A water-quality reconnaissance was conducted at the south Dade County solid-waste landfill near Goulds, Florida, from December 1977 through August 1978. The landfill is located directly on the unconfined Biscayne aquifer, which, in the study area, is affected by saltwater intrusion. Water samples collected from six monitor well sites at two depths and four surface-water sites were analyzed to determine the chemical, physical, and biological conditions of the ground water and surface water of the study area. Results indicated that water quality beneath the landfill was highly variable with location and depth. Leachate was generally more evident in the shallow wells and during the dry-season sampling, but was greatly diluted and dispersed in the deep wells and during the wet season. High concentrations of contaminants were generated primarily in areas of the landfill with the most recent waste deposits. Chloride (limited to the shallow wells and the dry season), alkalinity, ammonia, iron, manganese, lead, phosphorus, and organic nitrogen indicate leachate contamination of the aquifer. Water-quality characteristics in the surface waters were generally only slightly above background levels. (USGS)