Brackish Water Resources and Recharge Rates in the Capitan Reef Aquifer, Southeastern New Mexico and West Texas

The Capitan Reef is a Permian-age karstic limestone aquifer that encircles the Delaware Basin in southeastern New Mexico and west Texas. The reef aquifer is the principal source of fresh water for the city of Carlsbad, New Mexico. However, throughout most of its extent water in the reef is too saline for human consumption. Both the petroleum industry and potash mining industry have recently expressed interest in exploiting brackish water resources in the reef aquifer for water flooding mature oil fields and processing potash ore. The impact of brackish water withdrawals on fresh water resources near Carlsbad and baseflow into the Pecos River is thought to be minimal, because of a partial hydraulic barrier that inhibits communication between the western and eastern segments of the reef. This hydraulic barrier is attributed to low-permeability sediment deposited in submarine channels that cut across the reef during middle Permian time. Water levels in the eastern segment of the reef aquifer declined by several tens of meters through the 1970s and 1980s because of withdrawals by the petroleum industry, as measured in a series of monitoring wells installed by the U.S. Geological Survey. However, in the past three decades water levels in the eastern segment have risen by >100 m, raising questions about rates and sources of recharge to the reef.