U.S. Department of the Interior
Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997
U.S. GEOLOGICAL SURVEY Open-File Report 99-252
OCEAN
Bay
Prepared In cooperation with the AMERICAN SAMOA ENVIRONMENTAL PROTECTION AGENCY Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997
By Scot K. Izuka
U.S. GEOLOGICAL SURVEY Open-File Report 99-252
Prepared in cooperation with the
AMERICAN SAMOA ENVIRONMENTAL PROTECTION AGENCY
Honolulu, Hawaii 1999 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY Charles G. Groat, Director
The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.
For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 677 Ala Moana Blvd., Suite 415 Box 25286 Honolulu, HI 96813 Denver, CO 80225-0286 CONTENTS
Abstract...... 1 Introduction...... 1 Setting...... 2 Acknowledgments ...... 2 Rainfall ...... 2 Western Tutuila Ground-Water Data...... 5 Tafunafou ...... 5 Malaeimi-Mesepa...... 5 Iliili...... 11 Malaeloa-Leone ...... 11 Aasufou...... 15 Central Tutuila Ground-Water Data...... 15 Fagaalu...... 17 Fagatogo...... 17 Pago Pago...... 17 Aua ...... 20 Laulii...... 21 Fagasa...... 22 Eastern Tutuila and Aunuu Ground-Water Data ...... 24 Auto ...... 26 Fagaitua...... 26 Alofau...... 27 Amouli ...... 27 Alao...... 28 Tula...... 28 Aoa ...... 30 Sailele...... 30 Masefau...... 31 Aunuu...... 31 Summary ...... 32 References Cited ...... 33 Appendix...... 33 Data Processing...... 33
Contents iii FIGURES 1. Map of Tutuila and Aunuu Islands, American Samoa ...... 3 2. Graphs showing monthly rainfall recorded at the Aasufou and Afono rain gages, Tutuila, American Samoa ... 4 3. Map showing wells in western Tutuila, American Samoa...... 6 4-12. Graphs showing: 4. Ground-water pumpage and chloride concentrations in Tafunafou, Tutuila, American Samoa...... 7 5. Ground-water levels in Tafunafou, Tutuila, American Samoa...... 9 6. Ground-water pumpage and chloride concentrations in the Malaeimi-Mesepa area, Tutuila, American Samoa...... 10 7. Ground-water levels in the Malaeimi-Mesepa area, Tutuila, American Samoa...... 11 8. Ground-water pumpage and chloride concentrations in Iliili, Tutuila, American Samoa ...... 12 9. Ground-water levels in Iliili, Tutuila, American Samoa...... 13 10. Ground-water pumpage and chloride concentrations in the Malaeloa-Leone area, Tutuila, American Samoa 13 11. Ground-water levels in Malaeloa, Tutuila, American Samoa...... 14 12. Ground-water pumpage and chloride concentrations in Aasufou, Tutuila, American Samoa...... 15 13. Map showing locations of wells in central Tutuila, American Samoa...... 16 14-25. Graphs showing: 14. Ground-water pumpage and chloride concentrations in Fagaalu, Tutuila, American Samoa ...... 18 15. Ground-water levels in Fagaalu, Tutuila, American Samoa...... 18 16. Ground-water pumpage and chloride concentrations in Fagatogo, Tutuila, American Samoa...... 18 17. Ground-water levels in Fagatogo, Tutuila, American Samoa...... 19 18. Ground-water pumpage and chloride concentrations in Pago Pago, Tutuila, American Samoa...... 19 19. Ground-water levels in Pago Pago, Tutuila, American Samoa...... 20 20. Ground-water pumpage and chloride concentrations in Aua, Tutuila, American Samoa ...... 21 21. Ground-water levels in Aua, Tutuila, American Samoa...... 22 22. Ground-water pumpage and chloride concentrations in Laulii, Tutuila, American Samoa ...... 23 23. Ground-water levels in Laulii, Tutuila, American Samoa ...... 23 24. Ground-water pumpage and chloride concentrations in Fagasa, Tutuila, American Samoa ...... 24 25. Map showing wells in eastern Tutuila and Aunuu, American Samoa ...... 25 26-35. Graphs showing: 26. Ground-water pumpage and chloride concentrations in Auto, Tutuila, American Samoa...... 26 27. Ground-water pumpage and chloride concentrations in Fagaitua, Tutuila, American Samoa...... 26 28. Ground-water pumpage and chloride concentrations in Alofau, Tutuila, American Samoa ...... 27 29. Ground-water levels in Amouli, Tutuila, American Samoa...... 27 30. Ground-water pumpage and chloride concentrations in Alao, Tutuila, American Samoa...... 28 31. Ground-water pumpage and chloride concentrations in Tula, Tutuila, American Samoa ...... 29 32. Ground-water pumpage and chloride concentrations in Aoa, Tutuila, American Samoa ...... 30 33. Ground-water pumpage and chloride concentrations in Sailele, Tutuila, American Samoa ...... 31 34. Ground-water pumpage and chloride concentrations in Masefau, Tutuila, American Samoa...... 31 35. Ground-water pumpage and chloride concentrations on Aunuu, American Samoa...... 32
iv Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 Conversion Factors
Multiply by to obtain inch (in.) 2.54 centimeters foot (ft) 0.3048 meter mile, statute (mi) 1.609 kilometers square mile (mi2) 2.590 square kilometers gallons per day (gal/d) 3.785 liters per day million gallons per day (Mgal/d) 0.04381 cubic meter per second
Abbreviations used in water-quality descriptions mg/L = milligrams per liter
Vertical datum All elevations in this report are referenced relative to mean sea level.
Contents v Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997
By Scot K. Izuka
Abstract Most wells in central and eastern Tutuila were pumped at rates less than 0.1 million gallons per Ground-water and rainfall data for the period day. Wells in the Fagatogo, Pago Pago, and Aua October 1987 through September 1997 from Tutu areas, which averaged more than 0.4 million gal ila and Aunuu, American Samoa, are plotted in lons per day of pumpage, are exceptions. Some time-series graphs and summarized. The data wells in central and eastern Tutuila had chloride include pumpage and chloride concentrations from concentrations that frequently exceeded 500 milli 53 production wells on Tutuila, including 5 new grams per liter. In the 12-month period ending Sep wells that were put into production between Octo tember 1997, chloride concentrations in the ber 1996 and September 1997, 3 production wells production wells in Aua rose to the highest levels on Aunuu, water-level measurements from 16 on record. In the 12-month period ending Septem wells on Tutuila, and rainfall data from 2 gages on ber 1997, water levels in Tafunafou, Iliili, Pago Tutuila. Pago, and Laulii remained at about the same eleva tion above mean sea level as in previous years, Mean annual rainfall was 164 inches at the water levels in Aua remained below mean sea level gage in Afono and 210 inches at the gage in Aasu- as in previous years, and water levels in Malaeimi fou during the period October 1987 through Sep and Fagaalu declined relative to previous years. tember 1997. Rainfall in the 12-month period from October 1996 through September 1997 totaled 210 The three production wells on Aunuu have inches at the Afono gage and 234 inches at the been pumped at various rates less than 0.1 million Aasufou gage. gallons per day and had chloride concentrations usually in excess of 500 and often in excess of In the Tafuna-Leone Plain, most wells were 1,000 milligrams per liter. pumped at rates from 0.2 to 0.5 million gallons per day and had chloride concentrations usually less than 500 milligrams per liter. In the 12-month INTRODUCTION period ending September 1997, the combined pumpage from wells in the Tafuna-Leone Plain The American Samoa Government, through the was about 6.3 million gallons per day and the chlo American Samoa Environmental Protection Agency ride concentrations in most wells remained below (ASEPA), American Samoa Power Authority (ASPA), 200 milligrams per liter. In Aasufou, wells pro and the Department of Public Works (DPW), has main tained a cooperative effort with the U.S. Geological duced 0.04 to 0.05 million gallons per day and Survey (USGS) to collect the principal data needed to chloride concentrations remained near 15 milli monitor ground-water resources on Tutuila, the largest grams per liter. and most populated island in the South Pacific
Abstract archipelago of American Samoa, and the small, nearby part of Tutuila is composed of Pliocene- to Pleistocene- island of Aunuu (fig. 1). For convenience of discussion, age shield-volcano alkalic basalts, andesites, and tra the wells on Tutuila are grouped into three regions, chytes that have relatively low permeabilities (Stearns, western, eastern and central, as shown in figure 1. The 1944; Macdonald, 1944, 1968; Davis, 1963; Bentley, data are discussed by area (groups of closely spaced 1975). The Tafuna-Leone Plain is composed of younger wells) within each of the regions. Following the well- (Holocene age), more permeable lava flows and pyro- naming convention used by ASPA, the areas in this clastic cones (Stearns, 1944; Davis, 1963; Bentley, report bear the name of the nearest village. 1975). Ground-water production is high on the Tafuna- This report summarizes pumpage and chloride- Leone Plain. Elsewhere on Tutuila, wells are located in concentration data from 53 wells on Tutuila and 3 wells small valleys or low-lying areas near the coast. Wells on Aunuu that were in production during the period drilled on the top of Olotele Mountain near Aasufou are October 1987 through September 1997. Although some the only exception. of these wells have not been pumped in recent years, The small island of Aunuu (0.6 mi2), less than 1 mi they are included in this report for historical purposes. off the southeastern shore of Tutuila, is a tuff (consoli The concentration of chloride ions is an indicator of the dated volcanic ash) cone with a coastal plain on its salinity of ground water pumped from wells; salinity is western side. The coastal plain is about 2,000 ft wide in a principal factor limiting the availability of ground the east-west direction and 4,000 ft long in the north- water on oceanic islands. south direction and is composed of partly consolidated The report also summarizes water levels monitored marine and terrigenous sediment. Two marshes are in the period from October 1987 through September present on Aunuu: one in the center of the tuff cone and 1997 at 15 non-pumping wells and 1 pumping well on the other at the inland edge of the coastal plain where it Tutuila. Rainfall data from the same period from two abuts the slope of the tuff cone. All of the ground-water gages are summarized in this report to allow compari production on Aunuu comes from wells in the coastal sons with the ground-water data. plain sediments. This report is the third in a series of ground-water data summaries (Izuka, 1996, 1997). The purpose of these reports is to present the data in time-series graphs Acknowledgments to facilitate analysis of trends. Each successive report in the series updates the previous report by adding the next This report was produced under a cooperative 12 months of data. The discussion of the data for most agreement with the ASEPA. Data were collected by the areas is presented in two parts consisting of: (1) a gen ASPA. The author gratefully acknowledges Togipa eral description of the well field and long-term history, Tausaga (Director, ASEPA), Abe Malae (Director, and (2) a section highlighting trends in the most recent ASPA), Sheila Wiegman (ASEPA), and Wilfredo 12 months and comparing them to trends in the previous Carreon (ASPA) for their assistance. years (except when an area either has no data in the most recent 12-month period, or has data only from the RAINFALL most recent 12-month period). Mean annual rainfall at the gage in Afono near Setting Pioa Mountain was 164 in. and 210 in. at the rain gage in Aasufou (fig. 1), during the period October 1987 Tutuila is a volcanic island of about 53 mi2 in the through September 1997. Plots of mean monthly rain tropical South Pacific (fig. 1). The island is narrow and fall show a seasonal pattern with a wet season from elongate in the east-west direction and characterized October through April and a dry season from May to mostly by steep, deeply eroded mountains that rise September (fig. 2). The seasonal pattern is also apparent abruptly from the ocean to elevations as high as 2,140 in the 3-month backward-looking moving average in ft. The exception to this general topography is the rela the period between 1987 and 1992, but is obscured in tively flat Tafuna-Leone Plain in the southwest which the relatively high rainfall period between late 1994 extends from Tafunafou to Leone. The mountainous through 1995.
2 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 170°50' 170°45' 170°40' 170°35'
1 Afono rain gage » -* Pago Pago Harbor
CENTRAL Cape Taputapu TUTUILA
14°20'
3 MILES I 0 1 3 KILOMETERS
30 D) I Figure 1. Tutuila and Aunuu Islands, American Samoa and geographic divisions used in this report. AASUFOU RAIN GAGE AFONO RAIN GAGE I.U i i I i 0.7
0.6 0.8 - - i n 0.5 0.6 1| V j±UJ If |p ill 0.4 1 . > 1 *;; 11 11 j; Is i ' - " . 0.4 1 1 ; ; 0.3
. 'i ! i Ni" 0.2 ^ ...... ». ,.... 02 O N D J F M A M J J A S ONDJFMAMJJAS MONTH MONTH
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
1988 1989 1990 1991 1992 1993
AASUFOU croc LJJUJ >°- < U) uj
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
mx it
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
Figure 2. Rainfall recorded at the Aasufou and Afono rain gages, Tutuila, American Samoa.
4 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 Trends during the 12-month period ending Sep Trends during the 12-month period ending Sep tember 1997. Rainfall in the 12-month period from tember 1997.- Only wells 33, 60, 61, 72, and 81 had October 1996 through September 1997 totaled 210 in. at reported pumpages in the 12-month period ending Sep the Afono gage, and 234 in. at the Aasufou gage. Both tember 1997. Pumpage at well 33 continued in an irreg of these totals are higher than the mean annual rainfall ular pattern as it had since 1991. Pumpage at well 60 for the 10-year period October 1987 through September was about 0.4 Mgal/d, a rate at which the well had been 1997. pumped since early 1996. Well 60 was pumped at about 0.4 Mgal/d as it had been since early 1996, and well 72 was pumped at about 0.5 Mgal/d as it had been since WESTERN TUTUILA GROUND-WATER 1995. Pumpage at wells 61 and 81 remained about the DATA same as in the previous 9 years (fig. 4). The total pro duction from wells in Tafunafou averaged 1.6 Mgal/d Western Tutuila is the site of the most productive over the 12-month period. wells on Tutuila, including the those on the Tafuna- Leone Plain, which include wells in Tafunafou, Malae Prior to October 1996, all Tafunafou wells for imi, Mesepa, Iliili, and Malaeloa (fig. 3). Also included which data are available had shown increases in chlo in western Tutuila are the wells in Aasufou near the ride concentrations, but chloride concentrations summit of Olotele Mountain (in previous reports of this decreased during the 12-month period since October series [Izuka, 1996, 1997], this area was referred to as 1996. Water levels at monitor wells 1, 2, and 5 have Aoloaufou based on the 1:24,000-scale topographic continued the long-term trend, varying within 1 or 2 ft map by the USGS [1989], but in this report the area is of mean sea level through most of this period (fig. 5). referred to as Aasufou, which is how it is referred to by ASPA). Malaeimi-Mesepa
Wells 67, 69, 88, and 89 are in Malaeimi Valley, Tafunafou and well 85 is in Mesepa (fig. 3). Well 67 has pumped The wells in Tafunafou (fig. 3) are among the most an average of 0.3 Mgal/d over the period shown in fig productive on Tutuila. The wells are densely clustered ure 6. Well 85 was pumping at about 0.3 Mgal/d in 1984, but pumpage was increased to about 0.5 Mgal/d in the village of Tafunafou and each has produced about in 1986. Well 88 produced about 0.2 to 0.4 Mgal/d 0.2 to 0.5 Mgal/d over various periods (fig. 4). Most between 1991 and 1994, was not in operation for 2 years wells show long periods of relatively steady pumping beginning late 1994, then resumed pumping at about 0.2 rates interrupted occasionally by periods of low or no to 0.5 Mgal/d in late 1996. Pumpage at well 89 began in pumpage (on the pumpage graphs, a wide bar that is 1985 at about 0.2 to 0.4 Mgal/d and increased to 0.5 much lower than the adjacent bars may indicate that Mgal/d in late 1989. Chloride concentrations in water non-pumping periods are included in that interval [see from these wells have remained below 60 mg/L. appendix]); two wells (61 and 81) have been pumped continuously at nearly the same rate for the entire 10- Well 69 began pumping in 1988 and produced year period shown in figure 4. Chloride concentrations about 0.01 Mgal/d until early 1990, but chloride con centrations rose to more than 500 mg/L despite the low at Tafunafou wells have varied over a large range from pumping rate (fig. 6); no pumpage has been reported 15 to more than 1,500 mg/L, but, with the exception of from this well since 1990. wells 53 and 77, Tafunafou wells have produced water with chloride concentrations mostly below 500 mg/L. Water-level monitoring began at well 88 in 1991, The time-series graphs of chloride concentration show while it was still a production well. Water levels mea a sawtooth pattern, with gradual rises during dry periods sured during pumping dropped as much as 72 ft below and sharp drops during rainy periods (figs. 2 and 4). mean sea level (fig. 7). The well stopped production in Water levels in non-pumping monitor wells in Taf late 1994, at which time water levels began to rise as unafou varied mostly within 1 or 2 ft of mean sea level high as 90 ft above mean sea level before pumping resumed again in late 1996. (fig- 5).
Western Tutuila Ground-Water Data 5 170°50' 170°48' 170°46' 170°44' 170°42'
14°20' Pago Pago International Airport
WELL AND NUMBER Aasufou 14°22' -1-
Figure 3. Wells in western Tutuila, American Samoa. TAFUNAFOU 33 0.60 1111111111111111111111111 u 11 n 111111111111111111111111111111111111111111111111111111
400
TAFUNAFOU 46 0.60 111111111111111111 n 1111111111111111111111111111 n 11111111111111111111 iiiiiimiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiinil 1,200
0.40 - - 800
0.20 - - 400
1997
TAFUNAFOU 53 0.12 2.000
0.09 1,500
0.06 1,000
0.03 500
0 .L.....L... 0 1994 1995 1996 1997
TAFUNAFOU 60 1.00
TAFUNAFOU 61 11111111 800
1988 1997
Figure 4. Ground-water pumpage and chloride concentrations in Tafunafou, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.)
Western Tutuila Ground-Water Data 7 TAFUNAFOU 66 0.80
1997
TAFUNAFOU 72
TAFUNAFOU 77 O ^ 0.081 1,600 <
1,200
800
400 ~
1990 1991 1992 1993 1994 1995 1996 1997 O
TAFUNAFOU 81 0.80 400
1997
Figure 4. Ground-water pumpage and chloride concentrations in Tafunafou, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) -Continued.
8 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 -10 1990 1991 1992 1993 1994 1995 1996 1997
TAFUNAFOU 2
20IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIMIIMIIIIIIIIMIIIIIIIIIMMIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIMIIIIIIIII
10 w»^«] VM.W"******^"*-"**" /» * *»*^» H,
_1Q II I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I 1988 1989 1990 1991 1992 1993 1994 1995 1996 I 1997
TAFUNAFOU 5
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
DATE
Figure 5. Ground-water levels in Tafunafou, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.)
Western Tutuila Ground-Water Data 9 MALAEIMI 67 1.00
1997
MALAEIMI 69
U.UH 1 ' i 1 1 1 i 1 1 M i 1 1 M i 1 1 1 1 i 1 1 1 i i i M i 1 1 i 1 1 1 1 i 1 1 1 1 1 1 1 1 i M i 1 1 1 1 1 i i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 1 i i M 1 1 1 1 1 i 1 1 M 1 1 1 1 1 1 1 1 1 1 1 i M 1 1 i 1 1 1 1 1 1 i i 1 1 1 i 1 1 1 - OUU
0.03 - . - 600 0.02 - M*\ + +} - 400 0.01 it, \J"i - 200 If [ jfj JJVJU _f^l|fl J DC 1 11 Hilt 11 npj ml II _____[;:";-' H LU 0 1 1 r i yiiiyirify nttliyyiir'r'r'rii::- :m M i i i i M i MM i M i i M i i i MM 1 1 i M i i i i i i i i M i \ \ i i i i i i i i i i i i i i i i i 1 1 i i i i M in i n t 1 988 I 1 989 1990 1 99 1 1 992 1 993 1 994 1 995 1 996 1997 ** ^ LU S D. Q CO LU MALAEIMI 88 < D. tr co 0-60 1 1 1 1 1 1 II 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 I M I 1 1 I 1 1 I 1 1 I 1 I M 1 1 1 I I 1 1 M 1 I 1 I 1 1 1 I 1 1 I 1 1 I I 1 1 1 I 1 1 1 I 1 1 1 1 I 1 1 1 1 1 I 1 II 1 1 I I 1 1 1 1 II 1 1 1 1 1 1 1 I 1 1 I 1 1 1 I 1 1 1 1 1 -.60 CD z _i O - _i 2 _ - ( < 0.40 i_ If 40 2 O M r-j __ l\ ^] p i ; ; z"
O fi | rrn.Llip| | 1 O - i^1 Ij 0.20 l^-Jw%C-^i^/ miw^i ^ 20
0 1 i | !YTJlir«lilu(lilliil»lll yUllillillUll HSHIIrtlil JlltlUi i 1 i l i ill i i i i i i i i iiiiriilti iliriTifili'ilifJllIt llliflidHI lilfllM MtJtiMtili JtiJi; :iS : ri!f6il[lli ill 1i : i 1 1 1 1 1 n 1988 | 1989 | 1990 1991 1992 1993 1994 1995 1996 1997
MESEPA 85 0.80
Figure 6. Ground-water pumpage and chloride concentrations in the Malaeimi-Mesepa area, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.)
10 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 MALAEIMI 88
1997
Figure 7. Ground-water levels in the Malaeimi-Mesepa area, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.)
Trends during the 12-month period ending Sep over this period. Chloride concentrations in well 84 fre tember 1997. The total production from wells in the quently exceeded 500 mg/L and show a gradually Malaeimi-Mesepa area averaged 1.6 Mgal/d in the 12- increasing trend since 1987. Water levels monitored at month period ending September 1997 (fig. 6). Wells 67 well 115 have varied by ±2 ft around a median of about and 85 continued pumping at rates close to their long- 5 ft (fig. 9). term average rates of 0.3 to 0.6 Mgal/d. Chloride con Trends during the 12-month period ending Sep centrations in water from both wells remained below 60 tember 7P97.--During the 12-month period ending Sep mg/L throughout this period. The highest chloride con tember 1997, total production from wells in Iliili centration reported from well 85 (50 mg/L) was mea averaged 1.1 Mgal/d. Pumpage at wells 62, 79, and 84 sured in December 1996. continued at about the same rate as in the previous 3 Well 89 pumped at about 0.5 Mgal/d until March years (fig. 8). Well 76 continued to pump at about 0.3 1997, and was shut down in April 1997 because of Mgal/d as it had since April 1996. Chloride concentra mechanical problems. Chloride concentrations in this tions in wells 62, 76, and 79 declined in late 1996, but well during pumping remained below 40 mg/L (fig. 6). from then until September 1997 fluctuated a few tens of Pumpage at well 88 has averaged 0.3 Mgal/d milligrams per liter around a median of about 100 mg/L. between October 1996 and September 1997 (fig. 6). Chloride concentrations in well 84 continued on a grad Chloride concentrations from this well have varied ual rising trend that began in 1987. Water levels at well between 15 and 30 mg/L during this period. 115 during this period continued to show the same vari ation of 1 to 2 ft around a median of about 5 ft above Water levels in well 88 in the 12-month period mean sea level, as in the previous 9 years (fig. 9). ending September 1997, which corresponds approxi mately to the period when pumping resumed at the well, declined sharply (fig. 7). The water level in the well was Malaeloa-Leone as low as 24 ft below mean sea level (October 1997) during this period. The Malaeloa-Leone area (fig. 3) has six produc tion wells, 70, 80, 91, 92, 93, and 119, which have pumped a total of about 2.2 Mgal/d since 1987 (fig. 10). mm Chloride concentrations in wells 70,80,91, and 92 have remained under 100 mg/L over the entire period of Iliili is on the Tafuna-Leone Plain less than 1 mile pumping. Chloride concentrations in well 93 have risen from the southern coastline of Tutuila (fig. 3). Four periodically to about 100 mg/L during periods of lower- wells, 62,76,79, and 84 have produced a total of about than-average rainfall (compare with Aasufou rainfall 1.2 Mgal/d since 1987 (fig. 8). Chloride concentrations record, fig. 2), but remained below 50 mg/L over most at wells 62, 76, and 79 have remained below 250 mg/L of the pumping period.
Western Tutuila Ground-Water Data 11 0.20 -
1997
ILIILI 76 0.60 | 111111111111111111111 300
0.40 - - 200
- 100
ILIILI 79 0.40 200
0.30 150
0.20 100
0.10 50
0 ilktlli tiu.iL .1 juiiui. m liiiiii until it I Minimi ..1.1.1 tminlti ±11 '.»':! i . i': Q 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
ILIILI 84 0.80 800
Figure 8. Ground-water pumpage and chloride concentrations in Iliili, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.)
12 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 ILIILI115 h- LU UJ-J 10
_ LU LU
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
DATE
Figure 9. Ground-water levels in Iliili, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.)
MALAELOA 91 1.00
MALAELOA 92 0.60 on
n n- 040 i n - 80 , '-: / 1 : < i ~~ ;q rf~~1 n - 40 0.20 - ; Fl 'i _ 4- t j SHH 1 ", »t** )( ( \ i'f H ^ ', i < \, 0 1 1 , 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 l'l t¥l till 1 !'I 1 1 II t t t 1 111 I in III 1 I I LI I I 1 1 1 j i mi 1 n. LLL i 1 1 i i i il LL J K .. r\ 1988 1989 | 1990 1991 1992 1993 1994 1995 1996 1997
MALAELOA 93
DATE Figure 10. Ground-water pumpage and chloride concentrations in the Malaeloa-Leone area, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.)
Western Tutuila Ground-Water Data 13 LEONE 80 0.80
LEONE 70 0.80 11111111111111111111111111111111111111111111111 80
1997
Figure 10. Ground-water pumpage and chloride concentrations in the Malaeloa-Leone Area, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) - Continued
MALAELOA 92
HI < U- ID
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 LII tr
Figure 11. Ground-water levels in Malaeloa, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.)
Chloride concentrations in well 119 have exceeded Water levels were monitored at well 92 until 1990, 500 mg/L several times during the period of record (fig. during which time water levels fluctuated 1 to 10 ft 10). As in well 93, the chloride concentrations in well above mean sea level (fig. 11). Water levels have not 119 peaked during periods of lower-than-average rain been monitored in this area since 1990. fall, except that the peaks were more frequent and rose Trends during the 12-month period ending Sep to higher concentrations at well 119. Time-series graphs tember 1997.~During the 12-month period ending Sep of chloride concentration in both well 93 and well 119 tember 1997, total production from wells in the show a sawtooth pattern similar to the pattern seen in Malaeloa-Leone area averaged 2.0 Mgal/d (fig. 10). the Tafunafou chloride-concentration record. Pumpage at wells 70, 80, and 93 in the Malaeloa-Leone
14 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 AASUFOU 128
0.08 _ 40
0.06 - n - 30 --> k i. t- 0.04 - Ifl1 Lr 20 ; f' f M*, 0.02 y T : 10 U| 0 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I I I I I I M I 1 1 1 1 1 1 1 1 1 1 1 I M I I I I I I 1 I 1 1 1 1 1 1 1 1 1 1 1 II I 1 M 1 1 I 1 1 1 1 1 M \ 1 1 in ,«, ,, :,, L L J.L 1 lit I it - 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 | 1997
AASUFOU 129 0.08
0.06
0.04
0.02
1988 1989 1990 1991 1992 1993 1997
DATE
Figure 12. Ground-water pumpage and chloride concentrations in Aasufou, Tutuila, American amoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.)
area was about the same as in previous years shown in Trends during the 12-month period ending Sep the graphs in figure 10. Pumpage at well 119 was higher tember 1997.--During the 12-month period ending Sep than in mid-1995 to mid-1996. Pumpage at well 91 was tember 1997, pumpage averaged 0.05 Mgal/d at well halted near the end of 1996, but resumed in 1997 at 128 and 0.030 Mgal/d at well 129, which is the same as about the same rate (0.4 Mgal/d) as in the previous 9 the average rate of pumpage since the wells began pro years. Pumpage at well 92 was reduced and stopped in duction in 1994 (fig. 12). Chloride concentrations in late 1996 and early 1997, but resumed in February 1997 both wells have remained at 15 mg/L throughout this at about 0.3 Mgal/d. period. Chloride concentrations in all wells except well 119 remained below 100 mg/L during the 12-month CENTRAL TUTUILA GROUND-WATER period ending September 1997. Chloride concentrations DATA in well 119 were below 250 mg/L during most of this period, except in July 1997 when chloride concentra Most of the wells in central Tutuila lie in small val tions reached 540 mg/L. leys surrounding the embayment of Pago Pago Harbor (fig. 13). Wells in Fagaalu, Fagatogo, Pago Pago, and Aasufou Aua lie in valleys whose mouths form smaller embay- ments nested within the larger embayment of Pago Pago Wells 128 and 129 in Aasufou develop water from Harbor. To the north of the harbor a high cliff extends pyroclastic deposits at the crest of Olotele Mountain eastward from Pago Pago to Aua. Fagasa and Laulii lie (fig. 3). The wells have pumped about 0.03 to 0.05 in valleys outside the drainage area of Pago Pago Har Mgal/d each since they were put in production in 1994 bor. (fig. 12). Chloride concentrations have remained less Because of the large natural harbor in Pago Pago, than 20 mg/L throughout most of the pumping period. central Tutuila is the industrial center on the island. Vil No water levels have been reported for Aasufou. lages lie mostly on the relatively flat valley floors and
Central Tutuila Ground-Water Data 15 170°44 170°38'
EXPLANATION 1 °7 WELL AND NUMBER Afono
Figure 13. Wells in central Tutuila, American Samoa. coastal plain and extend a short distance up the adjoin about 1 Mgal/d from 1986 to 1988. From 1988 to 1992, ing hillsides. Ground water is developed mostly from well 101 was shut off and well 102 was pumped at a rate wells in the valleys, but a pipeline connects the southern of about 0.9 Mgal/d (fig. 16). Pumpage was switched shore of central and eastern Tutuila with the more pro back to well 101 in 1992 but reduced to about 0.5 ductive wells of western Tutuila. The wells in Fagasa Mgal/d. Chloride concentrations at both pumped wells are not connected to this pipeline. remained mostly below 50 mg/L throughout the period of record. Fagaalu Water levels monitored in well 101 in 1986 prior to the beginning of pumping were about 20 ft above mean Ground-water in Fagaalu on the western side of sea level (Izuka, 1996,1997). Between 1988 and 1992, Pago Pago Harbor (fig. 13) is produced from well 127, when well 102 was being pumped and well 101 was which has been pumped intermittently at an average of used only for water-level monitoring, water levels in about 0.05 Mgal/d since late 1992 (fig. 14). Chloride well 101 were near mean sea level, and occasionally concentrations from this well remained below 100 mg/L dropped 2 to 3 ft below mean sea level (fig. 17). For a during this period. brief period in mid-1992, pumping at both 101 and 102 ceased, and water levels in well 101 began to rise. Water levels in Fagaalu have been monitored at well 126 since 1987 (fig. 15). Before 1989, water levels Trends during the 12-month period ending Sep at well 126 were between 70 and 80 ft above mean sea tember 7PP7.--Pumping at well 101 during the 12- level. The well was deepened in 1989 and the upper part month period ending September 1997 continued at sealed to prevent seepage from a nearby stream. After about 0.5 Mgal/d, which is about the same rate as in pre the well was sealed, the water level dropped to about 25 vious years since pumping resumed in 1992 (fig. 16). ft above mean sea level, then climbed to about 60 ft Chloride concentrations in the well have remained between 1989 and 1991. Between 1991 and early 1996, under 50 mg/L. water levels remained near 60 ft above mean sea level, then dropped sharply to about 30 ft. Reasons for this Pago Pago second sharp drop are not yet known. Trends during the 12-month period ending Sep Pago Pago, located at the farthest inland extension tember 1997. Pumpage at well 127 rose sharply in of the Pago Pago Harbor embayment, has production mid-1996 (fig. 14). In the 12-month period ending Sep wells 105, 107,163, and 165 (fig. 13). Between 1988 tember 1997, pumpage at well 127 averaged 0.13 and 1995, well 105 was pumped at a rate of about 0.2 Mgal/d, which is more than double the average pump- Mgal/d, except when pumping was halted briefly in late age of the previous 4 years (0.05 Mgal/d). Pumpage in 1991. Beginning in mid-1995, the well was pumped August and September 1997 exceeded 0.20 Mgal/d. intermittently. Well 107 has been pumped at about 0.5 Chloride concentrations in water from the well have Mgal/d (fig. 18) since late 1988. Well 163 began pump continued on an increasing trend that began in mid- ing in mid-1995 at about 0.4 Mgal/d, and a new produc 1995, although the concentrations did not exceed 100 tion well, 165, began pumping in late 1997. All of the mg/L. Pago Pago wells have maintained chloride concentra tions of less than 50 mg/L throughout their periods of After water levels in monitor well 126 dropped to record. about 30 ft above mean sea level in early 1996, water levels fluctuated within a few tens of feet of this eleva Pre-pumping water levels at well 105 fluctuated tion through September 1997 (fig. 15). between 47 and 50 ft above mean sea level (fig. 19). Pumping water levels are not available at well 105. Water levels at well 107 during pumping initially Fagatogo declined from about 20 ft to about 3 ft above mean sea level and dropped as low as 1 ft below mean sea level Pumpage in the Fagatogo area (fig. 13) has alter between 1989 and 1990, but have remained at about 5 ft nated between wells 101 and 102. Well 101 produced above mean sea level since then.
Central Tutuila Ground-Water Data 17 FAGAALU127
Figure 14. Ground-water pumpage and chloride concentrations in Fagaalu, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.)
FAGAALU 126
Figure 15. Ground-water levels in Fagaalu, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.)
FAGATOGO 101
oiv>i\-*-"-i-» 8bbIntnc
oooooooc t- oooooooc CHLORIDECONCENTRATION,MILLIGRAMSINPERLITE ^v/-. nfl AOIOAOOo10moo PUMPAGE,INMILLIONGALLONSPERDAY mJ yt =t \ - 11II nwI ? 1988 1989 1990 19£ 1 1992 1993 1994 1995 1996 1997
FAGATOGOK32
- J fl nil , rill i, , liiiili 1 1 1 1 1 ,nfl [],,,,,,,, , i , , , , , i , , , i , , i , , , , 1 1 , i , , , 1988 1989 1990 19£ 1 1992 1993 1994 1995 1996 1997
DATE
Figure 16. Ground-water pumpage and chloride concentrations in Fagatogo, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.)
18 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 PUMPAGE, IN MILLION GALLONS PER DAY WATER-LEVEL, IN FEET RELATIVE TO MEAN SEA LEVEL
Q. co -n 8. fi» (5- co 3 c o 1 S S 5 io* CD Q. -« ' o o l§ CD *< S.?1 CD CI Q) 00 2. -3 COO Wf/> Z3 Q) CO <. lii CO (/) 55 S 3 Q) CD W -o O CO > TJ C a 3 111 CO ?P_ . . s 13 W O CD CD s = CO O Tl CO 3 Q. O O 3 CO 3;_, 3- s! I-O s"D w... °o' I s § CD C_ &s;§> 0) O "f F fl0) > ^§ IT O o ^ (D 0) =
II3 Co QL O f« CD p 5f ^ ? 13 CO m CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER PAGO PAGO 105 1997 UJ UJ UJ ^ tr ^ PAGO PAGO 107 UJLLJ 30 20 10 0 -10 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 19. Ground-water levels in Pago Pago, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) Trends during the 12-month period ending Sep since pumping began. Pumpage at well 97 began at tember 1997.- In late 1996 through early 1997, well about 0.4 Mgal/d and initial chloride concentrations 105 was pumped intermittently at an average rate of were below 100 mg/L, but after about 2 years of steady 0.02 Mgal/d as it had been since 1995, but in mid-1997, pumping, chloride concentrations began rising sharply. pumping was increased to 0.2 to 0.4 Mgal/d. In the 12- By late 1987, pumpage at well 97 had been halted month period ending September 1997, pumpage at well because of rising chloride concentrations, and between 107 averaged 0.5 Mgal/d, which is about the same rate 1987 and 1990, the well was pumped only intermit maintained since 1988, and pumpage at well 163 aver tently. Chloride concentrations at the well decreased aged 0.3 Mgal/d, about the same rate since 1995 slowly when pumpage was lowered or halted, but (fig. 18). Pumpage at the new well (165) averaged 0.3 quickly rose again when pumpage resumed. In 1991 Mgal/d. pumping resumed at a more constant rate of about 0.4 Chloride concentrations in well 105 fluctuated, but Mgal/d, and chloride concentrations rose to more than did not exceed 50 mg/L. Chloride concentrations in 500 mg/L, occasionally exceeding 800 mg/L. wells 107 and 165 during the 12-month period ending Pumpage at well 99 began in 1985 at about 0.3 September 1996 have remained near 20 mg/L with fluc Mgal/d (Izuka, 1996, 1997). As in well 97, initial chlo tuations of about 10 mg/L. Chloride concentrations at ride concentrations were below 100 mg/L, but began the new well (165) ranged between 15 and 20 mg/L. steadily rising after about lV2 years. In late 1987, well Water levels monitored at well 107 remained at about 5 99 was still pumping at about 0.3 Mgal/d and this pump ft above mean sea level, as it has since 1994 (fig. 19). ing rate continued with few decreases to about 1989 (fig. 20). By late 1987, chloride concentrations were in Aua excess of 400 mg/L and remained near 400 mg/L most of the time from 1988 through 1990, even several Aua (fig. 13) has two wells that have pumpage months after pumpage was reduced to about 0.2 Mgal/d records between October 1987 and September 1997. in 1989. Chloride concentrations began declining in Well 97 began pumping in 1984 and well 99 began 1990 and by 1991, the chloride concentrations were pumping in 1985 (Izuka, 1996, 1997). Pumpages and near 200 mg/L. Chloride concentrations stayed at 100 to chloride concentrations at the wells have varied greatly 200 mg/L until mid-1994 when pumpage was increased 20 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 AUA97 0.80 2,000 1992 1993 1994 1995 1997 DATE Figure 20. Ground-water pumpage and chloride concentrations in Aua, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) to 0.5 Mgal/d and chloride concentration rose to more reached the highest concentration on record for the well than 500 mg/L. (740 mg/L) in September 1997. Water levels monitored in pumping well 99 in late During the 12-month period ending September 1985 through 1989 are nearly all below mean sea level, 1997, water levels in well 98 were 12 to 15 ft below some by as much as 60 ft (Izuka, 1996, 1997). Water mean sea level, as they had been since 1995 (fig. 21). levels measured in non-pumping well 98 began declin ing and have fallen to about 15 to 20 ft below mean sea level since nearby well 97 returned to production in Laulii 1991. Water levels measured at non-pumping well 103 have mostly remained a few feet above mean sea level Laulii, on the south coast of Tutuila about 0.5 mi but occasionally dropped a few feet below mean sea east of Pago Pago Harbor (fig. 13), has one pumping level during the period 1987 to 1992 (fig. 21). well (96) and one monitor well (106). Pumpage at well 96 averaged 0.07 Mgal/d through the period of record Trends during the 12-month period ending Sep (fig. 22). Chloride concentrations in this well have tember 1997. -- From October 1996 through April remained less than 100 mg/L over the period of record, 1997, pumpage at well 97 averaged 0.4 Mgal/d, which but show more variability since 1992. Water levels at is about the same rate as in previous months since mid- well 96 prior to pumping varied between 18 and 21 ft 1995 (fig. 20). Chloride concentrations in well 97 con above mean sea level (fig. 23). Water levels at well 106 tinued on a rising trend that began in 1995 and reached have fluctuated between 16 and 28 ft above mean sea the highest concentration on record for the well (1,200 level. mg/L) in April 1997. Pumpage at the well was halted in May 1997. Trends during the 12-month period ending Sep tember 7 PP7.--Pumpage at well 96 during the 12-month Between October 1996 and September 1997, period ending September 1997, averaged 0.08 Mgal/d pumpage at well 99 averaged 0.2 Mgal/d, which is an which is slightly higher than the average pumpage for increase compared with the average of the previous 12 the period of record (fig. 22). Chloride concentrations months (fig. 20). Chloride concentrations in well 99 during the 12-month period ending September 1997 continued on an increasing trend that began in 1995 and Central Tutuila Ground-Water Data 21 -20 1997 AUA99 -100 1988 1989 1990 1991 1992 | 1993 1994 1995 1996 1997 AUA 103 20 | | | | | I I I I I I I I I I M I I I I I I I I I I I I I I I I I I I I I I I M I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I -20 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 21. Ground-water levels in Aua, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) varied from 20 to 60 mg/L, which is similar to the vari below 100 mg/L from 1991 through early 1995, but ation in chloride concentrations recorded at this well fluctuated greatly since then, and occasionally since 1982. exceeded 400 mg/L. Water levels in monitor well 106 during the 12- Well 142 has been pumped intermittently at an month period ending September 1997 ranged from 16 to average rate of 0.005 Mgal/d since 1991, but pumpage 24 ft above mean sea level (fig. 23). The water level has been more persistent in the period from 1994 measured in November 1996 is the lowest on record for through 1996 (fig. 24). The range of variation in chlo this well. Water levels measured in December 1996, ride concentrations at well 142 increased since pumping and in May and June 1997 are among the lowest began in 1991, through 1995, and showed an overall recorded for this well. increasing trend. Chloride concentrations at this well decreased sharply in early 1995 corresponding to a brief period of reduced pumpage, then increased again in Fagasa 1996 when pumpage increased. Fagasa is in a small valley on the northern coast of Well 143 began pumping in 1997; its pumping rate central Tutuila (fig. 13). Well 141 in Fagasa has and chloride concentrations are discussed below. pumped intermittently with an average of 0.014 Mgal/d Trends during the 12-month period ending Sep (fig. 24). Chloride concentrations at well 141 remained tember 1997. Pumpage at well 141 averaged 0.021 22 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 LAULII 96 0.15 1992 1993 1994 1995 1996 1997 Figure 22. Ground-water pumpage and chloride concentrations in Laulii, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) LAULII 96 22 20 18 IT I- LU LU-" LU < LL LU 16 ^W 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 LAULII 106 m m LU cc 20 10 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 23. Ground-water levels in Laulii, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) Central Tutuila Ground-Water Data 23 rm600 - 400 0.02 - - 200 1997 FAG ASA 142 0.03 1,200 O 0.02 - - 800 0.01 - - 400 1997 FAGASA 143 0.015 - rr 30 0.010 - 20 0.005 10 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i,i 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 24. Ground-water pumpage and chloride concentrations in Fagasa, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) Mgal/d from October through December 1996; chloride cut into the island by stream erosion. Drowning of the concentrations ranged from 130 to 150 mg/L (fig. 24). lower parts of the valleys has created many embay- Pumpage at well 141 was halted in January 1997. ments along both the northern and southern coasts (fig. Pumpage at well 142 averaged 0.012 Mgal/d from 25). Valley-fill and coastal sediments create the only October through December 1996; chloride concentra flat-lying areas in this rugged part of the island. Eastern tions at this well during this period ranged from 115 to Tutuila is more sparsely populated than central and 360 mg/L (fig. 24). Pumpage at well 142 also was western Tutuila. Most of the population is distributed in halted in January 1997. Well 143 began pumping in small villages on the flat-lying terrain at the mouths of 1997 at an average rate of 0.007 Mgal/d and had chlo valleys. Ground water in eastern Tutuila has been devel ride concentrations ranging between 15 and 30 mg/L. oped from production wells in low-lying areas near the villages of Auto, Fagaitua, Alofau, Alao, Tula, Aoa, Sailele, and Masefau. A non-pumping well in Amouli EASTERN TUTUILA AND AUNUU has been used to monitor water levels. GROUND-WATER DATA Aunuu is an island off the southeastern shore of Tutuila (fig. 25). The population of Aunuu resides on a Eastern Tutuila is formed by steep mountains that coastal plain on the western end of the island. The area rise abruptly from the coastline. Short valleys have been is served by three infiltration galleries, also on the 24 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 170°40' 170°38' 170°36' 170°34' m Q) W » 3 g Q. I 5 o Q) ST Figure 25. Wells in eastern Tutuila and Aunuu, American Samoa. AUTO 166 §s 1 1 1 1 1 1 1 1 1 1 1 =!° 0.0015 - ,7 60 -_M 0.0010 - > 40 LiJ ^ ooc £§ 0.0005 20 2° 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 I 1 M 1 I 1 1 1 1 1 1 M 1 I 1 1 . n 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 26. Ground-water pumpage and chloride concentrations in Auto, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) FAGAITUA 125 < 0.03 _ ill _ 3,000 S 0.02 _ _ 2,000 CO J #>Jl 0 0.01 - - 1,000 IMI ^SrTw^i"; 0 0 ! ( 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 luiliLLI i ilirrii liiHini mild!, Hllilniii 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 z 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 O FAGAITUA 164 1 0.06 1,200 LU 0 I < 0.04 _ \- 800 CL 0.02 ;- 400 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I M II III 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 j 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 27. Ground-water pumpage and chloride concentrations in Fagaitua, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) coastal plain. Several small dug wells are used to obtain Fagaitua drinking water, but the withdrawal rate from these wells is small compared with the pumpage at the infiltration Fagaitua has two production wells. Well 125 (fig. galleries. 25) has a pumping record between 1989 and 1991, although the chloride concentration record extends back to 1988 (fig. 27). The water meter was reported to be Auto malfunctioning on April 24, 1989. It is not known how long prior to this date the meter was malfunctioning. At Reports of pumpage at new well 166 in Auto on the the beginning of the record, chloride concentrations southern coast of Tutuila (fig. 25) began in July 1997. were already higher than 1,000 mg/L. Chloride concen Pumpage averaged 0.0016 Mgal/d for the first two full trations rose to nearly 2,000 mg/L in 1989 during a months of reported pumpage (fig. 26). Chloride concen period when the well was pumping about 0.03 Mgal/d trations ranged from 40 to 65 mg/L. 26 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 ALOFAU 32 Figure 28. Ground-water pumpage and chloride concentrations in Alofau, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) AMOUL1122 I-UJ LiJ -1 20 11111 n 111111111111111111 LiJ < LL LU Z «> Well deepened -_z 10 I I -i < LiJ LiJ f*+*»+m «»%y ^ ^ -« ft 5 -JO 0 UJUJ O M 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 29. Ground-water levels in Amouli, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) and rainfall was lower than average (fig. 2). Pumpage mg/L. Pumpage gradually decreased to zero from mid- was reduced in 1989 and stopped for a period in early 1990 to the end of 1991, at which time the chloride con 1990. Pumping resumed at about 0.01 Mgal/d in late centrations gradually decreased to less than 1,000 mg/L. 1990 and continued to 1991; chloride concentrations From late 1992 to 1994, pumpage resumed at a rate of remained at about 1,000 mg/L over this period. 0.01 to 0.02 Mgal/d and chloride concentrations fluctu Trends during the 12-month period ending Sep ated by several hundred milligrams per liter around a tember 1997. A new well (164) began pumping in median of about 800 mg/L. Fagaitua in April 1997 (fig. 27). Pumpage at the well, for the period April through August 1997, averaged Amouli 0.039 Mgal/d. The chloride concentration of the pumped water was 140 mg/L at the beginning of pump Amouli (fig. 25) had no production wells during ing in April 1997, but rose to 920 mg/L by July 1997. the 10-year period shown in figure 28, but had a well (122) that was used to monitor water levels (fig. 29). Water levels at this well have varied between 3 and 5 ft Alofau above mean sea level from 1987 through 1995. Well 32 in Alofau on the southern coast of Tutuila Trends during the 12-month period ending Sep (fig. 25) pumped at a rate of about 0.05 Mgal/d in 1988- tember 1997.-In 1996, well 122 was deepened and 90 (fig. 28). During this period, chloride concentrations pumped during a short test (fig. 29). Water levels mea rose from less than 1,000 mg/L to more than 2,000 sured for the next few months after the deepening and Eastern Tutuila and Aunuu Ground-Water Data 27 ALAO 161 0.04 2,000 0.02 1,000 1988 1989 1990 1991 1992 1993 1994 1995 ALAO 162 0.06 1,200 0.04 800 - 0.02 h X]if-h H400 1 1 1 1 1 1 1 1 1 1 1 i Tn 1988 1989 1990 1991 1992 1993 1994 1995 1996 I 1997 DATE Figure 30. Ground-water pumpage and chloride concentrations in Alao, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) testing were 1 to 3 ft below mean sea level but water average rate of 0.0093 Mgal/d (fig. 30). In early and levels rose to almost 4 ft above mean sea level by Sep mid-1996, chloride concentrations in well 162 had been tember 1997. declining, but began increasing in mid-1996 and reached a high of 1,060 mg/L (highest on record for the well) in July 1997. Chloride concentrations in this well Alao declined to 540 mg/L by September 1997. Alao has production wells 161 and 162 (fig. 25). Well 161 has pumped an average of 0.018 Mgal/d since Tula 1994, and chloride concentrations have fluctuated between 40 and 1,160 mg/L (fig. 30). Pumpage at well Tula on the eastern end of Tutuila has production 162 began in 1995 at about 0.05 Mgal/d, but was wells 40, 104, and 108 (fig. 25). Records for well 40 reduced after a few months to intermittent pumpage began in 1991 when pumpage was about 0.04 Mgal/d averaging less than 0.01 Mgal/d. Initial chloride con (fig. 31). Pumpage was reduced to between 0.01 and centrations in the well were below 100 mg/L but have 0.02 Mgal/d by mid-1991. Between 1992 and 1995, the risen to more than 1,000 mg/L. well was pumped intermittently at an average of less Trends during the 12-month period ending Sep than 0.01 Mgal/d. The chloride concentration in well 40 tember 1997. During the 12-month period ending Sep has fluctuated greatly from less than 100 to nearly 2,000 tember 1997, pumpage at well 161 averaged 0.019 mg/L. During the period of intermittent pumpage, chlo Mgal/d (fig. 30). Chloride concentrations at well 161 ride concentrations remained mostly below 200 mg/L rose sharply to 1,160 mg/L in September 1996, then but twice was measured at more than 900 mg/L. From fluctuated by hundreds of milligrams per liter over the May 1995 to September 1996, the well was shut down next 12 months. and partially backfilled in an attempt to reduce chloride concentrations in the pumped water. Pumpage resumed During the 12-month period ending September at well 40 in September 1996. 1997, well 162 continued intermittent pumpage at an 28 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 TULA 40 i I i I I i i i i i i 1 1 1 1 1 1 1 1 1 1 1 n 1 1 1 1 1 1 1 1 1 1 1 1 U I I I 1 M 1 1 I I I 1 1 1 1 1 I I 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 - 0.04 2,000 0.03 - - 1,500 0.02 - i - 1,000 0.01 - j s iiiur "ifNlJl ~ 500 0 ( ! i i i i i i i i M I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M J| ILTlltilUll I...... / 11 mi it ill ntfLi 1 1 1 1 1 1 1 1 1 1 1 1 1 ^dffiL 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 | 1997 TULA 104 0.06 mr 0.04 - 0.02 Figure 31. Ground-water pumpage and chloride concentrations in Tula, Tutuila, American Samoa. (Connecting lines are intended as an aid for showing trends and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) Pumpage records for well 104 began in 1988, trations rose more frequently and to increasingly higher when the well produced about 0.05 Mgal/d (fig. 31). levels. Pumpage was gradually reduced to 0.03 Mgal/d by the Trends during the 12-month period ending Sep end of 1990, and was halted for the first half of 1991. tember 7PP7.--Pumpage at well 40 resumed in Septem Pumpage resumed in mid-1991 at less than 0.02 ber 1996 at a rate of about 0.01 Mgal/d (fig. 31). The Mgal/d. Chloride concentration in the early part of the first chloride concentration reported since the resump record for well 104 remained below 200 mg/L, but rose tion of pumpage was 1,860 mg/L, but chloride concen sharply to as high as 420 mg/L in September 1995, then trations quickly declined and have remained less than fluctuated by hundreds of milligrams per liter through 150 mg/L since then. most of 1996. Well 104 was shut off between September and Pumpage at well 108 varied from 0 to about 0.06 December 1996 (fig. 31). From December 1996 to Sep Mgal/d, with an average of about 0.03 Mgal/d over the tember 1997, well 104 pumped at an average of 0.014 period of record (fig. 31). Chloride concentrations in Mgal/d. Chloride concentrations at this well during this well 108 in the period from 1989 to early 1990 were period were below 100 mg/L, which is lower than all mostly below 200 mg/L with occasional brief rises to as but a few of the chloride concentrations on record for high as 300 mg/L, but after mid-1990, chloride concen this well. Eastern Tutuila and Aunuu Ground-Water Data 29 AOA 151 0.03 - - 150 0.02 - ri~h 1 100 ^' $ 0.01 w 50 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M1 1 111 i uit 1 111 till ll.tl ill till (111 i tin r i M i i i i HIM ilili ilil !i 1 1 1 1 1 i 1 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 AOA 152 0.06 0.04 - - F3 200 - 0.02 - 100 '< H i i SI 1 1 1 1 1 1 M 1 1 1 1 1 1 1 M 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 M I I I I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 LJ 1 II II \ \ di I n 1 M 1 1 1 1 1 1 1 1 1 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 DATE Figure 32. Ground-water pumpage and chloride concentrations in Aoa, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Connecting lines omitted where period between successive data points exceeds 6 months. Data from the American Samoa Power Authority.) During the 12-month period ending September at the well continued on a gradual rising trend that 1997, pumpage at well 108 decreased relative to pump- began when the well began pumping in 1992. No pump- age in early 1996 (fig. 22). During this period, chloride age has been reported for well 152 since July 1996. The concentrations at well 108 continued a pattern of highly last chloride concentrations reported for well 152 variable chloride concentrations from 115 to 540 mg/L. (October 1996) was 80 mg/L. Aoa Sailele Aoa lies in an embayment on the northeastern Sailele, on the northeastern coast of Tutuila has shore of Tutuila (fig. 25). Two production wells in the one production well (well 130, fig. 25) that has pro village are sited adjacent to a low-lying swampy depres duced 0.01 to 0.03 Mgal/d since 1987 (fig. 33). Chloride sion in the back of Aoa Bay. Well 151 has pumped 0.02 concentrations were about 500 mg/L through the first 4 to 0.03 Mgal/d since late 1992 and well 152 pumped years of pumping, then gradually rose beginning in between 0.03 to 0.04 Mgal/d from late 1994 to mid- 1991 and reached as high as 1,400 mg/L in 1993. This 1996 (fig. 32). Chloride concentrations in well 151 were rise in chloride concentrations occurred during a period below 200 mg/L but have risen since the well began of below-average rainfall between 1987 and 1992 (fig. pumping. Chloride concentrations in well 152 varied 2) and after a period of high pumpage in 1992 and 1993. between 55 and 140 mg/L. Chloride concentrations since then have fluctuated Trends during the 12-month period ending Sep between 80 and 1,040 mg/L. tember 7PP7.~Well 151 was pumped at an average rate Trends during the 12-month period ending Sep of about 0.017 Mgal/d during the 12-month period end tember 7PP7.--During the 12-month period ending Sep ing September 1997 (fig. 32). Chloride concentrations tember 1997, pumpage at well 130 averaged 0.01 30 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 SAILELE 130 o Figure 33. Ground-water pumpage and chloride concentrations in Sailele, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) MASEFAU 241 60 I- 1EC =!Q ZLU IXI Q- 40 o< occ LUO 111111 20 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 O DATE Figure 34. Ground-water pumpage and chloride concentrations in Masefau, Tutuila, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) Mgal/d (fig. 33). Chloride concentrations were mostly and 303) that began pumping in 1992 at about 0.01 to in excess of 500 mg/L and reached as high as 1,040 0.05 Mgal/d each (fig. 35). Pumpage at well 301 shows mg/L (August 1997). an increasing trend since pumping began. Pumpage at well 302 showed an increasing trend between 1992 and early 1994, but decreased in late 1994. Pumpage at well Masefau 303 has been intermittent over the period of record. Chloride concentrations in all wells were initially low Masefau, located in an embayment on the northern coast of Tutuila, has one new production well (well 241, but rose quickly as pumping continued. Chloride con fig. 25). Pumpage records for well 241 began in August centrations in wells 301 and 302 were mostly in excess 1997. The well was pumped at about 9,000 gal/d of 500 mg/L and have exceeded 1,000 mg/L more than between August and September 1997 (fig. 34). Water once over the period of record. Chloride concentrations from the well had a chloride concentration of 40 mg/L in well 303 have also exceeded 1,000 mg/L several in August 1997, and 30 mg/L in September 1997. times, but were mostly below 500 mg/L. Trends during the 12-month period ending Sep tember 1997.--During the 12-month period ending Sep Aunuu tember 1997, pumpage at well 301 averaged 0.04 Mgal/d, which is about twice the average pumpage in Ground-water production on Aunuu (fig. 25) previous years since 1992 (fig. 35). Well 302 continued comes from three infiltration galleries (wells 301, 302, Eastern Tutuila and Aunuu Ground-Water Data 31 O.IOniiimmiiiiiiiiimiiiiiiiiiiiiiiimiiiiiiiiiiiiiimiiiiiii m 2,000 - 1,000 1988 1989 1990 1991 1992 AUNUU 302 AUNUU 303 0.04 2,000 I A* t 0.02 A: 1,000 / / s . ft "^njf }\ \r-~- N * ' ^ ' : h - '2 1 1 1> ih 1 l 1 1 1 1 ilife If, fftrT_f Vn 1988 1989 1990 1991 1992 1993 1994 1995 r 1997 DATE Figure 35. Ground-water pumpage and chloride concentrations on Aunuu, American Samoa. (Connecting lines provided only as a visual aid and do not imply interpolation between data points. Data from the American Samoa Power Authority.) to pump at an average of 0.008 Mgal/d, which is about SUMMARY the same rate that had persisted at this wells since pumpage was reduced in 1994. Well 303 was pumped Ground-water and rainfall data summarized for the intermittently, as it had been since 1992. No meter read period October 1987 through September 1997 from ing was reported for well 301 in September 1997; for Tutuila and Aunuu, American Samoa, include pumpage well 302 in July, August, and September 1997; and for and chloride concentrations from 53 production wells well 303 in August and September 1997. on Tutuila (including new wells 143 in Fagasa, 164 in Fagaitua, 165 in Pago Pago, 166 in Auto, and 241 in Chloride concentrations in the three Aunuu wells Masefau), 3 production wells on Aunuu, water-level were relatively high in October 1996 but decreased measurements from 16 wells on Tutuila, and rainfall sharply by January 1997 (fig. 35). Between January and data from 2 gages on Tutuila. September 1997, chloride concentrations varied between 180 and 1,200 mg/L at well 301, between 104 Mean annual rainfall at the gage in Afono near and 1,240 mg/L at well 302, and between 60 and 560 Pioa Mountain was 164 inches, and 210 inches at the mg/L at well 303. rain gage in Aasufou during the period October 1987 through September 1997. Rainfall in the 12-month 32 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997 period from October 1996 through September 1997 trend that began in 1992, well 302 pumped at about the totaled 210 inches at the Afono gage, and 234 inches at same rate that had persisted since 1994, and well 303 the Aasufou gage. was pumped intermittently, as it had been since 1992. In Most wells in the Tafuna-Leone Plain (Tafunafou, the 12-month period ending September 1997, chloride Malaeimi-Mesepa, Malaeloa-Leone, and Iliili) have concentrations in the three Aunuu wells varied between been pumped at rates from 0.2 to 0.5 Mgal/d and have 60 and 1,240 mg/L. had chloride concentrations usually less than 500 mg/L. The high production and low chloride concentrations REFERENCES CITED continued through the 12-month period ending Septem ber 1997, when combined pumpage from the Tafuna- Bentley, C.B., 1975, Ground-water resources of American Leone Plain was 6.3 Mgal/d, with 1.6 Mgal/d from the Samoa with emphasis on the Tafuna-Leone Plain, Tutu wells in Tafunafou, 1.6 Mgal/d from wells in the Malae ila Island: U.S. Geological Survey Water-Resources imi-Mesepa area, 2.0 Mgal/d from the Malaeloa-Leone Investigations Report 29-75, 32 p. area, and 1.1 Mgal/d from Iliili, and chloride concentra Davis, D.A., 1963, Ground-water reconnaissance of Ameri tions in most wells remained below 200 mg/L. In the can Samoa: U.S. Geological Survey Water-Supply Paper 12-month period ending September 1997, measured 1608-C, 21 p. water levels in Tafunafou and Iliili remained at about Izuka, S.K., 1996, Summary of ground-water and rainfall the same elevation relative to mean sea level as in the data for Tutuila and Aunuu Islands, American Samoa, previous 10 years, but water levels in Malaeimi have for July 1984 through September 1995: U.S. Geological declined overall since mid-1996. Survey Water-Resources Open-File Report 96-116,44 p. Izuka, S.K., 1997, Summary of ground-water data for Tutuila In contrast most wells in central and eastern Tutu- and Aunuu, American Samoa, for July 1985 through ila, as well as in the uplands of western Tutuila, have September 1996: U.S. Geological Survey Water- been pumped at rates less than 0.1 Mgal/d. Wells in Resources Open-File Report 97-654, 44 p. Fagatogo, Pago Pago, and Aua were exceptions; some Macdonald, G.A., 1944, Petrography of the Samoan Islands: wells in these areas have been pumped at rates of more Geological Society of America Bulletin, v. 56, p. 1,333- than 0.4 Mgal/d. Some of the wells in central and east- 1,362. em Tutuila frequently had chloride concentrations in Macdonald, G.A., 1968, A contribution to the petrology of excess of 500 mg/L. In the 12-month period ending in Tutuila, American Samoa: Geologischen Rundschau, September 1997, chloride concentrations in both pro v. 57, no. 3, p. 821-837. duction wells in Aua rose to the highest levels on record Stearns, H.T., 1944, Geology of the Samoan Islands: Geolog for those wells. In the 12-month period ending Septem ical Society of America Bulletin, v. 55, p. 1,279-1,332. ber 1997, measured water levels in Pago Pago remained U.S. Geological Survey, 1989, Topographic map of Tutuila at about the same elevation above mean sea level as in Island, American Samoa: 1:24,000 scale. the previous 3 years, measured water levels in Aua remained below mean sea level as in the previous 2 APPENDIX years, and measured water levels in Fagaalu continued the trend established in early 1996 when water levels Data Processing dropped relative to the previous 4 years. Water levels measured in Laulii in the 12-month period ending Sep Pumpage and chloride-concentration data of all tember 1997 included the lowest levels measured in the pumping wells, water levels of selected nonpumping last 10 years. and pumping wells, and rainfall data were collected by The three production wells on Aunuu have been ASPA and sent to the USGS, where the data were pro pumped at various rates less than 0.1 Mgal/d. Chloride cessed as described below. concentrations in these wells have varied greatly, but Daily rainfall recorded at the rain gages were remained mostly above 500 mg/L and often exceeded summed over each month and the monthly totals were 1,000 mg/L. In the 12-month period ending in Septem divided by the number of days in each month to obtain ber 1997, pumpage at well 301 continued the increasing the monthly mean rainfall, in inches per day. The 3- References Cited 33 month backward-looking moving average was com the capacity of the pump in the well) were corrected by puted by averaging a given month's rainfall with the first classifying the type and possible cause of the error rainfall of the 2 months immediately preceding it. The and making appropriate corrections (Izuka, 1996). In a mean monthly rainfall for a given month, for example few cases in which the source of the error could not be October, is the arithmetic average of the mean monthly determined, the meter reading was eliminated and the rainfall for all Octobers in the 10-year period of this next correct reading was used in the calculation. In such report. cases, the bar on the graph appears wider because it rep Chloride concentrations were determined by a resents an average pumpage over a longer period. A field titration kit. A quality-control check was con wide bar does not necessarily indicate steady pumpage; ducted in 1984 and 1985 in which splits of 123 ground- steady pumpage is indicated by numerous bars of the water samples from Samoa were analyzed using the same height. field titration kits and laboratory titration. Comparison If pumpage at a well was halted for a month or of the results indicated that for most of the samples, the more and the date of the shutdown, the last reading after field measurement was lower than the laboratory mea the shutdown, and the date of the start-up are unknown, surement. In four samples, the field measurement was the difference between the last meter reading prior to more than 100 mg/L less than the laboratory titration. the shutdown and the first meter reading after resump The cause of the discrepancy was not determined. More tion was divided by the number of days between the two detailed records of the field titration have been kept readings. This results in a bar that is relatively low since the 1984-85 check, but there have been no subse (because no water was pumped during part of the inter quent quality-control checks. Although a few measure val) and wide (because there was a long interval ments showed large discrepancies, 87 percent of the between meter readings). Therefore, a wide bar that is field determinations were within 50 mg/L of the labora much lower than the adjacent bars probably indicates tory measurement. For the purposes of this report, the that the well was shut down during some part of the accuracy of the chloride-concentration data is sufficient interval spanned by the bar. to track general trends in the quality of well water. This is the third in a series of ground-water data Average pumpage rates in this report were calcu reports for Tutuila and American Samoa. Errors and lated directly from meter readings supplied by ASPA. omissions discovered since the publication of the last Pumpage over an interval was computed by taking the report (Izuka, 1997) have been corrected in this report. difference between successive readings and dividing by the number of days between the readings. This allowed the pumping rates of intervals of different duration to be compared. Occasional errors in the meter readings (identified because they yielded negative pumpages or pumpages that were too high to have been obtained with 34 Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997