G

round-WaterResourcesofSaipan,

CommonwealthoftheNorthernMarianaIslands

U.S.DepartmentoftheInterior

U.S.GeologicalSurvey

Carruth –– Ground-Water Resources of Saipan, Commonwealth of the Northern Mariana Islands –– WRIR 03-4178

ByRobertL.Carruth

U.S.GeologicalSurveyWater-ResourcesInvestigationsReport03-4178

2003

Mañagaha

Island

PHILIPPINE

SEA

PACIFIC

OCEAN

Laolao

Bay

Tanapag

Harbor

Fanonchuluyan

Bay

So

u

th

Fk

T alufofo

S

tr

Rapu gau Str

145°44'

Puerto

Rico

Calhoun

Sablan

Quarry

and

MauiIV

Marpi

Quarry

Gualo

Rai

Chalan

Kiya

SanVicente

DanDan

IsleyField

andObyan

Koblerville

Kagman

145°48'

15°16'

15°12'

15°08'

SabanetaPt

MuchotPt

INaftanPt

AginganPt

Lake

Susupe

SanRoque

San

AntonioCh

alan

Kanoa

Mt.Tagpochau

Saipan

International

Airport

Akgak

Capital

Hill

Preparedincooperationwiththe

COMMONWEALTHUTILITIESCORPORATION

COMMONWEALTHOFTHENORTHERNMARIANAISLANDS
PREPARED IN COOPERATION WITH THE

COMMONWEALTH UTILITIES CORPORATION

COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS

WATER-RESOURCES INVESTIGATIONS REPORT 03-4178

Land use, geography, geology–SHEET 1 OF 3

Carruth, R.L., 2003, Ground-Water Resources of Saipan, Commonwealth of the Northern Mariana Islands

arily on and adjacent to the western coastal plain and the plateau areas

Kagman Peninsula. The interior of the island and most of the northern

ted. Parts of the central uplands and the northern region of the island

d grassland, and small pockets of primary forest. Land uses include

ufacturing, small businesses, agriculture, and residential activities.

ptic systems, and commercial activities may present a potential for

people in 2000 (U.S. Census Bureau, 2001), resides primarily in rural

he southern plateau, and on the Kagman Peninsula, occupying about 70

g public, commercial, and residential areas. Public land accounts for about

cent, and residential land about 35 percent. Public land use includes the

ultural cooperatives, Lake Susupe and adjacent wetland areas, parks, and

otel resorts, golf courses, garment manufacturing, and small businesses.

farming and grazing, and homestead developments. The remaining 30

assland, secondary forest, and isolated regions of primary forest.

for ground-water contamination include (1) quarries used for the extraction

solid-waste dump site near Puerto Rico, (3) small-scale sewage-waste

ted away from the sewer-treatment distribution system, (4) commercial

uch as gasoline stations, dry cleaners, and automotive repair and painting

ding toxic materials, was dumped at the unlined solid-waste dump located

n February 2003, the dump was closed and a new landfill constructed to

USEPA) specifications was opened at Bañaderu on the northern end of the

ated by a succession of nearly horizontal limestone platforms and

scend from the sea towards central uplands in the northern three

rn, and northern coasts are backed by limestone cliffs of varying relief

and coves. The western coast is formed by a narrow coastal plain of

e coastal plain is a small brackish lake surrounded by an extensive

s a shallow lagoon bordered by a barrier reef.

ds that make up the CNMI, Saipan is only about 13 mi long north to south

mi2 island has a maximum elevation of 1,555 ft above sea level at Mount

2 ft at the top of the Kalabera cliffs (Laderan Kalaberan Lichan), toward

f Saipan were separated into six principal physiographic subdivisions by

ivisions, the central uplands cover the largest land area and most of the

s encompass northern and southern terraced limestone uplands that are

slopes that are dissected by erosion into short, rugged valleys and steep

au, the central uplands are bordered by a group of high volcanic hills that

et of limestone platforms and terraced benches that form a terraced pattern

orms are conspicuous, broad, and relatively flat areas at the southern,

f the central uplands. The elevations of the limestone platforms range from

occur around and between the limestone platforms. The southeastern

w limestone platforms and terraced benches bordering the eastern coast in

t. The Donni clay hills belt extends northward from Mount Laulau as an

ith an average width of 1/2 mi. The area is marked by short and rounded

ravines at elevations from about 100 to 500 ft.

nuously south from the beaches at San Roque to Agingan Point and ranges

rn coastal plain is predominately composed of emerged calcium carbonate

d to elevations generally not more than 15 to 20 ft. Part of the coastal plain

ch surrounds the brackish-water Lake Susupe. Lake Susupe has an area of

ground water flows into the lake during periods of low lake stage (Wong

-coast beach is a shallow lagoon which is separated from the Philippine

of Saipan (modified from

Figure 3. Aerial photo looking east over Mañagaha Island towards Saipan (see figure 2 for viewpoint of photograph on map).

Base modified from USGS topographic map

of Saipan Island, 1:25,000. 1983

CENTRAL UPLANDS

LOW LIMESTONE PLATFORMS

LOW TERRACED BENCHES

DONNI CLAY HILLS BELT

SOUTHEASTERN COASTAL FAULT RIDGES

WESTERN COASTAL PLAIN

WETLAND

MOUNTAIN PEAK LOCATION, NAME, AND

ELEVATION, IN FEET ABOVE SEA LEVEL

VIEWPOINT AND DIRECTION OF PHOTOGRAPH

IN FIGURE 3

EXPLANATION

0 1 2 MILES

0 1 2 KILOMETERS

145 ̊44'

145 ̊48'

15 ̊16'

Sabaneta Pt

Laolao

Kattan Pt

I Naftan Pt

Laderan Kalaberan

Lichan

Laderan Kalaberan

Lichan

820

778

1,555

942

772

Pidos

Kalahe

Mt. Achugau

Mt. Tagpochau

Mt. Laulau

Pidos

Kalahe

Mt. Achugao

Mt. Tagpochau

Mt. Laulau

Mt. Laulau

820

778

1,555

942

772

772

EXPLANATION

GEOLOGIC UNIT

Deposits of Pleistocene and Holocene Age - Emerged limesand,

beach, wetland, artificial fill, and volcanic outwash

Tanapag Limestone - Raised fringing-reef limestone, generally

below elevations of 100 feet

Mariana Limestone - Clastic and reef limestone with argillaceous

rubbly facies

Tagpochau Limestone - Dominated by a massive, compact,

inequigranular pinkish limestone, but also includes rubbly, marly,

tuffaceous and transitional carbonate facies

Fina-Sisu Formation - Interlayered andesitic marine tuffs and andesite

flow rocks

Densinyama Formation - Includes marine transitional rocks and

volcanically derived conglomerates, tuffaceous sandstone, and

andesitic breccia

Hagman Formation - Andesitic breccia, tuff, lava flows, conglomerate,

and tuffaceous limestone

Sankakuyama Formation - Dacitic tuff, breccia, and flow rocks

LINE OF SECTION

FAULT - High angle or vertical

Surficial geology

Geologic sections - Arrows show direction of thrust

SELECTED WELL NEAR SECTION LINE AND NAME

MAP SECTION

limestones volcanic rocks

0 1 2 MILES

0 1 2 KILOMETERS

145 ̊44'

145 ̊48'

15 ̊12'

15 ̊16'

15 ̊14'

15 ̊10'

15 ̊08'

Sabaneta Pt

Muchot Pt

Laolao Kattan Pt

15 ̊06'

I Naftan Pt

Agingan Pt

(A) Surficial geology

Mt. Talufofo

Mt. Achugao

A

A'

B

B'

C

C'

A A'

Pidos

Kalahe

Mt. Tagpochau

Mt. Laulau

Pidos

Kalahe

Mt. Tagpochau

Mt. Talufofo

Mt. Laulau

Qr

Tt

Td

Th

Ts

Qta

Qm

Tf

Qr

Ts

Td

Th

Qta

Qm

Tf

Qr

Tt

Td

Th

Ts

Qta

Qm

Tf

Qr

Ts

Td

Th

Qta

Qm

Tf

Mañagaha

Island

Tanapag II Spring

(Bobo Mames)

Tanapag I Spring

(Bobo Agatan)

KAS-1

GR-151

KG-2

KG-4

KV-18

KV-15

OB-9

OB-9

Papago

Spring

San Roque

CENTRAL UPLANDS LIMESTONE PLATFORM

WESTERN COASTAL PLAIN

Mañagaha

Island

Barrier reef

Mt. Tagpochau

photo courtesy of www.delbenson.com
Base modified from

U.S.Geological Survey, 1:25,000, Island of Saipan, 1983

Shaded relief from USGS digital elevation model

Mañagaha

Island

PHILIPPINE

SEA

PACIFIC

OCEAN

Laolao

Bay

Tanapag

Harbor

Fanonchuluyan

Bay

South Fk T alufofo Str

Rapu gau

Str

145°44'

Puerto

Rico

Puerto

Rico

Calhoun

Sablan Quarry

and

Maui IV

Marpi

Quarry

Gualo

Rai

Chalan Kiya

San Vicente

Dan Dan

Isley Field

Koblerville and Obyan

Kagman

145°48'

15°16'

15°12'

15°08'

Kagman

Peninsula

Sabaneta Pt

Muchot Pt

I Naftan Pt

Agingan Pt

Lake

Susupe

San Roque

San

Antonio

Chalan

Kanoa

Vertical scale greatly exaggerated

TRANSITION ZONE

FRESHWATER

SALTWATER

VOLCANIC ROCK

(low permeability)

TRANSITION

ZONE

Coastal

spring flow and

seepage to

ocean

Spring

discharge

or gaining

stream

Recharge

Runoff

Evaporation

Precipitation

Ground-water

flow

Water table Ocean

Water table

WEST EAST

Potable part of

freshwater lens

Freshwater-saltwater

coastal aquifer

High-level limestone aquifer

Yield from water wells

placed in this material

generally is very low

LIMESTONE

(high permeability)

LIMESTONE

(high permeability)

1) Before pumping: well has

already penetrated high chlorideconcentration in the upper transition

zone

3) After prolonged pumping: upconing

causes chloride concentrations to continue

to increase until a new equillibrium

is reached

2) During pumping: upconing

causes chloride concentrations to

rise higher than initial concentrations

Well

Pumped waterPumped water

FRESHWATER

UPPER

TRANSITION

ZONE

Original

water level Water table

Ground surface

Saltwater

upconing

Drawdown

in well

250 mg/L

1000 mg/L

5000 mg/L

Chloride

concentration

1) Before pumping 2) During initial pumping 3) After prolonged pumping

Well

Pumped

water Pumpedwater

FRESHWATER

TRANSITION ZONE

TRANSITION ZONE

RISES

TRANSITION ZONE

CONTINUES TO RISE

Saltwater intrudes well

Drawdown in well

Original water level Water table

Ground surface

1) Before pumping 2) During initial pumping 3) After prolonged pumping

Well

Pumped water Pumped water

FRESHWATER

TRANSITION ZONE

TRANSITION ZONE

RISES

TRANSITION ZONE

STABILIZES AT A LEVEL BELOW

THE BOTTOM OF THE WELL

Drawdown Sc in well reened

interval

Original water level Water table

Ground surface

A. Low chloride concentrations result from a properly developed freshwater lens

B. High chloride concentrations result from wells that penetrate into the freshwater-saltwater transition zone

C. Chloride concentrations increase over time from wells that penetrate too close to the transition zone and/or are pumped at excessive rates

Pumped

water

TRANSITION ZONE

TRANSITION ZONE

FRESHWATER

FRESHWATER Original freshwater boundary

Freshwater boundary

Freshwater boundary

Saltwater

upconing

Cone of

depression Drawdown

Original water table

Water table

Water table

Ground surface

Inland migration

of brackish water and

reduced spring flow

and seepage to ocean

Coastal spring flow and

seepage to ocean

Ground-water Spring flow

flow

Ocean

Ocean

BEFORE PUMPING

DURING PUMPING

Figure 6. Effects of ground-water withdrawal on the potable part of the freshwater lens in a high

permeability island aquifer.

Figure 7. Rainfall at CPA Tower rain gage, departure from mean monthly (van der Brug, 1985) rainfall,

municipal ground-water withdrawal, and chloride concentration at municipal wells, Saipan. Chloride and

pumpage data from Commonwealth Utilities Corporation. Rainfall data from Commonwealth Ports Authority

(CPA).

Figure 9. Diagram showing how (A) low chloride concentrations result from a properly developed freshwater

lens, (B) high initial chloride concentrations result from a well that penetrated into the freshwater-saltwater

transition zone, and (C) chloride concentrations increase as a result of pumping from a well that penetrates

close to the transition zone and/or is pumped at a rate that is excessive given the proximity of the bottom

of the well to the transition zone.

Figure 12. Daily mean water level at Akgak monitor well 1 (AG-MW1), daily mean discharge at Donni

Spring, and monthly rainfall at Saipan International Airport, 1969-99. Monthly rainfall data from

University of Guam Water and Environmental Research Institute (WERI).

Figure 5. Schematic hydrogeologic section through part of Saipan showing ground-water flow pattern and

salinity structure. Line of section shown on figure 8.

0 1 2 MILES

0 1 2 KILOMETERS

Mt. Tagpochau

AG-MW1

Donni Spring (Bobo I Denni)

Tanapag II Spring (Bobo Mames)

Tanapag I Spring (Bobo Agatan)

Achugao Spring (Bobo Achugao)

Mt. Tagpochau

Tanapag II Spring (Bobo Mames)

Tanapag I Spring (Bobo Agatan)

Donni Spring

(Bobo I Denni)

Achugao Spring (Bobo Achugao)

CPA

Tower

Isley Reservoir

Isley Reservoir

Saipan

International

Airport

DD-MW1

AG-MW1

ST-MW1

KG-MW3

IF-MW1

KV-MW1

KV-MW1

IF-MW2

OB-MW1

IF-MW1

Donni Spring

(Bobo I Denni)

MUNICIPAL WELL FIELD AND NAME

LOW-PERMEABILITY VOLCANIC ROCKS AT OR ABOVE SEA LEVEL

MONITOR WELL AND NAME

DEEP-PROFILING MONITOR WELL AND NAME

RAINFALL STATION AND NAME

SEA-LEVEL STATION

DEVELOPED SPRING AND NAME

LINE OF SECTION -- SEE FIGURE 5

EXPLANATION

PREPARED IN COOPERATION WITH THE

COMMONWEALTH UTILITIES CORPORATION

COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS

WATER-RESOURCES INVESTIGATIONS REPORT 03-4178

Ground water, rainfall, and chloride concentrations–SHEET 2 OF 3

Carruth, R.L., 2003, Ground-Water Resources of Saipan, Commonwealth of the Northern Mariana Islands

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Chloride concentration in well water.–Chloride concentration is used as a quantitative measure of salinity, and a

concentration of 250 mg/L (about 1.3 percent seawater chloride concentration) is the USEPA recommended limit for

drinking water. A summary of mean daily volume-weighted chloride concentration at municipal well fields in

October 1998 is shown in table 1. The volume-weighted average chloride concentrations account for well

withdrawal rate and weights chloride concentrations measured at each well by the volume of water pumped at that

well. The volume-weighted average chloride concentrations from all well fields in early October 1998 ranged from a

low of 63 mg/L in the Akgak and Capital Hill well fields, to a high of 2,853 mg/L in the Maui IV well field (table 1).

The volume-weighted chloride concentration of water from all well fields except Akgak and Capital Hill exceeded

250 mg/L. Chloride concentrations of water from production wells, analyzed quarterly by the CUC, are shown with

estimated withdrawal data for 1995–2000 in figure 7.

Specific conductance was measured by the USGS throughout the water column in six deep-profiling monitor wells

using a down-the-hole sampler. The samples were analyzed for chloride concentration by the CUC laboratory. All

deep-profiling monitor wells are in freshwater-saltwater coastal aquifers; about 96 percent of municipal groundwater withdrawal is from these aquifers. Vertical chloride-concentration profiles of the deep-profiling monitor wells

are shown in figure 8. Data from deep-profiling monitor wells IF-MW2, OB-MW1, and KG-MW3 indicate that the

thickness of the potable part of the freshwater lens near these wells ranges from about 30 to 45 ft. At deep-profiling

monitor wells DD-MW1, KV-MW1, and ST-MW1, the data show that, although there is an upper zone of fresher

water about 30 to 40 ft thick, the chloride concentration exceeds that of potable freshwater. None of the production

wells near KV-MW1 produce water with a chloride concentration less than 250 mg/L, and most produce water with

over 1,000 mg/L chloride concentration.

The chloride concentration of water pumped at production wells depends on the position of the transition zone

relative to the pump intake in the well. The transition zone will rise when the wells are pumped (fig. 9). Historically,

many production wells in the coastal aquifers were completed and screened into the freshwater/saltwater transition

zone or near the bottom of the freshwater layer. At new well fields in Obyan and Kagman, the CUC gave careful

consideration to well depth relative to sea level, well spacing, pumping rates, and the results of a study of groundwater occurrence and estimated well yields from the Mariana Limestone (Hoffmann and others, 1998). The chloride

concentration of water from the new well fields in Obyan and Kagman has remained low compared to the volumeweighted average chloride concentration of water from all municipal production wells (fig. 7).

In addition to the daily fluctuation in water level caused by the ocean tides, water levels in wells in the coastal

aquifers also vary over longer time periods in response to non-tidal changes in sea level (fig. 11). The sea level at the

Saipan Sea Port ranged from about 0.55 ft to 2.15 ft elevation (relative to mean sea level) from 1998 through 2000.

During the period of tide gage record that corresponds to the well records, water levels in the coastal-aquifer wells

ranged from about 1.45 ft to 2.55 ft elevation (fig. 11).

Even in properly constructed and spaced well fields, increased pumping rates and/or a thinning of the freshwater

lens due to decreased recharge during periods of drought may cause the transition zone to rise to the level of the

pump intakes, causing chloride concentrations in the pumped water to rise. For example, the chloride concentration

of water from municipal well MQ-1 in the As Matuis area (Marpi Quarry) was about 300 mg/L at a pumping rate of

60 gal/min during a pumping test in September 1992 (unpublished pumping-test data on file at the USGS Saipan

Field Office). The pumping rate was increased to 115 gal/min in an attempt to meet a higher demand for water in the

area and the chloride concentration increased to 3,900 mg/L in April 1996. Additionally, during the drought

associated with the 1997–98 El Niño, the volume-weighted average chloride concentration of water from all

municipal production wells increased from about 850 mg/L to 1,150 mg/L (fig. 7), indicating that the transition zone

rose relative to the level of the pump intakes in many production wells.

The chloride-concentration data in table 1 and figures 7 and 8 indicate that many wells on Saipan were either (1)

drilled into the freshwater-saltwater transition zone below the freshwater layer, effectively preventing the production

of potable water (fig. 9B), or (2) drilled close to the transition zone and operated at a pumping rate that is excessive

given the proximity of the well to the transition zone, causing an eventual rise in chloride concentration (fig. 9C).

For wells in the freshwater-saltwater coastal aquifers, the data presented here show that pumping-induced upconing

of the transition zone is a major constraint on well location, spacing, depth, and pumping rate.

CHANGES IN THICKNESS OF THE FRESHWATER LENS

The thickness of the freshwater lens changed at some of the monitor wells as a result of seasonal recharge, a

drought, and possibly due to ground-water withdrawal. Freshwater thickness decreased by about 10 to 12 ft at

wells IF-MW2 and KG-MW3 after a period of significantly less than average rainfall associated with the 1997–98

El Niño. Freshwater thickness did not change significantly at well OB-MW1 from October 1998 to October 1999,

when wet-season rainfall in 1999 was closer to average.

Chloride concentrations with respect to depth in monitor wells IF-MW2 and KG-MW3 were higher after the

drought associated with the 1997–98 El Niño in the Pacific (see figs. 7 and 8). The thinning of the freshwater lens

results from a decrease in the amount of recharge to the aquifer relative to discharge during dry weather. In both

wells, the base of potable water and the midpoint of the transition zone (9,500 mg/L chloride concentration) rose 10

ft or more between September 1998 and October 1999; a decrease of freshwater thickness of about 25 percent. Some

of the freshwater thickness decrease at KG-MW3 may also be attributable to increased pumping from new

production wells that were activated in September 1998 (fig. 7).

Rainfall during the 1999 wet season also was lower than normal but closer to average than the previous wet season

in 1998. The depth to the base of potable water increased at KG-MW3 by about 3 ft between March and October

1999. The increase in thickness of the freshwater lens at KG-MW3 shown in figure 8 may be more indicative of the

average yearly change due to wet season recharge. The thickness of the potable part of the freshwater lens did not

change significantly at well OB-MW1 from October 1998 to March 1999, a period when rainfall was about 66

percent of average (fig. 8).

After a normal wet season, the thickness of the freshwater lens would be expected to increase in response to an

increase in recharge. The chloride-depth profiles show no increase in freshwater thickness or only a slight increase

(about 3 ft) in 1998 and 1999. Because the 1998–99 wet seasons were drier than average, the freshwater lens would

not be expected to increase to the same size as it would after a wet season of more typical rainfall. The data illustrate

the importance of continuing data collection in the deep monitor wells to more fully understand how wet season

recharge affects the availability of fresh ground water on Saipan.

WATER-LEVEL AND SPRINGFLOW RECORDS

Water levels fluctuate daily as much as 0.25 ft in wells closest to the coast in response to ocean tides. Wells in

the interior of the island typically do not show daily water-level fluctuations caused by ocean tides (water levels in

high-level aquifers show no fluctuation). Water levels in all coastal-aquifer wells rise and fall in response to nontidal short-term and seasonal changes in sea level. Changes in the water-table elevation in the coastal aquifers

caused by varying recharge are difficult to evaluate because of the dominance of water-level changes caused by

sea-level variations. In contrast, water-level elevation in the high-level limestone aquifers and flow from springs

that partially drain these aquifers fluctuate seasonally and are sensitive to periods of low rainfall.

The record of hourly water level in well KG-MW3 during January 1–15, 1999 shows that the water-table elevation

fluctuates in response to the ocean tide (fig. 10). The semi-diurnal tidal signal from the ocean is attenuated as it

travels through the aquifer and the daily fluctuation of the water table decreases with increasing distance from the

ocean. The daily water-level changes in well KG-MW3, about 3,000 ft from the coast, average about 0.25 ft.

Monitor wells IF-MW1 and OB-MW1, about 4,500 ft and 3,700 from the coast, respectively, show no daily waterlevel change. Attenuation of the daily tidal signal also is affected by aquifer permeability; lower aquifer permeability

results in greater attenuation.

The difficulty in determining the effects of recharge and withdrawal on the water table in the coastal aquifers is

illustrated in figure 11. For example, the rise in water level of nearly 0.6 ft in IF-MW1 and OB-MW1 from May to

September 1998 corresponds to a similar change in sea level and masks the decline in recharge during the period of

lower than average rainfall. All of the fluctuations in water level in the monitored wells in the coastal aquifers appear

to be directly in response to changes in sea level.

Water level and springflow in the high-level limestone aquifers in the central uplands are not sensitive to sea level;

however, water-level in the high-level limestone aquifers and flow from springs fluctuate seasonally and are

sensitive to periods of low rainfall (fig. 12). The dry weather associated with the 1997–98 El Niño (as well as 1983

and 1987 El Niño events) affected the water level in the high-level limestone aquifers. From January 1998 to March

1999 the water level at monitor well AG-MW1 decreased from 407 ft to 378 ft (fig. 12). The water-level elevation at

AG-MW1 decreased to 376 ft during the 1983 El Niño.

Many high-level springs and seeps are found in the central uplands of Saipan, but most have a low discharge

(about 5 to 10 gal/min) and may not flow during the dry season. H.T. Stearns (U.S. Geological Survey, written

commun., 1944), estimated that the total flow of high-level springs in the dry season is 250,000 gal/d, and about

1,000,000 gal/d in the wet season. Springflow at Donni Spring, the largest of the developed high-level springs,

fluctuates seasonally from less than 1 ft3/s in the dry season, to over 7 ft3/s in some wet seasons (fig. 12) (1 ft3/s is

equal to about 450 gal/min). Flows of 2 to over 8 ft3/s at Donni Spring are short duration and follow periods of

heavy rainfall. The continuous-recording gage at Donni Spring was discontinued in 1983.

GROUND-WATER RESOURCE: SATURATED LIMESTONES

The primary municipal water supply for the island of Saipan comes from ground water. Saturated limestones

form the principal aquifers on the island. Rainwater infiltrates the high-permeability limestones and maintains a

freshwater body within the island. As on other oceanic islands, fresh ground water on Saipan is underlain by

saltwater. Some fraction of the fresh ground water can be withdrawn by wells, but freshwater quality and

availability can be affected by overpumping or sustained periods of dry weather.

On Saipan, the position of the volcanic basement rocks relative to sea level and the overlying limestone affects the

occurrence of ground water. Most of the recoverable fresh ground water in Saipan is found in limestones that extend

from the land surface to some distance below sea level (fig. 5). A smaller amount of recoverable fresh ground water

is found in limestones that overlie volcanic basement rocks above sea level. Test drilling has shown the volcanic

basement rocks contain fresh ground water; however, the volcanic rocks generally are not considered an aquifer

because of their low permeability (permeability describes the ease with which water can move through rock). In

contrast, the limestone generally has high permeability resulting from intergranular pores and spaces between the

accumulated material as well as larger voids, which formed when the limestone was deposited or developed later by

dissolution.

Ground-water withdrawal from wells, saltwater upconing, and regional lens depletion.–Some fraction of fresh

ground-water recharge can be withdrawn continuously by wells, in effect capturing a fraction of the natural

discharge. The most efficient means of developing freshwater from a thin lens is to locate widely spaced wells near

the water table where the lens is thickest and to maintain low, uniform pumping rates at each well (fig. 6). This

spreads withdrawal over a wide area and skims freshwater from the lens. The more widespread the withdrawal, the

greater the fraction of recharge that can be withdrawn with salinity acceptable for the municipal supply. Saltwater

upconing can contaminate wells if the lens is too thin, if wells are too deep (too close to the transition zone), or if too

much water is withdrawn from a small area. Even if wells are designed and placed to minimize local upconing, the

lens will gradually shrink to a size that is in balance with the withdrawal. This regional shrinkage raises the

transition zone closer to the wells, potentially close enough to increase the salinity of pumped water. Shrinkage of

the freshwater lens due to dry weather can also contribute to high salinity in wells.

RAINFALL, GROUND-WATER WITHDRAWAL, AND CHLORIDE CONCENTRATIONS IN WELL WATER

Saipan receives about 80 in. of rainfall annually and has distinct wet and dry seasons. All fresh ground water

on Saipan originates as rainfall. About 11 Mgal/d is withdrawn from 140 continuously operated municipal wells

located primarily in the southern, east-central, and central regions of the island. Most production comes from

well fields in southern Saipan, accounting for about 6.4 Mgal/d. The volume-weighted chloride concentration of

pumped water from municipal well fields ranges from less than 100 mg/L in the Akgak and Capital Hill well

fields to over 2,000 mg/L in the Maui IV, Puerto Rico, and Marpi Quarry well fields. Chloride-concentration data

from monitor and municipal wells indicate that pumping-induced upconing of the transition zone is a major

constraint on well location, spacing, depth, and pumping rate.

Rainfall.–Seasonal differences in rainfall define distinct wet and dry seasons on Saipan (fig. 7). The months of July

through November (the wet season) receive about 67 percent (53 in.) of the annual rainfall; January through May

(the dry season) receive 21 percent (17 in.) of the rainfall; and December and June (transitional months) receive 12

percent (10 in.) of the rainfall. Rainfall records for Saipan are available for most years since 1901 from German,

Japanese, and U.S. sources; however, there is confusion about the location of some rain gages and no long-term

records are available for any one location (unpublished rainfall data on file at the USGS Saipan Field Office). From

1901 to 2000, the annual totals of rainfall ranged from a low of 34.23 in. in 1998 at the Commonwealth Ports

Authority (CPA) Tower rain gage at Isley Field, to a high of 145.07 in. in 1978 at the former Hakmang

Communication Center on the Kagman Peninsula. The lowest monthly rainfall recorded from 1901 to 2000 was 0.1

in. in the dry season month of January 1998 at the Isley Reservoir rain gage at Isley Field (unpublished rainfall data

on file at the USGS Saipan Field Office). In 1998, rainfall at some Saipan stations was less than half of normal, the

lowest 12-month rainfall recorded since data collection began in 1901. The highest amount of monthly rainfall

recorded for the period of record was 73.25 in. in August, 1978, when tropical storms Carmen, Winnie, and Tess

passed over the island. The record high monthly rainfall was recorded at the Hakmang Communication Center on the

Kagman Peninsula. Rainfall from tropical storms makes up a significant percentage of the total annual rainfall and a

lack of storms may significantly contribute to drought conditions.

Rain that falls on Saipan is evaporated, consumed by plants, runs directly off the land surface into the ocean, or

recharges ground water. The proportion of rainfall that recharges ground water depends on several factors, including

soil type and thickness, geology, climate, vegetation, and topography. Estimates of ground-water recharge from

previous studies range from about one quarter to one third of the annual rainfall (Mink, 1987). Using a water-budget

accounting procedure on daily rainfall data at the Saipan airport from 1987 to 1997, about 30 percent (23 in.) of

rainfall is estimated to recharge ground water on Saipan (S.B. Gingerich, USGS, written commun., 2000).

Gingerich’s (2002) calculation procedure is described in a hydrologic study of Tinian where the same procedure was

used for 1987 to 1997 Tinian rainfall data.

Ground-water withdrawal.–Ground water is pumped and distributed by the CUC, the municipal water purveyor for

the CNMI. On Saipan, about 140 municipal production wells are active continuously. Pumps typically are operated

at maximum capacity 24 hours per day, except when one or more pumps are turned off for maintenance or

replacement. The production wells are unequally divided into 15 well fields (fig. 8). Accurate records of groundwater production rates are sparse. In October 1998, a synoptic survey was done to meter and record production rates

at all municipal wells and developed springs. A summary of the results of the survey to determine municipal groundwater withdrawal are shown in table 1. Complete results of the synoptic survey are given in Carruth (2000). Daily

production at each well was determined by multiplying the instantaneous meter reading in gallons per minute by

1,440 minutes per day; this method of estimating daily withdrawal is considered reasonable over short periods of

time because all production wells are operated continuously. Municipal ground-water withdrawal in October 1998

for the entire island was about 11.15 Mgal/d, and withdrawal from southern Saipan well fields accounted for about

57 percent of the total. From a review of available records at the CUC, estimated withdrawal and chlorideconcentration data for 1995–2000 are shown in figure 7. Increases in withdrawal correlate to the activation of new

wells or well fields.

Aquifers where water-level elevation is affected by ocean tides (coastal aquifers).–As in other small oceanic

islands, most of the available fresh ground water in Saipan is in a freshwater-saltwater coastal-aquifer system where

a lens-shaped body of fresh and brackish ground water floats on denser saltwater within the island (fig. 5). Most

ground-water withdrawal on Saipan is from the Mariana Limestone aquifer, a coastal aquifer composed of wellindurated, coarsely porous, fragmental limestones that locally contain sedimentary facies of reworked volcanic

materials.

Aquifers that overlie volcanic basement rocks that extend above sea level (high-level aquifers).– In the central

uplands of Saipan, fresh ground water is found in limestone aquifers that overlie lower-permeability volcanic

basement rocks that extend above sea level (fig. 5). Ground-water in these high-level limestone aquifers is above the

influence of short-term sea-level fluctuations and has a low salinity, originating entirely from rainfall. The horizontal

extent and saturated thickness of these aquifers are limited and overpumping or sustained periods of dry weather can

affect ground-water availability. Ground water from high-level limestone aquifers is withdrawn at the Akgak and

Capital Hill well fields. Additionally, many low-discharge springs and seeps partially drain high-level aquifers in the

central uplands. Water from Donni Spring, Tanapag I and II Springs, and Achugao Spring contributes to the

municipal supply. Water level in the high-level aquifers and flow from springs that partially drain these aquifers

fluctuate seasonally and are sensitive to periods of low rainfall. Water level and springflow are highest during the

wet season and decline throughout the dry season, reaching their lowest levels during sustained periods of below

normal rainfall.

Theoretical freshwater lens and actual conditions on Saipan.–The Ghyben-Herzberg principle commonly is used

to relate the thickness of a freshwater lens in an ocean-island aquifer to the density difference between freshwater

and saltwater. The principle states that the theoretical interface between freshwater and saltwater is at a depth below

sea level that is 40 times the elevation of the water table above mean sea level (Todd, 1980). In reality, instead of a

sharp freshwater-saltwater interface, freshwater is separated from saltwater by a transition zone in which salinity

grades from freshwater to saltwater. In many field studies, the Ghyben-Herzberg interface depth has been found to

correspond to the depth of about a 50-percent mix of freshwater and saltwater. Under equilibrium flow conditions in

permeable aquifer systems, the Ghyben-Herzberg principle may provide a reasonable estimate of freshwater depth if

the transition zone is thin relative to the thickness of the freshwater lens.

Definition of potable freshwater.–Salinity in a freshwater lens is gradational, from an upper freshwater core through

the underlying transition zone to saltwater. A chloride concentration of 250 mg/L is the maximum contaminant level

(MCL) for drinking water recommended as a secondary standard by the USEPA (U.S. Environmental Protection

Agency, 1991). Secondary standards are not mandatory requirements, but instead establish limits for constituents

that may affect the aesthetic qualities of drinking water (taste and odor, for example). In this report, the potable part

of the freshwater lens is defined as water having a chloride concentration less than or equal to 250 mg/L. Seawater

has a chloride concentration of about 19,200 mg/L (Thurman, 1990).

Ground-water flow, recharge, and temporal variations in lens size.–Water flows continuously in a freshwater lens.

Rainfall infiltrates and recharges the aquifer, where frictional resistance to flow causes the water to accumulate and a

lens to form. Freshwater flows by gravity to the shore, where it discharges as diffuse seepage and as springflow at

shoreline and submarine springs (fig. 6). On small islands such as Saipan, mixing in the transition zone results

mainly from tidal fluctuations superimposed on the gravity-driven flow of freshwater toward the shore. Under

conditions of steady recharge and no pumping, the lens would have a fixed size. In reality, rainfall (and therefore

recharge) is episodic and seasonal, and lens volume fluctuates naturally with time. The lens discharges continuously

throughout the year, but shrinks during dry periods when recharge diminishes or ceases. The lens expands during

high recharge episodes, which commonly occur within a definable wet season.

Figure 8. Municipal well fields, low-permeability volcanic rocks at sea level, and chloride concentration

with depth at deep-profiling monitor wells, Saipan (water samples collected by the USGS were analyzed

for chloride concentration by the CUC laboratory).

Akgak

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

2,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

DEPTH BELOW

WATER TABLE, NI FEET

0

20

40

60

80

100

120

140

160

180

9/28/98

3/10/99

10/15/99

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

2,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

DEPTH BELOW

WATER TABLE, NI FEET

0

20

40

60

80

100

120

140

160

180

9/24/98

3/15/99

10/14/99

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

2,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

DEPTH BELOW

WATER TABLE, NI FEET

0

20

40

60

80

100

120

140

160

180

7/20/99

10/18/99

Koblerville monitor well 1 (KV-MW1)

Obyan monitor well 1 (OB-MW1)

Saddok Tasi monitor well 1 (ST-MW1)

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

2,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

DEPTH BELOW

WATER TABLE, NI FEET

0

20

40

60

80

100

120

140

160

180

10/5/98

3/9/99

10/18/99

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

2,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

DEPTH BELOW

WATER TABLE, NI FEET

0

20

40

60

80

100

120

140

160

180

3/11/99

7/23/99

10/14/99

Figure 10. Selected hourly ground-water levels and sea level, Saipan, January 1-15, 1999. Sea-level

data from the University of Hawaii Sea Level Center (UHSLC).

Table 1. Summary of synoptic survey to determine municipal ground-water production and mean daily

volume-weighted chloride concentration at municipal well fields, Saipan, October 1998.

[Mgal/d, million gallons per day; mg/L, milligrams per liter; --, not applicable]

Well field Well field

location name

Southern Isley Field 35 2.53 849

Saipan Obyan 13 0.91 296

Koblerville 20 2.13 1,425

Dan Dan 6 0.41 710

San Vicente 4 0.31 1,116

Chalan Kiya 2 0.12 1,990

Subtotal 80 6.41 --

Central Kagman 15 1.07 1,017

Saipan Sablan Quarry 11 0.84 557

Akgak 6 0.56 63

Capital Hill 3 0.38 63

Calhoun (Navy Hill) 2 0.35 1,421

Maui IV area 3 0.29 2,853

Puerto Rico 2 0.18 2,300

Gualo Rai 2 0.09 1,074

Donni Springs 0.36 73

Subtotal 44 4.12 --

Northern Marpi Quarry (As Matuis) 3 0.40 2,044

Saipan Tanapag I and II and --

--

0.22 91

Achugao Springs

Subtotal

Mean daily volume-weighted chloride-concentration value for all southern Saipan well fields

Mean daily volume-weighted chloride-concentration value for all central Saipan well fields

Mean daily volume-weighted chloride-concentration value for all northern Saipan well fields

3 0.62 --

985

843

Mean daily volume-weighted chloride-concentration value for all Saipan well fields 953

1,343

Total 127 11.15 --

1

Daily well-field production determined by multiplying the cumulative well discharge in gallons per minute by 1,440 minutes/day;

the method is considered reasonable because all wells are operated continuously.

2 Calculated with chloride and pumpage data from Commonwealth Utilities Corporation.

Number of

pumped wells

volume-weighted chloride

Mean daily

concentration2 (mg/L)

Pumpage1

(Mgal/d)

Akgak

Capital Hill Capital

Hill

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

2,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

DEPTH BELOW

WATER TABLE, NI FEET

0

20

40

60

80

100

120

140

160

180

3/12/99

7/21/99

10/20/99

Dan Dan monitor well 1 (DD-MW1)

Isley Field monitor well 2 (IF-MW2)

Kagman monitor well 3 (KG-MW3)

YEAR

No data - continuous

recording gage

discontinued in 1983

69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99

MONTHLY RAINFALL, IN INCHES

0

5

10

15

20

25

30

Donni Spring (Bobo I Denni)

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0

1

2

3

4

5

6

7

8

9

10

No data No data

Akgak monitor well 1 (AG-MW1)

DAILY MEAN WATER LEVEL,

IN FEET RELATIVE TO MEAN SEA LEVEL

350

360

370

380

390

400

410

420

430

440

450

El Niño episodes

1983 1987 1998

Akgak monitor well 1

0

5

10

15

20

DEPARTURE FROM

MEAN MONTHLY RAINFALL,

IN INCHES

MONTHLY MEAN RAINFALL, IN INCHES

-10

-8

-6

-4

-2

0

2

4

6

8

10

IF-MW1

1998 1999 2000

WATER LEVEL, IN FEET RELATIVE TO MEAN SEA LEVEL

0.0

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

0.5

1.0

1.5

2.0

2.5

3.0

OB-MW1

KG-MW3

Sea level

Drought associated

with the 1997-98 El Niño

Figure 11. Monthly mean rainfall of all Saipan stations and selected daily mean ground-water levels

and sea level, Saipan, 1998-2000. Sea-level data from the University of Hawaii Sea Level Center

(UHSLC).

YEAR

0

5

10

15

20

-10

-8

-6

-4

-2

0

2

4

6

8

10

0

1

2

6

7

8

9

10

11

12 Municipal ground-water withdrawal

All production wells

Obyan well field

New Kagman wells

YEAR

1995 1996 1997 1998 1999 2000

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

MUNICIPAL GROUND-WATER WITHDRAWAL,

IN MILLIONS OF GALLONS PER DAY

DEPARTURE FROM

MEAN MONTHLY

RAINFALL, IN INCHES

MONTHLY MEAN RAINFALL, IN INCHES

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

All production wells

Chloride concentration

Obyan well field

New Kagman wells

Drought

associated

with 1997-98

El Niño

Lowest

annual rainfall

on record -

34.23 inches

Increased average

chloride concentration

at all production wells

JANUARY

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 -1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

IF-MW1 KG-MW3 OB-MW1

Sea level

W

ATER LEVEL, IN FEET RELATIVE TO MEAN SEA LEVEL
100

0.5

0.5

1

2

3

3

1

2

5

0.5

2

5

5

2

2

2

1

100

200

300

200

100

5

2

1

0.5

300

400

400

400

500

500

200

300

5

2

1

0.5

100

500

500

600

WATER-TABLE CONFIGURATION AND DIRECTIONS OF GROUND-WATER FLOW

The water table is highest in low-permeability volcanic rocks that are above sea level, primarily in the central part

of the island. The water table is relatively flat beneath the limestone plateau areas where high-permeability

limestones extend below sea level. Ground water flows from the central uplands, where the water-table elevation is

highest, towards the coast, where the water-table elevation is lowest. Depressions in the water table due to groundwater withdrawal can cause ground-water flow patterns to change in the vicinity of production wells; water-level

data indicate this may be happening at the Isley Field well field.

The water-table contours define the elevation of the top of the water table relative to sea level; all rock below the

water table is fully saturated (fig. 13). Areas of significant mounding (from 30 to over 600 ft) occur in the northcentral part of the island where low-permeability volcanic rocks extend above sea level. The relatively flat watertable surface (from 0.5 to 3 ft) occurs in areas where high-permeability limestones extend below sea level. Areas

underlain by rocks of moderate to low permeability, such as impure limestone mixed with sediments of weathered

volcanic material, have water levels from three to several tens of feet elevation.

Measured water levels in the central uplands, where low-permeability volcanic rocks occur above sea level, range

from about 30 ft to over 600 ft. The highest measured water levels are about 605 ft at Unnamed Seep 1, and 580 ft

about half a mile to the south at exploratory well TH-17. Figure 13 illustrates the steepness of the water table in the

central uplands, in effect defining the area where low-permeability volcanic rocks are above sea level.

In the limestone coastal aquifers, the water table is no more than a few feet above sea level, and the slope of the

water table is nearly flat (fig. 13). The water-table map reflects pumping conditions in the coastal aquifers because

withdrawal from the production wells had been steady during the preceding months. Depressions in the vicinity of

the Isley Field and Kagman well fields indicate that ground-water withdrawal is causing ground-water flow patterns

to change near some production wells (see fig. 13). Drawdown from pumping diverts some of the oceanward

ground-water flow to wells. To what degree the water-table configuration represents the long-term average

configuration is not known.

Preparation of the water-table contour map.–Available recent and historic water-level data were integrated to

prepare the water-table map. As stated previously, water levels in the coastal aquifers can fluctuate in response to the

ocean tide and other changes in sea level. Thus, water levels in the coastal-aquifer system primarily are based on an

average of at least 1 year of monthly water-level measurements at 14 monitor wells (fig. 13 and table 2). Pumping

water levels at municipal production wells and water levels at wells with questionable measuring-point elevations

were not used in the preparation of the water-table elevation map. Water-level elevations in the developed high-level

limestone aquifer beneath the Akgak well field are based on an average of several years of monthly measurements at

AG-MW1 and on static water-level measurements at nearby production wells (fig. 13 and table 2). Additional waterlevel elevations in the central uplands are based on the discharge elevations of high-level springs and seeps, depths to

water measured at exploratory wells completed in volcanic rock, and on water levels from other wells in high-level

limestone aquifers, such as wells in the Capital Hill well field.

Depth to water in each well was measured and subtracted from each well’s measuring-point elevation to obtain the

height of water above mean sea level. The measuring-point elevations are referenced to mean sea-level datum

benchmarks around the island established in 1968 by the USGS (unpublished USGS data on file at the Saipan Field

Office). At all monitor wells and municipal production wells used for preparation of the water-table map, measuringpoint elevations were surveyed either by the USGS using turning-point leveling to an accuracy of about 0.02 ft, or by

a private land-surveying contractor to the CUC. At some of the upland exploratory wells (fig. 13) used to collect

water-level data in the volcanic rocks, measuring-point elevations were estimated from the USGS 1:25,000

topographic map of Saipan.

Discharge elevations of the developed springs (Donni Spring, Tanapag I and II Springs, and Achugao Spring)

were surveyed by a private land-surveying contractor for the CUC. Because of the remoteness of the undeveloped

springs and seeps (fig. 13), discharge elevations used were from H.T. Stearns (U.S. Geological Survey, written

commun., 1944) or estimated from the USGS topographic map.

THICKNESS AND SEAWARD BOUNDARY OF THE FRESHWATER LENS

Vertical sections through central and southern Saipan show that the freshwater lens is thicker towards the interior

of the island and thins considerably toward the coasts. The freshwater lens thins in the vicinity of the Isley Field

well field possibly because of saltwater upconing due to ground-water withdrawal. The potable part of the

freshwater lens pinches out before reaching the coast probably because of a combination of inland ground-water

withdrawal and tide-induced mixing in high permeability limestone and coastal sediments. Between the area

where the potable part of the freshwater lens pinches out and the coastline, brackish water occurs immediately

below the water table.

In general, for a given recharge, the presence of low permeability rock results in high water levels and a thick

freshwater lens. Conversely, for a given recharge, the presence of high permeability rocks results in low water levels

and a thin freshwater lens.

Vertical sections.–The thickness of the potable part of the freshwater lens beneath Saipan is shown in vertical

sections in figure 13 (D-D', E-E', and F-F'). Each deep-profiling monitor well shown in the vertical sections was

sampled at about 6-ft depth intervals starting at the water table using a 3-ft long bailer lowered to the desired depth in

the well. Field measurements included temperature and specific conductance, and chloride concentration was

determined by the CUC laboratory using titration. The chloride concentration of the samples is considered to

represent the chloride concentration in the aquifer at the elevation and date the sample was collected in the well. The

vertical sections are based on samples collected from ST-MW1, KG-MW3, OB-MW1, IF-MW2, DD-MW1, KVMW1, and IF-MW4 on October 14–20, 1999.

Section D-D'.–Section D-D' shows that the freshwater lens in October 1999 was thick in the north-central part of the

island, reaching elevations of 550 ft above mean sea level in low-permeability volcanic rocks. The depth of the

freshwater lens below sea level in the low-permeability volcanic rocks has not been measured; however, where

ground-water flow is downward, the freshwater lens likely is thinner than predicted by the Ghyben-Herzberg

principle. The potable part of the freshwater lens thins considerably in limestones towards the Kagman Peninsula and

the east coast, as well as towards the west coast. At well KG-MW3, the potable part of the freshwater lens was about

32 ft thick on October 14, 1999. Towards the west coast part of section D-D', the freshwater lens pinches out before

reaching well ST-MW1, probably as a result of extensive tide-induced mixing in the high permeability limestone in

the vicinity of the well. Additionally, section D-D' shows that fresh ground water occurs in limestones that overlie

the lower-permeability volcanic basement rocks above sea level. Average saturated thickness of the high-level

limestone aquifer developed at the Akgak well field is about 100 ft, with a seasonal variation of as much as 50 ft.

Section E-E'.–Section E-E' shows that the freshwater lens is thickest in the southern region near OB-MW1, and

pinches out before reaching the coasts to the northeast and to the south. The maximum thickness of the freshwater

lens on October 18, 1999 was about 45 ft in section E-E', measured at well OB-MW1. The lens was thinner in the

vicinity of IF-MW2 (about 30 ft thick on October 15, 1999) possibly because of saltwater upconing from groundwater withdrawal at the Isley Field well field. The Isley Field well field is the largest well field on the island,

withdrawing about 2.5 Mgal/d from 35 wells. Brackish water at the surface at DD-MW1 indicates that the potable

part of the freshwater lens pinches out some distance before reaching the coast in the north part of section E-E'.

Section F-F'.–Section F-F', drawn from the west through the Koblerville well field and to the east through the Isley

Field well field, shows that the freshwater lens is thin (about 30 ft on October 15, 1999) at well IF-MW2, and limited

in the horizontal extent to the area beneath the 200-ft elevation limestone plateau in the vicinity of the Isley Field

well field. At well KV-MW1, brackish water exists at the water table, indicating that the freshwater is extensively

mixed with saltwater. Ground-water withdrawal at the Koblerville, Isley Field, and Obyan well fields (about 5.57

Mgal/d from 68 wells) probably caused brackish water to intrude upward and landward into parts of the aquifer that

formerly contained freshwater.

Small island freshwater lens at true scale.–Section D-D' shown in figure 13 is drawn with the vertical scale greatly

exaggerated. If the section is drawn with no vertical exaggeration, the extreme thinness of the freshwater lens on a

small island is more evident as is the difficulty of withdrawing freshwater without causing saltwater upconing.

LOCATION AND CONSTRUCTION OF SELECTED WELLS

Well-construction details of 140 municipal production wells, 14 monitor wells, and 8 central upland exploratory

wells that were drilled, operated, or monitored during 1945 to 2000, are shown in table 2. The wells are divided into

15 well fields, defined by the general location on the island. About 60 percent of the production wells are in six well

fields in the southern region of the island, primarily at the Isley Field, Obyan, and Koblerville well fields (fig. 8).

Another eight well fields in the central part of the island make up 35 percent of the municipal production wells, and

four production wells are in northern Saipan.

Monitor wells are located within the major well fields; most are drilled into the top of the freshwater lens except

wells ST-MW1, KG-MW3, DD-MW1, KV-MW1, IF-MW2, and OB-MW1 which were drilled into the transition

zone. These transition-zone (deep-profiling) monitor wells are important because they provide information about the

temporal changes in thickness of the freshwater lens and underlying transition zone as a result of variations in

rainfall and ground-water withdrawal.

Exploratory wells from which water levels in the volcanic rocks were obtained are shown in table 2. Table 2 also

shows the discharge elevations of high-level springs and seeps used to further define water-level elevations in the

central uplands. The water levels reported in the table are the same as those used for the water-table configuration

(fig. 13), with the exception that pumping water levels were not used.

SUMMARY AND CONCLUSIONS

This report presents findings of an ongoing study of the occurrence, movement, and availability of ground-water

resources of Saipan, Commonwealth of the Northern Mariana Islands. The cooperative efforts between the USGS

and the CUC have led to a better understanding of how fresh ground-water occurs and moves within the limestones

and volcanic rocks that make up the island.

Land use, geography, and geology.–Population centers of Saipan are primarily on and adjacent to the western

coastal plain and the plateau areas at the southern end of the island and the Kagman Peninsula. Land uses include

hotel resorts, golf courses, garment manufacturing, small businesses, agriculture, and residential activities. The

surface terrain of Saipan is dominated by a succession of nearly horizontal limestone platforms and terraces,

separated by steep scarps, that ascend from the sea towards central uplands in the northern three fourths of the island.

Saipan is a subareal peak on the Mariana island arc and consists of a volcanic core overlain by younger limestones.

Limestones and calcareous deposits dominate the surface lithology, comprising about 90 percent of the surface

exposures. Volcanic rocks are exposed over the remaining 10 percent of the land surface.

Ground-water resource.–On Saipan, the position of the volcanic basement rocks relative to sea level and the

overlying limestones affects the occurrence of ground water. Most of the available fresh ground water in Saipan is in

a freshwater-saltwater coastal-aquifer system. A smaller amount of recoverable fresh ground water occurs in

limestones that have a base above sea level on volcanic basement rocks. The primary aquifers on Saipan are

composed of fragmental limestones that locally contain sedimentary facies of reworked volcanic materials.

Rainfall, ground-water withdrawal, and chloride concentrations in well water.–Saipan receives about 80 in. of

rainfall annually and has distinct wet and dry seasons. All fresh ground water on Saipan originates as rainfall. About

11 Mgal/d is withdrawn from 140 continuously operated municipal wells located primarily in the southern, eastcentral, and central regions of Saipan. Most production comes from well fields in southern Saipan, accounting for

about 6.4 Mgal/d. The mean daily volume-weighted chloride concentration of pumped water from municipal well

fields ranges from less than 100 mg/L in the Akgak and Capital Hill well fields to over 2,000 mg/L in the Maui IV

and Puerto Rico, and Marpi Quarry well fields.

Changes in thickness of the freshwater lens.–The thickness of the freshwater lens changed at some of the monitor

wells as a result of seasonal recharge, a drought, and possibly due to ground-water withdrawal. Freshwater thickness

decreased by about 10 to 12 ft at wells IF-MW2 and KG- MW3 after a period of less than average rainfall in 1998

due to the El Niño weather phenomenon. Freshwater thickness did not change significantly at well OB-MW1 from

October 1998 to October 1999, when rainfall was 66 percent of the average rainfall.

Water-level and springflow records.–Changes in the water-table elevation in the coastal aquifers caused by varying

recharge are difficult to evaluate because of the dominance of water-level changes caused by sea-level variations. In

contrast, water-level elevation in the high-level limestone aquifers and flow from springs that partially drain these

aquifers fluctuate seasonally and are sensitive to periods of low rainfall. Water levels fluctuate daily in wells closest

to the coast in response to ocean tides. Wells in the interior of the island typically do not show daily water-level

fluctuations due to ocean tides. Water levels in all coastal-aquifer wells rise and fall in response to non-tidal shortterm and seasonal changes in sea level.

Water-table configuration and directions of ground-water flow.–The water table reaches its highest points in lowpermeability volcanic rocks that are above sea level, primarily in the central area of the island. The water table is

relatively flat beneath the plateau areas where high-permeability limestones extend below sea level. Ground water

flows from the central highlands, where the water-table elevation is highest, towards the coast, where the water-table

elevation is lowest.

Thickness and seaward boundary of the freshwater lens.–The freshwater lens is thick in the interior of the island

and thins considerably toward the coasts. The potable part of the freshwater lens ranges from hundreds of feet thick

in low-permeability volcanic rocks in the north-central area of the island, to about 30 to 45 ft thick in limestones in

the coastal aquifers. The potable part of the freshwater lens pinches out before reaching the coast probably because

of a combination of inland ground-water withdrawal and tide-induced mixing in high-permeability limestones and

coastal sediments.

Limitations to ground-water availability.–Data from monitor wells and analysis of records of pumpage, water

quality, and water levels indicate that the main factors limiting potable ground-water availability on Saipan are

saltwater intrusion, lowering of water levels, and the reduction of discharge to the ocean and to the developed highlevel springs.

When water is withdrawn from a freshwater lens, the freshwater lens shrinks and brackish water or saltwater will

intrude upward and landward into parts of the aquifer that formerly contained freshwater. The degree of saltwater

intrusion depends on several factors, including the hydraulic properties of the rocks, recharge rate, pumping rate, and

well location. The effect of intrusion on a particular well depends on the vertical and horizontal distance between the

well and the transition zone. The constraints imposed by saltwater intrusion can be minimized by (1) locating wells

where the potable part of the freshwater lens is thicker, (2) ensuring that wells do not penetrate to depths near the

transition zone, and (3) determining pumping rates that can be maintained without causing the intrusion of saltwater

into the well.

REFERENCES CITED

Carruth, R.L., 2000, Summary of hydrologic data for 1998, Saipan, Commonwealth of the Northern Mariana Islands: U.S. Geological Survey Open-File

Report 00-301, 39 p.

Cloud, P.E., Schmidt, R.G., and Burke, H.W., 1956, Geology of Saipan Mariana Islands, Part 1. General Geology: U.S. Geological Survey Professional

Paper 280-A, 126 p.

Gingerich, S.B., 2002, Geohydrology and numerical simulation of alternative pumping distributions and the effects of drought on the ground-water flow system

of Tinian, Commonwealth of the Northern Mariana Islands: U.S. Geological Survey Water-Resources Investigations Report 02-4077, 46 p.

Hoffmann, J.P., Carruth, R.L., and Meyer, William, 1998, Geology, ground-water occurrence, and estimated well yields from the Mariana Limestone, Kagman

area, Saipan, Commonwealth of the Northern Mariana Islands: U.S. Geological Survey Water-Resources Investigations Report 98-4077, 38 p.

Meijer, A., Reagan, M., Ellis, H., Shafiqullah, M., Sutter, J., Damon, P., and Kling, S., 1983, Chronology of volcanic events in the eastern Philippine Sea in

Hayes, D. E. (ed.), The tectonic and geologic evolution of southeast Asian seas and islands: Part 2: Geophysical Monograph 27, American Geophysical

Union, p. 349-359.

Mink, J.F., 1987, Hydrological characterization of the ground-water resources, island of Saipan: Report to the Division of Environmental Quality, Department of

Public Health and Environmental Services, Commonwealth of the Northern Mariana Islands, 59 p.

Thurman, H.V., 1990, Essentials of oceanography, 3rd Edition: Columbus, Ohio, Merrill Publishing Company, 398 p.

Todd, D.K, 1980, Groundwater Hydrology: New York, Wiley, 535 p.

U.S. Census Bureau, 2001, 2000 census of population and housing, Commonwealth of the Northern Mariana Islands: 248 p.

U.S. Environmental Protection Agency, 1991, Secondary maximum contaminant levels (section 143.3 of part 143, National secondary drinking water

regulations): U.S. Code of Federal Regulations, Title 40, Parts 100 to 149, revised through July 1, 1991.

Van der Brug, Otto, 1985, Compilation of water resources development and hydrologic data of Saipan, Mariana Islands: U.S. Geological Survey WaterResources Investigations Report 84-4121, 578 p.

Wong, M.F., and Hill, B.R., 2000, Reconnaissance of hydrology and water quality of Lake Susupe, Saipan, Commonwealth of the Northern Mariana Islands,

1990: U.S. Geological Survey Water-Resources Investigations Report 00-4054, 32 p.

145 ̊44'

145 ̊48'

15 ̊12'

15 ̊16'

San Roque

Tanapag

15 ̊14'

15 ̊10'

15 ̊08'

Mt. Tagpochau

Tanapag

Harbor

Sabaneta Pt

Garapan

Muchot Pt

Laolao Kattan Pt

South Fk Tal ufofo S tr

Rapugau

Str

Bird

Island

Forbidden

Island

15 ̊06'

PHILIPPINE

SEA

PACIFIC

OCEAN

I Naftan Pt

Agingan Pt

0 1/2 1 MILE

0 0.5 1 KILOMETER

Laolao

Bay Chalan

Kanoa

San

Antonio

Saipan

International

Airport

San

Jose

Susupe

Lake

Susupe

D

WEST EAST

D'

E E'

F

F'

F F'

WATER-TABLE CONTOUR -- Shows elevation of

water table (1990-2001). Interval, in feet, is variable.

Datum is mean sea level. Dashed where inferred.

GENERALIZED DIRECTION OF GROUND-WATER FLOW

LINE OF SECTION

ROADS

MUNICIPAL PRODUCTION WELL AND NAME

MONITOR WELL AND NAME

SPRING AND NAME

UPLAND EXPLORATORY WELL AND

NAME

EXPLANATION FOR WATER-TABLE MAP

PREPARED IN COOPERATION WITH THE

COMMONWEALTH UTILITIES CORPORATION

COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS

WATER-RESOURCES INVESTIGATIONS REPORT 03-4178

Water-table configuration, thickness of freshwater lens, and well locations–SHEET 3 OF 3

Carruth, R.L., 2003, Ground-Water Resources of Saipan, Commonwealth of the Northern Mariana Islands

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Base modified from

U.S. Geological Survey, 1:25,000,

Island of Saipan, 1983

LIMESTONE (high permeability)

VOLCANIC ROCK (low permeability)

? ?

?

250

10,000

?

?

?

250

10,000

?

?

?

-300

-200

-100

SEA LEVEL

500

400

300

200

100

600

700

800

900

1,000

1,100

1,200

FEET

-200

SEA LEVEL

400

200

600

800

1,000

1,200

ST-MW1

(10/14/99)

AG-MW1

(10/14/99) BEND IN SECTION

KG-MW3

(10/14/99)

1,354

3,152

10,785 12,459

14,774

7,929

1,798 136

186

8,470

14,183

16,891

2,585

140

KG-MW3

(10/14/99)

136

186

8,470

14,183

16,891

2,585

140

60

water table

250

10,000

250

10,000

BEND IN SECTION

BEND IN SECTION

BEND IN SECTION

BEND IN SECTION

BEND IN SECTION

Papago Spring

?

?

?

? ?

?

?

?

?

D

D'

E'

E

F

F'

Donni Spring

(Bobo I Denni)

OB-1

OB-MWI

Figure 13. Configuration of the water table with selected municipal wells, monitor wells, upland exploratory wells, and

springs, Saipan. Lines of section show thickness of freshwater lens (to a depth of 250 mg/L chloride concentration)

and transition zone, October 1999.

CH-5

Water temperature is given in degrees Celsius (∞C), which can be converted to degrees Fahrenheit (∞F) by using the equation:

∞F = 1.8 × ∞C + 32

Air temperature is given in degrees Fahrenheit (∞F), which can be converted to degrees Celsius (∞C) by using the following

equation:

∞C = (∞F − 32) / 1.8

Abbreviation used in water-quality descriptions:

mg/L, milligrams per liter

DATUMS

Vertical coordinate information is referenced relative to mean sea level.

Horizontal coordinate information for figure 13 and table 2 is referenced relative to the North American Datum of 1983 (NAD83), and is

referenced to Guam Datum 1963 for the remaining figures on sheets 1 and 2.

CONVERSION FACTORS, ABBREVIATED WATER-QUALITY UNIT, AND DATUMS

Multiply By To obtain

foot (ft) 0.3048 meter

cubic foot per second (ft

3

/s) 0.02832 cubic meter per second

gallon per day (gal/d) 3.785 liter per day

gallon per minute (gal/min) 3.785 liter per minute

million gallons per day (Mgal/d) 0.04381 cubic meter per second

mile (mi) 1.609 kilometer

square mile (mi

2

) 2.590 square kilometer

inch (in.) 25.4 millimeter

SALTWATER SALTWATER FRESHWATER D D'

No vertical exaggeration - illustrates thinness of freshwater lens in permeable limestone

0 5,000 FEET

-300

-200

-100

SEA LEVEL

500

400

300

200

100

FEET

IF-MW2

(10/15/99)

49

246

3,029 11,425

15,512

15,069

640

98

OB-MW1

(10/18/99)

205 812 5,614 15,315

16,940

1,724

240

DD-MW1

(10/20/99)

394

1,034

7,091

17,285

3,570

419

water table

250

10,000

0 5,000 FEET

0 5,000 FEET

0 5,000 FEET

SEA LEVEL

500

400

300

200

100

-100

-200

-300

FEET

1,674

2,758

11,671

17,482

8,963

1,650

KV-MW1

(10/18/99)

IF-MW2

(10/15/99)

205 812 5,614 15,315

16,940

1,724

240

IF-MW4

(10/20/99)

637

water table

250

10,000

VOLCANIC ROCK

(low permeability)

Potable part of

freshwater lens

pinches out inland

of shoreline

LIMESTONE

(high permeability)

LIMESTONE

(high permeability)

SOUTH NORTH

LIMESTONE

(high permeability)

WEST EAST

LIMESTONE

(high permeability)

Vertical scale greatly exaggerated

Vertical scale greatly exaggerated

Vertical scale greatly exaggerated

FRESHWATER

TRANSITION ZONE AND SALTWATER

LINE OF EQUAL CHLORIDE

CONCENTRATION, IN MILLIGRAMS

PER LITER--Dashed where approximate or

inferred, interval is variable.

WELL NAME, SAMPLING DATE, AND

CHLORIDE CONCENTRATION AT

SAMPLED DEPTH, IN MILLIGRAMS

PER LITER

EXPLANATION FOR LINES OF

SECTION D-D', E-E', AND F-F'

250

220

211

208

205

202

105

SV-7

SV-6

SV-1

DD-8

DD-7

DD-4

DD-3

KV-9

OB-9

OB-8

OB-6

OB-4

OB-2

IF-8

MQ-9

MQ-8

MQ-5

GR-5

CL-5

CH-3

SQ-9

SQ-7

SQ-4

KG-9 KG-8

KG-7

KG-6

KG-4

KV-25

KV-22

KV-20

KV-19

KV-15

KV-13

OB-15

OB-13

IF-28

IF-19

IF-16

IF-10

MQ-11

AG-73

AG-70

SQ-12

KAS-3 KG-20

KG-16

KG-12

Mafnas

GR-154

PR-162

AG-121

Apatang

Fina Sisu

V. Duenas

E. Torres

217

204 201

108

106

102

101

SV-2

OB-7 OB-5

OB-3

OB-1

IF-7

IF-6 IF-5 IF-4

IF-3

IF-2 IF-1

MQ-3

MQ-1

GR-4

CL-3 CL-2

CH-2

CH-1

SQ-6

SQ-5

KG-3

KG-2

KV-24

KV-23

KV-21

KV-18

KV-17

KV-16

KV-12

KV-11

KV-10

OB-14

OB-12

OB-11

OB-10

IF-25

IF-24

IF-23 IF-22

IF-21

IF-20 IF-18

IF-17

IF-15

IF-14

IF-13

IF-11 IF-12

MQ-10

AG-72

AG-50

AG-45

SQ 11

SQ-10

KAS-2

KAS-1 KG-76 KG-19

KG-18

KG-15

KG-14

KG-13 KG-10 KG-11

Maui 1

KV-116

KV-113

KV-111

GR-151

MA-145

MA-144

SQ-150 SQ-149

SQ-148

KG-131

PR-163B

D. Torres

Donni Spring

Papago Marsh

Papago Spring

Donni Spring 2

Unnamed

Seep 3

Unnamed Seep 2

Tanapag I Spring

Tanapag II Spring

East Achugao Spring

Radio Hill Spring 4 Radio Hill Spring 1

Natural Bridge Spring 2

Unnamed Seep 1

Radio Hill Spring 3 Radio Hill Spring 2

Natural Bridge Spring 1

TP-9

W-43

W-58

TP-10

TH-17

Cepedas Farm

Botanical Garden

TP-8

CH-5

ED-2

ED-1

DD-MW1

ST-MW1

KG-MW2

KV-MW1

OB-MW1

IF-MW5

IF-MW4

IF-MW3

IF-MW2

IF-MW1

AM-MW1

AG-MW1

KG-MW3

KG-MW1

Table 2. Location and construction of municipal wells, monitor wells, exploratory wells, and springs. [Well identifications in bold are monitor wells. Datum is mean sea level. --, no data]

Measuring- Hole bottom Casing bottom Casing inside Type of Open interval Water-level Water-level Water-level

Well Date well point elevation elevation elevation diameter open interval elevation elevation date time

Well field identification drilled (feet) (feet) (feet) (inches) (feet) (feet)

Kagman KG-2 1987 15 10 145 45 244.28 -146 -146 8 screen -95 to -146 16.78 2 04/17/91 --

KG-3 Nov-88 15 10 145 45 232.59 -28 -28 8 screen -10 to -28 19.83 2 11/29/90 --

KG-4 Nov-88 15 10 32 145 46 01 229.46 -85 -85 8 screen -- 17.27 2 01/08/91 --

KG-6 Oct-90 15 10 47 145 46 06 236.01 -44 -44 8 screen 26 to -44 -7.34 1 05/12/99 08:45

KG-7 Dec-95 15 10 33

37 55

34 57

145 46 30 214.00 -16 -16 8 screen 4 to -16 0.98 1 05/12/99 09:07

KG-8 Sep-95 15 10 44 145 46 27 215.57 -14 -14 8 screen 6 to -14 1.55 1 05/12/99 09:20

KG-9 Aug-98 15 10 39 145 46 38 186.46 -5 0 8 screen 20 to 0 1.81 1 05/12/99 09:30

KG-10 Feb-98 15 10 11 145 46 08 229.52 -8 -8 8 screen 12 to -8 1.63 2 05/12/99 10:45

KG-11 Apr-98 15 10 08 145 46 14 235.35 -6 -6 8 screen 14 to -6 1.63 2 05/12/99 11:10

KG-12 Jul-98 15 10 11 145 46 24 220.44 -5 -5 8 screen 15 to -5 1.17 1 05/12/99 11:20

KG-13 Apr-98 15 10 15 145 46 29 208.75 -7 -7 8 screen 12 to -7 1.81 1 05/12/99 11:30

KG-14 Mar-98 15 10 15 145 46 37 214.39 -7 -7 8 screen 13 to -7 -- -- --

KG-15 May-98 15 10 25 145 46 39 176.57 -6 -6 8 screen 14 to -6 2.87 2 05/12/99 09:50

KG-16 Sep-98 15 10 21 145 46 47 140.07 -4 -4 8 screen 16 to -4 1.92 1 05/12/99 12:30

KG-18 Feb-99 15 10 35 145 46 13 213.87 -- -- 6 screen -- 8.27 2 05/12/99 10:05

KG-19 Nov-98 15 10 29 145 46 08 222.70 -7 -- -- -- -- 1.78 1 05/12/99 10:15

KG-20 Dec-98 15 10 20 145 45 51 237.95 -22 -- -- -- -- 12.23 2 05/12/99 10:25

KG-76 1956 15 10 27 145 45 58 233.15 -145 -145 12 screen -- 15.59 2 10/01/91 --

KG-131 Oct-81 15 10 26 145 46 01 228.05 -126 -56 8 screen 24 to -56 18.41 2 02/04/91 --

KAS-1 Jul-98 15 10 26 145 46 17 214.25 -9 -4 6 screen 16 to -4 1.88 2 05/12/99 10:35

KAS-2 Aug-98 15 10 17 145 46 15 203.60 -8 -3 6 screen 17 to -3 1.36 2 05/13/99 08:20

KAS-3 Jun-70 15 10 21 145 46 21 204.50 -20 -15 8 screen -- -- -- --

KG-MW 1 1956 15 10 28 145 46 00 227.94 -141 -- -- open hole -- 11.9 2 3 -- --

KG-MW 2 1989 15 10 09 145 46 09 233.30 -97 -68 8 screen 33 to -68 4.63 3 -- --

KG-MW 3 1989 15 10 15 145 46 47 176.09 -121 -- -- open hole -- 2.14 3 -- --

Sablan Quarry SQ-4 Jan-84 15 13 17 145 44 49 159.68 -42 -42 8 screen 3 to -42 3.77 2 03/04/90 --

SQ-5 Feb-84 15 12 56 145 44 48 333.23 -38 -38 8 screen 6 to -38 2.76 2 01/31/92 --

SQ-6 Mar-84 15 13 03 145 44 45 275.59 -34 -34 8 screen 3 to -34 5.17 2 10/30/90 --

SQ-7 Mar-84 15 13 07 145 44 46 243.56 -34 -34 -- -- -- 3.98 2 03/18/91 --

SQ-9 May-84 15 13 00 145 44 46 289.88 -14 -14 8 screen 23 to -14 4.01 2 01/22/91 --

SQ-10 Jun-95 15 12 51 145 44 37 305.93 -9 -4 8 screen 16 to -4 -- -- --

SQ 11 Jun-95 15 12 44 145 44 30 350 M -18 -13 8 screen 7 to -13 -- -- --

SQ-12 Aug-95 15 12 47 145 44 33 291 M -14 -14 6 screen 6 to -14 -- -- --

SQ-148 Mar-83 15 13 18 145 44 48 146.03 -30 -30 8 screen 0 to -30 6.77 2 10/25/90 --

SQ-149 Mar-83 15 13 13 145 44 47 195.28 -24 -24 8 screen 14 to -24 5.55 2 11/01/90 --

SQ-150 Apr-83 15 13 15 145 44 48 196.57 -133 -133 8 screen 12 to -133 7.53 2 10/31/90 --

Akgak AG-45 Oct-69 15 11 38 145 45 11 584.36 398 398 8 screen 441 to 398 424.842 04/11/92 --

AG-50 Nov-69 15 11 38 145 45 06 649.32 319 319 8 screen 363 to 319 422.54 2 03/12/91 --

AG-70 Jan-78 15 11 36 145 45 06 634.88 311 311 8 screen 382 to 311 403.89 2 10/02/91 --

AG-72 Dec-77 15 11 32 145 45 06 655.19 305 356 8 screen 386 to 356 406.75 2 10/06/91 --

AG-73 Feb-78 15 11 29 145 45 06 682.89 308 311 8 screen 405 to 311 418.81 2 04/08/91 --

AG-121 Jul-79 15 11 24 145 45 07 694.43 338 346 10 screen 378 to 346 -- -- --

AG-MW 1 Jan-45 15 11 35 145 45 08 617.74 378 378 6 screen 458 to 378 382 3 -- --

Capital Hill CH-1 Feb-90 15 12 25 145 44 58 869.00 306 316 8 screen 396 to 316 347 1 05/11/99 13:55

CH-2 Oct-89 15 12 28 145 44 59 834.86 239 295 8 screen 455 to 525 343 1 06/01/00 09:11

CH-3 Oct-96 15 12 27 145 44 57 843.54 -- -- -- -- -- 355 1 05/11/99 13:30

Calhoun CL-2 -- 15 12 24 145 44 16 552.11 -28 -28 10 screen 5 to -28 5.28 2 02/24/91 --

(Navy Hill) CL-3 -- 15 12 24 145 44 17 -- -- -- -- -- -- -- -- --

CL-5 Feb-01 15 12 23 145 44 17 553.53 -17 -15 8 screen 5 to -15 -- -- --

Maui IV Maui IV 1945 15 12 44 145 44 20 -- -- -- -- -- -- -- -- --

MA-144 Jan-71 15 12 51 145 44 35 215.54 -8 -8 8 screen -3 to -8 4.8 2 12/17/90 --

MA-145 Mar-82 15 12 55 145 44 42 243.78 -24 -24 8 screen 6 to -24 4.46 2 12/13/90 --

Puerto Rico PR-162 Jun-82 15 13 16 145 44 24 153.12 -18 -18 8 screen 12 to -18 3.79 2 10/01/90 --

PR-163B Jan-92 15 13 18 145 44 24 162 -28 -- -- -- -- -- -- --

ST-MW 1 Mar-92 15 13 26 145 44 21 57.08 -203 -- -- open hole -- 2.43 3 -- --

Gualo Rai GR-151 -- 15 11 24 145 43 38 304.92 -3 -3 8 screen 12 to -3 5.77 2 01/18/91 --

GR-154 -- 15 11 24 145 43 35 269.94 -21 -21 8 screen 5 to -21 4.85 2 01/17/91 --

GR-4 Jun-00 15 11 08 145 43 41 558 -24 -20 8 screen 10 to -20 -- -- --

GR-5 Jul-02 15 11 06 145 43 44 550 -15 -10 8 screen 10 to -10 -- -- --

Marpi Quarry MQ-1 Sep-90 15 15 23 145 47 37 459.31 -20 -- -- -- -- -- -- --

MQ-3 Jul-92 15 15 14 145 47 29 375 M -21 -- -- -- -- -- -- --

MQ-5 Oct-92 15 15 19 145 47 33 400 M -30 -- -- -- -- -- -- --

MQ-8 Mar-00 15 15 28 145 47 44 413 -12 -6 8 screen 14 to -6 -- -- --

MQ-9 Sep-01 15 15 14 145 47 10 206 -10 -9 6 screen 11 to -9 -- -- --

MQ-10 Nov-01 15 15 10 145 47 09 215 -10 -9 6 screen 11 to -9 -- -- --

MQ-11 Nov-01 15 15 07 145 47 06 210 -10 -9 6 screen 11 to -9 -- -- --

AM-MW 1 Aug-92 15 15 19 145 47 32 397.16 -73 -- -- open hole -- 2.13 3 -- --

Isley Field IF-1 Nov-91 15 07 55 145 43 30 167.09 -23 -13 8 screen 7 to -13 -- -- --

IF-2 May-96 15 07 52 145 43 55 182 M -12 -11 8 screen 9 to -11 -- -- --

IF-3 May-97 15 07 50 145 43 48 175.79 -14 -12 8 screen 8 to -12 -- -- --

IF-4 May-97 15 07 46 145 43 41 179.53 -6 -4 8 screen 16 to -4 0.96 1 05/11/99 10:20

IF-5 Oct-96 15 07 44 145 44 00 184.32 -12 -10 8 screen 10 to -10 1.04 1 05/11/99 08:35

IF-6 Mar-96 15 07 42 145 43 51 179 M -11 -10 8 screen 10 to -10 2.7 1 05/11/99 08:25

IF-7 Sep-96 15 07 41 145 43 42 179.97 -14 -12 8 screen 8 to -12 1.71 2 03/08/90 --

IF-8 Aug-96 15 07 38 145 43 34 185.24 -12 -10 8 screen 10 to -10 1.16 1 05/11/99 10:00

IF-9 -- -- -- -- -- -- -- -- -- --

IF-10 1996 15 07 26 145 43 27 202.40 -13 -12 8 screen 8 to -12 2.8 2 05/10/99 11:30

IF-11 Apr-92 15 07 37 145 43 50 184.97 -13 -13 8 screen 7 to -13 -- -- --

IF-12 May-97 15 07 37 145 43 56 183.61 -10 -8 8 screen 12 to -8 -- -- --

IF-13 Oct-95 15 07 40 145 44 04 188 M -8 -- 8 screen -- -- -- --

IF-14 May-97 15 07 44 145 44 13 224.18 -8 -6 6 screen 10 to -6 3.63 2 05/11/99 10:30

IF-15 Apr-97 15 07 48 145 44 20 214.15 -10 -8 6 screen 12 to -8 -- -- --

IF-16 May-92 15 07 44 145 44 25 199.05 -11 -11 8 screen 9 to -11 -- -- --

IF-17 1996 15 07 38 145 44 32 178.51 -14 -12 8 screen 8 to -12 -- -- --

IF-18 1997 15 07 31 145 44 37 170.88 -10 -8 6 screen 12 to -8 1.49 2 05/11/99 10:50

IF-19 1997 15 07 38 145 44 19 213.77 -10 -8 6 screen 12 to -8 -- -- --

IF-20 1997 15 07 35 145 44 12 189.72 -10 -8 6 screen 12 to -8 1.27 1 05/11/99 08:45

IF-21 Jan-97 15 07 32 145 44 04 187.55 -14 -12 8 screen 8 to -12 -- -- --

IF-22 Dec-96 15 07 29 145 43 57 198.28 -14 -12 8 screen 8 to -12 0.06 1 05/11/99 08:55

IF-23 Mar-79 15 07 28 145 43 49 207.11 -13 -13 8 screen 0 to -13 3.5 2 03/11/91 --

IF-24 Jun-97 15 07 30 145 43 44 199.27 -10 -8 8 screen 12 to -8 1.06 1 05/11/99 09:05

IF-25 Sep-82 15 07 27 145 43 54 205.38 -7 -7 8 screen 1 to -7 1.64 2 03/04/91 --

IF-28 -- 15 07 15 145 43 16 200 M -- -- -- -- -- -- -- --

101 May-82 15 07 30 145 43 55 202.68 -24 -24 8 screen 3 to -24 1.95 2 03/12/91 --

102 Mar-82 15 07 35 145 43 51 190.83 -20 -20 8 screen 8 to -20 1.66 2 03/08/91 --

105 Mar-82 15 07 51 145 43 42 177.43 -51 -51 8 screen 2 to -51 2.48 2 12/11/90 --

106 Mar-82 15 07 40 145 43 48 180.32 -29 -29 8 screen -3 to -29 1.93 2 11/06/90 --

108 Apr-82 15 07 32 145 43 52 199.04 -20 -20 8 screen 8 to -20 1.66 2 03/26/91 --

201 -- 15 07 38 145 44 04 184.60 -29 -29 8 screen 5 to -29 1.46 2 03/07/91 --

202 -- 15 07 35 145 44 05 184.30 -29 -29 8 screen 5 to -29 1.59 2 03/13/91 --

204 -- 15 07 42 145 43 59 182.96 -36 -36 8 screen 0 to -36 1.71 2 03/07/90 --

205 -- 15 07 41 145 43 56 182.67 -31 -31 8 screen 5 to -31 2.02 2 11/27/90 --

208 -- 15 07 28 145 43 51 207.68 -19 -11 8 screen 29 to -11 1.58 2 03/04/91 --

211 Oct-91 15 07 55 145 43 51 169.01 -26 -23 8 screen -- -- -- --

217 Jan-92 15 07 51 145 43 49 173.70 -4 -4 8 screen -- -- -- --

220 Jan-92 15 07 48 145 43 50 174 M -21 -19 -- -- -- -- -- --

IF-MW 1 Apr-92 15 07 50 145 43 51 176.27 -124 -- -- open hole -- 1.92 3 -- --

IF-MW 2 Nov-91 15 07 36 145 43 55 185.75 -169 -- -- open hole -- 1.69 3 -- --

IF-MW 3 Dec-89 15 07 23 145 43 42 209.22 -113 -- -- open hole -- 3.90 3 -- --

IF-MW 4 May-92 15 07 44 145 44 26 195.74 -118 -- -- open hole -- 1.92 3 -- --

IF-MW 5 Dec-97 15 07 08 145 43 10 192.08 -8 -- -- open hole -- 2.05 3 -- --

Obyan OB-1 Nov-96 15 07 21 145 44 39 210.99 -9 -7 6 screen 11 to -7 1.85 1 05/11/99 11:15

OB-2 Dec-95 15 07 19 145 44 32 230.15 -15 -13 8 screen 17 to -13 -- -- --

OB-3 Dec-95 15 07 16 145 44 25 225.80 -22 -20 8 screen 24 to -20 1.45 1 05/10/99 13:50

OB-4 Nov-95 15 07 12 145 44 15 199.87 -16 -14 8 screen 18 to -14 -- -- --

OB-5 Nov-95 15 07 09 145 44 08 206.18 -10 -8 8 screen 12 to -8 1.28 1 05/10/99 13:40

OB-6 Nov-95 15 07 06 145 44 00 205.91 -12 -10 8 screen 14 to -10 -- -- --

OB-7 Dec-95 15 07 03 145 43 53 206.96 -11 -9 8 screen 13 to -9 1.11 1 05/10/99 14:55

OB-8 Dec-95 15 07 00 145 43 45 217.44 -17 -15 8 screen 19 to -15 -- -- --

OB-9 Dec-95 15 06 56 145 43 34 214.76 -10 -8 8 screen 12 to -8 -0.66 1 05/10/99 13:30

OB-10 Dec-95 15 06 53 145 43 27 206.11 -12 -10 8 screen 14 to -10 -- -- --

OB-11 Dec-95 15 06 50 145 43 20 199.99 -18 -16 8 screen 20 to -16 1.51 1 05/10/99 13:20

OB-12 Jul-97 15 06 49 145 43 11 189.77 -15 -10 6 screen 10 to -6 -- -- --

OB-13 Jul-97 15 06 47 145 43 02 178.02 -15 -10 6 screen 6 to -2 1.4 2 05/10/99 13:05

OB-14 Feb-01 15 07 14 145 44 40 219.18 -15 -15 8 screen 5 to -15 1.7 04/18/01 08:15

OB-15 Apr-01 15 07 08 145 44 44 233.40 -12 -6 6 screen 15 to -6 -- -- --

OB-MW 1 Dec-89 15 07 05 145 44 00 206.12 -149 -- -- open hole -- 2.11 3 -- --

Koblerville KV-9 May-71 15 07 35 145 43 06 101.45 -15 -15 8 screen -9 to -15 1.48 2 02/18/91 --

KV-10 Jun-71 15 07 42 145 43 03 105.68 -17 -17 8 screen -11 to -17 2.3 2 02/12/91 --

KV-11 Jul-71 15 07 31 145 43 15 100.69 -13 -13 8 screen -6 to -13 1.32 2 10/29/90 --

KV-12 Jun-91 15 07 43 145 42 57 102.66 -- -- -- -- -- 0.66 2 05/10/99 10:37

KV-13 Jun-91 15 07 44 145 42 55 102.35 -20 -15 8 screen 5 to -15 -- -- --

KV-15 Jan-77 15 07 29 145 43 08 108.35 -18 -18 8 screen 0 to -18 1.43 2 02/19/90 --

KV-16 May-77 15 07 32 145 43 07 104.49 -20 -20 8 screen -4 to -20 1.39 2 02/11/92 --

KV-17 Jun-77 15 07 31 145 43 03 106.72 -18 -18 8 screen -2 to -18 1.24 2 03/20/90 --

KV-18 Sep-92 15 07 40 145 42 59 -- -- -- -- -- -- -- -- --

KV-19 Sep-92 15 07 38 145 42 50 108 M -2 -- -- -- -- -- -- --

KV-20 Sep-92 15 07 07 145 42 14 97 M -- -- -- -- -- -- -- --

KV-21 Sep-92 15 07 27 145 42 22 -- -- -- -- -- -- -- -- --

KV-22 Jun-93 15 07 26 145 42 19 104 M -26 -21 -- -- -- -- -- --

KV-23 -- 15 07 25 145 42 16 -- -- -- -- -- -- -- -- --

KV-24 -- 15 07 23 145 42 13 -- -- -- -- -- -- -- -- --

KV-25 -- 15 07 21 145 42 08 -- -- -- -- -- -- -- -- --

KV-111 Mar-82 15 07 31 145 43 08 107.14 -14 -14 8 screen -1 to -14 1.67 2 12/07/90 --

KV-113 Mar-82 15 07 42 145 43 13 92.80 -25 -25 8 screen 2 to -25 1.72 2 12/06/90 --

KV-116 Feb-83 15 07 39 145 43 00 109.41 -18 -18 8 screen -1 to -18 0.27 2 10/27/90 --

Mafnas -- 15 07 15 145 42 56 -- -- -- -- -- -- -- -- --

Maui 1 Jul-45 15 07 22 145 43 07 -- -- -- -- -- -- -- -- --

Kumoi 3 Jan-91 -- -- -- -- -- -- -- -- --

KV-MW 1 Mar-99 15 07 42 145 42 59 106.93 -133 -133 6 screen 27 to -133 2.20 3 -- --

Dan Dan DD-3 Nov-91 15 09 05 145 43 49 162.57 -12 -- -- -- -- 1.77 2 01/29/92 --

DD-4 -- 15 09 10 145 43 45 -- -- -- -- -- -- -- -- --

DD-7 Oct-70 15 08 47 145 43 56 177.92 -3 -3 8 screen 2 to -3 2.95 2 01/29/92 --

DD-8 Jan-71 15 08 10 145 43 44 -- -- -- -- -- -- -- -- --

Apatang Jan-93 15 08 21 145 43 16 117.42 -6 -- 8 screen -- -- -- --

D. Torres -- 15 08 54 145 43 44 -- -- -- -- -- -- -- -- --

DD-MW 1 Nov-92 15 08 19 145 44 03 256.49 -161 -- -- open hole -- 3.07 3 -- --

San Vicente SV-1 -- 15 09 27 145 44 25 315.54 -10 -10 8 screen 4 to -10 2.46 2 10/05/91 --

SV-2 May-79 15 09 10 145 44 14 325 M -- -- -- -- -- -- -- --

SV-6 -- 15 09 02 145 44 16 300 M -- -- -- -- -- -- -- --

SV-7 -- 15 09 11 145 44 19 300 M -- -- -- -- -- -- -- --

Chalan Kiya E. Torres -- 15 10 01 145 43 22 -- -- -- -- -- -- -- -- --

V. Duenas -- 15 09 53 145 43 35 -- -- -- -- -- -- -- -- --

Fina Sisu Fina Sisu Aug-99 15 09 00 145 43 11 131.00 -18 -18 6 screen 20 to -18 -- -- --

Upland Radio Hill Spring 1 -- 15 13 36 145 45 24 -- -- -- -- -- -- 499 -- --

springs, Radio Hill Spring 2 -- 15 13 54 145 45 38 -- -- -- -- -- -- 348 -- --

seeps, and Radio Hill Spring 3 -- 15 13 52 145 46 02 -- -- -- -- -- -- 574 -- --

exploratory Radio Hill Spring 4 -- 15 13 37 145 46 02 -- -- -- -- -- -- 400 -- --

wells used East Achugao Spring 1 -- 15 13 52 145 46 35 -- -- -- -- -- --

-- -- -- -- -- --

318 -- --

to define East Achugao Spring 2 -- 131 -- --

water levels Papago Spring -- 15 10 59 145 45 19 -- -- -- -- -- -- 541 -- --

in the central Papago Marsh -- 15 11 12 145 45 29 --

-- -- -- -- -- --

-- -- -- -- -- 541 -- --

uplands Natural Bridge Spring 1 -- 15 11 38 145 45 41 -- -- -- -- -- -- 427 -- --

Natural Bridge Spring 2 -- 15 11 34 145 45 44 -- -- -- -- -- -- 394 -- --

Unnamed Seep 1 -- 15 12 57 145 45 25 -- -- -- -- -- -- 605 -- --

Unnamed Seep 2 -- 15 12 53 145 45 39 -- -- -- -- -- -- 525 -- --

Unnamed Seep 3 -- 15 10 03 145 44 57 -- -- -- -- -- -- 525 -- --

Tanapag I Spring -- 15 13 55 145 45 18 -- -- -- -- -- -- 130 -- --

Tanapag II Spring -- 15 14 07 145 45 23 -- -- -- -- -- -- 66 -- --

Donni Spring -- 15 11 53 145 46 02 -- -- -- -- -- -- 261 -- --

Donni Spring 2 -- 15 12 05 145 45 46 -- -- -- -- -- -- 443 -- --

Botanical Garden Sep-90 15 10 20 145 44 48 640.00 40 -- -- -- -- 415 10/25/90 --

Cepedas Farm Sep-90 15 09 52 145 44 23 510.00 -30 -- -- -- -- 490 09/20/90 --

W-58 Apr-45 15 12 26 145 46 16 161.60 -62.4 -55.4 6 -- -- 57 -- --

ED-1 Nov-98 15 11 59 145 45 38 637.73 387.73 -- -- -- -- 491 -- --

ED-2 Dec-98 15 11 47 145 45 31 589.39 339.39 -- -- -- -- 570 -- --

CH-5 Aug-92 15 12 04 145 45 27 575.00 345 -- -- -- -- 495 -- --

W-43 Mar-45 15 12 47 145 45 39 556.40 489.4 501.4 6 -- -- 530 -- --

TH-17 Apr-80 15 12 32 145 45 16 615.00 280 -- -- -- -- 580 -- --

TP-8 Jan-01 15 11 17 145 44 19 967 -66 open hole -- -- -- 80 -- --

TP-9 Nov-99 15 11 14 145 44 18 948 -25 open hole -- -- -- 80 02/17/00 --

TP-10 Jul-99 15 11 06 145 44 17 928 128 open hole -- -- -- -- -- --

M Estimated from USGS 1:25,000 topographic map of Saipan, 1983, and unpublished data

1 Pumping water level 2 Static water level 3 Static water level based on at least one year of monthly static water-level measurements

Latitude

North

Longitude

East

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M