Summary of ground-water and rainfall data for Tutuila and Aunuu Islands, Americn Samoa, for July, 1984 through September, 1995

Abstract

Ground-water and rainfall data for the period from July 1984 through September 1995 from the islands of Tutuila and Aunuu have been summarized in time-series graphs that can be used to analyze for historical trends. The data include pumpage and chloride concentrations from 50 production wells on Tutuila and 3 production wells on Aunuu, water-level measurements from 12 wells on Tutuila, and rainfall from 2 gages on Tutuila. Rainfall averaged 13.2 inches per month at the rain gage at Afono near Pioa Mountain and 17.6 inches per month at the rain gage at Aasufou over the period from 1984 to 1995. Late 1987 to early 1992 was a dry period with below- average rainfall, whereas rainfall in 1994 through September 1995 was higher than average. The Tafunafou-Malaeimi-Mesepa well field and the Leone-Malaeloa well field each pumped about 2.4 to 4 million gallons per day. Chloride concentrations of water pumped from the well fields were usually less than 500 milligrams per liter but chloride concentrations have exceeded 500 milligrams per liter during periods when rainfall was below average. Iliili wells pumped about 1.3 to 1.4 million gallons per day from four production wells, three of which had chloride concentrations under 200 milligrams per liter, and the fourth having chloride concentrations usually under 500 milligrams per liter. Water in wells at Aua, Fagaitua, Alofau, Alao, Tula, and Sailele had chloride concentrations frequently in excess of 500 milligrams per liter. Water levels at Aua during pumping dropped as low as 60 ft below sea level. Chloride concentrations at Fagaalu, and Aoa have remained below 200 milligrams per liter and chloride concentrations at Fagasa have usually remained below 500 milligrams per liter. These well fields have been pumped for less than 5 years at pumpage rates of less than 0.1 million gallons per day at each well field. The Fagatogo and Pago Pago well fields have each produced about 0.75 to 1.0 million gallons per day while maintaining chloride concentrations below 100 milligrams per liter. Water levels in monitor wells in these well fields have dropped below sea level on occasion. Chloride concentrations on Aunuu frequently exceeded 500 milligrams per liter and reached nearly 2,000 milligrams per liter since the wells began pumping in 1992 at a rate of 0.01 to 0.03 million gallons per day each.