Test holes NC-6 and NC-11 were drilled in the municipalities of Hatillo and Isabela, respectively, as part of a study of the aquifers in the Northern Coastal Province of Puerto Rico. Test holes NC-6 and NC-11 were drilled to depths of 2,574 and 2,120 feet below land surface, respectively. Geologic and hydrologic data collected during drilling included continuous core, water-quality samples, water-level measurements, and estimates of aquifer yields from the water-bearing zones. Test hole NC-6 penetrated five formations ranging in age from late Oligocene to early Pliocene: the Lares Limestone, the Cibao Formation, the Los Puertos Formation, the Aymamon Limestone, and the Quebradillas Limestone. This test hole also penetrated a water-table aquifer and six artesian aquifer. Test hole NC-11 penetrated four formations ranging in age from late 01igocene to middle Miocene: the San Sebastian Formation, the Cibao Formation, the Los Puertos, and the Aymamon Limestone. A water-table aquifer and four artesian aquifers were penetrated by this well.