Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1993 through March 1995

This report contains hydrologic and climatic data that describe the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1993 through March 1995, although the report focuses on hydrologic events from January through March 1995. Cumulative rainfall for January through March 1995 was about 42 inches which is higher than the mean cumulative rainfall of about 33 inches for the same 3 months in a year. January and February are part of the annual wet season and March is the start of the annual dry season. Rainfall for each month was above average from the respective mean monthly rainfall. Ground- water withdrawal during January through March 1995 averaged 894,600 gallons per day. Withdrawal for the same 3 months in 1994 averaged 999,600 gallons per day. At the end of March 1995, the chloride concentration of the composite water supply was 26 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 March 1995 ranged between 19 and 49 milligrams per liter. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations decreased since November 1994. The deepest monitoring wells show declines in chloride concentration by as much as 4,000 milligrams per liter. A fuel leak 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 by recirculating about 150,000 gallons of water each day.