent, and five radioactive constituents that were greater than the reporting levels. Concentrations of other constituents in the blank sample were less than their respective reporting levels. The 11 replicate samples and their respective primary samples generated 293 pairs of analytical results for a variety of chemical and radiochemical constituents. Of the 293 data pairs, 258 were statistically equivalent at the 95-percent confidence level; about 88 percent of the analytical results were in agreement.