Effects of Phosphate Mining 

on the Ground Water of 

Angaur, Palau Islands 

Trust Territory of the 

Pacific Islands

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1^608-A

Prepared in cooperation with the Trust 

Territory of the Pacific Islands
Effects of Phosphate Mining 

on the Ground Water of 

Angaur, Palau Islands 

Trust Territory of the 

°acific Islands

By TED ARNOW

CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND 

OCEANIA

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1608-A

Prepared in cooperation with the Trust 

Territory of the Pacific Islands

 JNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B« Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington 25, D.C.
CONTENTS

	Page 

Abstract____-_- ___________________________________________________ A-i

Introduction- _____________________________________________________ 2

Purpose and scope___--________________________________________ 2

Previous investigations-________________________________________ 3

Location and culture__________________________________________ 4

Climate._____________________________________________________ 8

Tides________________________________________________________ 8

Wells and test holes____________________________________________ 9

Geology and mining-______________________________________________ 12

General geology.______________________________________________ 12

Phosphate deposits.___________________________________________ 14

Ground water.____________________________________________________ 14

Source._______---_-----_-_-______-__-_-___-_-_______________. 14

Water-level fluctuations._______________________________________ 15

Quality of water._________________________________________________ 19

Rainwater.________________________________________________ 19

Ground water__ _ ________________________________________ 19

Effects of mining on the ground-water body __________________________ 27

Effects of backfilling on the ground water in province A_ _______________ 35

Summary and conclusions __________________________________________ 38

References_ _____________________________________________________ 38

ILLUSTRATIONS

Page 

FIGURE 1. Outline map of the Palau Islands________----___ ___________ A-4

2. Outline map of Angaur____________ _____________________ 6

3. Average monthly meteorological data for Angaur___________ 9

4. Map of Angaur showing locations of wells and test holes and 

mean elevation of the water table at selected observation 

stations._ ___________________________________________ 10

5. Generalized geologic map of Aiigaur. ____________________ 13

6. Water-level fluctuations in wells 4, 10, and 12, and rainfall on

Angaur, 1951-54_______ _____________________________ 16

7. Map showing lag of tide fluctuations in wells and lakes behind

ocean tides at Angaur_________________________________ 17

8. Map showing magnitude of ratio of ocean tides to tidal

fluctuations in wells and lakes on Angaur________________ 18

9. Five-week moving average of chloride content of water at 

wells 1 and 4, and combined pumpage from wells 1 and 2, 

Angaur, 1950-54____________________________________ 21

10. Five-week moving average of chloride content of water at well

10, Angaur, 1950-54__________________________________ 22

11. Variation of chloride content of water in lakes 1, 7, and 11,

and monthly rainfall on Angaur, 1949-55____-_----_ ____- 25
IV ILLUSTRATIONS

Page 

FIGURE 12. Variation of chloride content of water from wells 13 and 14

and pumpage from well 13, Angaur, 1950-52___ _________ A-26

13. Variation in chloride content of water with depth in test

holes 12, 13, and B-7--_----------------_--------__-_- 27

14. View of a mining area near lake 1 at the beginning of mining

on July 14, 1952. ___________________________________ 28

15. View of the mining area shown in figure 14 on October 4,

1952, after mining and backfilling were completed- _______ 29

16. Generalized isochlor map of ground water in Angaur, February 12-15, 1951___-__________-__-_____-_-______-__- 30

17. Generalized isochlor map of ground water in Angaur, May 19,

1952________________________________________________ 31

18. Generalized isochlor map of ground water in Angaur, February 9, 1953_______-_____________-________-_______-_ 32

19. Generalized isochlor map of ground water in Angaur, June 7,

1954________________________________________________ 33

20. Generalized isochlor map of ground water in Angaur, May

31, 1955__-_-___________-_-_______-________-_______/_ 34

21. Variation in chloride content of water from well 11 in backfilled part of lake 3, Angaur, 1951-55- __________________ 36

22. Variation in chloride content of water from two depths in

test hole 16 in backfilled part of lake 3, Angaur, 1952-55. _ 37

TABLES

Page 

TABLE 1. Classification and suitability of soils on Angaur Island, 1948___ A-7

2. Records of selected wells and test holes on Angaur Island-_____ 11

3. Length of record used to determine mean water levels at

observation stations on Angaur Island. ___________________ 16

4. Chloride content of rainwater, Angaur Island- _____________ 19

5. Chemical analyses of ground water from Angaur Island. ______ 23

6. Volumetric capacity of lakes on Angaur Island_____-._______. 28
CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

EFFECTS OF PHOSPHATE MINING ON THE GROUND

WATER OF ANGAUR, PALAU ISLANDS, TRUST

TERRITORY OF THE PACIFIC ISLANDS

By TED ABNOW

ABSTRACT

Mining of phosphate ore on Angaur Island by mechanized methods created 

large water-table lakes, which became filled with brackish or saline water. A 

hydrologic investigation was started in 1949 to determine whether the saline 

water in the lakes would spread to surrounding areas and cause damage to 

agricultural lands and the water supply.

Angaur, which is in the Palau Islands in the southwestern part of Micronesia, 

is administered as part of the Trust Territory of the Pacific Islands, under a 

trusteeship granted to the United States by the United Nations. The island 

has an area of 3.2 square miles and has a maximum altitude of about 150 feet. 

The climate is tropical oceanic. The average annual temperature is 82° F; the 

average annual rainfall is aboiit 125 inches; and the average relative humidity 

is about 80 percent.

The northwestern third of Angaur (province A) consists topographically of a 

series of concentric ridges and depressions which are underlain largely by wellcemented coralline limestone of Pliocene, Pleistocene, and Recent ages. The 

remaining two-thirds of Angaur (province B) is a low plain underlain in the 

northern and central parts by a low platform of coralline rubble of Pleistocene 

and Recent age and in the southern part by sandy and rubbly beach deposits 

of Recent age. Province A contained extensive phosphate deposits of which 

more than 3 million tons were mined in 1909-55.

Weekly water-level measurements at 35 wells, test holes, and lakes indicate 

that the water table averages about 2 feet above mean sea level in the beach 

deposits, about half a foot above mean sea level in the rubble deposits, and 

about 1.35 feet above mean sea level in the coralline limestone.

Water samples obtained weekly at the observation sites indicate that the 

ground water in province A is not of uniform quality, as large variations in 

salinity occur throughout the area. In contrast, the ground water in province 

B is of relatively uniform quality, and contains less than 1,000 ppm (parts per 

million) of chloride in most places.

In province A removal of earthy phosphate which had acted as a seal allowed 

the infiltration of saline water through solution channels exposed at the 

bottom of several of the lakes. The sampling program showed no indication

A-l
A-2 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

of large-scale movement of saline water out of the lakes into adjacent ground 

water. Provinces A and B apparently function as independent ground-water 

units, and the quality of the ground water in province B has not been noticeably 

affected by mining activities in province A.

The lakes were backfilled with limestone rubble to reduce the possibility of 

underground movement of saline water out of the lakes. The gross permeability 

of the backfill material is less than that of the surrounding limestone in 

province A, and, as the rate of influx of saline water was curtailed, the recharge of fresh water from rainfall tended to reduce the salinity of the ground 

water in the fill. In parts of the backfilled area the salinity of the water at 

the water table decreased rapidly in less than 1 year, as a layer of fresh water 

was built up at the water table.

INTRODUCTION

PUBPOSE AND SCOPE

Tlie investigation on which this report is based was carried out in 

Aiigaur for the purpose of determining the effects of phosphate mining 

on the ground water of the island.

Mining of phosphate on Angaur began in 1909 during German administration of the island and continued from 1914 to 1944 under Japanese administration. Mechanized methods were introduced just before the start of World War II. From June 1946 to June 1947 mining 

was carried on by an American contractor under the control of the 

U.S. Navy. Mining was resumed on June 30, 1949, by a Japanese 

company, the Phosphate Mining Co., Ltd. (Rinko Kaihatsu Kaisha), 

at first under the supervision of the Supreme Commander, Allied 

Powers, and after April 1952 under a contract with the High Commissioner of the Trust Territory of the Pacific Islands.

The removal of phosphate by mechanized methods left deep pits extending below the water table, which created lakes. The geologic 

structure of Angaur is such that sea water, propelled by tidal action, 

intruded the lakes and made them brackish or saline. Hydrologic 

investigations were begun in December 1949 as a result of concern by 

the administration of the Trust Territory that the encroachment of 

saline water from the lakes might cause damage to agricultural lands 

and the water supply on Angaur. At the request of the High Commissioner of the Trust Territory of the Pacific Islands, the U.S. Geological Survey began a systematic study in January 1951, after having 

made preliminary studies beginning in 1949.

The investigation since 1951 has consisted of sampling ground 

water for chemical analyses; measurement of water levels in wells, test 

holes, and lakes; collection of meteorologic data; and maintenance of
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-3

a tide gage in the harbor. The officials of the mining company provided excellent cooperation in the work, and many of the detailed 

observations in the investigation were made by the company's engineering staff. Fifteen administrative reports covering the work were 

submitted to the High Commissioner's office during January 1951 to 

March 1955. The first 11 reports were prepared by Ted Arnow and 

the last 4 by E. W. Bishop. This report is based largely on the data 

collected from December 19-19 to March 1955.

The program was financed by the administration of the Trust Territory of the Pacific Islands, and direct support was provided by 

personnel at the district headquarters in Palau, and at the liaison office 

in Angaur.

PREVIOUS INVESTIGATIONS

The geology and soils of Palau, including Angaur, were mapped by 

personnel of the U.S. Geological Survey and the U.S. Department of 

Agriculture assigned to the Office of the Engineer, Far East Command. The fieldwork was done during February 1947 to November 

1948. The soils of Angaur were described by Templin and others 

(written communication, 1949) ; a preliminary description of the 

geology and phosphate deposits of Angaur was prepared by Irving 

(written communication, 1950) ; and a full discussion of the geology 

and mineral resources of Angaur was included in a report of Palau by 

the U.S. Geological Survey (written communication, 1956).

A survey team consisting of C. K. Wentworth of the Board of 

Water Supply, Honolulu, Hawaii, and D. A. Davis and A. C. Mason 

of the U.S. Geological Survey visited Angaur for 10 days in December 

1949 at the request of the High Commissioner of the Trust Territory 

and the Supreme Commander, Allied Powers. The purpose of the 

survey was to determine the nature and extent of possible damage 

caused by mining to the ground-water supply and agricultural lands, 

and to determine methods of preventing additional damage and of 

restoring any land already damaged. The survey team began the 

hydrologic program which continued through 1955. The results of the 

survey were published in 1955 (Wentworth and others, 1955).

A second survey team of Japanese scientists, Risaburo Tayama, 

Sold Yamamoto, and Takashi Tsuyama, visited Angaur from January 23 to March 4, 1950, at the request of the Phosphate Mining 

Co. At the suggestion of the second team, the hydrologic program 

was expanded by the construction of additional observation wells 

and the collection of more detailed meteorologic data. A short 

description of the geology of Angaur subsequently was prepared by 

Ttivama (1951).
A-4 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA 

LOCATION AND CULTURE

The approximate center of Angaur is at long 13-±°8M:5" E. and lat 

6°54'15" N. The island is about 730 nautical miles southwest of 

Guam, 580 miles east of Davao, Philippine Islands, and 500 miles

FIGURE 1. Outline map of the Palau Islands and inset showing their position in the

Pacific Ocean.
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-5

north of New Guinea (fig. 1). Angaur is a part of the Palau Islands, 

western Caroline Islands, which are in the large group of Pacific 

islands known as Micronesia (tiny islands). Most of Micronesia, 

including Angaur, is in the Trust Territory of the Pacific Islands, 

a trusteeship granted to the United States by the United Nations.

Angaur is the southernmost of the Palau Islands. It has several 

narrow fringing reefs, but it lies outside the main Palau reef (fig. 

1). The island has an area of 3.2 square miles and can be divided 

into two topographic provinces, labeled A and B in figure 2. Province A, which covers about the northwestern third of the island, 

contains an irregular circular limestone ridge whose maximum altitude is about 150 feet. This ridge encloses a basin about 2,000 feet 

in diameter, the floor of which is generally less than 10 feet above 

sea level. An excavation formed by mining, called lake 7, lies within 

this basin (fig. 2). South and east of the main circular ridge is a 

series of low roughly concentric ridges and intervening depressions. 

Lakes 1, 2, 3, and 11, also formed by mining, lie in these depressions.

Province B, which covers the remaining two-thirds of the island, 

is a low southward-sloping platform that stands a maximum of about 

25 feet above sea level. A large swamp covers about 124 acres in the 

southern part of this province. Many lakes and ponds in depressions 

created by early mining and recent quarrying operations are scattered 

throughout the island, but there are no surface streams.

The vegetal cover on Angaur was almost completely destroyed 

by military activities during the assault and occupation of the island 

by United States forces in 1944. A dense scrub growth now covers 

the island except for the roads, the mining and industrial areas, and 

the village area. A classification of soil types and data outcrop suitability are shown in table 1.

The indigenous population of Angaur in 1954 was about 410. The 

people are considered to have Indonesian ancestry from which they 

inherited some Mongoloid features. Some Negroid characteristics 

are a result of Melanesian admixture in later but still prehistoric 

times (U.S. Geological Survey, written communication, 1956). Their 

language is of the Indonesian type. The people, obtain virtually all 

their food from the island and the surrounding sea the men fish 

and the women practice primitive subsistence agriculture. Their diet 

consists basically of fish and the starchy tubers of taro and manioc, 

and minor quantities of fruits and vegetables. Rice is imported and 

paid for with funds obtained as royalties derived from the mining. 

Prior to 1943 the coconut palm was an important source of food, and 

the copra harvested was a source of income; however, infestation by 

the rhinoceros beetle (Oryetes rhinoceros) has completely destroyed 

the productive palms on the island.

605285 61 2
A-6 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

134"09'E

6°54'N

1 MILE

CONTOUR INTERVAL 50 FEET 

DATUM IS MEAN SEA LEVEL

EXPLANATION

Boundary between topographic provinces

Boundary between rock units

 

Tide gage

FIGURE 2. Outline map of Angaur showing roads, lakes, and topographic provinces.

The possession of land, especially agricultural land, is of prime 

importance in Palauan society. The most valuable type of agricultural land is swampland on which wetland taro (Goloccma esculent a] , an aroid with edible tuberous rootstocks, can be grown. The 

ceremonial exchange of pieces of this taro plays an important part in 

many social functions. Whether to allow the destruction of some of 

the swamplands in order to obtain the underlying deposits of phosphate was a particularly difficult decision for the Angaurese. At
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGATJR A-7

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A-8 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

first they refused to allow mining 011 this land, but they finally granted 

permission when the amount of money offered by the mining company was sufficiently large.

CLIMATE

Angaur has a tropical oceanic climate in which the year is divided 

into two seasons. The northeast trade winds prevail from October 

until May or June and the southwest monsoon begins in July and 

lasts through September. The trade-wind season is one of slightly 

higher temperatures and slightly lower rainfall. During the monsoon 

season there are many storms of several days' duration. Typhoons 

rarely strike Palau; most of them pass north of the islands. Average 

monthly meteorological data for Angaur are shown graphically in 

figure 3.

Rainfall data were collected intermittently by the Jaluit Co. of 

Germany from 1909 through 1911 (Bryan, 1946; U.S. Navy, 1943). 

The Phosphate Mining Co. made meteorologic observations from 

October 1949 to May 1955. On the basis of partial records for 1909-11 

and complete records for October 1949 to March 1954, the rainfall 

at Angaur averages 125 inches per year, and no monthly average is 

less than 7 inches. The extremes in monthly rainfall during the period 

of record were 2.11 inches in April 1953 and 31.30 inches in December 

1949.

The air temperature on Angaur is very uniform. The mean annual 

temperature, based on data collected from 1950 through 1953, is 82°F. 

The monthly extremes during the same period were 80° and 85°F. 

The relative humidity at Angaur is uniformly high throughout the 

year. The average relative humidity for 1950 through 1953 was 80 

percent, and the monthly extremes were 71 and 88 percent. The mean 

wind velocity on Angaur from 1950 to 1953 was 7.2 miles per hour. 

The monthly extremes during the same period were 4.3 and 21 miles 

per hour.

No evaporation data are available for Angaur. Conditions of temperature, relative humidity, and wind velocity on Guam, however, 

are similar to those on Angaur. The evaporation from a class A 

Weather Bureau pan at the Fena filter plant on Guam was 82.4 inches 

in 1955 and 89.3 inches in 1956. Evaporation on Angaur probably is 

of the same order of magnitude.

TIDES

Tidal observations on Angaur are made in the small-boat harbor on 

the west coast by means of a continuously recording tide gage (fig. 2). 

The tides are semidiurnal and have an average range of about 3% feet.
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A~9 

20

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC. 

FIGURE 3. Graphs showing average monthly rainfall, temperature, humidity, and wind

velocity on Angaur.

WELLS AND TEST HOLES

Dug wells on Angaur are numbered consecutively in a series called 

wells, and drilled holes are numbered consecutively in a series called 

test holes. The locations of 30 selected wells and test holes are shown
A-10 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

134°09'E

- -- 6°54'N

1 MILE

Lake-sampling point

Firs* number is Mie/( or test-hole n 

Number in parentheses is mean ele 

of water table, infect above mean se

Rainwater sampling site

Boundary between rock units

FIGURE 4. Map of Angaur showing locations of wells, test holes, and rainwater sampling 

sites, and mean altitude of the water table at selected observation stations.

on figure 4, and pertinent data for the wells and test holes are given 

in table 2.

Wells 1 to 8 were dug before the beginning of hydrologic studies in 

1949. Well 13 was dug in 1951 for a supply of cooling water at the
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-ll

powerplant in the mining camp. All other wells and test holes were 

constructed, after 1949 for use as observation wells.

Wells were not used on Angaur before the German administration, 

and the Angaurese obtained their water from rain catchment on trees. 

Before World War II, under the Japanese administration, wells 1 and 

2 were pumped as a source of water supply. During the war, under 

administration of the U.S. Armed Forces, water was pumped mostly 

from well 3 and to a lesser extent from some of the other wells. After 

World War II, wells 1 and 2 supplied water for the mining-camp area, 

and well 3 was pumped as a source of water for the Angaurese village. 

Well 13 supplied cooling water for the powerplant, and since 1953

TABLE 2. Records of selected wells and test holes on Angaur

Well or

test hole

No.

Depth

tfeet)

Diameter

(inches)

Altitude of

treasuring

point above

irean sea

level (feet)

Casing Aquifer Sampling depth

Wells

1 

2 

3 ---

4___ _ ______

5 

6 - -

8 -----_

11 ________

12

13 

14 

15- 

16 ------

24

21)

11

10

9

18

12

17

9

8

3

48

42

6J

96

48

36

oo

22

42

22

oo

99

20. 95

9.79

9.90

9.56

16.93

11.91

2.56

2 17

6.27

5.45

2.82

 .do 

 do 

Oil drum.. .

 ..do ... -

 do 

 do 

 do 

--.do. __--

 -do - 

Rubble-. 

--.do -

Rubble. 

Baekfill-__________

phosphatic 

limestone. 

 _do 

 do ..- 

Backfill.-- ____-_-

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Test holes

3 

4 .......

5 

6 

8 .... .... -

9 ..-- ..

10 .

12 

13. 

14 

15 

16 

B-7 .

37

12

10

17

41

36

42

43

21

2!$ 014

2.2

23-a

2i-2

21 2

2J 2

2.1 2

2} 2

2J-2

2J-2

2 1 -;

21 -)

9 4°

10.49

9.98

8.63

7.18

8.27

7.95

23.39

9 on

3.25

9 99

_....doi-. 

 .do 

 .do 

 . -do 

 .do 

 ..do .. -

 ..do -

___ _.do 

 .doL 

- doi .

-.-.do .

. -doi.. -.

- do... -----

 .do . --._ 

 do 

 .do . .

- do -----

. .do ......

 do 

phat ic limestone.

Backfill-. 

 .do... -- -

and 35 ft. below 

water table. 

Water table, and 20

and 35 ft below 

water table.

Do.

Do.

Do.

Do.

Do.

Do.

and 30 ft below 

water table. 

Do.

Water table, and 10

and 20 ft below 

water table. 

Do.

Water table, and

every 3.3 ft below 

water table.

Cased with pwforated pipe.
A-12 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

small quantities of water have been pumped from well 6 to augment 

the rain-catchment supplies used at the U.S. Coast Guard station in 

the northeastern part of the island. No water was used for irrigation, 

and there probably will be no such use of water in the future.

The monthly pumpage from wells 1 and 2 between 1950 and 1954 

averaged about 3 million gallons and reached a peak exceeding 6 million gallons in March 1951 (fig. 9). The pumpage from well 3 averaged about half a million gallons per month during the same period. 

About 25 percent of the water pumped from all wells was lost from a 

leaky piping system that was laid soon after the occupation of Angaur 

in 1944. After the Phosphate Mining Co. left Angaur in 1955, pumping virtually ceased at all wells except well 6 at the Coast Guard 

station.

Because of its high mineral content compared with rainwater, the 

water from well 3 supplying houses in the native village was used by 

the Angaurese only for washing and cooking. The Angaurese prefer 

rainwater for drinking; and, even in dry seasons, rainfall is more than 

sufficient for an adequate supply of drinking water for the present 

population. The rainwater is caught on corrugated-iron rooftops and 

stored in reclaimed oil drums from which it is dipped as needed.

GEOLOGY AND MINING 

GENEBAL GEOLOGY

According to the U.S. Geological Survey (written communication, 

1956) the rocks of Angaur consist of coralline limestone of Pliocene 

and Pleistocene ages; coralline rubble and limestone of Pleistocene and 

Recent age; and calcareous sand, coralline rubble, and swamp deposits of Recent age. The areal distribution of these rocks is shown 

on the generalized geologic map (fig. 5).

The Pliocene and Pleistocene limestone underlies the northwestern 

part of the island which is dominated by the high concentric ridges 

in topographic province A (fig. 2). The limestone is a calcareous 

skeleton-debris rock composed of fragments of coral, algae, and some 

Foraminifera, all bound together by a fine-grained calcareous cement. 

The hard, brittle rock is white to cream colored on fresh surfaces, 

but it is light to dark gray on weathered surfaces because of a coating 

of lichens or algae. The rock has been subject to solution on a large 

scale, and much of it has a cellular or honeycomb structure. Large 

deep solution cavities persist for hundreds of yards, and a karrenfeld 

topography is present where solution has been most extensive. Individual pits and pinnacles having nearly vertical walls are 30 to 80 

feet wide, and have a vertical relief of 40 to 60 feet.

Rubble and limestone of Pleistocene and Recent age underlies the 

northeastern and central parts of the island. The rubble is com-
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR 'A-13

134°09'E

Coralline limestone, composed of 

unsorted or poorly sorted coralline 

fragments, sand, and fine material, generally indurated

Geologic contact, approximately 

located

FIGURE 5. Generalized geologic map of Angaur. (After U.S. Geological Survey, written

communication, 1956.)

posed of poorly sorted soft powdery to sandy unconsolidated coralline 

material containing many well-indurated blocks of all sizes. These 

unconsolidated deposits make up the broad low platform forming

6052S5 61 3
A-14 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

the northern part of province B. The limestone consists of indurated 

coralline material similar to the rubble. It forms the low concentric 

ridges lying in the eastern part of province A and underlies narrow 

coastal bands around the northwestern part of the island. The rubble 

has a high permeability, but it is not cut by deep solution pits and 

caverns. The limestone is cavernous, but probably less so than the 

older limestone of Pliocene and Pleistocene ages.

The sand and rubble of Eecent age are composed of light-brown 

to white calcareous sand, coralline rubble, and boulders of modern 

and ancient beaches. These deposits lie in narrow bands around the 

northeast, southeast, and west coasts, and underlie the lowland in 

the southern part of province B. The swamp deposits are largely 

organic muck that has accumulated in low areas in the southern part 

of province B and in depressions between concentric ridges in 

province A.

PHOSPHATE DEPOSITS

The phosphate deposits on Angaur are mainly in province A. According to Irving (written communication, 1950) the ore is a mixture 

of tricalcium phosphate (Ca3P2O8 ) and calcium carbonate (CaCO3 ) 

and consists of four distinct types; nodular, oolitic, rock phosphate, 

and earthy. The oolitic deposits, which average about 33 percent in 

phosphate content (P2O5 ), lie mainly above the present water table 

and were, therefore, the source of the bulk of the ore removed in the 

early stages of mining. The earthy deposits lie mainly below the 

water table and make up the bulk of the ore removed during mechanized mining in the later stages. The original source of the phosphate was the excrement of large numbers of sea birds (Ilutchiiison, 

1950). It is estimated that a total of more than 3% million tons of 

ore had been shipped from Angaur when mining was discontinued in 

1955.

GROUND WATER

SOURCE

The only source of fresh water on Angaur is the rain that falls 

directly on the island. Owing to the small size of the island and 

the absence of mountains, there is little variation in the areal distribution of rainfall. A comparison of measurements made for 2 years 

at 2 rain gages, one near the boat basin on the west coast and the 

other 1 mile to the northeast, shows less than a 4-percent variation. 

Owing to the high permeability of the rocks that make up the island, 

surface runoff is insignificant except during heavy storms, when 

there is a small amount of sheet flow into the ocean. Part of the 

rainfall evaporates before entering the ground, part is subject to 

evapotranspiration from the soil zone, and the remainder percolates
A-16 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

WELL \

\

\

\

a \

N

WELL 10

^\

\

\

\

\y WELL 12

ATIO HES

JFMAMJJASONOJFMAMJJASONDJFMAMJJASONDJFMA

1951 1952 1953 1954 

FIGURE 6. Graphs showing water-level fluctuations in wells 4, 10, and 12, and rainfall on

Angaur, 1951-54.

TABLE 3. Length of record used to determine mean water levels at observation

stations on Anyanr Island

[Weekly observations unless otherwise noted]

Station Station

Well 1 _ _

2

3

4

5

6

7

10

11

12

13

14

15

16

Lake 1

2 north

2 south

7B

7E

1 Monthly observations.

Length of

record

(months)

36

36

36

_ 36

38

36

38

36

32

36

36

35

35

30

36

30

36

36

30

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

B-7 1 _ _

Length of

record

(months)

38

34

35

36

36

36

36

36

36

36

23

31

31

25

24

26
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-15

down to the ground-water reservoir. The natural discharge of water 

from the ground-water reservoir takes place partly by liquid flow 

into the ocean along the shore and partly by evapotranspiration into 

the atmosphere.

WATER-LEVEL FLUCTUATIONS

The altitude of the water table above mean sea level at 35 observation stations in w^ells, test holes, and lakes on Angaur is shown in 

figure 4. The altitudes are the arithmetic means of individual measurements made at weekly intervals at random times during the day 

and at random stages of the ocean tide. The length of record used 

for each station is showTn in table 3. The altitude of the land surface 

at each station w^as determined by spirit leveling.

Fluctuations of the water table at a w^ell in each of the three major 

geologic units on Angaur (w^ells 4, 10, and 12) and monthly variations of rainfall during 1951-54 are showTi in figure 6. The hydrographs for the wells showT a pattern of seasonal fluctuation that is 

similar to the pattern of rainfall. The fluctuations differ in magnitude among the w^ells, but the same overall pattern is followed by all 

three wells. Water levels are highest during March through August, 

when the rainfall is greatest, and lowest during September through 

February, when the rainfall is least.

In the well-cemented coralline limestone that underlies province A 

the mean altitude of the water table at 25 observation stations averaged 

1.35 feet above mean sea level. In the beach deposits that underlie the 

southern part of province B the mean altitude of the w^ater table at 

3 observation stations averaged 1.97 feet above mean sea level. The 

highest average water level observed was 2.10 feet above mean sea level 

at w^ell 5, which is in beach deposits about 290 feet from the shore 

at the south end of the island. In the coralline rubble deposits that 

underlie the northern and central parts of province B the mean 

altitude of the water table at 7 observation stations was 0.53 feet above 

mean sea level.

The head, or the height of the water table above mean sea level, in 

each area indicates, among other things the ability of the rocks underlying the area to transmit raimvater from the surface downward and 

laterally toward the ocean. The absence of surface drainage channels 

indicates that the rocks in each area are permeable enough to absorb 

all available recharge. On the assumption of a uniform rate of 

recharge over the island, the relatively low altitude of the water table 

in the area underlain by coralline rubble in province B indicates that 

these deposits are highly permeable, and that ground water moves 

relatively fast toward the zone of discharge at the shore. The relatively high altitude of the water table in the southern part of Anguar
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-17

134°09'E

1 MILE

EXPLANATION

O 2(3-36)

Well

.12(248)

Test hole

X L7(3:45)

Lake-sampling point

First number is well, test-hcle, or lake mimt.fr. 

Number in parentheses is lag behind ocean 

tides in hours cvd tninvtft

FIGURE 7. Map showing lag of tide fluctuations in wells and lakes behind ocean tides at 

Angaur. (Lag in hours and minutes.)

indicates that the sandy materials are less permeable than the rubble 

and limestone underlying the remainder of the island, or that the sandy 

deposits are underlain at a shallow depth by reef rock having a relatively low permeability.

The lag of tidal fluctuations of the water table behind the ocean 

tides at selected observation stations is shown in figure 7, and the magnitude of tidal fluctuations in the ocean compared to those of the 

ground-water levels .at the observation stations is shown in figure 8. 

Continuous recordings of the ocean tides were made with an automatic'

605285 61 4
A-18 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

water-level recorder in the small-boat harbor on the west coast of the 

island. Similar instruments recorded water levels for periods of 1 

week or more at each of the ground-water observation stations.

The records of tidal fluctuations of the ground water made at observation stations in different parts of the island are not strictly comparable because they are all referred to the ocean-tide record made 

at a single point in a restricted basin 011 the west side of the island. 

The magnitude and time of maximum and minimum ocean tides probably vary significantly from place to place around the shore of the

134°0'5'E

6°54'N1 MILE

Lake-sampling point

First number is well, test-hole, orlakt nuuihri 

Number in parentheses is ratio of tine u, 

ocean to tide in well

FIGDBB 8. Map showing magnitude of ratio of tidal fluctuations in the ocean to tidal 

fluctuations in wells and lakes in Angaur.
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-19

island, and many of the ground-water observation stations probably 

are influenced most by the tides at the closest shore. The tidal data, 

however, do provide some indication of the relative permeability of 

the rocks in the immediate vicinity of the observation stations.

QUALITY OF WATER

BAINWATEB

It is commonly believed that rainwater has no dissolved mineral 

content. Actually, floating salt crystals carried by the wind from 

the sea are dissolved by the falling raindrops. Salt crystals also 

are deposited on rooftops and other surfaces where later they may be 

dissolved by the rain. The chloride content of six samples ot! rainwater is shown in table 4.

Sample 3, which had the highest chloride content 11) ppm (parts 

per million) was obtained from the roof of a house that is only 140 

feet from the shore (fig. 4). There are no trees between the house 

and the shore, and salt crystals can be blown directly from the sea to 

the roof. Sample 5, obtained on the same day from a rain gage about 

half a mile from the shore had only 2.9 ppm of chloride. Much of 

the area between the gage and the ocean is covered by forest. The 

lowest chloride content was 2.1 ppm (sample 6). The sample was 

caught on a piece of new plastic material, which was rinsed thoroughly 

with falling rainwater before the sample was collected. The sample 

had no contact with contaminated surfaces. The total chloride content, therefore, must have resulted from solution of salt crystals in the 

air while the rain was falling.

GBOUND WATEB

Water samples were obtained at weekly intervals from most 

existing observation stations on Angaur for December 1949 through 

May 1955. The samples were analyzed for chloride content in the

TABLE 4. Chloride content of rUinwater, Angaur Island

[Analyses from the Pho'sphate "Mining Co., May 24, 1953, unless otherwise noted]

Sample

1__ -

2

3_____________

4__^______.___

5___-_________

6 ?

Sampling site *

Worswick's rooftop

Rain gage (near harbor)

Rain gage (near well 11)

Plastic material ___

Chloride 

content 

(.ppm)

5. 4

4. 9

19

5. 4

2.9

2. 1

Distance 

from shore 

(.feet)

300

300

140

100

2,600

180

1 Locations of sampling sites are shown in figure 4.

2 Analysis from U.S. Geological Survey laboratory, Salt Lake City, Utah, July 6, 1951.
A-20 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

chemical laboratory of the Phosphate Mining Co. An additional 

21 samples of water were obtained for comparison purposes at 

scattered observation stations during 1951-53 (table 5). These 

samples were analyzed in the laboratory of the U.S. Geological Survey 

at Salt Lake City, Utah.

The fluctuations in chloride content of the water from a representative well in each of the three major geologic units in Angaur are shown 

in figures 0 and 10. Like the water levels, the chloride content of the 

ground water responds to rainfall. (Compare figs. 9 and 10 with fig. 

6.) The magnitude of changes in chloride content differs among the 

wells, but in general the chloride increases during the spring and early 

summer, as a result of small recharge from the low rainfall during the 

winter, and decreases during the late summer and autumn, as a result 

of increased recharge from heavy summer rains.

The ground water in province A is not of uniform quality; large 

variations in salinity occur throughout the area (figs. 16-20). The 

variations are due partly to the effects of long solution channels in the 

limestone that are connected with the sea, partly to the scattered beds 

of earthy phosphate that function as relatively impermeable groundwater barriers, and partly to lakes and ponds that were formed when 

the phosphate beds were mined. Tidal movements through the long 

solution fissures bring salt or brackish water into the lakes and ponds 

and cause a gradual increase in the salinity of these bodies. The rate 

and degree of contamination depend on the number and size of hydraulic connections with the ocean. Equilibrium in the salinity of a given 

lake or pond may be reached when the salt content of the water approaches that of sea water or when the freshening effects of rainfall 

balance the salting effects of incoming sea water.

For example, lake 7 had been in existence since 1942 and its salinity 

content, although fluctuating sharply from month to month, had 

reached a long-term equilibrium by 1950 (fig. 11). In February 1951 

a definite current of water could be seen entering and leaving the lake 

at high and low tide, respectively, through a zone of fissures about 

15 feet wide. The average chloride content of 10 samples of the water 

moving into the lake was 15,700 ppm, whereas that of 10 samples of 

the water moving out of the lake was 14,600 ppm. 1 The effect on the 

chloride content of the intermittent influx of saline water is offset 

by precipitation directly 011 the lake.

The variations in salinity that exist or that may be induced in 

province A are illustrated also by the effects of pumping at well 13

1 According to Sverdrup (1942, p. 166) the total dissolved-mineral content of open ocean 

water averages about 35,000 ppm. About 55 percent Cabout 19,000 ppm) of the dissolved 

matter is chloride. A sample of ocean water obtained 2% miles north of Angaur contained 

20,000 ppm of chloride, and the average chloride content of two samples obtained half a 

mile west of Aiigaur was 19,700 ppm.
VX (££ t^ '" '" ''' ''J "'J "/ %u ^Z '" '/' /'S ' £' //' "/' '/ ''" \4& '{ '" ''' ''' ''' '" '/' "' ^^ ^^ ^Z ''' -'^ ''' "J ''' " ''' ''' ''' '" ''' ''' '' ''' _ JASONDJFMAMJJASONDJ FMAMJJASONDJFMAMJJASOND JFMA MAM

FIGURE 9.

1950 1951 

-Graphs showing 5-week moving average of chloride content of water at wells 1 and 4, and combined pumpage

from wells 1 and 2, Angaur, 1950-54.
A-22 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

NomiiAi y3d siyvd NI 'INSINOO
TABLE o. Chemical analyses of ground water from 

[Analyses by U.S. Geological Survey. Dissolved constituents give

Source of water

Well 1 

I.. . ____________

3- 

4

(j

10 

13- 

Test hole 13: 

Water table... ______

(20 feet below

Test hole 16: 

Water table .. _ .

(38 feet below

Lake 1... .. . .. _ 

1 

T..... .............

Date of 

collection

July 3, 1951 

May 21,1953 

Feb. 2, 1951 

May 21,1953

May 21,1953 

Apr. 7, 1952

May 21,1953 

Feb. 2,1951 

May 22,1953 

Apr. 7, 1952

__ do _ __

 do.. 

July 3, 1951 

Apr. 7, 1952

-__-do-----_

 do-. -

---do-- -

Feb. 2, 1951 

May 22, 1953 

Feb. 2, 1951

O 

1

3.6 

2.7 

4.9

2.4

1.6 

1.3 

1.4

2.8 

5.1

. 7

I

0.05 

.02 

.05 

.05

~".~05~ 

.05 

.04 

.07 

.08 

.06 

.20

.11 

.70 

.36

.35 

.04 

.08 

.10

Calcium (Ca)

go

85 

90 

92 

53

77 

46 

132 

135 

117 

54 

54 

30

70 

99 

205

287 

52 

43 

289

e

.2 

£

03

13 

7.9 

12 

9.2

18 

11 

127 

149 

92 

37 

43

26 

121 

342

617 

71 

62 

953

eoelium (Na)

62 

14 

38

9.7

70 

974 

1,300

607 

534 

7,400

Potassium (K)

2.9 

1.8 

1.7

2.5

3.0 

35 

41

38 

19 

269

Bicarbonate (HCO3)

260 

286 

294 

248 

204 

130 

124 

324 

292 

218 

150 

270

319 

180 

110

260 

162 

102 

112

Carbonate (CCh)

0

0 

14 

0 

20 

0

6 

12 

31 

12

0 

12 

10

(1 

22 

10 

14

6

OJ

13

Oj

19 

14 

12 

7.8 

2.3 

47 

24 

24(1 

304 

209 

55 

10

34 

244 

713

1,210 

109 

94 

1,960

Chloride (CD

142 

120 

24 

70 

38 

42 

260 

126 

1.810 

2, 280 

1,450 

570 

680 

260

420 

1,680 

5,690 

9,520

1,120 

950 

13, 700

1 Micromhos at 25° C.
A-24 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

(fig. 12). Well 13 is in earthy phosphate, and the bottom of the well 

is li/4 feet above bedrock, which is a phosphatic limestone. Well 14, 

which is 10 feet east of well 13, penetrates the same earthy material 

and ends iy2 feet above the bedrock. In spite of the short distance 

between the wells, the pumping at well 13 had no noticeable effect 

on the chloride content of the water at well 14. The lack of effect 

indicates that the saline water entering well 13 was drawn up from 

the bedrock in the form of a sharp cone. Changes in the chloride 

content of the water in well 14 apparently were in response to seasonal fluctuations in precipitation. The cone at well 13 was prevented from spreading and affecting well 14 by the tightness of the 

layer of earthy phosphate between the two wells.

On May 23, 1953, well 13 was pumped at the average rate of 58 

gpm (gallons per minute) for 8 hours. The maximum observed drawdown at well 13 was 0.36 foot. The drawdown at well 14 was too 

small to be measured. Pumping conditions were such that the waterlevel measurements do not permit precise hydraulic analysis. A 

rough evaluation of the data, however, suggests that the coefficient of 

transmissibility of the aquifer is several hundred thousand gallons 

per day per foot.

Abrupt increases in salinity with depth in province A were indicated 

by sampling at test hole B-7, the results of which are showTn in the 

graphs in figure 13. The casing in test hole B-7 is perforated throughout its full length, and samples were obtained by means of a container 

which was opened at successively greater depths. The curves show 

that on June 30,1951, the chloride content of water at a depth of about 

13 feet below sea level increased from 440 to 1,100 ppm in a vertical 

distance of less than 2 feet, and on January 13, 1953, the chloride content increased from 370 to 3,440 ppm in a distance of about iy2 feet. 

Thus, at least in test hole B-7, there is only a thin transition zone of 

low to high salinity beneath the thin fresh-water body.

In contrast to that in province A, the ground water in province B is 

of relatively uniform quality. Throughout most of the province, except in parts near the shore, the water contains less than 1,000 ppm 

of chloride (figs. 16-20). The freshest water is in the southern part 

of the province in the area underlain by beach deposits. Throughout 

most of this area the chloride content of the water is less than 100 ppm.

The curves in figure 13 show that the fresh-water body in province 

B (test holes 12 and 13) is thicker than in province A (test hole B-7), 

and suggest that the transition zone from low to high salinity also is 

thicker. Sampling at test hole 12 showed a chloride content of 175 

ppm at the water table and 223 ppm at about 31 feet below sea level, an 

increase of only 48 ppm in a vertical distance of 33 feet. In samples 

from test hole 13 the chloride content remained nearly constant to a
IN PRECIPITATION, 

INCHES

MILLION PER PARTS IN CHLORIDE, 

ONJNIIVE NO QNIIOHO ' anvoNV 
A-26 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

350C 

3000

Q2500

Ij 

_j

^ 2000

tr

UJ

CL 1500

inI 

cc 1000

«i 

CL

^ 500

Q

E ° 

o

_J

Q 1000

500 

tr> o

o

=! ^ 3 

^ O 

^ 2

UJ°

O u_ 

£° !

July 9 Pumping resumed 24 hours a day 

/during construction of cooling pond

July 26 New cooling pond 

in operation

^\

1950

If IV 1 | 

-January 13 Pumping started 24 hours a day

JFMAMJ JASOIMDJFMAMJJASOIMD

1951 1952

FIGURE 12. Graphs showing variation of chloride content of water from wells 18 and 14, 

and pumpage from well 13, Angaur, 1950 52.

depth of nearly 12 feet below sea level and then began to increase, 

but at a greater depth and less sharply than in the samples from test 

holeB-7 (fig. 13).

The records of salinity and the effects of pumping at wells 1 and 2 

also indicate that the fresh-water body is thicker and more extensive in 

province B than in province A. Figure 9 shows a plot of the 5-week 

moving average of the chloride content of well 1 during a 4-year period 

in which the combined pumpage at well 1 and adjacent well 2 averaged 

more than 3 million gallons per month and at times exceeded 6 million 

gallons per month. At no time during the period of record did the 

moving average exceed 250 ppm. This is in contrast to the situation at 

well 13 in province A, where the chloride content rose from less than 

400 ppm to more than 2,500 ppm after 3 months of pumping at the 

rate of about 2.5 million gallons per month (fig. 12).
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-27

0

5

i 

u. 

^ 10

D. 5.

£ 15 i 

1

u. 

0

Q 20 

25

30 

32

- t

- 1 C 1

: *

\ s

=i

E «

_ 1

I

:

i\ _

\ C^. 1

\

ii- i

SEA LEVEL

~-xej°. Jg5j

\.... rest hole 13 j

1 ,

'

953

1

;

E

|

E

E

E

E

E

E

^

1000 2000 3000 4000

CHLORIDE CONTENT OF WATER, IN PARTS PER MILLION

FIGURE 13. Graphs showing variation in chloride content of water with depth in test

holes 12, 13, and B-7.

EFFECTS OF MINING ON THE GROUND-WATER BODY

The phosphate on Angaur was removed by strip mining. In the 

early days, ore above the water table was mined mainly by hand from 

pockets in the limestone. The method left the land pockmarked with 

holes and useless for future agriculture. In later operations the ore 

occurring in extensive beds below the water table was removed by 

draglines (fig. 14), which had a bucket capacity of l1/^ cubic yards 

and could mine to a maximum depth of about IT feet. Wherever the 

mining operations extended below the water table a lake was created 

in which mining could be continued to a maximum depth of 26 feet 

by a floating suction dredge. The mining capacity of the dredge was 

3,800 short tons per month. Because of the intrusion of saline water 

into the excavations, lakes that remained after the completion of 

mining, in addition to being useless for agriculture, were a potential 

menace to adjacent wetlands where taro was grown and to the public 

water supply in the southern part of Angaur.

All the lakes were in province A, where the bedrock contains long 

solution channels. Some of the channels extend from the lake bottoms 

directly to the sea or to zones where the ground water is saline. Influx
A-28 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

of saline water through the solution channels at high tide caused the 

water in the lakes to become saline soon after they were formed.

Owing to the comparatively large capacity of the lakes (table 6), 

the Trust Territory administration became very concerned about the 

immediate or eventual effects of encroachment of saline water. To 

reduce the possibility of damage, the Phosphate Mining Co. was required to fill the lakes with limestone rubble quarried outside the 

mining area. The lakes were filled to a level slightly above the water 

table, and the surface of the fill was made level so that the land 

eventually might be suitable for farming (fig. 15).

TABLE 6. Volumetric capacity of five Jakes on An-gaur Island

Lake

Capacity

.(millions of

gallons)

. ______28

-40 

.43 

.35 

.62

After January 1951, mining was carried out in a manner calculated 

to reduce to a minimum the length of time that the lakes were allowed 

to remain unfilled. This was done by mining each new area in sections, 

and by backfilling each section immediately after mining was completed (figs. 14, 15). During the mining, samples of water were 

obtained daily from a series of observation wells which ringed the 

mining area in order to observe any movement of saline water out of 

the mining area into the surrounding farmland or into province B.

PIGDRB 14. View of a mining area near lake 1 at the beginning of ruining on July 14, 1952.
»;i^'-4^^t,idifm^^^i,^Ml!f!^f^Af^^'yr 

: f't-'i. >>^i%?;^*s*>^,fi(lRfc^;tBfcn i^^^^%ig^f».i

___^____ ^**'^ifti^srf>iiW^;i3^i^iiiS^'%ifffftf5^

FKJURK 15. View of the mining area shown in figure 14 on October 4, 1952. a
A-30 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

6°54'N1 MILE

.2811

Test hole

Lake or pond sampling point

iimfin is cliliiridr ronttnt, ui pnrli per 

million

Backfilled area

 100 

Isochlor.in parts per million

FIGURE 16. Oeneralized isoclilor map of ground water in Aagaur, February 12-15, 1951.

If such movement had occurred, mining would have been suspended.

Actually there was no indication of appreciable spreading of saline 

water from the lakes. Figures 16-20 show the chloride content of 

the water at the water table at most available observation stations
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-31

x30

Lake or pond sampling point

Number is chloride content, in parts per

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 17. Generalized isochlor map of ground water in Angaur, May 19, 1952.

at annual intervals during 1951-55. The chloride at every observation station fluctuated noticeably during the period, but there was no 

indication of any large-scale movement of saline water from one area 

to another. The area in the southern and central parts of the island,
A-32 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

134°09'e

,1375

Test hole

Lake or pond sampling point

\umber is chloride content, m part.- per

million

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 18. Generalized isochlor map of ground water in Angaur, February 9, 1953,

which contains water having less than 100 ppm of chloride, narrowed 

somewhat during the period; but there is no indication that this 

resulted from the mining operations in province A. The boundary 

between provinces A and B in the central part of the island roughly
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-33

1 MILE

Test hole

Lake or pond sampling point 

Number is chloride content, in parts per

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 19. [Generalized isochlor map of ground water in Angaur, June 7, 1954.

corresponds with the position of the 1,000-ppm isochlor. Little significant change in the position of this isochlor is noticeable during the 

5-year period.
A-34 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

134 0 09'E

6°54'N

EXPLANATION

Well

,162

Test hole

X 14,159

Lake or pond sampling point

Number is chloride content, in parts per 

million

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 20. Generalized Lsochlor map of ground water in Angaur, May 31. 1955.

No data are available to indicate the salinity of the ground water 

in province A before mining began in 1909, and it is not certain whether 

the water in that province was fresh at that time. The data shown 

in figures 16-20, however, indicate that provinces A and B apparently 

function as independent ground-water units, and that the quality of
IN PRECIPITATION. 

INCHES

MILLION PER PARTS IN CHLORIDE. 

DNINJIM: NO QNHOHD anvoNv gg-y 
A-26 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

350C

3000

July 9 Pumping resumed 24 hours a day 

/during construction of cooling pond

July 26 New cooling pond 

I / in operation

umping reduced 

to 12 hours a day

I ! VII 

January 13 Pumping started 24 hours a day

JFMAMJ JASOND JFMAMJJASOND

FIGURE 12. Graphs showing variation of chloride content of water from wells 13 and 14, 

and pumpage from well 13, Angaur, 1950 52.

depth of nearly 12 feet below sea level and then began to increase, 

but at a greater depth and less sharply than in the samples from test 

holeB-T (fig. 13).

The records of salinity and the effects of pumping at wells 1 and 2 

also indicate that the fresh-water body is thicker and more extensive in 

province B than in province A. Figure 9 shows a plot of the 5-week 

moving average of the chloride content of well 1 during a 4-year period 

in which the combined pumpage at well 1 and adjacent well 2 averaged 

more than 3 million gallons per month and at times exceeded 6 million 

gallons per month. At no time during the period of record did the 

moving average exceed 250 ppm. This is in contrast to the situation at 

well 13 in province A, where the chloride content rose from less than 

400 ppm to more than 2,500 ppm after 3 months of pumping at the 

rate of about 2.5 million gallons per month (fig. 12).
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-27

0 

5

LJ_

S 10

CL

£ 15 iLJ_

O

§ 20

ii25

30 

32

E

~

f

\ 

\

[i:

- 01

 "o

r

\

?

X<9

\:

X

v^

'' «

\

;/

- t

1 SEA

&*> **,

 o....l«tholel3.j,,lylj

i

1 LEVEL

1

;953__

1

E

:

E

E

E

E

E

E

1000 2000 3000 4000

CHLORIDE CONTENT OF WATER, IN PARTS PER MILLION

FIGURE 13. Graphs showing variation in chloride content of water with depth in test

holes 12, 13, and B-7.

EFFECTS OF MINING ON THE GROUND-WATER BODY

The phosphate 011 Angaur was removed by strip mining. In the 

early days, ore above the water table was mined mainly by hand from 

pockets in the limestone. The method left the land pockmarked with 

holes and useless for future agriculture. In later operations the ore 

occurring in extensive beds below the water table was removed by 

draglines (fig. 14), which had a bucket capacity of l1/^ cubic yards 

and could mine to a maximum depth of about IT feet. Wherever the 

mining operations extended below the water table a lake was created 

in which mining could be continued to a maximum depth of 26 feet 

by a floating suction dredge. The mining capacity of the dredge was 

8,800 short tons per month. Because of the intrusion of saline water 

into the excavations, lakes that remained after the completion of 

mining, in addition to being useless for agriculture, were a potential 

menace to adjacent wetlands where taro was grown and to the public 

water supply in the southern part of Angaur.

All the lakes were in province A, where the bedrock contains long 

solution channels. Some of the channels extend from the lake bottoms 

directly to the sea or to zones where the ground water is saline. Influx
A-28 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

of saline water through the solution channels at high tide caused the 

water in the lakes to become saline soon after they were formed.

Owing to the comparatively large capacity of the lakes (table (5), 

the Trust Territory administration became very concerned about the 

immediate or eventual effects of encroachment of saline water. To 

reduce the possibility of damage, the Phosphate Mining Co. was required to fill the lakes with limestone rubble quarried outside the 

mining area. The lakes were filled to a level slightly above the water 

table, and the surface of the fill was made level so that the land 

eventually might be suitable for farming (fig. 15).

TABLE 6. Volumetric capacity of five lakes on An-gaur Island

Lake

Capacity 

.(millions of

gallons) 

-______28

_____40 

_____43 

_____35 

.____62

After January 1951, mining was carried out in a manner calculated 

to reduce to a minimum the length of time that the lakes were allowed 

to remain unfilled. This was done by mining each new area in sections, 

and by backfilling each section immediately after mining was completed (figs. 14, 15). During the mining, samples of water were 

obtained daily from a series of observation wells which ringed the 

mining area in order to observe any movement of saline water out of 

the mining area into the surrounding farmland or into province B.

FIGURE 14. View of a mining area near lake 1 at the beginning of mining- on July 14, 1952.
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-29
A-30 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

6°54'N

134°09'E

1 MILE

Well

.2811

Test hole

Lake or pond sampling point

umlter ix chloride content, in parts per

million

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 16. iGeneralized isochlor map of ground water in Angaur, February 12-15, 1951.

If such movement had occurred, mining would have been suspended.

Actually there was no indication of appreciable spreading of saline 

water from the lakes. Figures 16-20 show the chloride content of 

the water at the water table at most available observation stations
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-31

6°54'N

1 MILE

.640

Test hole

X 30

Lake or pond sampling point

Number is chloride content, in parts per

million

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 17. Generalized isochlor map of ground water in Angaur, May 19, 1952.

at annual intervals during 1951-55. The chloride at every observation station fluctuated noticeably during the period, but there was no 

indication of any large-scale movement of saline water from one area 

to another. The area in the southern and central parts of the island,
A-32 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

134°09'£

°54'N 

Well

,1375

Test hole

Lake or pond sampling point

Number is chloride content, in parts per

milliim

Backfiiied area

 tOO 

Isochlor, in parts per million

FIGURE 18. Generalized isochlor map of ground water in Angaur, February 9, 1953.

which contains water having less than 100 ppm of chloride, narrowed 

somewhat during the period; but there is no indication that this 

resulted from the mining operations in province A. The boundary 

between provinces A and B in the central part of the island roughly
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-33

134 0 09'E

 6°54'N

1 MILE

EXPLANATION

0 134

Well

.134

Test hole

x288

Lake or pond sampling point

Number is chloride content, in parts per 

million

Backfilled area

 100 

Isochlor, in parts per million

FIGURE 19. (Generalized isochlor map of ground water in Angaur, June 7, 1954.

corresponds with the position of the 1,000-ppm isochlor. Little significant change in the position of this isochlor is noticeable during the 

5-year period.
A-34 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

134°09'E

1 MILE

,162

Test hole

xlt.159

Lake or pond sampling point

Number is chloride content, in parts per

million

Backfilled area

 100 

Isochlor, in parts per million

P'IGURE 20. Generalized isochlor map of ground water in Angaur, May 31, 1955.

No data are available to indicate the salinity of the ground water 

in province A before mining began in 1909, and it is not certain whether 

the water in that province was fresh at that time. The data shown 

in figures 16-20, however, indicate that provinces A and B apparently 

function as independent ground-water units, and that the quality of
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-35

the ground water in province B has not been noticeably affected by 

mining activities in province A.

EFFECTS OF BACKFILLING ON THE GROUND WATER IN

PROVINCE A

The most saline water on Angaur is found in lakes in province A. 

Mining operations in the lakes removed the seal of earthy phosphate 

overlying the highly permeable limestone, thereby exposing solution 

channels that extend to deeper zones containing saline water. The 

extent to which the phosphate seal was broken is indicated by both the 

magnitude of the tidal fluctuations in the lakes and the salinity of the 

lake water. In lake 1, where the seal was only slightly penetrated, 

the ratio of ocean tide to lake tide was 47: 1, and the chloride content 

did not rise much above 1,000 ppm (figs. 8, 11). In lake 2 a greater 

penetration caused a tidal ratio of 4:1 and a chloride content that 

mostly was less than 4,000 ppm but occasionally rose as high as 12,000 

ppm. The seal was most completely breached at lakes 7 and 11, in 

which the tidal ratio was 7:1 and 5:1 respectively, and the chloride 

content at times exceeded 14,000 ppm, or 75 percent of the average 

chloride content of sea water in the area.

To reduce the possibility of the underground movement of saline 

water from the lakes into the croplands surrounding them and 

possibly even into province B, the Phosphate Mining Co. was required 

to backfill the lakes with limestone rubble (fig. 15). The backfill 

material is less permeable than the cavernous limestone in province A. 

Measurements made in 1952 and 1953 showed that tidal fluctuations in 

4 observation wells in the backfilled area had an average lag of 3 hours 

45 minutes behind the ocean tides and an average ratio of ocean tide 

to lake tide of 10:1 (figs. 7, 8). By comparison, in 12 other observation wells in limestone in province A the average lag was only 2 hours 

40 minutes and the average ratio was oi/2 : 1. Thus the backfilling of 

the lakes reduced the rate of influx of saline water into the mined areas 

and eliminated the open reservoirs into which saline water could enter 

freely from subterranean solution channels.

As the backfill curtailed the rate of influx of saline water, recharge 

of fresh water from rainfall caused a decrease in the salinity of the 

ground water in the backfill material. The fluctuations of chloride 

content in well 11 and test hole 16, both in backfilled areas of former 

lake 3, are shown in figures 21 and 22. The chloride content of the 

water at well 11 was about 3,300 ppm at the completion of backfilling 

in February 1951. It dropped to a low of 250 ppm by October 1952, 

after which the chloride content apparently fluctuated in a state of 

dynamic equilibrium with recharge from rainfall. Since April 1954
A-36 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

8888

o m o m

H3d SldVd Nl '3Qia01HO
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-37

N0mil/\l d3d SldVd Nl '
A-38 CONTRIBUTIONS TO THE HYDROLOGY OF ASIA AND OCEANIA

the chloride content at well 11 for the most part has been less than 

500 ppm. This is much less than the chloride content at any other 

observation station in province A (fig. 20).

The freshening process followed a similar pattern at test hole 16 

(fig. 22), but the equilibrium concentration of chloride at the water 

table apparently is about 2,000 ppm much greater than at well 11. 

The equilibrium concentration 20 feet below the water table at test 

hole 16 is about 7,000 ppm.

SUMMARY AND CONCLUSIONS

Water-level measurements and quality-of-water data collected in 

province B on Angaur Island indicate the presence of a relatively 

uniform body of fresh ground water which is probably in the approximate form of the classical Ghyben-Herzberg lens (Brown, 1925; 

Wentworth, 1939,1947). In contrast, the ground water in province A 

is not of uniform quality and throughout much of the area the water 

has a high salinity. Because of the high permeability of the cavernous limestone, it is possible that a Ghyben-Herzberg lens never 

existed in province A.

The mining of phosphate by mechanized methods in province A 

resulted in the creation of large water-table lakes. The breaking 

of the earthy-phosphate seal in the bottoms of several of the lakes 

allowed the influx of saline water by tidal movement through large 

solution cavities. The lakes were backfilled to prevent the eventual 

spreading of the saline water from the lakes into surrounding wetland 

agricultural areas and into province B.

Data collected for 6 years show no significant increase of salinity 

in province B owing to mining operations in province A. The two 

provinces apparently function as independent ground-water units.

Backfilling of the lakes reduced the rate of influx of saline water, 

and the salinity of the ground water in the backfilled areas decreased 

rapidly; a state of dynamic equilibrium was reached within 1 year. 

The equilibrium concentration of the salt, however, was not uniform 

throughout the backfilled area.

REFERENCES

Brown, J. S., 1925, A study of coastal ground water: U.S. Geol. Survey WaterSupply Paper 537,101 p.

Bryan, E. H., Jr., 1946, A geographic summary of Micronesia and notes on the 

climate of Micronesia: U.S. Commercial Co., Econ. Survey rept. [on 

microfilm].

Hutchinson. G. E., 1950, The biogeochemistry of vertebrate excretion: Am. Mus. 

Nat. History Bull., v. 9(3. 554 p.
EFFECTS OF PHOSPHATE MINING ON GROUND WATER, ANGAUR A-39

Sverdrup, H. V., Johnson, M. W., and Fleming, R. H., 1942, The oceans: New

York, Prentice-Hall p. 166. 

Tayama, Risaburo, 1951, Geology of Angaur Island: Tohoku Univ., Inst. Geology

and Paleontology, Short Papers no. 3, p. 91-108. 

U.S. Navy, 1943, Weather summary for Hydrographic Office Publication number

273, Naval Air Pilot, West Pacific, Caroline and Marshall area: U.S.

Navy Hydrographic Office, 107 p.

 1948, Handbook on the Trust Territory of the Pacific Islands : U.S. Navy,

Office of the Chief of Naval Operations, 305 p. 

Wentworth, C. K., 1939, The specific gravity of sea water and the Ghyben-Herzberg ratio at Honolulu: Univ. Hawaii Bull. 8, v. 18, 24 p.

 1947, Factors in the behavior of ground water in a Ghyben-Herzberg system: Pacific Sci., v. 1, p. 172-184.

VTentworth, C. K., Mason, A. C., and Davis, D. A., 1955, Salt-water encroachment as induced by sea-level excavation on Angaur Island: Econ. Geology, 

v. 50, no. 7, p. 669-680.

o