Abstracts: The largest ground-water supplies from the 150 to 450-foot thick carbonate-rock aquifer in southwest Ohio are available in a 2,800 square-mile area on the crest and eastern flank of the Cincinnati arch. Well production in the high-yield area is mainly from the Newburg zone, a permeable stratum in the lower part of the Bass Island group. A structure contour map on the top of the Lockport Dolomite shows that the Newburg zone conforms to the configuration of the Cincinnati arch. The chemical quality of the water in the consolidated-rock aquifers is intimately related to the regional flow system, and undergoes a progressive change from a calcium bicarbonate-type in recharge areas to a calcium sulfate-type in areas of natural discharge.