Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1992 through June 1994

Abstract

This report contains hydrologic and climatic data that describe the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data are presented from January 1992 through June 1994. This report concentrates on data from 1994, and references historic data from 1992 and 1993. Total rainfall for the first half of 1994 was 51 inches which is 48 percent of the mean annual rainfall of 106 inches. In comparison, total rainfall for the first six months of 1993 and 1992 was 56 inches and 51 inches, respectively. Annual rainfall totals in 1993 and 1992 were 95 inches and 93 inches, respectively. Ground-water withdrawal has averaged 975,000 gallons per day through June 1994, while withdrawals in 1993 and 1992 averaged 954,000 gallons per day and 936,000 gallons per day, respectively. In each of the five areas of ground- water production, withdrawals have remained steady since 1991. At the end of June 1994, the chloride concentration of the composite water supply was 68 milligrams per liter, well below the 250 milligrams per liter secondary drinking water standard established by the U.S. Environmental Protection Agency. Chloride concentrations of the composite water supply from January through June 1994 ranged between 37 and 90 milligrams per liter. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations have increased very slightly since March 1994 coinciding with the start of the dry season. There has been a general trend of increasing chloride concentrations in the deeper monitoring wells since the 1992 dry season, which began in March 1992. A fuel spill at Air Operations caused the shutdown of ten wells in May 1991. Four of the wells resumed pumping for water-supply purposes in April 1992. The remaining six wells are being used to hydraulically contain and divert fuel migration.