Prepared in cooperation with the Commonwealth of Puerto Rico 

Hydrogeology of Puerto Rico and the Outlying Islands 

of Vieques, Culebra, and Mona 

Puerto Rico 

Mona Culebra 

Vieques 

Scientific Investigations Map 3296
 

U.S. Department of the Interior 

U.S. Geological Survey 

Hydrogeology of Puerto Rico and the Outlying Islands 

of Vieques, Culebra, and Mona

By Fernando Gómez-Gómez, Jesús Rodríguez-Martínez, and Marilyn Santiago

Prepared in cooperation with the Commonwealth of Puerto Rico

Scientific Investigations Map 3296

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Gómez-Gómez, Fernando, Rodríguez-Martínez, Jesús, and Santiago, Marilyn, 2014, Hydrogeology of Puerto Rico and 

the outlying islands of Vieques, Culebra, and Mona: U.S. Geological Survey Scientific Investigations Map 3296, 40 p. 

plus 2 pls., http://dx.doi.org/10.3133/sim3296.

ISSN 2329-132X (online)
iii

Contents

Introduction.....................................................................................................................................................1

Previous Work .......................................................................................................................................1

Methodology Used to Prepare the Hydrogeologic Maps ..............................................................2

Generalized Characteristics of the Islands ...............................................................................................2

Physiography and Vegetation.............................................................................................................4

Puerto Rico....................................................................................................................................4

Vieques ..........................................................................................................................................4

Culebra...........................................................................................................................................8

Mona..............................................................................................................................................9

Climate..................................................................................................................................................10

Geology.................................................................................................................................................14

Hydrology .............................................................................................................................................16

Contents of the Hydrogeologic Map.........................................................................................................20

Description of Aquifer Systems........................................................................................................20

North Coast Province................................................................................................................20

West Coast to Río Grande de Arecibo Area.................................................................20

Río Grande de Arecibo to Río de la Plata Area............................................................25

Río de la Plata to Río Espíritu Santo Area.....................................................................26

South Coast Province................................................................................................................28

Patillas to Ponce Area .....................................................................................................28

Tallaboa-Guayanilla-Yauco-Guánica Valleys...............................................................30

West Coast Province.................................................................................................................32

Río Guanajibo ....................................................................................................................32

Río Yaguez..........................................................................................................................33

Río Grande de Añasco .....................................................................................................33

Río Culebrinas ...................................................................................................................33

East Coast Province ..................................................................................................................33

Fajardo Area ......................................................................................................................33

Naguabo-Humacao Area ................................................................................................33

Yabucoa Valley ..................................................................................................................33

Maunabo Valley ................................................................................................................34

Lajas Valley .................................................................................................................................34

Interior Province ........................................................................................................................36

Vieques and Culebra Islands ...................................................................................................36

Mona Island................................................................................................................................37

Summary and Conclusions ........................................................................................................................38

Selected References ..................................................................................................................................38
iv

Figures

1. Map showing location of Puerto Rico, Vieques, Culebra, and Mona Islands ....................3

2. Map showing geographic regions of Puerto Rico and outlying islands..............................5

3. Map showing generalized topographic relief of Puerto Rico ...............................................6

4. Map showing generalized topographic relief and geographic features

of Vieques island...........................................................................................................................7

5. Map showing generalized topographic relief and geographic features

of Culebra island ...........................................................................................................................8

6. Map showing generalized topographic relief and geographic features

of Mona island...............................................................................................................................9

7. Map showing climatic subdivisions of Puerto Rico and outlying islands .........................11

8. Map showing distribution of mean annual precipitation in Puerto Rico...........................12

9. Graph showing 10-year moving average rainfall trends at San Juan and Aguirre, 

Puerto Rico ..................................................................................................................................13

10. Map showing generalized geology of Puerto Rico and the outlying islands....................15

11. Map showing principal perennial streams and surface-water gaging stations

in Puerto Rico ..............................................................................................................................17

12. Map showing 10-digit hydrologic units for Puerto Rico.......................................................18

13. Diagram showing generalized water balance for the island of Puerto Rico....................19

14. Map showing groundwater provinces and aquifers of Puerto Rico and

outlying islands ...........................................................................................................................21

15. Map showing generalized surficial geology of the North Coast Limestone

aquifer system and the location of deep exploratory test wells.........................................22

16. Stratigraphic chart showing varied nomenclature used for the same rocks

in the North Coast Province......................................................................................................23

17. Generalized hydrogeologic cross section through the North Coast Limestone

aquifer system between the Río Grande de Arecibo and the Río Grande

de Manatí near Barceloneta.....................................................................................................24

18. Graph showing initial heads in test wells penetrating the Lares Limestone

in the lower aquifer......................................................................................................................25

19. Graph showing head change at selected industrial and public-supply wells 

in the North Coast Limestone lower aquifer in the area of Barceloneta ..........................27

20. Generalized hydrogeologic cross section through the North Coast Limestone

aquifer system in the San Juan area.......................................................................................27

21. Map showing areal extent of the South Coastal Alluvial Plain aquifer system

and major irrigation infrastructure ..........................................................................................29

22. Generalized hydrogeologic cross section through the South Coastal 

Alluvial Plain aquifer system near Ponce...............................................................................31

23. Generalized hydrogeologic cross section through the Río Tallaboa 

alluvial valley aquifer west of Ponce.......................................................................................31

24. Generalized hydrogeologic cross section through the lower Río Guanajibo

alluvial valley aquifer near Cabo Rojo.....................................................................................32

25. Map showing Lajas Valley and major geographic features near the

southwestern coast of Puerto Rico .........................................................................................35

26. Map showing location of generalized surficial geology of Mona Island..........................37
v

Tables

1. Geographic regions of Puerto Rico ...........................................................................................4

2. Basic streamflow statistics for selected gaging stations in Puerto Rico .........................16

Plates

1. Hydrogeologic map of the island of Puerto Rico

2. Hydrogeologic maps of the islands of Vieques, Culebra, and Mona, Puerto Rico

Acknowledgments

The authors are indebted to numerous U.S. Geological Survey staff for their contributions in the 

publication of the report: former staff members Rafael Dacosta and Vicente Quiñones-Aponte, 

who compiled data from available reports and files for use in the preparation of the preliminary 

hydrogeologic base map, and Thalia Veve for her cartographic work. Also José Alicea and 

Francisco Maldonado for their contribution to the illustrations; Wanda Molina for reviewing 

the groundwater withdrawal estimates; and Sigfredo Torres-González, Robert Renken, and 

José Rodríguez for their dedication in advancing the state of knowledge of the islands’ 

hydrogeology as part of the Caribbean Islands Regional Aquifer System Analysis Program.
vi

Conversion Factors and Datums

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 2.471 acre

square kilometer (km2

) 247.1 acre

Flow rate

cubic meter per second (m3

/s) 35.31 cubic foot per second (ft3/s)

liter per second (L/s) 15.85 gallon per minute (gal/min) 

cubic meter per day (m3

/d) 264.2 gallon per day (gal/d) 

millimeter per year (mm/yr) 0.03937 inch per year (in/yr) 

Transmissivity*

meter squared per day (m2

/d) 10.76 foot squared per day (ft2/d)

Specific capacity

liter per second per meter (L/s/m) 0.01077 cubic feet per second per foot 

(ft3

/s/ft)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F =(1.8 ×°C) +32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F – 32 )/ 1.8

Vertical coordinate information is referenced to local mean sea level.

Horizontal coordinate information is referenced to the Puerto Rico Datum, 1940 adjustment.

Altitude, as used in this report, refers to distance above mean sea level.

*Transmissivity: The standard unit for transmissivity is cubic meter per day per square meter 

per meter of aquifer width [(m3/d)/m2]m. In this report, the mathematically reduced form, meter 

squared per day (m2/d), is used for convenience.
Hydrogeology of Puerto Rico and the Outlying Islands 

of Vieques, Culebra, and Mona

By Fernando Gómez-Gómez, Jesús Rodríguez-Martínez, and Marilyn Santiago

Introduction

The regulatory agencies of the Commonwealth of Puerto 

Rico, in particular the Puerto Rico Department of Environmental 

and Natural Resources (PRDENR), are in need of easily accessible information that might help them to properly manage the 

groundwater resources of Puerto Rico and its outlying islands. 

This information would be preferentially presented as a series of 

hydrogeologic maps complemented with geologic cross sections 

and textual notes. Consequently, the Commonwealth requested 

the U.S. Geological Survey (USGS) to prepare a report 

including the main elements of the hydrogeology of Puerto 

Rico and the outlying islands of Vieques, Culebra, and Mona 

obtained from previous studies conducted by the USGS.

The hydrogeologic maps of Puerto Rico and the outlying 

islands will be useful to hydrogeologists, groundwater specialists, and water-resources managers and planners in developing 

and protecting water resources in these islands. In addition, 

these maps can serve as catalysts in promoting future research 

within areas where current hydrogeologic information is 

limited or insufficient and can contribute toward promoting 

scientific interaction between countries in the Caribbean region.

Hydrogeologic maps were prepared for Puerto Rico and 

the outlying islands of Vieques, Culebra, and Mona by using 

a geographic information system (GIS) format. The hydrogeologic map of Puerto Rico is shown on plate 1 at a scale 

of 1:240,000. The hydrogeologic maps of the outlying islands 

are shown on plate 2 for Vieques, Culebra, and Mona at a 

scale of 1:50,000.

The principal objective of the hydrogeologic maps of 

Puerto Rico and the outlying islands of Vieques, Culebra, and 

Mona is to present information regarding the hydrogeologic and 

hydrologic characteristics of the islands in relation to specific 

geologic settings. Two primary features are depicted on the 

hydrogeologic maps. The first feature identifies geographic areas 

underlain by locally important aquifers as well as areas where 

groundwater availability is limited to nonexistent. The second 

feature differentiates groundwater occurrence according to the 

principal water-bearing units that compose the aquifers. Waterbearing units are depicted on the map as fissured units (carbonate 

rocks), intergranular deposits (alluvial or associated deposits), or 

a combination of both (Struckmeiser and Margat, 1995).

Previous Work

The first hydrogeologic map of Puerto Rico including the 

outlying islands of Vieques, Culebra, and Mona was prepared 

in 1965 by the U.S. Geological Survey (USGS) at a scale of 

1:240,000 (Briggs and Ackers, 1965). At that time, available 

hydrogeologic information depicted on the map included

1. Information from surficial geologic maps prepared at 

various scales, such as 1:20,000 and smaller.

2. Information on well characteristics and drillers’ 

lithologic logs.

3. Information obtained from the report “A comprehensive 

assessment of the groundwater resources of Puerto Rico 

and the outlying islands” (McGuinnes, 1948).

The 1965 hydrogeologic map of Puerto Rico was used as 

the basis for constructing the hydrogeologic maps presented 

in the current report. The 1965 map was especially useful in 

helping delineate the hydrogeologic unit boundaries described 

on the current maps. Information from a geologic map 

prepared by R.D. Krushensky (Bawiec, 1998) was also used.

The USGS has conducted numerous hydrologic and 

hydrogeologic investigations in cooperation with agencies of 

the Commonwealth of Puerto Rico since 1965. In addition, by 

1987, the USGS was operating a network of 43 streamflowgaging stations, 56 surface-water-quality monitoring stations, 

and 31 groundwater-level monitoring sites throughout 

Puerto Rico (Curtis and others, 1987). By 2010, the network 

had expanded to include 88 streamflow-gaging stations, 

55 surface-water-quality stations, and 92 groundwater-level 

monitoring sites (U.S. Geological Survey, 2010). Results from 

interpretive studies have been made available to the public in 

published reports and maps. Data have been made available 

through the Water Resources Data report series, published 

annually from 1965 to 2011, and most recently in digital 

format. Many reports on the water resources of Puerto Rico 

and the islands of Vieques, Culebra, and Mona have been 

published (http://pr.water.usgs.gov/publications/). Only those 

reports available through 2002 served as the primary sources 

of information in developing the recent hydrogeologic maps 

and preparing this report.
2 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Most of the information presented on the recent maps 

and in this report were derived from the federally funded 

USGS Caribbean Islands Regional Aquifer-System Analysis 

(CI-RASA) Program. Thus, readers are encouraged to 

review the reports prepared as part of that Program and other 

information available to the general public from the USGS 

National Water Information System (http://pr.water.usgs.gov/).

Methodology Used to Prepare the 

Hydrogeologic Maps

The hydrogeologic maps of the main island of Puerto 

Rico and the outlying islands were developed by reviewing 

available hydrologic and hydrogeologic data up to about 

2002. An exception was the data provided on water use and 

groundwater withdrawals, which were estimated from 2005. 

The hydrogeologic data were summarized and interpreted in a 

format that could be understood by non-specialists as well as 

groundwater hydrology and water-resources specialists. The 

steps taken to prepare the hydrogeologic maps follow:

1. Existing literature was reviewed to determine those 

aquifer areas that had been studied in detail versus 

those aquifer areas that had been studied only as part 

of regional assessments.

2. Automated and non-automated databases were searched 

to compile information on well characteristics, the 

quality of groundwater, and streamflow statistics.

3. Geographic areas with deficient information were 

delineated. Missing information was obtained either 

by directly contacting government agencies that 

had collected groundwater data in those areas or 

by performing actual field surveys.

4. Preliminary maps and figures were constructed in 

preparation for developing the hydrogeologic map 

for the island of Puerto Rico and outlying islands.

5. Individual map overlays were reviewed for qualityassurance purposes and to make modifications where 

necessary prior to completing the final map plates.

Generalized Characteristics of the Islands

Puerto Rico and its adjacent islands of Vieques, Culebra, 

and Mona lie along the northeastern boundary of the Caribbean 

Sea between latitudes 17°58' N. and 18°32' N. and between 

longitudes 65°15' W. and 68°00' W. (fig. 1). The total land area of

the four islands is 8,927 square kilometers (km2) —Puerto Rico 

is 8,713 km2, Vieques is 132 km2, Culebra is 30 km2, and Mona 

is 54 km2. In 2010, the total population of Puerto Rico (including 

Vieques and Culebra) was 3,725,789 with approximately 

50 percent of the population living at or in the vicinity of the 

two major urban centers on the main island of Puerto Rico —

San Juan to the north and Ponce to the south (fig. 1). Specifically, 

the population was distributed among the four islands as 

follows: Puerto Rico had 3,714,670 inhabitants; Vieques had 

9,301 inhabitants; Culebra had 1,818 inhabitants; and Mona had 

no permanent inhabitants (U.S. Bureau of the Census, 2012). 

The economic and social settings of Puerto Rico have 

been transformed substantially since World War II. Originally 

an agriculturally dependent economy based on sugarcane, 

tobacco, and coffee, Puerto Rico’s economy has since become 

more diversified. The principal forces driving the island’s 

economy include industrial development (in other words, 

pharmaceuticals and chemical products, electronics, textiles, 

and food processing); construction (i.e., industrial, commercial, residential, and public works infrastructure); commerce 

(i.e., retail sales and exports); financial services (i.e., banking); 

and tourism. The successful diversification of the economy 

beyond agriculture has been confirmed by labor statistics. 

In 2000, the total labor force consisted of 915,882 persons 

of which about 1 percent (10,300) worked in agriculture or 

related enterprises. The remaining labor force was employed 

in management (27 percent) service, including government 

(16 percent), sales (28 percent), production and transportation 

(16 percent), and construction (12 percent) (http://www.dol.gov/

ofccp/pdf/reveeopr2.pdf). In 2007, the total labor force 

consisted of 1,014,970 persons of which less than 1 percent 

(10,000) worked in agriculture or related enterprises. 

The economic and social settings of Vieques differ 

greatly from that of Puerto Rico. Until 1943, sugarcane 

cultivated within the coastal plain served as the principal 

source of income for the island’s population. In 1943, the 

U.S. Navy occupied the island, using nearly 75 percent of the 

land for training purposes. In 2004, the U.S. Navy transferred 

most of the occupied land to the U.S. Fish and Wildlife 

Service and to the Municipality of Vieques.

On Culebra, during the period from 1943 to 1973, 

about 30 percent of the land was under the jurisdiction of 

the U.S. Navy. By 1973, the U.S. Navy ceased nearly all 

operations on the island, retaining only 25 hectares (ha) 

at Punta Flamenco. The remaining land was transferred to 

the Commonwealth of Puerto Rico under stipulations of 

U.S. Public Law 93-166, which established certain restrictions 

on future land uses. The restrictions were intended primarily 

to comply with requirements of the National Environmental 

Policy Act to protect endangered species. As a result, about 

380 ha or 15 percent of the island was designated as a wildlife 

refuge for migrating species of birds and sea turtles, including 

the leather back and green turtles, which use most of the 

island’s sandy beaches as nesting areas. The wildlife refuge 

is managed cooperatively by the Puerto Rico Department of 

Natural and Environmental Resources and the U.S. Fish and

Wildlife Service. An additional 316 ha are to be retained by the 

U.S. Fish and Wildlife Service in exchange for about 108 ha of 

land on the adjacent island of Culebrita, which has been part 

of the U.S. National Wildlife Refuge system since 1909.

The entire island of Mona is protected as a sanctuary for 

59 endemic plant and animal species and as a wildlife refuge 

for migrating species. A number of pre-Colombian archaeological sites and places of historical interest also are located 

on the island.
Generalized Characteristics of the Islands 

3

"

"

"

" "

"

" "

"

"

"

"

"

"

"

"

"

"

CARIBBEAN SEA

ATLANTIC OCEAN

Culebra

Vieques

Guaynabo

Aguadilla

Arecibo

VegaBaja Toa Baja Bayamón

Río Grande Toa Alta

Trujillo Alto

Caguas

Mayagüez Humacao

Ponce

CaboRojo Juana Díaz

Carolina

San Juan

65°30' 66°00' 66°30' 67°00'

18°30'18°00'

PUERTO

RICO

CARIBBEAN SEA

GULF

OF

MEXICO

ATLANTIC OCEAN

60° 70° 80° 90° 100°

30°20°10°

Figure 1. Location of Puerto Rico, Vieques, Culebra, and Mona Islands.

Base from U.S. Army Corps of Engineers, 2007

Main urban center with population greater than 50,000 (U.S. Bureau of the Census, 2010)

0 10 20 MILES0 10 20 KILOMETERS

EXPLANATION

UNITED STATES

SOUTH AMERICA

PUERTO RICO

67°55'

18°10'

18°5'

Mona

Figure 1. Location of Puerto Rico, Vieques, Culebra, and Mona Islands.
4 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Physiography and Vegetation

Geographically, Puerto Rico and the outlying islands 

have been subdivided into 11 regions on the basis of similar 

landforms and climate characteristics (fig. 2; table 1; Picó, 

1964). The physical diversity characterizing each region is 

complex and beyond the scope of this report; however, the 

following summary describes the primary physiographic 

features of each island.

Puerto Rico

The principal physiographic feature of Puerto Rico is 

the Cordillera Central and the Sierra de Cayey, which form a 

continuous mountain range extending in an east-west direction 

nearly the entire length of the island (fig. 3). The foothills, 

which separate the coastal plain from the mountains, begin at 

an altitude of about 300 meters (m). Throughout most of the 

mountainous areas, ridge tops reach altitudes of 700 m with a 

maximum altitude of 1,338 m found at Cerro de Punta north 

of Ponce. Within the mountainous areas, hillsides are steep 

with about 50 percent of the land having slopes greater than 

45 percent.

The predominant physiographic feature characterizing the 

western two-thirds of the northern coast is karst terrain, which 

extends inland as much as 20 kilometers (km). The karst 

topography varies from typical solution feature landforms, 

such as sinkholes and cockpits (intersecting star-shaped 

dolines or sinks), to residual tower karst features, which 

are landforms distinguished by elongated plains bounded 

by steep-sided hills or mogotes (haystack hills). In general, 

solution karst landforms are more typical of inland areas, and 

residual tower karst landforms predominate at lower altitudes 

along the north coast (Monroe, 1976). The most distinctive 

feature along the south coast of Puerto Rico is the marked 

contrast between the intense green foliage of cultivated crops 

grown on irrigated lands within the coastal plain and alluvial 

valleys and the semi-arid conditions and sparse vegetation 

growing within the foothills and karst terrain of the southwest.

Vieques

The principal physiographic feature of Vieques is a 

relatively broad plain that slopes to the south from a central 

ridge extending across the western half of the island (fig. 4). 

Altitudes along most of the length of the ridge reach 100 m 

with a maximum altitude of 301 m at Monte Pirata. The land 

has a slope of about 12 percent between an altitude of 50 m 

and the coast. Above this altitude, the slope increases to about 

40 percent. As of 2002, most of the island was in pasture 

or brush.

Table 1. Geographic regions of Puerto Rico (modified from 

Picó, 1964).

[Areas adjusted to agree with that given in U.S. Bureau of the Census, 1991; 

areas exclude off-shore cays and islets]

Geographic region Hectares Percent of 

total area

1. North Coastal Plain 119,395 13.4

 A. Sub-humid western area 33,377

 B. Humid alluvial area 86,018

2. Humid Valleys of the East Coast 27,800 3.1

 A. Fajardo area 9,864

 B. Naguabo-Humacao valleys 11,365

 C. Yabucoa valley 4,939

 D. Maunabo valley 1,632

3. Caguas Valley 12,868 1.4

4. Valleys of the West Coast 23,208 2.6

 A. Culebrinas-Culebras valleys 4,217

B. Córcega area 462

 C. Añasco valley 4,665

 D. Guanajibo valley 13,864

5. South Coastal Plain 87,779 9.8

 A. Ponce-Patillas Coastal Plain 47,067

 B. Tallaboa valley 2,210

 C. Guayanilla-Guánica area 6,080

 D. Lajas valley 13,763

 E. Southwest mountain belt 18,659

6. Semi-arid southern foothills 88,270 9.9

7. Humid Northern Foothills 185,956 20.8

 A. Cretaceous northeast area 66,549

 B. Interior Limestone belt 95,852

 C. Atalaya mountains 23,555

8. Humid Mountains of the East 133,561 15.0

9. Rainy Mountains of the West 171,168 19.2

10. Sierra de Luquillo 21,331 2.4

11. Vieques, Culebra, and Mona 21,620 2.4

 A. Vieques 13,200

 B. Culebra 3,000

 C. Mona 5,420

Total 892,956 100.0
Generalized Characteristics of the Islands 5

"

"

"

"

"

"

" " "

"

" "

"

" "

"

"

"

" " "

"

"

"

"

"

"

" " "

" "

"

"

"

"

" " "

"

"

"

"

"

"

" " " "

" " "

" "

"

"

"

"

" "

"

"

"

" "

"

" "

"

"

" " "

"

"

"

"

AguasBuenas

Guaynabo

Isabela

Aguadilla

Arecibo

Vega

Baja Hatillo Camuy

Quebradillas

Barceloneta Manatí

Dorado

Vega

Alta

Toa Baja

Cataño

Moca

Loíza

Bayamón

Río

Grande

Aguada Canóvanas

Florida

Toa Alta

SanSebastián

Luquillo

Trujillo Alto Morovis Rincón Ciales Corozal Lares

Culebra

Culebra

Vieques

Utuado

Naranjito

Añasco Gurabo

Jayuya

Naguabo

Orocovis Las Marías Comerío

Las

Piedras

Mayagüez

Juncos

Adjuntas

Barranquitas Cidra San

Lorenzo

Maricao

Humacao

Aibonito

Villalba

Coamo

Coamo

SanGermán

Ponce

Yauco

Cabo

Rojo Cayey

Isabel II Hormigueros

Juana

Díaz

Sabana

Grande

Guayanilla

Peñuelas

Yabucoa Patillas

Guayama Salinas

Lajas

Maunabo

"

SantaIsabel

Arroyo

Guánica

Fajardo

Ceiba

Carolina

San Juan

Base modified from Picó, 1964

EXPLANATION

Geographic region

—

 See table 1Town and name

Figure 2. Geographic regions of Puerto Rico and outlying islands.

0 10 20 MILES0 10 20 KILOMETERS

65°30' 66°00' 66°30' 67°00'

18°30'

18°00'

C A R I B B E A N S E A

A T L A N T I C O C E A N 

67°55'

18°10'

18°05'

Mona

1-A7-B

7-C

4-B

9

4-C

4-D

4-A

1-B

7-A 10

2-A

8

3

2-B

6 2-C

5-A

5-D

5-C

2-D

2-D

5-E 5-E

5-B

11-C

11-B

11-A

 Figure 2. Geographic regions of Puerto Rico and outlying islands (see table 1 for region numbers).
6 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

#

65°30’ 66°00' 66°30’ 67°00'

18°30’

18°00'

Base from the U.S. Geological Survey National Elevation Dataset

EXPLANATION

Altitude, in meters above  mean sea levelTown and nameMountain peak

C A R I B B E A N S E A

A T L A N T I C O C E A N 

Figure 3. Generalized topographic relief of Puerto Rico.

0 10 20 MILES0 10 20 KILOMETERS

Cerro de

Punta

Sierra deLuquillo

Sea level to 7576 to 299300 to 599600 to 899900 to 1,200

C o r d i l l e r a C e n t r a l S i e r r a

d e C a y e y

" Ponce

" Ponce

Figure 3. Generalized topographic relief of Puerto Rico.
Generalized Characteristics of the Islands 

7

Desenbarcadero

Mosquito

Isabel II

#

Monte Pirata

301 m

Resolución

Punta Salinas

Esperanza

EnsenadaHonda

PlayaGrande Isabel II

EXPLANATION

Altitude, in meters above mean sea level Town and nameMountain peak

Sea level to 1011 to 5051 to 100101 to 301

Figure 4. Generalized topographic relief and geographic features of Vieques Island.

Base from the U.S. Geological Survey National Elevation Dataset

C A R I B B E A N S E A

V I E Q U E S S O U N D

65°20' 65°25' 65°30' 65°35'

18°10'18°05'

0 2 4 MILES0 2 4 KILOMETERS

Figure 4. Generalized topographic relief and geographic features of Vieques island.
8 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Culebra

The principal physiographic feature of Culebra is Ensenada Honda, which is a natural bay located on the south 

side of the island (fig. 5). The bay is sheltered from the trade winds and is about 12 m at its maximum depth. The 

terrain of Culebra is hilly with slopes ranging between 20 and 40 percent. As of 2002, most of the land was in 

pasture or brush.

EXPLANATION

Altitude, in meters above

 mean sea level 

Town and name

Sea level to 30

31 to 100

101 to 193

Figure 5. Generalized topographic relief and geographic features of Culebra Island.

Base from the U.S. Geological Survey National Elevation Dataset

V I E Q U E S S O U N D

A T L A N T I C O C E A N

Culebra

Culebra

65°20' 65°15'

18°20'

18°15'

0 2 4 MILES

0 2 4 KILOMETERS

ISLA CULEBRITA

CAYO NORTE

Canal de Cayo Norte

Canal de Luis Peña

Ensenada Honda

Punta Flamenco

CAYO DE LUIS PEÑA

Figure 5. Generalized topographic relief and geographic features of Culebra island.
Generalized Characteristics of the Islands 9

Mona

Two physiographic features dominate the landscape of Mona (fig. 6). First, the island is encircled by cliffs that 

rise vertically upward from the ocean along more than 50 percent of the coastline. Second, the interior of the island 

is characterized by a limestone tableland that reaches an average altitude of 60 m. The tableland is nearly flat, with 

the exception of sinkhole depressions in an area covering less than 170 ha. The sinkhole depressions are the only 

areas on the island where soil is found, with the exception of the coastal plain. The reddish silt loam derived from 

weathering of the limestone bedrock fills the depressions and provides support for a forest of trees that average 6 m 

in height. The only other forest vegetation on the island is located within a 320-ha tract of land on the coastal plain. 

The remainder of the island vegetation is predominantly low dry forest shrubs and cactus.

Cabo Noreste

Cabo Norte

Cabo Barrio

Nuevo

Punta

Arenas

Playa del Uvero

Punta Caigo o no Caigo

Punta 

los Ingleses

Punta Este

Cueva de Frío

67°55' 67°50'

18°7'30"

18°05'

18°2'30"

Base from the U.S. Geological Survey National Elevation Dataset

M O N A P A S S A G E

M O N A P A S S A G E

Coastal Plain

60

50

50

60

40

60

80

70

70

70

90

70

80

30

60

60

50

40

40

50 50

40

30

50

50

40

50

60

50

Figure 6. Generalized topographic relief and geographic features of Mona Island.

0 1 2 MILES

0 1 2 KILOMETERS

Cuevas del

Centro

EXPLANATION

Altitude, in meters above

 mean sea level 

Sea level to 30

31 to 60

61 to 92

Topographic contour—

 Contour interval 

 10 meters

Los Corrales

de Los Indios

Cueva

de los

Pájaros

Figure 6. Generalized topographic relief and geographic features of Mona island.
10 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Climate

In general, the east-west trending Cordillera Central 

and Sierra de Cayey mountains form an insular hydrologic 

divide that separates the island of Puerto Rico into two 

climatologically distinct regions. The northern two-thirds of 

the island has a relatively humid climate whereas the southern 

one-third of the island is semi-arid.

The National Oceanic and Atmospheric Administration 

(1982) subdivided the island of Puerto Rico into six climate 

areas and designated a seventh climate area in the outlying 

islands (fig. 7). Local climate variability within each 

subdivision and in the outlying islands is attributed to local 

differences in topographic relief and the effect of prevailing 

trade winds. Along the northern coast of Puerto Rico and 

in the outlying islands, prevailing trade winds are from 

the northeast. Along the southern coast of Puerto Rico, the 

east-west trending mountains affect wind patterns. In this 

area, the predominant wind direction is from the southeast 

during daylight hours, whereas prevailing winds are from the 

northeast during the period from midnight to early morning. 

Prevailing winds along the western end of Puerto Rico at 

Mayagüez differ from other areas on the island. Predominant 

winds in this area are from the west, which is nearly opposite 

to the prevailing northeast trade winds. Prevailing west 

winds are infrequent throughout other areas of the island. For 

example, in the San Juan area, west prevailing winds occur 

less than 3 percent of the time and generally are associated 

with the passing of cold fronts across the island.

Mean monthly air temperatures in Puerto Rico and the 

outlying islands vary little throughout the year. Air temperatures 

generally are warmest during the month of August and coolest 

during the months of January and February. In coastal areas, 

annual air temperatures range from a mean maximum of 

27 degrees Celsius (°C) to a mean minimum of 24 °C. In 

interior mountainous areas (that is, Eastern and Western Interior 

climate subdivisions; fig. 7), annual air temperatures range from 

a mean maximum of 25 °C to a mean minimum of 22 °C.

Air temperatures fluctuate little throughout the year 

as a result of relatively constant insolation (that is, solar 

radiation) and seawater temperatures. The rate of delivery of 

solar radiation is nearly constant because the difference in 

daylight hours varies little throughout the year. Between the 

longest day of the year (13 hours, 13 minutes) and the shortest 

day (11 hours, 2 minutes), the amount of daylight differs by 

only slightly more than 2 hours. Mean monthly seawater 

temperatures vary by only about 4 °C; the mean maximum 

water temperature of 28 °C occurs in October, and the mean 

minimum water temperature of 24 °C occurs in January.

The spatial distribution of rainfall in Puerto Rico is 

variable (fig. 8). Rainfall is greatest in the Sierra de Luquillo 

rainforest in the eastern part of Puerto Rico. The mean annual 

total rainfall in Sierra de Luquillo is 4,305 millimeters per year 

(mm/yr). The least amount of rainfall occurs in the vicinity of 

Guánica at Ensenada in southwestern Puerto Rico. In this area, 

the mean annual total rainfall is 768 mm/yr.

Pronounced orographic effects from the Cordillera 

Central and the Sierra de Cayey mountains in Puerto Rico 

result in high rainfall amounts occurring on the windward 

side of the mountains, which is north of the insular hydrologic 

divide. The opposite occurs south of the divide on the leeward 

side of the mountains, where coastal areas lie within a rain 

shadow resulting in lower rainfall amounts. Orographic effects 

on rainfall are not as pronounced in the outlying islands, with 

the exception of Vieques. 

Rainfall on the island of Vieques differs substantially 

between the leeward or west side of the island and the 

windward or east side of the island. In general, rainfall occurs 

more frequently on the west side of Vieques. Although rainfall 

data are insufficient to quantify amounts, estimates indicate 

that the difference in rainfall between the east and west ends 

of the island could be as much as 345 mm/yr. Rainfall in the 

eastern part of the island may be similar to that of the island 

of Culebra where the mean annual total rainfall is 925 mm/yr. 

The mean annual total rainfall in the western part of Vieques, 

at Playa Grande and Resolución, is 1,270 mm/yr (fig. 4). The 

mean annual total rainfall on the island of Mona is 915 mm/yr.

Although rainfall data are limited, certain vegetation 

adapted for life with a limited water supply (such as 

xerophytes) serve as strong indicators about rainfall 

distributions on Vieques. The growth of xerophytes is 

prevalent on the east side of the island where rainfall is 

limited as opposed to the west side of the island where 

rainfall is more abundant.

Major rainfall events producing substantial volumes of 

rain in Puerto Rico and the outlying islands are caused by one 

of two climate mechanisms—the passage of an easterly wave 

or the passage of a cold front. Easterly waves generally occur 

during May to November with some having sufficient intensity 

to evolve into tropical storms and (or) hurricanes. Cold fronts 

generally occur during November to April and may produce 

sufficient rainfall to cause flooding even during the period 

from December to March, which is a relatively dry period. 

The number of easterly waves or cold fronts passing over the 

region in any given year ultimately determines whether the 

region experiences relatively dry conditions or wet conditions. 

As a result, localized droughts occur yearly within many of 

the geographic areas of Puerto Rico.
Generalized Characteristics of the Islands 11

Vieques

Culebra

Arecibo

3 ESE

Dorado

2 WNW

Trujillo

Alto 2 SSW

Jájome

Alto

Río Piedras

Exp. station

San Juan

Intl AP

Manatí 2E

Monte Bello Manatí

Quebradillas

65°30' 66°00' 66°30' 67°00'

18°30'

Base from National Oceanic and Atmospheric Administration

C A R I B B E A N S E A

A T L A N T I C O C E A N 

EXPLANATION

National Weather Service rainfall station

Canóvanas

Rincón

Guayabal

Aceituna

Cidra 1E

Cayey 1E

Fajardo

Maunabo

Aguirre

Yabucoa

1 NNE

Humacao

2 SSE

Guayama

2 E

Roosevelt

Roads

Pico Del

Este

Juncos 1 SE

Aibonito

1 S

Morovis 1 N

Coamo

2 SW

Gurabo

substation

Corozal

substation

NegroCorozal

Barranquitas

North Coastal

South

Coastal

Northern Slopes

Southern Slopes

Western Interior

Eastern Interior

Arecibo

Observatory

Guajataca Dam

Cacaos-Orocovis

Cerro Maravilla

Corral Viejo

Adjuntas

1 NW

Adjuntas

substation

Ensenada 1 W

Jayuya

Utuado

Lares

Mayaguez AP

Coloso

Ponce

4E

Dos Bocas

Maricao

2 SSW

Maricao

fish hatchery

Mayaguez

City

San

Hacienda

Constanza

Sebastián

2 WNW

Central

San Francisco Magueyes Island

Lajas

substation

Caonillas Utuado

Mora Camp

Figure 7. Climatic subdivisions of Puerto Rico and outlying islands.

0 10 20 MILES0 10 20 KILOMETERS

Borinquen AP

CaleroCamp

Isabela

substation

Juana

Díaz Camp 18°00'

67°55'

18°10'

18°5'

Mona

Figure 7. Climatic subdivisions of Puerto Rico and outlying islands.
12 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona 65°30' 66°00' 66°30' 67°00' 18°30' 18°00' EXPLANATION Mean annual precipitation 1971–2000, in millimeters C A R I B B E A N S E A A T L A N T I C O C E A N 

Figure 8. Distribution of mean annual precipitation in Puerto Rico .

0 10 20 MILES0 10 20 KILOMETERS

1,583 1,341 1,481 1,410

1,246

1,744

1,367

1,908

1,771

1,855

2,297 1,886

1,459

1,871

1,914

1,635

1,802

1,895

1,296

2,355 2,464

1,846 1,951

2,046

2,428

2,213

1,778

1,143

769 799 768

Base from National Oceanic and Atmospheric Administration

1,230

768 to 1,2551,256 to 1,6301,631 to 1,9501,951 to 2,5002,501 to 3,4053,406 to 4,305

1,709

1,831

1,711

1,542

1,567 1,443

1,230 1,432

1,513

1,264

991

901

1,009

1,229

1,321

1,817

994

1,728

2,055

2,042

4,305

1,906

1,645 1,577

1,754

1,752 1,289

1,575

1,327

1,341 1,481 1,410

1,744

1,908

1,771

1,855

2,297 1,886

1,459

1,871

1,914

1,635

1,802

1,895

1,296

2,355 2,464

1,846 1,951

2,046

2,428

2,213

1,778

1,143

769 799 768

National Weather Service rainfall station and precipitation amount at station

Figure 8. Distribution of mean annual precipitation in Puerto Rico.
Generalized Characteristics of the Islands 13

Extended, extreme drought conditions affecting the entire 

region of Puerto Rico and the outlying islands have occurred 

on three occasions during the 20th century. The first extreme 

drought began in the late 1920s and continued through 1930. 

The second severe drought began in the mid 1960s and 

ended in 1968. The third severe drought affected primarily 

the eastern half of the main island of Puerto Rico throughout 

most of 1994 (fig. 9). During the drought of the 1960s, mean 

annual rainfall on the main island of Puerto Rico was about 

1,100 millimeters (mm) in 1967 (Colón, 1983) compared to 

the 30-year normal (1931–60) of 1,825 mm/yr. The drought 

of 1994 resulted in a rainfall deficiency of about 30 percent 

throughout the eastern part of the island and was particularly 

notable in its effect on the availability of public-supply water 

for more than 1 million people living within the San Juan 

metropolitan area and the city of Caguas. Historical references 

indicate that other severe droughts have reportedly affected 

the southern coast of Puerto Rico from Guayama to Cabo Rojo 

during the period 1892 to 1894 (Wilson, 1899) and during the 

period 1871 to 1874. Evidence of the severity of this latter 

drought period was found in a decree written by the Ponce 

mayor, Rafael de Leon, on May 17, 1874. In the decree, the 

mayor reminded citizens of the law prohibiting the cutting 

of forested areas without first obtaining the proper permits in 

light of the severe drought, which affected the area for more 

than 3 years (Neumann, 1913).

1,700

1,600

1,500

1,400

1,300

1,200

1,100

1,000

900

800

1900 1920 1940 1960 1980 2000 2020

10-year moving average rainfall, in millimeters per year

Year

Old San Juan

Aguirre

EXPLANATION

Figure 9. 10-year moving average rainfall pattern at selected meteorological stations in

Puerto Rico. 

10-year moving average rainfall

Figure 9. 10-year moving average rainfall trends at San Juan and Aguirre (66-0152), Puerto Rico 

(San Juan station (66-8808) at Old San Juan, discontinued in 1976).
14 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Geology

A generalized description of the geology of Puerto 

Rico and adjacent islands is presented below. Information 

was obtained from reports compiled by Bogart and others 

(1964) and from studies conducted by Meyerhoff (1933), 

Zapp and others (1948), Mattson (1960), Briggs (1961), 

Glover (1971), and Monroe (1980). During the late 1980s, 

an extensive exploratory drilling program was conducted 

within the largest aquifer systems in northern and southern 

Puerto Rico. Thousands of meters of cores from 15 locations 

along the northern coast were used by Hartley (1989) and 

Scharlach (1990) for interpretation of the stratigraphy and 

depositional history of the Oligocene and Miocene rocks. 

Along the southern coastal plain, exploratory drilling was also 

conducted in the area from Ponce to Salinas. Core data were 

used to describe the depositional history within the fan-delta 

plain and the relation of the plain to tectonic and eustatic 

sea level changes (Renken and others, 1995). Details of the 

updated interpretations of the island’s geologic framework and 

the relation of the geology to the hydrogeologic setting are 

presented in Renken and others (2002). 

The central core of Puerto Rico consists primarily of 

volcanic and intrusive rocks of Cretaceous and early Tertiary 

age (fig. 10). The volcanic rocks are predominately ashy 

shale, agglomerate, and tuff, and most of them are thoroughly 

indurated. These rocks are interbedded with thick, dense lava 

flows and relatively thin beds of limestone that have been 

partly recrystallized in many places. The volcanic rocks and 

interbedded limestones have been complexly faulted, folded, 

metamorphosed, and intruded by dioritic rocks. The massive, 

dense dioritic intrusions are exposed by erosion in two large 

areas and many small areas on the island (plate 1). Massive, 

dense serpentinite and associated silicified rocks underlie 

large areas in the southwestern part of the island (plate 1). The 

central igneous core of the island is flanked on the north and 

south by clastic sediments and limestones of Oligocene and 

Miocene age.

Within the middle Tertiary sequence, the older clastic 

sediments are composed predominately of poorly sorted 

mixtures of gravel, sand, and finer materials. The sediments 

grade upward into thick beds of relatively pure limestone. 

Along the northern coast, the limestone has been subjected to 

extensive solutional activity, which has resulted in the formation of mature karst topography. Unconsolidated deposits of 

Pleistocene and Holocene age form a discontinuous coastal 

plain. The sediments throughout most parts of the north and 

northeast consist mostly of carbonaceous sandy clay, except 

at the stream valleys where the sediments grade inland to 

alluvial deposits. At the western coast stream valleys, the 

deposits are derived from weathered tuff and shale and consist 

mostly of clay and silt. Alluvium deposited at the southern 

and southeastern coasts is rich in coarse-grained sand and 

gravel except near the shoreline where it grades into swamp 

deposits. After the deposition of limestone during the middle 

Tertiary period, Puerto Rico was arched, uplifted, and tilted 

to the northeast. The islands of Vieques and Culebra are part 

of the Puerto Rican block and are separated from Puerto 

Rico by the submergence that resulted from the tilting to the 

northeast and by the eustatic increase in sea level during the 

Holocene period.

Vieques island is underlain in the eastern half by andesites 

of Late Cretaceous age deposited in a marine environment 

and in the western half by an extensive dioritic rock intrusion 

(fig. 10). Limestones of Miocene age fringe the southern coast 

and the extreme eastern end of the island, and deposits of 

alluvium as much as 20 m thick form a relatively extensive 

plain toward the southwest. Culebra island is underlain by 

volcanic and intrusive rocks of Cretaceous age. In the northcentral part, these rocks have been intruded by diorite. Alluvial 

deposits are predominately composed of silt and clay, but in 

the major stream courses near the coast these deposits contain 

some sand and gravel. Mona island is a limestone plateau, 

bounded by steep to vertical cliffs that rise 60 m above mean 

sea level. Except for a thin soil cover present only in large 

upland depressions, the entire island consists of limestone 

and calcitic dolomite. Two major units have been identified; 

from oldest to youngest these are the Isla de Mona Dolomite 

of early or middle Miocene age, with a maximum exposed 

thickness of 80 m (base concealed by the sea), and the Lirio 

Limestone of Miocene age, with a maximum exposed thickness of 40 m (Kaye, 1959). A narrow, low-lying coastal terrace 

exists along the southern perimeter of the island formed by an 

elevated reef of Pleistocene age with a thin cover of sand.
Generalized Characteristics of the Islands 15

Vieques

Culebra

65°30' 66°00' 66°30' 67°00'

18°30'

18°00'

Base modified from Briggs and Ackers, 1965

C A R I B B E A N S E A

A T L A N T I C O C E A N 

EXPLANATION

Unconsolidated alluvial and other surficial deposits (Quaternary)Limestone and terrigneous clastics (Cretaceous to middle Tertiary)Igneous rocks: granitoid intrusive (Cretaceous to Tertiary)Undifferentiated igneous rocks: lavas and volcaniclastics (Cretaceous to early Tertiary)Serpentinite (Late Jurassic to Early Cretaceous)Line of geologic cross section 

E

E'

D'

D

C'

C

C'C

A'

A

B'

B

Figure 10. Generalized geology of Puerto Rico and outlying islands.

0 10 20 MILES0 10 20 KILOMETERS

67°55'

18°10'

18°5'

Mona

Figure 10. Generalized geology of Puerto Rico and the outlying islands.
16 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Hydrology

The island of Puerto Rico is considered to have an 

abundant supply of water compared to the smaller islands 

of Vieques, Culebra, and Mona. On the main island, about 

41 perennial streams discharge to the sea (fig. 11). All of the 

perennial streams are located north of the Cordillera Central 

mountains, except the Río Guanajibo and Río Grande de 

Añasco, which are located in the southwestern and western 

parts of Puerto Rico, respectively. The longest river is the 

Río de la Plata, which has a total length of 100 km and 

discharges to the west of San Juan. The headwaters of 

the Río de la Plata are in the Sierra de Cayey (the eastern 

extension of the Cordillera Central) at an altitude of 700 m. 

The largest stream basin is the Río Grande de Loíza in 

northeastern Puerto Rico; the basin covers about 750 km2

. 

Additional information about the principal watersheds in 

Puerto Rico is listed in table 2.

Table 2. Basic streamflow statistics for selected gaging stations in Puerto Rico.

[km2, square kilometers; m3/s, cubic meters per second; m3/d, cubic meters per day]

Stream basin

Drainage area at

gaging station,

in km2

USGS

gaging station

(period of record)

a

Estimate of 7-day

10-year low flow,

in m3

/s

b

Mean discharge,

in m3

/s)

(years used to

estimate discharge)

c 100-year

flood peak,

in m3

/s

North Coast Drainage Basin

Río Tanamá 47.7 50028000

(1959 –2010)

0.26 1.42

(1960 –2010)

307

Río Grande de Manatí 143 50031200

(1965–2010)

0.26 2.69

(1965–2010)

1,550

Río Grande de Manatí d

332 50035000

(1960 –2010)

0.71 7.08

(1946 –2010)

4,033

Río Grande de Loíza 233 50055000

(1959 –2010)

0.51 6.17

(1960 –2010)

1,947

Río Grande de Loíza 25.5 50061800

(1967–2010)

0.07 0.80

(1967–2010)

425

Río Espíritu Santo e

22.3 50063800

(1966 –2010)

0.15 1.68

(1966 –2010)

689

East Coast Drainage Basin

Río Fajardo f

38.6 50071000

(1961–2010)

0.10 1.91

(1961–2010)

798

South Coast Drainage Basin

Río Grande de Patillas 47.4 50092000

(1966 –2010)

0.19 1.72

(1966 –2010)

927

Río Inabón 25.1 50112500

(1964 –2010)

0.04 0.52

(1964 –2010)

563

Río Guayanilla 49 50124200

(1981–2010)

0.07 0.72

(1986 –2010)

1,133

West Coast Drainage Basin

Río Guanajibo g

311 50138000

(1973–2010)

0.25 5.55

(1973–2010)

7,930

Río Grande de Añasco h

244 50144000

(1963–2010)

1.22 9.74

(1963–2010)

4,622

Río Culebrinas 184 50147800

(1967–2010)

0.65 8.47

(1967–2010)

1,960

a

Low-flow values from Santiago-Rivera (1992, 1996, 1998).

b

From U.S. Geological Survey (2010). 

c

Values from Ramos-Ginés (1999).

d

About 29,000 m3/d diverted for public supply upstream of

gaging station; area excludes 15.5 km2 diverted to south coast from

Lago Guineo and Lago de Matrullas. 

e

About 2,800 m3/d diverted for public supply upstream of gaging station.

f

About 28,000 m3/d diverted for public supply upstream of gaging station.

g

About 16,000 m3/d diverted for public supply upstream of gaging station.

h

Area excludes 103 km2 diverted to south coast by dams at Lago Yahuecas, 

Lago Guayo, Lago Prieto, and Lago Toro.
Generalized Characteristics of the Islands 17

65°30’ 66°00' 66°30’ 67°00'

18°30’

18°00'

Base from U.S. Geological Survey National Elevation Dataset

EXPLANATION

C A R I B B E A N S E A

A T L A N T I C O C E A N 

Figure 11. Principal perennial streams and surface-water gaging stations in Puerto Rico.

0 10 20 MILES0 10 20 KILOMETERS

50092000

Continuous gaging stationBasic streamflow statistics listed in table 2 

Río Culebrinas

Río Yagüez

Río Grande de

Añasco

Río

Grande

Río Guayabo

Río Guanajibo

Río Guajataca

Río Camuy

Río Grande de

Arecibo

Río Grande de

Manatí

Río Cibuco

Río de la Plata

Río de Bayamón

Río Piedras

Río Herrera

Río Espíritu Santo

Río Mameyes

Río Sabana

Río Fajardo

Río Santiago

Río Blanco

Río Humacao

Río Guayanés

Río Maunabo

Río Grande de Patillas

Río Nigua

Río Nigua

Río Cañas

Río Jacaguas

Río Inabón

Río Bucaná

Río Portugués

Río Matilde

Río Tallaboa

Río Guayanilla

Río Yauco

Río Loco

Río Descalabrado

Río Coamo

Río Guamaní

Río Grande

de Loíza

50147800

50144000 50028000 50031200 50035000

50124200

50138000

50112500

50055000

50092000

50061800

50063800

50071000

Figure 11. Principal perennial streams and surface-water gaging stations in Puerto Rico.
18 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona 65°30’ 66°00' 66°30’ 67°00' 18°30’ 18°00' Base from U.S. Geological Survey National Elevation Dataset EXPLANATION 10-digit hydrologic unit code and name C A R I B B E A N S E A A T L A N T I C O C E A N 

Figure 12. 10-digit hydrologic units for Puerto Rico.

0 10 20 MILES0 10 20 KILOMETERS

1

12

18

20

19

17

16

15

14

21

13 11

9

10

8

7

6

5

4

3

2

2101000201 Río Cibuco watershed2101000202 Río Grande de Manatí watershed2101000203 Caño Tiburones coastal watershed2101000204 Río Grande de Arecibo watershed2101000205 Quebrada Los Cedros to Río Camuy watersheds2101000301 Río Culebrinas watershed2101000302 Río Grande de Añasco watershed2101000303 Río Yagüez watershed2101000304 Río Guanajibo watershed2101000401 Quebrada Boquerón to Río Loco watersheds

2101000402 Río Yauco to Río Tallaboa watersheds

2101000403 Río Matilde to Río Descalabrado watersheds2101000404 Río Coamo to Río Seco watersheds2101000405 Río Guamaní to Río Jacaboa watersheds2101000501 Río Maunabo to Río Humacao watersheds2101000502 Río Antón Ruíz to Río Fajardo watersheds2101000503 Río Herrera to Las Cabezas de San Juan 

 coastal watersheds 2101000504 Río Grande de Loíza watershed2101000505 San Juan Bay Estuary watershed2101000506 Río de Bayamón to Río Hondo watersheds2101000507 Río de la Plata watershed

123456789

1011

12131415161718192021

Hydrologic unit boundary

Figure 12. Ten-digit hydrologic units for Puerto Rico.
Generalized Characteristics of the Islands 19

In Puerto Rico, the demand for water for a variety 

of purposes has resulted in the construction of diversion 

structures in about 2,600 km2 or nearly 60 percent of the 

total watershed area that is underlain by volcanic rocks. 

Use of these diversion structures has resulted in the complete 

capture of annual low flows in several small perennial 

streams and in the Río Grande de Loíza and the Río de 

la Plata, which are two of the largest watersheds on the 

island. The Río Grande de Loíza and the Río de la Plata 

watersheds (fig. 12) are the principal sources of public 

water supply for the San Juan metropolitan area. In 2005, 

the total streamflow diverted from these watersheds for 

public water supply was about 660,000 cubic meters per 

day (m3/d) or 7.6 cubic meters per second (m3/s) with about 

40 percent diverted to filtration plants that serve a metropolitan population of about 1.4 million (Molina-Rivera and 

Gómez-Gómez, 2008).

The general water balance for the island of Puerto Rico 

and the amount of water available from surface-water and 

groundwater sources is graphically illustrated in figure 13. 

In an average year, the island receives about 1,825 mm of 

rainfall, of which 1,189 mm or nearly 65 percent is lost to 

evapotranspiration. Of the total remaining available water, 

groundwater accounts for about 53 mm (or 14.6 m3/s) and 

streamflow accounts for about 583 mm (or 161 m3/s); about 

76 mm (or 21 m3/s) of streamflow is available as baseflow to 

lowland areas. A common occurrence in streams on the island 

of Puerto Rico is the loss of an indeterminate amount of baseflow to coastal wetlands or aquifers during low-flow periods 

when sandbars seal river outlets preventing direct outflow to 

the sea. These low-flow periods include February and March 

for streams draining watersheds underlain by volcanic rocks, 

and July and August for streams receiving drainage from the 

North Coast Limestone belt.

Figure 13. Generalized water balance for the island of Puerto Rico.

Groundwater

withdrawals in

South Coastal

Alluvial Plain

aquifer system

7 mm 

Groundwater 

withdrawals in

interior province

1 mm 

Groundwater 

withdrawals in

North Coast Limestone

aquifer system

13 mm 

Groundwater discharges to

wetlands and seabed from

the North Coast Limestone

aquifer system

27 mm 

Groundwater 

discharges 

to wetlands

and seabed

along the

South Coast

3 mm 

Groundwater flow in the

North Coast Limestone

lower aquifer system

2 mm 

Evapotranspiration

1,189 mm Storage capacity

in reservoir

25 mm 

Precipitation

1,825 mm 

Surface-water

runoff

583 mm 

Surface water 

low flow

76 mm 

Saline

groundwater NOT TO SCALE

Figure 13. Generalized water balance for the island of Puerto Rico.
20 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Contents of the Hydrogeologic Map

The hydrogeologic map shows the location and spatial 

extent of the groundwater provinces on the main island of 

Puerto Rico and the outlying islands of Vieques, Culebra, and 

Mona. The most intensively developed and extensive of these 

provinces are the North Coast and the South Coast on the main 

island of Puerto Rico. 

Description of Aquifer Systems

Puerto Rico is subdivided into six groundwater 

provinces on the main island and two additional provinces 

on the outlying islands of Vieques, Culebra, and Mona. 

These provinces have been primarily segregated on the 

basis of similar geologic units and physiographic features, 

following the classification of McGuinnes (1948). These 

provinces were originally published by Molina-Rivera 

and Gómez-Gómez (2008). As illustrated in figure 14, the 

eight groundwater provinces consist of the (1) North Coast 

Province, (2) South Coast Province, (3) West Coast Province, 

(4) East Coast Province, (5) Lajas Valley, (6) Interior Province, 

(7) Vieques and Culebra islands, and (8) Mona island.

North Coast Province

The North Coast Province covers about 2,100 km2 and 

is underlain by the North Coast Limestone aquifer system, 

which includes the most productive and extensive aquifers in 

Puerto Rico (fig. 14). Aquifers in the North Coast Province are 

formed by carbonates, predominantly limestone, and terrigenous clastic beds of Tertiary age that extend from the west 

coast to the San Juan metropolitan area. In the area extending 

from the Río Grande de Arecibo to the Río Espíritu Santo, 

which is east of San Juan, fine-grained coastal plain deposits 

overlie the limestone and terrigenous clastic beds and serve as 

a semiconfining unit.

Limestone and terrigenous clastic units in the North 

Coast Province show no evidence of faulting or deformation 

in the outcrop areas. The units dip northerly averaging about 

5 degrees in outcrop areas and strike about 47 minutes east 

(Giusti and Bennet, 1976). 

In the North Coast Province, rocks of middle Tertiary age, 

which constitute the main aquifers, have been subdivided in 

ascending order, from oldest to youngest, into the following 

stratigraphic units: San Sebastián Formation, Mucarabones 

Sand, Lares Limestone, Cibao Formation, Aguada Limestone 

(also known as Los Puertos), Aymamón Limestone, and the 

Camuy Formation (also known as the Quebradilla Limestone) 

(figs. 15, 16). The San Sebastián Formation is not considered 

to be a water-bearing unit. The formation overlies volcanic 

bedrock and primarily consists of clay with secondary amounts 

of sand and gravel and locally, sandy limestone (Monroe, 1980). 

Toward the eastern part of the North Coast Province, the San 

Sebastián Formation is absent, mostly replaced by the partially 

time-equivalent (partially of the same age) Mucarabones Sand. 

Fresh groundwater in the North Coast Limestone aquifer 

system is found in two principal aquifers identified as the 

upper and lower aquifers. The upper aquifer is located within 

the Aymamón and Aguada Limestone units, and within alluvial 

stream valleys and coastal plain deposits. The lower aquifer 

is located within limestone members (bioherms) of the Cibao 

Formation, the Lares Limestone, and the Mucarabones Sand. 

The Montebello Limestone Member of the Cibao Formation 

is the most productive unit of the lower aquifer. Areally, the 

lower aquifer is a regionally important source of groundwater 

in the area between the Río Grande de Arecibo and the 

Río Grande de Manatí (fig. 17).

The hydrogeologic properties of the carbonate rocks 

differ substantially, owing to diverse depositional environments that result from processes including uplift and 

northward tilting of the island’s platform, eustatic changes in 

sea level, the evolution of north-flowing streams during the 

deposition of limestone units, and the development of drainage 

features resulting from solutional and erosional processes. 

On the basis of the substantially different hydrogeologic 

properties that characterize the carbonate rocks underlying 

the North Coast Province, the region has been divided into 

three subareas: (1) West Coast to Río Grande de Arecibo 

area, (2) Río Grande de Arecibo to Río de la Plata area, and 

(3) Río de la Plata to Río Espíritu Santo area (Gómez-Gómez 

and Heisel, 1980; fig. 14). The following sections describe the 

hydrogeologic features of each subarea.

West Coast to Río Grande de Arecibo Area

The West Coast to Río Grande de Arecibo area is characterized by cliffs that rise 45 m above mean sea level along much 

of the coast. As a result, there is no coastal plain in this area. 

The water-table altitude ranges from mean sea level to as much 

as 275 m above mean sea level within the Lares Limestone 

at a distance of about 6 km from the shoreline. West of the 

Río Guajataca, the water-table altitude reaches a maximum of 

150 m within the Cibao Formation; the level of the water table 

may be controlled by the water level in the Lago de Guajataca 

reservoir, which has a spillway altitude of 197 m. Test drilling 

conducted during 1986 near Hatillo (site number NC-6, fig. 15) 

and during 1987 near Isabela (site number NC-11, fig. 15) 

penetrated permeable units of the Cibao Formation 

(and possibly the Lares Limestone) that contained fresh 

groundwater under confined conditions at depth near the coast.

Hydraulic characteristics of the aquifer system in this 

area are poorly known. Few existing wells tap the aquifer 

within the Aymamón and Aguada Limestones and have yields 

that range from 3 to 6 liters per second (L/s). Specific capacity 

generally is less than 0.2 liter per second per meter (L/s/m) of 

drawdown. Data obtained during exploratory drilling during 

1986 and 1987 near Hatillo and Isabela (sites NC-6 and 

NC-11, respectively, fig. 15) indicated that the aquifer had a 

maximum head of 45 m above mean sea level at site NC-6 

(about 20 m below the land surface datum) and 18 m above 

mean sea level at site NC-11 (about 70 m below the land 

surface datum).
Contents of the Hydrogeologic Map 21

P

Q

I

H

F

G

5

N

K

M

6

L

J

3

A B

C

1

7

E D

2

4 O

Vieques

Culebra

65°30' 66°00' 66°30' 67°00'

18°30'

18°00'

C A R I B B E A N S E A

A T L A N T I C O C E A N 

EXPLANATION

West Coast to Río Grande de Arecibo areaRío Grande de Arecibo to Río de la Plata areaRío de la Plata to Río Espíritu Santo area

ABC

South Coastal Alluvial Plain aquifer system

Tallaboa-Guayanilla-Yauco-Guánica ValleysRío Guanajibo ValleyRío Yaguez ValleyRío Grande de Añasco Valley

D

E

F

GH

North Coast ProvinceSouth Coast ProvinceWest Coast ProvinceEast Coast ProvinceLajas ValleyInterior ProvinceVieques and Culebra islandsMona island

12345678

Río Culebrinas ValleyFajardo areaNaguabo-Humacao area

Yabucoa ValleyMaunabo ValleyCaguas-Juncos ValleyCayey ValleyEsperanzaResolución

I

J

K

L

M

N

O

P

Q

Gravel, sand, silt, and clayCarbonates, predominantly limestoneIgneous rock: lavas, volcaniclastic,  and intrusives

North Coast Limestone aquifer system

GROUNDWATER PROVINCES AQUIFER NAMES LITHOLOGY

Figure 14. Groundwater provinces and aquifers of Puerto Rico and outlying islands (adapted from Molina-Rivera and Gómez-Gómez, 2008).

0 10 20 MILES0 10 20 KILOMETERS

67°55'

18°10'

18°05'

Mona

8

Base from U.S. Geological Survey Digital data

Figure 14. Groundwater provinces and aquifers of Puerto Rico and outlying islands (adapted from Molina-Rivera and Gómez-Gómez, 2008).
22 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona EXPLANATION Generalized surficial geology Coastal Plain Deposits Camuy Formation Aymamón Limestone Aguada Limestone Undifferentiated Cibao Formation Montebello Limestone Member of the Cibao Formation Lares Limestone Mucarabones Sand San Sebastián Formation Undifferentiated igneous rocks Base modified from Gómez-Gómez, 1987

Deep test well site and number

Figure 15. Generalized surficial geology of the North Coast Limestone aquifer system and the location of deep exploratory test wells.

0 10 20 MILES0 10 20 KILOMETERS

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

NC-8

NC-11

NC-7 NC-6 NC-10

NC-5

IAS-1

NC-4

NC-14

NC-9

NC-2 NC-13

NC-1 NC-15

NC-3 NC-12

65°45' 66°00' 66°15' 66°30' 66°45' 67°00' 67°15'

18°30'18°15'

NC-6

!(

A T L A N T I C O C E A N 

Figure 15. Generalized surficial geology of the North Coast Limestone aquifer system and the location of deep exploratory test wells.
Contents of the Hydrogeologic Map 23

SYSTEM SERIES NORTH COAST

Geologic unit

QUATERNARY

HOLOCENE

PLEISTOCENE

Alluvial, terrace, beach, and swamp deposits

TERTIARY

PLIOCENE

Camuy Formation1

MIOCENE

Upper

Middle

Aymamón Limestone

Aguada (Los Puertos) Limestone

Lower

Río Guatemala Group

Upper unnamed member

Montebello 

Limestone 

Member

Unnamed 

mudstone

unit2

Quebrada Arenas

and Río Indio 

Limestone 

Member3

OLIGOCENE

Lares Limestone

San Sebastián Formation4

EOCENE

Volcanic, volcaniclastic, and intrusive igneous rocks

PALEOCENE

CRETACEOUS

Upper

Lower

JURASSIC

Cibao

Formation

Mucarabones

Sand 

1

Called the Quebradillas Limestone in some reports. 

2

Subsurface only. 

3

Both members may function as confining units in downdip areas. 

4

Contains local permeable beds in undip areas that may be hydraulically connected to the lower aquifer.

Figure 16. Stratigraphic chart used for the same rocks in the North Coast Province.

Figure 16. Stratigraphic chart showing varied nomenclature used for the same rocks in the North Coast 

Province (modified from Renken and others, 2002).
24 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

CAÑO

TIBURONES

NC-5

Coast

FLORIDA

San Sebastián Formation and volcanics

Aymamón Limestone

Lares Limestone

Montebello Limestone Member of the Cibao Formation 

Aguada Limestone

ATLANTIC

OCEAN

500

METERS

400

300

200

100

Sea level

100

200

300

400

500

600

700

800

Upper member of the Cibao Formation

Fresh

Saline Saltwater

VERTICAL EXAGGERATION APPROXIMATELY ×25

A A'

Aymamón

Limestone

0 1 2 3 4 5 KILOMETERS

0 1 2 3 4 5 MILES

Designates part of well open to aquifer

Potentiometric surface of lower aquifer 

in outcrop areas

Potentiometric surface of upper aquifer

Upper aquifer

Lower aquifer

EXPLANATION

Figure 17. Generalized hydrogeologic cross section through the North Coast 

Limestone aquifer system between the Río Grande de Arecibo and the Río Grande 

de Manatí near Barceloneta (line of section along longitude 66 37' 39" shown in 

figure 10).

Figure 17. Generalized hydrogeologic cross section through the North Coast 

Limestone aquifer system between the Río Grande de Arecibo and the Río Grande de 

Manatí near Barceloneta (line of section along longitude 66°37'39" shown in figure 10).
Contents of the Hydrogeologic Map 25

Recharge to the aquifer occurs primarily from rainfall 

infiltrating throughout limestone outcrop areas and possibly 

as seepage from the Lago de Guajataca reservoir, which was 

constructed in 1928. Groundwater discharges to the coast 

and along the main rivers. Springflow along the south-facing 

escarpment, near the shoreline and along the main rivers, 

also may constitute substantial aquifer discharge features 

in this part of the North Coast Limestone aquifer system. 

Groundwater withdrawals in this area are estimated to be less 

than 20,000 m3/d.

Río Grande de Arecibo to Río de la Plata Area

Groundwater in the 800-km2 Río Grande de Arecibo 

to Río de la Plata area is unconfined in the Aymamón and 

Aguada Limestones, in alluvial valleys, and in areas where the 

Montebello Limestone Member of the Cibao Formation and 

the Lares Limestone crop out (fig. 17). In 1968, groundwater 

was found to be confined in wells drilled into the down-dip 

sections of the Montebello and Lares Limestones in the 

vicinity of Barceloneta. In the vicinity of Barceloneta, heads 

initially were as much as 150 m above mean sea level (or 

generally 60 m above the land surface datum). By 1990, 

14 artesian water-supply wells had been drilled in the area 

between Barceloneta and Manatí. 

The lateral extension of the lower artesian aquifer was 

defined during test drilling conducted between 1986 and 1988. 

Hydraulically, the lower aquifer is the down-dip extension of 

the Montebello Limestone Member of the Cibao Formation 

and the regionally extensive Lares Limestone. Transmissivity 

of the lower aquifer near the coast is greatest in the 

Montebello Limestone Member; in the vicinity of Barceloneta, 

the transmissivity is estimated to range from 100 to 200 meters 

squared per day (m2/d) and decreases to less than 100 m2/d 

near the Río Grande de Arecibo. East of Río Grande de 

Manatí, the Montebello Limestone Member is replaced by a 

time-equivalent mudstone unit. Due to low transmissivities, the 

potential development of groundwater in the underlying Lares 

Limestone is limited. Although the Lares Limestone is laterally 

extensive, comprising the entire lower aquifer, transmissivity 

within outcrop areas is estimated to be less than 25 m2/d. In 

areas near the coast where deep wells tap confined parts of 

the lower aquifer, transmissitivities are less than 45 m2/d.

During 1986 and 1987, test wells tapping the lower 

aquifer were drilled in areas near the coast between the west 

end of Laguna Tortuguero (test well IAS-1, fig. 15) and the 

Río de la Plata (test well NC-13, fig. 15). Head measurements 

made in these wells indicated a general lowering of the 

potentiometric surface to the east (fig. 18). The configuration 

of the potentiometric surface indicates that along the downdip section east of the Río Grande de Manatí, the regional 

direction of groundwater flow in the lower aquifer is east with 

regional discharge occurring beneath the coastal plain east of 

the Río de la Plata. The eastern-most discharge area may be in 

the vicinity of the wetlands at Sabana Seca, which is located 

about 5 km east of the Río de la Plata.

100

80

60

40

20

0

Distance from west end of Laguna Tortuguero, in kilometers

Head, in meters above mean sea level

IAS-1

NC-14

NC-9 NC-2

NC-8

NC-13

Does not penetrate

the Lares Limestone

Figure 18. Initial heads in test wells penetrating, in the lower aquifer, the Lares Limestone.

Variations of head with the logarithm of distance indicate possible aquifer discharge

eastwards to wetlands east of the town of Toa Baja (for actual distance subtract 10 to the

indicated distance on graph, test well locations shown in figure 15)

10 20 30 40 50 60 70 80 90 100

Figure 18. Initial heads in test wells penetrating the Lares Limestone in the North Coast 

Limestone lower aquifer. Variations of head with the logarithm of distance indicate possible 

aquifer discharge eastward to wetlands east of the town of Toa Baja (for actual distance 

subtract 10 from the indicated distance on the graph; test well locations shown in figure 15).
26 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

The unconfined or upper aquifer, which is contained 

within the Aymamón and Aguada Limestones in the area 

between the Río Grande de Arecibo to Río de la Plata, is 

the most productive aquifer in the North Coast Province. 

The aquifer, however, exists mostly as a lens of freshwater 

overlying saltwater with the thickness of the freshwater lens 

controlled primarily by natural aquifer discharge features 

such as streams, wetlands, or springs, or locally, by artificial 

discharge features such as drainage works and water-supply 

wells. In general, the freshwater lens extends inland to about 

the 3-m potentiometric surface contour, which is located 

approximately along latitude 18°26' or generally 5 km from 

the coastline. Inland from this latitude in the area between the 

Río Grande de Arecibo and the Río Cibuco, the upper part of 

the Cibao Formation forms the base of the upper aquifer and 

hydraulically separates the unconfined upper aquifer from the 

underlying confined lower aquifer.

East of the Río Cibuco and inland from about latitude 

18°26', the upper part of the Cibao Formation does not seem 

to fully confine the groundwater contained in the Cibao 

Formation and Lares Limestone. Transmissivity values for the 

freshwater part of the unconfined aquifer overlying saltwater 

near the coast typically range from 2,000 to 15,000 m2

/d 

and decrease rapidly inland. In the part of the upper aquifer 

contained within the Aguada Limestone and bounded beneath 

by the Cibao Formation, the transmissivity commonly is less 

than 500 m2/d. Farther inland where the groundwater in the 

Cibao Formation and Lares Limestone is unconfined, the 

transmissivity is less than 20 m2/d; locally, the transmissivity 

could be zero in the chalk units of the Lares Limestone.

As in the western part of the North Coast Province, 

groundwater flow in this area has been modified substantially 

from predevelopment conditions. The most notable change 

has been the dewatering of coastal wetlands, particularly 

the Caño Tiburones in the area between the Río Grande de 

Arecibo and the Río Grande de Manatí, and the construction 

of a drainage channel that connects Laguna Tortuguero with 

the Atlantic Ocean (plate 1). At Caño Tiburones, water levels 

were lowered from about 1 to 2 m above mean sea level 

in 1930 to as much as 2 m below mean sea level in 1980 

as a result of constructing extensive drainage canals, tidal 

gates, and a dewatering pumping station. In 1998, however, 

agricultural use was completely phased out and an area of 

about 2,800 ha was declared a natural preserve by the Puerto 

Rico Department of Natural and Environmental Resources 

(http://www.drna.gobierno.pr). At Laguna Tortuguero, 

the ocean outlet lowered the water level in this relatively 

freshwater lagoon (the dissolved solids concentration was 

1,000 milligrams per liter (mg/L) in 1988) from about 1.5 m 

above mean sea level in 1940 (Bennet and Giusti, 1972) 

to about 0.75 m above mean sea level in 1975 (QuiñonesMarquez and Fusté, 1978). East of Laguna Tortuguero in 

the area between the Río Cibuco and the Río de la Plata, the 

potentiometric surface declined as much as 3 m within the 

coastal plain between 1946 and 1983 (Gómez-Gómez and 

Torres-Sierra, 1988).

Prior to 1930, the development of groundwater supplies 

was relatively minor. Total groundwater withdrawal within 

the area increased from about 38,000 m3

/d in 1940 to about 

280,000 m3/d in 1985. After 1985, withdrawals for publicsupply use began to decline and were substantially reduced 

after completion of the North Coast Superaqueduct in 2000, 

which made water available to the San Juan metropolitan 

area from the Río Grande de Arecibo Basin. In 2005, groundwater withdrawals were estimated at about 150,000 m3

/d 

(Molina-Rivera and Gómez-Gómez, 2008). Of the total 1985 

withdrawals, an estimated 10,000 m3/d were withdrawn for 

industrial uses from the lower aquifer by artesian wells located 

in the general vicinity of Barceloneta and Manatí. In the 

vicinity of Barceloneta, the head in the lower aquifer declined 

from 150 m above mean sea level in 1968 to 96 m above mean 

sea level in 1989 (fig. 19). Prior to 1985, heads measured 

in flowing artesian wells tapping the lower aquifer declined 

to near land surface as a result of groundwater withdrawals. 

By 1985, however, a reduction in withdrawals resulted in 

the stabilization of heads in the lower aquifer to about 1990 

(fig. 19). Between 1990 and 2002, heads decreased and were 

near 65 m above mean sea level in 2002.

Río de la Plata to Río Espíritu Santo Area

In the Río de la Plata to Río Espíritu Santo area, fresh 

groundwater is unconfined within the undifferentiated coastal 

plain deposits and the alluvial deposits of the major streams and 

within the Aguada Limestone, the Cibao Formation, and the 

Mucarabones Sand. In the area between the Río de Bayamón 

and the Río Piedras, groundwater is confined in the basal 

part of the Cibao Formation or possibly the basal part of the 

Aguada Limestone and in the Mucarabones Sand (Anderson, 

1976). In the area between the Río de Bayamón and the Río 

Piedras, fresh groundwater in the Aymamón and Aguada 

Limestones is limited primarily to the inland-most parts of the 

formations as a result of saltwater encroachment (fig. 20).

Alluvium, terrace deposits, blanket sand, beach, and 

dune deposits overlie the Aymamón and Aguada Limestones 

throughout most of the area. The thickness of these deposits 

ranges from a maximum of 100 m within major stream valleys to 

about 30 m or less elsewhere. Except for an increase in sand and 

clay in the eastern part of the formation, the Aguada Limestone 

is similar in lithology to other areas west of the Río de la Plata.

In the Río de la Plata to Río Bayamón area, the Cibao 

Formation consists of limestone, sand, and clay. West of 

the Río de Bayamón, the Cibao Formation intertongues and 

grades laterally eastward into the Mucarabones Sand. Similarly, 

the Aguada Limestone is intercalated with chalky beds of the 

Cibao Formation and becomes indistinguishable from the 

Cibao Formation about 0.5 km east of the Río de la Plata. The 

Mucarabones Sand consists of fine to medium sand. Near the 

base of the Mucarabones unit, the sand coarsens and the formation contains gravel and lenses of greenish-gray sandy clay. The 

Mucarabones Sand reaches a maximum thickness of 100 m in 

the area between the Río de la Plata and the Río de Bayamón.
Contents of the Hydrogeologic Map 27

160

140

120

100

80

60

40

20

11/20/1960 5/13/1966 11/3/1971 4/25/1977 10/16/1982 4/7/1988 9/28/1993 3/21/1999 9/10/2004 3/3/2010

Head, in meters above mean sea level

Month/day/year

RCA

Union Carbide 1

Bristol

MSDQ-4

PRASA CD 1

NC-5

Abbott

Sterling 2

Figure 19. Head change at selected industrial and public-supply wells in the North Coast

Limestone lower aquifer in the area of Barceloneta.

EXPLANATION

Figure 19. Head change at selected industrial and public-supply wells in the North Coast 

Limestone lower aquifer in the area of Barceloneta.

Quaternary

deposits

Bahía de

San Juan

Viejo

San Juan Atlantic

Ocean

Potentiometric

surface

Highway 2

Aguada Limestone

0

0

1

1

2 KILOMETERS

2 MILES

VERTICAL EXAGGERATION ×6

Figure 20. Generalized hydrogeologic cross section through the North Coast Limestone aquifer system

in the San Juan area (line of section shown in figure 10).

B B'

?

?

?

100

100

200

300

400

500

600

Sea level

METERS

Brackishsaline water

Aymamón Limestone

San Sebastián Formation

Cibao Formation

Mucarabones Sand

Undifferentiated lower Tertiary and upper Cretaceous formations

Freshwater

Unconsolidated

deposits

Figure 20. Generalized hydrogeologic cross section through the North Coast Limestone aquifer 

system in the San Juan area (line of section shown in figure 10).
28 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

The Aguada Limestone is the principal source of freshwater between the Río de la Plata and Sabana Seca (plate 1). 

Transmissivities in this area range from 1,000 to 2,000 m2/d. 

Eastward from Sabana Seca, both the Cibao Formation and 

the Mucarabones Sand are hydraulically interconnected near 

their outcrop areas. Aquifer tests conducted in wells tapping 

both the Cibao and the Mucarabones units indicate the 

estimated transmissivity to be less than 1,000 m2/d. Few wells 

exclusively tap the Mucarabones Sand; therefore, the potential 

of this unit as a water-supply source in down-dip areas is 

unknown. The surficial coastal plain deposits essentially are 

the only source of freshwater in areas east of the Río Grande 

de Loíza. Groundwater within the coastal plain deposits 

exists as a freshwater lens or lenses overlying saltwater. The 

thickness of the freshwater lenses is not more than 30 m, 

which limits groundwater development for domestic uses and 

supplies for watering livestock (Torres-González, 1984).

The groundwater resources of the Río de la Plata to the 

Río Espíritu Santo area were among the first to be developed 

or affected by dewatering works along the north coast. The use 

of groundwater in the area is minimal because of widespread 

saltwater intrusion. Most well fields have been abandoned or 

destroyed except in the western part of the area between the 

Río de la Plata and Sabana Seca, where saltwater intrusion has 

been limited by reducing groundwater withdrawals. Overall 

groundwater withdrawals in the Río de la Plata to the Río 

Espíritu Santo area are estimated to be less than 5,000 m3

/d.

South Coast Province

The South Coast Province covers about 800 km2 along 

the southern coast of Puerto Rico. Aquifers in this region are 

composed of coalescing alluvial fans and terrace deposits 

that form a continuous coastal plain in the area from Ponce 

to Patillas, and limestones of Tertiary age that underlie 

alluvial stream valleys in the area extending from the Río 

Tallaboa to the Río Loco (fig. 14). West of the Río Loco, the 

occurrence of groundwater is limited to alluvial deposits of 

ephemeral streams.

On the basis of physiographic differences, the South Coast 

Province has been subdivided into two subareas: (1) the Patillas 

to Ponce area and (2) the Tallaboa-Guayanilla-Yauco-Guánica 

Valleys (Gómez-Gómez and Heisel, 1980). The following 

sections describe the hydrogeologic features of each subarea.

Patillas to Ponce Area

The Patillas to Ponce area of the South Coast Province is 

about 65 km long and averages about 5 km wide. The Patillas 

to Ponce area is underlain by the South Coastal Alluvial Plain 

aquifer system, which is the second most extensive aquifer in 

Puerto Rico (fig. 21). The coastal plain deposits that compose 

the aquifer system consist of a series of alluvial fans formed 

by sediment-laden, fast-flowing intermittent streams that 

originate at altitudes above 300 m and within 25 km of the 

Caribbean Sea. Below an altitude of about 45 to 30 m, coastal 

plain sediments are Holocene and Pleistocene (?) in age. 

Delta-fan deposits in this area contain a high proportion of 

sand and gravel at the apex of the major fans, becoming finer 

grained toward the coast and in interfluvial areas.

Coastal plain sediments are underlain by volcanic rocks 

in the area east of Río Coamo and by sedimentary rocks of 

middle Tertiary age throughout most of the coastal plain west 

of Río Coamo (plate 1). The volcanic rocks consist of massive 

to thick-bedded andesite tuff and welded tuff, porphyritic 

basalt, volcanic breccia, sandstone, and siltstone. Rocks of 

middle Tertiary age consist of the Juana Díaz Formation, 

which is overlain by the Ponce Limestone. The Juana Díaz 

Formation has been informally subdivided into a mudstone, 

a basal conglomerate, chalk beds, and upper clastic beds. 

The Ponce Limestone is largely a recrystallized limestone 

locally rich in reefal material that is relatively high in calcium 

carbonate. Where saturated, the Juana Díaz Formation 

contains saline groundwater (dissolved solids concentration 

greater than 1,000 mg/L). Also, because of its highly clayey 

nature and consequently low permeability, the Juana Díaz 

Formation is not considered to be an aquifer. In the vicinity 

of the Ponce urban area, the alluvium is underlain by the 

Ponce Limestone, which seems to have karstic features. These 

features are inferred by the specific capacity of wells that 

typically are less than 6 L/s/m, tapping alluvium exclusively, 

and as high as 32 L/s/m, tapping both alluvium and limestone.

Groundwater is unconfined within the alluvium, except 

along the coast where surficial deposits consisting of silt, clay, 

and swamp deposits serve as a semiconfining unit that hydraulically separates the surficial deposits from the underlying 

coarser more permeable alluvium. Throughout the coastal plain, 

the thickness of the alluvium differs substantially as a result 

of faulting and weathering of the bedrock units. In the area 

between Río Grande de Patillas and Río Jueyes, the depth to 

bedrock along the coast ranges from 128 m at Río Nigua fan to 

36 m near the mouth of Río Seco (fig. 21). In the area between 

Río Jueyes and the western limit of the coastal plain at Ponce, 

the thickness of the alluvium is about 915 m near the mouth of 

Río Coamo (test well site CPR-1, fig. 21) and about 120 m near 

the mouth of Río Cañas (test well site CPR-2, fig. 21). In the 

area west of Río Jacaguas, groundwater is present in both the 

alluvium and associated clastic deposits and in the underlying 

limestone (plate 1). Test drilling conducted near Ponce in 1987 

confirmed the occurrence of groundwater in the underlying 

limestone at a depth of 180 m below mean sea level (test well 

SC-7, figs. 21, 22; however, the dissolved solids concentration 

of groundwater increased with depth to 1,500 mg/L.

Transmissivity of the South Coastal Alluvial Plain 

aquifer system varies substantially between the alluvial fans 

and within each fan. The highest transmissivities were found 

within Río Nigua de Salinas (Río Salinas) and Río Coamo 

fans. Transmissivity is estimated to be as high as 6,500 m2

/d 

within the apex of each alluvial fan. East of Río Nigua fan, 

aquifer transmissivity is substantially lower, with values 

commonly less than 500 m2/d, except within Río Nigua fan at 

Arroyo where the transmissivity can be as much as 2,000 m2

/d. 
Contents of the Hydrogeologic Map 29 Base modified from Gómez-Gómez, 1991

Lago

Toa Vaca

Lago

Guayabal

Lago de

Patillas

Canal de

Juana Díaz

Canal de 

Patillas Canal de

Guamaní

Lago

Carite

Río

Jacaguas

Río

Cañas

Río

Coamo

Río

Jueyes Río

Guamaní

Río Descalabrado

Río

Nigua

Río Seco

Río

Tallaboa

Río Grande

de Patillas Río

Nigua

SC-5

SC-7

Po-130

CPR-1

CPR-2

66°00' 66°15' 66°30' 66°45'

18°15'

18°00'

EXPLANATION

Extent of alluvial depositsInsular hydrologic divideExisting irrigation canalU.S. Geological Survey test well and numberOil exploratory well and numberFlow direction

C A R I B B E A N S E A

0 5 10 KILOMETERS

Figure 21. Areal extent of the South Coastal Alluvial Plain aquifer system and major irrigation infrastructure.

Location of map area in Puerto Rico

0 5 10 MILES

SC-7

CPR-1

Figure 21. Areal extent of the South Coastal Alluvial Plain aquifer system and major irrigation infrastructure.
30 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

West of Río Descalabrado and east of Río Jacaguas, aquifer transmissivity is about 500 m2

/d . In the area west of Río Jacaguas, large

spatial variations in transmissivity exist; values of 500 m2/d are 

common, with values increasing to as much as 6,500 m2/d in areas 

underlain by karstified limestone within the municipality of Ponce.

In the Patillas to Ponce area, prior to construction of the 

first irrigation canals and diversions in the late 1800s, the 

source of recharge to the aquifer was from streamflow seepage 

and from rainfall infiltration through the alluvial and terrace 

deposits. Discharge from the aquifer occurred as flow to near 

shore and offshore springs, as seepage to the seabed and lower 

portions of stream channels, and as evapotranspiration from 

the shallow water table near the coast. Prior to the beginning 

of the 1900s, an extensive network of irrigation canals and 

reservoirs already existed in the area between Río Jacaguas 

and Ponce. Additionally, small-scale irrigation works existed 

in Río Coamo and Río Nigua fans and in the vicinity of 

Guayama and were limited to diversion of baseflows from 

streams near the foothills. The first large-scale surface-water 

irrigation system was completed in 1914 and consisted of the 

Canal de Patillas and Lago de Patillas reservoir; Lago Carite 

reservoir north of the insular hydrologic divide in the Río de 

la Plata watershed and a diversion tunnel to Río Guamaní; 

the Canal de Juana Díaz, Lago Guayabal, and Lago Coamo 

reservoirs. Originally, the combined flows through these 

canals averaged about 285,000 m3

/d. With the completion 

of Lago Guineo and Lago Matrullas reservoirs north of 

the insular hydrologic divide in the Río Grande de Manatí 

watershed and the completion of the diversion tunnel to Río 

Jacaguas in 1935, however, the system of reservoirs, tunnels, 

pump stations, and canals conveyed as much as 300,000 m3/d.

Large-scale groundwater development of the South 

Coastal Alluvial Plain aquifer system commenced in 1910 

with the construction of steam-operated pumps that were 

powered by kerosene. By 1925, about 50 of these pumping 

installations existed, most with capacities above 60 L/s and 

groundwater withdrawals totaling about 80,000 m3/d. The 

greatest expansion in construction of irrigation water-supply 

wells occurred during the 1930s when electricity was extended 

into the area, bagasse-fueled steam generators were installed 

at sugar mills, and deep turbine pumps were introduced. In 

addition, water works to supply irrigation needs and largescale dewatering operations were implemented during the 

late 1930s to control the spread of malaria and to reclaim 

additional land for sugarcane cultivation.

A review of well construction logs indicates that between 

1930 and 1987 the potentiometric surface along the coastal 

artesian zone declined by as much as 1.5 m in the Ponce area 

and by as much as 3.0 m at Santa Isabel. In the Río Nigua fan 

and toward the eastern part of the coastal plain, groundwater 

levels had not changed substantially between 1920 and 

1986. In general, aquifer recharge has been augmented by 

the irrigation-canal network with discharge occurring mainly 

through groundwater withdrawals and by drainage ditches. In 

1980, irrigation deliveries were approximately 240,000 m3

/d 

by means of the government-operated irrigation-canal network 

located east of Río Jacaguas. West of Río Jacaguas, a privately 

operated irrigation-canal network may have conveyed an additional 40,000 m3

/d. Net groundwater withdrawals (consumptive 

use) during 1980 averaged about 190,000 m3/d. Of this amount, 

about 40 percent was used for public water supply with the 

remainder designated for irrigation. By 2005, net groundwater 

withdrawals were estimated at about 170,000 m3/d, of which 

about 60 percent was for public supply, 35 percent for irrigation, and 2 percent for industrial use (industrial and thermoelectric) (Molina-Rivera and Gómez-Gómez, 2008).

Tallaboa-Guayanilla-Yauco-Guánica Valleys

The main aquifers in the Tallaboa-Guayanilla-YaucoGuánica valleys are formed by the alluvium deposited within 

the stream valleys. The alluvium consists of coarse sand and 

gravel that grade seaward to fine sand, silt, clay, and swamp 

deposits. Bedrock underlying these valleys consists of the Juana 

Díaz Formation in inland areas and the Ponce Limestone near 

the coast under conditions similar to those found in the Río 

Tallaboa valley (fig. 23). Although groundwater is present in 

outcrop areas, the bedrock generally is not considered to be an 

aquifer because of the low yield to wells and high concentration 

of dissolved solids from wells tapping the limestone bedrock 

exclusively; within outcrop areas, the dissolved solids concentration is about 2,000 mg/L. The valley alluvium is underlain 

by the Ponce Limestone, which has developed secondary 

porosity and is tapped by wells also open to the alluvium.

Groundwater in the Tallaboa-Guayanilla-Yauco-Guánica 

valleys is unconfined and occurs within the alluvial deposits 

and the Ponce Limestone. Near the coast, groundwater is 

present as a freshwater lens overlying saltwater. The saturated 

thickness of the freshwater lens throughout the lower parts of 

the valleys is unknown. Recharge to these aquifers is derived 

primarily from streamflow as seepage through the streambed 

or by spatial infiltration of streamflow diversions for irrigation 

where such practices occur. In all stream valleys except the 

Río Guayanilla valley, streamflow is derived in large part 

from reservoirs located north of the insular hydrologic divide 

(plate 1). Discharge occurs through groundwater withdrawals 

at wells, through seepage to streams in the lower parts of the 

valleys, by evapotranspiration within the near-shore part of 

the aquifer where the water table is near land surface, and to a 

lesser extent as seepage to the seabed. The hydrologic system 

in these valleys has been modified such that the relative importance of any aquifer recharge or discharge process could vary 

substantially from year to year. For example, gross groundwater withdrawals were estimated at about 150,000 m3

/d in the 

early 1970s; however, by 1985, withdrawals had diminished 

to about 75,000 m3/d as a result of the complete shutdown of 

the petrochemical complex in the Tallaboa and Guayanilla 

valleys and the closure of the island’s largest sugarcane mill at 

Guánica. By 2005, groundwater withdrawals were estimated 

at 55,000 m3/d, of which 57 percent was for public supply, 

38 percent for irrigation, 1 percent for domestic use, and the 

remaining 4 percent mostly for thermoelectric power production (Molina-Rivera and Gómez-Gómez, 2008).
Contents of the Hydrogeologic Map 31

Figure 22. Generalized hydrogeologic cross section through the South Coastal Alluvial Plain aquifer system near Ponce (line of section

shown in figure 10, location of Po-130, SC-7, and SC-5 shown in figure 21).

Volcanic

rocks

200

METERS

100

Sea

level

100

200

300

400

0

0

1 2 3 KILOMETERS

SC-5

SC-7

Juana Díaz Formation

Undifferentiated alluvial and 

terrigenous clastic deposits

Mostly claystone with marly

limestone and chalk

(moderate to

low permeability)

Claystone/Siltstone 

(relatively impermeable, not an aquifer)

C C'

Po-130

? ? ?

?

?

?

?

?

?

1 2 MILES

Limestone, clayey and rubbly

VERTICAL EXAGGERATION APPROXIMATELY ×10

Figure 22. Generalized hydrogeologic cross section through the South Coastal Alluvial Plain aquifer system near Ponce

(line of section shown in figure 10; location of Po-130, SC-7, and SC-5 shown in figure 21).

? ?

Figure 23. Generalized geologic cross section through the Río Tallaboa alluvial valley aquifer west

of Ponce (line of section shown in figure 10).

Alluvium

Water table

Approximate land surface

Caribbean Sea

Ponce Limestone

Juana Díaz Formation

VERTICAL EXAGGERATION APPROXIMATELY ×26

D

80

METERS

80

160

Sea level

D'

0

0

1

1

2 KILOMETERS

2 MILES

Figure 23. Generalized hydrogeologic cross section through the Río Tallaboa alluvial valley 

aquifer west of Ponce (line of section shown in figure 10).
32 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

West Coast Province

Four alluvial valleys form the principal aquifers of the 

West Coast Province (fig. 14): Río Guanajibo (130 km2), 

Río Yaguez (4 km2), Río Grande de Añasco (47 km2), and 

Río Culebrinas (25 km2) valleys. The following sections 

describe the hydrogeologic features of each valley area within 

the province. 

Río Guanajibo

The Río Guanajibo valley aquifer is formed by detrital clay, 

silt, sand, and gravel underlain by one or more beds of limestone 

(the limestone subsurface facies have not been correlated to 

outcrop facies, fig. 24). Alluvial sediments and other surficial 

deposits are as much as 30 m thick in the valley. Although the 

thickness of the limestone beds is unknown, it is estimated 

to be greater than 45 m. The underlying bedrock consists of 

volcanic and sedimentary rocks of Cretaceous age; the rocks are 

predominantly basaltic andesite and mudstone as indicated by 

information obtained from wells drilled into the bedrock (ColónDieppa and Quiñones-Marquez, 1985). In the southwestern part 

of the valley near Cabo Rojo where wells tap both alluvium 

and limestone and have yields of 25 L/s, aquifer transmissivity 

is about 245 m2

/d. The higher transmissivity in this part of the 

valley is attributed to the underlying limestone units.

Approximate land surface

VERTICAL EXAGGERATION APPROXIMATELY ×67

E

10

30

METERS

20

10

20

30

40

50

Sea level

E'

EXPLANATION

Mostly sand

Stratified gravel

Mostly detrital clay

Figure 24. Generalized hydrogeologic cross section through the lower Río Guanajibo

alluvial valley aquifer near Cabo Rojo (line of section shown in figure 10; 

adapted from Colón-Dieppa and Quiñones-Marquez, 1985).

Unconsolidated deposits

Limestone

Basaltic andesite?

“Gray rocks” as identified in driller’s log

 (possibly volcaniclastic rock)

Consolidated deposits

0

0

1

1

2 KILOMETERS

2 MILES

Figure 24. Generalized hydrogeologic cross section through the lower 

Río Guanajibo alluvial valley aquifer near Cabo Rojo (line of section shown 

in figure 10; modified from Colón-Dieppa and Quiñones-Marquez, 1985).
Contents of the Hydrogeologic Map 33

Río Yaguez

In the Río Yaguez valley, the alluvium has a maximum 

known thickness of 60 m and is the principal aquifer (Bogart 

and others, 1964). The alluvial deposits are underlain by 

alternating layers of clastic sediments and limestone. In an 

area where a 30-m-deep well tapped the alluvium, the estimated transmissivity was 90 m2

/d.

Río Grande de Añasco

In the Río Grande de Añasco valley, the alluvium is as 

much as 138 m thick and predominately consists of clay strata 

interbedded with sand and one or more beds of limestone that 

have a thickness of about 14 m. The few existing wells in the 

valley are insufficient to determine whether the limestone beds 

are laterally extensive or are discontinuous, isolated lenses. 

In an area where an 82-m-deep well tapped unconsolidated 

sediments and limestone, the estimated transmissivity was 

85 m2

/d.

Río Culebrinas

No hydrogeologic information is available for the Río 

Culebrinas valley.

Groundwater flows in these stream-valley aquifers under 

predevelopment conditions should be similar to the flows in 

the Río Grande de Añasco alluvial valley (Díaz and Jordan, 

1987). Recharge occurs primarily from rainfall infiltration, 

and discharge occurs as seepage to the streams and the seabed 

and as evapotranspiration. The latter may be the principal 

groundwater discharge mechanism in all valleys owing to the 

shallow water table. Extensive drainage ditches have been 

constructed in the Río Guanajibo, Río Grande de Añasco, 

and Río Culebrinas valleys to control waterlogging of soils; 

however, because of the high rainfall during most of the year, 

the water table remains near land surface. In the Río Yaguez 

valley, urbanization has covered nearly the entire area and use 

of the alluvial aquifer has essentially been abandoned. The 

only area where groundwater withdrawal is substantial is in 

the Río Guanajibo valley. Withdrawals in the Río Guanajibo 

valley primarily are for public supply and were estimated to be 

20,000 m3

/d in 1980 and about 21,500 m3/d in 2005 (MolinaRivera and Gómez-Gómez, 2008).

East Coast Province

The East Coast Province consists of the coastal area 

extending east of the Río Grande on the northeast side of 

the island to the Río Maunabo valley in the southeastern 

part of Puerto Rico (fig. 14). The province is subdivided into 

four major aquifer areas, which are identified as follows: 

(1) the Fajardo area covering about 33 km2

, (2) the NaguaboHumacao area covering about 114 km2

, (3) the Yabucoa valley 

covering about 50 km2, and (4) the Maunabo valley covering 

about 16 km2. The following sections describe the hydrogeologic features of the four major aquifer areas.

Fajardo Area

The Fajardo area extends from Punta Picúa on the north 

coast to Punta Lima on the east coast and is characterized by a 

narrow coastal plain and small alluvial stream valleys (plate 1). 

The alluvium, which forms the principal aquifer, consists of 

lenticular beds of clay, sand, and gravel, and weathered rock 

fragments at depths of less than 30 m. The highest wateryielding units are in the lower alluvial fan of the Río Fajardo 

where inflow to the aquifer from the river may be induced 

through gravel and sand deposits. Groundwater withdrawal 

was at one time greatest at the town of Fajardo; however, saltwater encroachment from the sea resulted in the abandonment 

of large production wells by the early 1960s. In the Fajardo 

area, transmissivity of the alluvial aquifer is largely unknown, 

but may be about 100 m2/d in lower parts of the valleys where 

the total thickness of the alluvium is greatest.

Naguabo-Humacao Area

Aquifers in the Naguabo-Humacao area are formed by 

the coalescing alluvial fans of the Río Santiago, Río Blanco, 

Río Antón Ruiz, Río Humacao, and Río Candelero (plate 1). 

Generally, the alluvium in this area consists of fine sand, silt, 

clay, and swamp deposits that have a total saturated thickness 

of less than 20 m in inland areas unaffected by saltwater 

encroachment and as much as 50 m near the coast. Estimates 

of aquifer transmissivities range from 55 to 185 m2/d (Graves, 

1989). In the Río Antón Ruiz alluvial valley where a test well 

was drilled into the alluvium, an estimated transmissivity 

of 140 m2/d was reported for a thickness of only 6 m. This 

estimate indicates that transmissivities in the Río Antón Ruiz 

alluvial deposits may be the highest in the entire NaguaboHumacao area. Transmissivities in the Río Antón Ruiz alluvial 

deposits may be as great as 1,000 m2/d on the basis of data 

obtained from an abandoned irrigation well located in the 

upper valley, which penetrated the alluvium to a depth of 50 m 

and yielded 32 L/s.

Yabucoa Valley

The Yabucoa valley area is characterized by the Río 

Guayanés valley that has incised down through the San 

Lorenzo batholith, which is a granodiorite intrusion (plate 1). 

The bedrock surface is irregular and lies within 50 m of land 

surface along most of the coast. The bedrock is overlain by 

alluvium, which forms the principal aquifer in this area. The 

alluvium largely consists of clay with appreciable amounts 

of sand. The thickness of the alluvial deposits is as much 

as 90 m in the central part of the valley, but averages 30 m 

in most areas (Robison and Anders, 1973). Estimates of 

aquifer transmissivity range from 185 to 465 m2/d in areas 

where the saturated thickness of the alluvium varies between 

40 and 50 m (Robison and Anders, 1973).
34 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Maunabo Valley

The principal aquifer in the Maunabo valley area is 

formed by alluvium that is up to 60 m thick. The alluvium 

consists of discontinuous, lenticular deposits of sand, gravel, 

and cobbles; however, drilling logs indicate that the lithology 

varies widely within the valley with some lenses containing 

coarser material than others. In general, lenses with coarser 

material are within the main axis of the valley along the 

Río Maunabo. Locally, aquifer transmissivity is as high as 

325 m2/d in areas where the saturated thickness of the alluvium is 30 m (Adolphson and others, 1977).

Generally, groundwater in the alluvial aquifers within the 

East Coast Province is unconfined. In the Naguabo-Humacao 

area, semiconfined conditions were found in the vicinity of 

the foothills where wells were drilled into the weathered 

rock zone underlying the alluvium (Graves, 1989). Similar 

conditions were found in the Yabucoa valley; however, the 

semiconfining conditions were attributed to anisotropy caused 

by stratification of the alluvial deposits. An analog model 

constructed for the aquifer system in the Yabucoa valley 

indicated that the stratified conditions of the unconsolidated 

sediments induced a lateral to vertical hydraulic conductivity 

ratio of about 1,600 to 1 (Robison and Anders, 1973). Such 

conditions are important in assessing groundwater/surfacewater relations and in properly defining potential groundwater 

development without inducing saltwater encroachment.

Discharge from aquifers in the East Coast Province has 

been modified substantially by groundwater withdrawals and 

by dewatering wetland areas. In the Fajardo area, discharge to 

lower segments of streams occurs as evapotranspiration near 

the coast where the water table is shallow and as subsurface 

seepage near the shore. In the Naguabo-Humacao area, groundwater generally discharges to coastal swamps. In the Yabucoa 

area, discharge occurs primarily as evapotranspiration (Robison 

and Anders, 1973). In the Maunabo area, most groundwater 

discharges to the Río Maunabo constituting nearly 50 percent 

of the annual streamflow (Adolphson and others, 1977). 

Groundwater withdrawals from aquifers in the East 

Coast Province are estimated at about 22,000 m3

/d. The 

greatest volume of groundwater is withdrawn in the Yabucoa 

valley area where the estimated pumpage is 13,000 m3/d. 

Groundwater withdrawals in the other areas are estimated to 

be about 6,000 m3/d in the Maunabo valley area, 1,800 m3/d 

in the Naguabo-Humacao area, and less than 40 m3/d in the 

Fajardo area (Molina-Rivera and Gómez-Gómez, 2008).

Lajas Valley

Lajas Valley in southwestern Puerto Rico covers 

about 130 km2

 and is bounded by ridges to the north and 

south (fig. 25). Topographically, the valley is bisected by a 

north-south trending drainage divide that parallels longitude 

67°04'00" and reaches a maximum altitude of 14 m. The 

valley floor slopes away from the divide to the east and west.

The valley is underlain by unconsolidated deposits of silt 

and clay that interfinger with coarse materials washed into the 

valley by ephemeral streams. The thickness of these deposits 

is as much as 90 m. The unconsolidated deposits are underlain 

by one or more limestone units of undetermined thickness and 

age. In highland areas, several limestone units have been identified including the Ponce Limestone of Miocene age and the 

Cotui Limestone, the Parguera Limestone, and the Melones 

Limestone all of Late Cretaceous age (Volkman, 1984).

Several aquifers are located in the Lajas Valley. The most 

extensive aquifer is a leaky confined aquifer that is present 

within the limestone units underlying the unconsolidated 

deposits (plate 1). Recharge to this aquifer occurs as rainfall 

that infiltrates through the coarse alluvium found along 

the edges of the valley; as runoff from ephemeral streams 

especially along the more humid north side of the valley; 

and since 1955, as seepage of surface water diverted into 

the valley from the extensive hydroelectric power/irrigation 

infrastructure, which conveys water from the Río Grande de 

Añasco Basin across the insular hydrologic divide and south to 

Lago Lucchetti and Lago Loco reservoirs.

The potentiometric surface of the leaky confined aquifer 

has a maximum altitude of about 4 m near the topographic 

divide of the valley floor. Discharge from the aquifer toward 

the west occurs as subsurface flow to coastal wetlands and the 

seabed and as evapotranspiration. Discharge from the aquifer 

to the east occurs as seepage to the Cienaga el Anegado, which 

is a marsh, and the Laguna de Guánica, which has been an 

ephemeral brackish-water lagoon since the mid-1950s when 

the lagoon was drained. These wetland areas were dewatered 

in the 1950s by construction of tile underdrains and drainage 

canals with discharge directed to the Bahía de Guánica.

Transmissivity estimates for the limestone aquifer 

range from 200 to 3,000 m2

/d (Anderson, 1977). The lowest 

transmissivity occurs in the area near the town of Lajas, and 

the highest values are measured in areas near the center of 

Lajas Valley. In the 1940s, groundwater withdrawals in Lajas 

Valley for irrigation purposes were estimated at 30,000 m3/d. 

Withdrawals for irrigation were halted prior to 1955 due to 

salinization problems at wells. As a result, groundwater was 

replaced with surface water obtained from basins north of the 

insular hydrologic divide and delivered to farm lands through 

the Lajas Valley irrigation-canal network.

Surface-water deliveries to the valley averaged about 

65,000 m3

/d until 1980 when much of the farm land that had 

been cultivated previously in sugarcane was abandoned. In 1982, 

surface-water deliveries averaged only 22,000 m3/d. Since about 

1990, groundwater withdrawals have been limited to small-yield 

domestic wells tapping the alluvium along the valley edges and 

several wells tapping limestone units along the northeast slopes. 

Yields from these wells range from 10 to 15 L/s. The dissolved 

solids concentration in groundwater within the limestone units 

generally is 4,000 mg/L, which makes the water unacceptable 

for most uses. Wells drilled into the limestone outcrop area 

in the northern part of the valley yield water with a dissolved 

solids concentration of about 600 mg/L. Wells tapping alluvial 

deposits along the valley edges generally yield water with a 

dissolved solids concentration of about 1,000 mg/L.
Contents of the Hydrogeologic Map 35

Bahía de Boquerón

Laguna

Cartagena

Laguna Rincón

Laguna de

Guánica

Lajas

Ciénaga

El Anegado Canal de Lajas

EXPLANATION

Extent of Lajas ValleyIrrigation canal

Bahía Sucia

Location of map area in Puerto Rico

Bahía

Montalva

66°55' 67°00' 67°05' 67°10'

18°00'

17°55'

Base from U.S. Army Corps of Engineers orthophotos 2007

C A R I B B E A N S E A

0 2 4 KILOMETERS

Figure 25. Lajas Valley and major geographic features near the southwestern coast of Puerto Rico.

0 2 4 MILES

Bahía

de Guánica

Figure 25. Location of Lajas Valley and major geographic features near the southwestern coast of Puerto Rico.
36 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Interior Province

The Interior Province comprises all areas within the 

interior part of the island that have not been described previously. The Interior Province also includes the volcanic and 

carbonate rocks that crop out in southwestern Puerto Rico. 

The only principal aquifers in this province are found in the 

Caguas-Juncos and the Cayey valleys, which have a total area 

of 141 km2 (fig. 14). 

The Caguas-Juncos valley covers about 130 km2 and is 

underlain by alluvial deposits that consist of clay, sand, and 

gravel. The maximum known thickness of the deposits is 

37 m; however, thicknesses generally are less than 18 m in 

most areas of the valley.

The Cayey valley covers about 11 km2 and also is underlain by alluvium that predominantly consists of clay and rock 

fragments. The average thickness of the alluvium is about 8 m; 

the thickness of the underlying weathered rock is as much as 

15 m. In both valley areas, the principal source of recharge to 

the aquifers is rainfall that percolates downward through the 

unconsolidated deposits and eventually infiltrates through the 

underlying weathered or fractured rocks. The average yield of 

wells tapping the aquifers in these valleys is 10 L/s.

A hydrologic assessment was conducted in the CaguasJuncos valley in the early 1990s (Puig and Rodriguez, 1993).

The data indicate that transmissivity in the valley ranges 

from 185 to 370 m2

/d in parts of the valley where the unconsolidated alluvium is at least 30 m thick. Groundwater 

withdrawals were estimated to be about 11,000 m3/d in 

1980 and about 12,300 m3/d in 2005 (Molina-Rivera and 

Gómez-Gómez, 2008).

In the Cayey valley, no hydrogeologic studies have 

been conducted; however, in areas of the valley where wells 

tap both the alluvium and the weathered rock, the estimated 

transmissivity is about 50 m2/d, and estimated groundwater 

withdrawals in 1990 were less than 2,000 m3/d.

Vieques and Culebra Islands

On the island of Vieques, the Esperanza and Resolución 

aquifers cover an area of 16 km2 and are the only principal 

aquifers containing freshwater (dissolved solids concentration 

less than 1,000 mg/L) (fig. 14). The aquifers are formed by 

alluvial deposits that thicken seaward from a feathers edge 

in inland areas, where volcanic rocks crop out, to as much 

as 27 m of saturated thickness along the coast. The alluvium 

predominantly consists of fine to coarse sand and clay, which 

is derived from the weathering of a granodiorite intrusive. The 

proportion of clay and silt in the unconsolidated deposits is 

greater in areas near the coast. Silt, clay, and swamp deposits 

interfinger with and locally cap the coarse alluvial sediments 

throughout most of the coast (Torres-Gónzalez, 1989). 

Estimates of aquifer transmissivity for the two aquifers range 

from 185 m2

/d in the vicinity of Ensenada Sombe (Sunbay) to 

less than 20 m2/d elsewhere on the island of Vieques.

Groundwater in the Esperanza and Resolución aquifers 

is unconfined, except near the coast where swamp deposits 

overlie the alluvium and result in semiconfined conditions. 

Recharge to both aquifers occurs during periods of intense 

rainfall. Recharge occurs as direct infiltration through the 

alluvial deposits or as infiltration of runoff from upland areas. 

Discharge occurs as seepage to wetlands or as subsurface 

seepage to the seabed near the shoreline. Groundwater was 

withdrawn primarily from the Esperanza aquifer for public 

water supply. Withdrawals of about 2,500 m3/d from the 

principal public water-supply well field near Ensenada Sombe 

(Sunbay) reached a peak in the mid 1970s. Withdrawals from 

the well field were reduced because of saltwater encroachment. In 1978, all withdrawals from the well field were 

discontinued when an underwater pipeline between Vieques 

island and Puerto Rico was completed. In 1990, the only 

major use of groundwater on Vieques island was for a military 

installation; withdrawals were estimated to be less than 

100 m3/d. By 2000, all military installations on the island were 

closed and withdrawals ceased.

Aquifers on Culebra island are formed by volcanic rocks 

and alluvial deposits underlying the coastal embayments 

(plate 2). The total estimated thickness of the unconsolidated 

deposits in the embayments (alluvium and weathered rock) 

is less than 18 m. Most wells on the island of Culebra are 

shallow, dug wells that supply water to livestock. To augment 

the water supply of the island, several wells were drilled 

within an upland depression; however, the sustained yield of 

these wells was less than 20 m3

/d. An underwater pipeline 

connecting Culebra to the public water supply of Vieques 

island was constructed around 1989.
Contents of the Hydrogeologic Map 37

Mona Island

Information on the groundwater resources of Mona 

island is sparse; only four shallow, dug wells are located in the 

coastal plain on the southwestern end of the island (plate 2; 

fig. 26). The coastal plain rises to about 5 m above mean sea 

level and consists of sand and reef deposits. No springs have 

been reported emerging from the cliffs even during major 

rainstorm events, which may indicate that the limestone and 

underlying calcitic dolomite have a high permeability and 

are capable of conveying a large percentage of the infiltrating 

rainfall to the water table. If an aquifer exists within the Isla de 

Mona Dolomite, it may resemble a typical Ghyben-Herzberg 

freshwater lens given the circular shape of the island and 

the propensity for dissolution in dolomites (Verrjuit, 1968). 

The groundwater quality, however, would most likely have a 

dissolved solids concentration greater than 1,000 mg/L, even 

at the apex of the freshwater lens as a result of the seawater 

aerosol over the island. Groundwater quality can be inferred 

from the analyses of water samples obtained from a pool in 

Cueva de los Pájaros (also known as Cueva del Caballo) and 

samples collected from the four dug wells and a brackishwater pond (Manglar Sardinera) at Punta Arenas (fig. 6; 

Puerto Rico Environmental Quality Board, 1973).

Cabo Noreste

Cabo Norte

Cabo Barrio Nuevo

Punta

Arenas

Punta Capitán

Punta Caigo o no Caigo

Punta 

los Ingleses

Punta Este

Cueva de Frío

Cueva

de los

Pájaros

67°55' 67°50'

18°7'30"

18°05'00"

18°2'30"

Base from U.S. Geological Survey, Map I-718, 1972

M O N A P A S S A G E

M O N A P A S S A G E

Piedra

del Carabinero

Coastal Plain

Figure 26. Generalized surficial geology of Mona Island.

0 1 2 MILES

0 1 2 KILOMETERS

Cuevas del

Centro

EXPLANATION

Beach deposits

Boulder deposits

Raised reef flat

Aluminous lateritic soil

Lirio Limestone

Isla de Mona Dolomite

Los Corrales de

los Indios

Figure 26. Generalized surficial geology of Mona Island.
38 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Summary and Conclusions

The availability of hydrogeologic maps for Puerto Rico 

and the outlying islands of Vieques, Culebra, and Mona 

are important to hydrogeologists, groundwater specialists, 

and water resource managers and planners. These maps, in 

combination with the report, serve as a source of information 

to all users by providing basic hydrogeologic and hydrologic 

knowledge in a concise illustrated format.

Puerto Rico and the outlying islands cover a total area 

of 8,927 square kilometers (km2 ). Of this total area, about 

3,500 km2 are underlain by hydrogeologic units that are 

classified as intergranular or fissured. These hydrogeologic 

units form the principal aquifer systems throughout Puerto 

Rico and the outlying islands. 

In Puerto Rico, the most extensive and intensely 

developed aquifers are the North Coast Limestone aquifer 

system and the South Coastal Alluvial Plain aquifer system. 

Withdrawals from these two aquifer systems constitute nearly 

70 percent of the total groundwater withdrawn in Puerto Rico.

The spatial extent of the North Coast Limestone aquifer 

system is about 2,000 km2

. Within this aquifer system, 

groundwater development is greatest in the 800-km2 area 

between the Río Grande de Arecibo and the Río de la Plata. 

This also is the area for which concern is the highest regarding 

the future use of groundwater as a primary source of water for 

domestic and industrial use. With an estimated withdrawal of 

280,000 cubic meters per day (m3/d), groundwater constituted 

the principal source of water within this area providing 

100 percent of the water for self-supplied industries and 

about 85 percent for public water supplies in 1985. By 2005, 

groundwater withdrawals decreased to 150,000 m3/d. 

The spatial extent of the South Coastal Alluvial Plain 

aquifer system is about 470 km2. The estimated consumptive 

groundwater withdrawal from the aquifer system was 

190,000 m3/d in 1980 and 170,000 m3/d in 2005. About 

60 percent and 40 percent of the groundwater withdrawal 

from the South Coastal Alluvial Plain aquifer system was 

used for public water supply and irrigation, respectively.

In the outlying islands of Vieques, Culebra, and Mona, 

only Vieques is underlain by aquifers of any local importance. 

The Resolución and Esperanza aquifers underlie an area 

covering 16 km2

 on the island of Vieques. Prior to 1978 

when an underwater public water-supply pipeline connecting 

Vieques to the main island of Puerto Rico was completed, 

groundwater withdrawal from the two aquifers was as much 

as 2,500 m3/d. Groundwater withdrawals in Vieques island in 

2005 were estimated at less than 100 m3/d.

The potential development of relatively untapped 

groundwater resources in Puerto Rico is limited to the Río 

Grande de Añasco valley and the Río Culebrinas valley in the 

western part of the island and to the Río Grande de Arecibo 

part of the North Coast Limestone aquifer system. In general, 

the North Coast Limestone and the South Coastal Alluvial 

Plain aquifer systems, which are the two principal groundwater-flow systems in Puerto Rico, show evidence of aquifer 

overdraft as indicated by regional increases in concentrations 

of dissolved solids.

Optimization of withdrawals through conjunctive use of 

both surface-water and groundwater sources and by instituting 

water conservation measures has the greatest potential to 

ensure the continued use of groundwater resources. In support 

of these efforts, programs also could be implemented to 

improve database information regarding groundwater withdrawals and the contribution of surface-water diversions to 

surface-water flow, especially within the southern coastal plain 

of Puerto Rico.

Selected References

Adolphson, G., Seijo, M.A., and Robison, T.M., 1977, Water 

resources of the Maunabo valley, Puerto Rico: U.S. Geological Survey Water-Resources Investigations Report 76–115, 

44 p.

Anderson, H., 1976, Ground water in the San Juan metropolitan area, Puerto Rico: U.S.Geological Survey WaterResources Investigations Report 41–75, 34 p.

Anderson, H.R., 1977, Ground water in the Lajas Valley, 

Puerto Rico: U.S. Geological Survey Water-Resources 

Investigations Report 68 –76, 45 p.

Bawiec, W.J., ed., 1998, Geology, geochemistry, geophysics, 

mineral occurrences, and mineral resource assessment for 

the commonwealth of Puerto Rico: U.S. Geological Survey 

Open-File Report 98–38.

Bennet, G., and Giusti, E.V., 1972, Ground water in the 

Tortuguero area, Puerto Rico—As related to proposed 

harbor construction: Commonwealth of Puerto Rico 

Water-Resources Bulletin 10, 25 p.

Bogart, D.B., Arnow, T., and Crooks, J.W., 1964, Water 

resources of Puerto Rico—A progress report: Commonwealth of Puerto Rico Water-Resources Bulletin 4, 102 p.

Briggs, R.P., 1961, Geology of the Kewanee Interamerican 

Oil, Co. test well number CPR4, northern Puerto Rico—

Oil and gas possibilities of northern Puerto Rico: San Juan, 

Puerto Rico Mining Commission, p. 1–23.

Briggs, R.P., and Ackers, J.P., 1965, Hydrogeologic map of 

Puerto Rico and adjacent islands: U.S. Geological Survey 

Hydrologic Investigations Atlas HA–197, scale 1:240,000.

Briggs, R.P., and Seiders, V.M., 1972, Geologic map of the 

Isla de Mona Quadrangle, Puerto Rico: U.S. Geological 

Survey Miscellaneous Geologic Investigations Map I-718, 

1 sheet, scale 1:20,000.

Colón, J.A., 1983, Algunos aspectos de la climatología de 

Puerto Rico: Acta Científica v. 1, no. 2–3, p. 55– 63.
Selected References 39

Colón-Dieppa, Eloy, and Quiñones-Marquez, Ferdinand, 

1985, A reconnaissance of the water resources of central 

Guanajibo valley Puerto Rico: U.S. Geological Survey 

Water-Resources Investigations Report 82–4050, 47 p.

Curtis, R.E., Aquino, Z., Diaz, P.L., and Vachier, R., 1987, 

Water records data Puerto Rico and the U.S. Virgin Islands 

water year 1987: U.S. Geological Survey Water-Data 

Report PR–87–1, 356 p. 

Díaz, J.R., and Jordan, D.G., 1987, Water resources of the 

Río Grande de Añasco—Lower valley, Puerto Rico: 

U.S. Geological Survey Water-Resources Investigations 

Report 85–4237, 48 p.

Giusti, E.V., and Bennett, G.D., 1976, Water resources of the 

north-coast limestone area, Puerto Rico: U.S. Geological 

Survey Water-Resources Investigations Report 42–75, 42 p.

Glover, L., III, 1971, Geology of the Coamo area, Puerto Rico, 

and its relation to the volcanic arc-trench association: U.S. 

Geological Survey Professional Paper 636, 102 p.

Gómez-Gómez, Fernando, 1987, Planning report for the 

Caribbean Islands Regional Aquifer-System Analysis 

Project: U.S. Geological Survey Water-Resources 

Investigations Report 86 – 4074, 50 p., 3 p.

Gómez-Gómez, Fernando, 1991, Hydrochemistry of the south 

coastal plain aquifer system of Puerto Rico and its relation 

to surface water recharge: American Water Resources 

Association monograph series no. 15, 113 p.

Gómez-Gómez, Fernando, and Heisel, J., 1980, Summary 

appraisals of the Nation’s ground-water resources—

Caribbean Region: U.S. Geological Survey Professional 

Paper 813–U, 32 p.

Gómez-Gómez, Fernando, and Torres-Sierra, Heriberto, 

1988, Hydrology and effects of development on the 

water-table aquifer in the Vega Alta quadrangle, Puerto 

Rico: U.S. Geological Survey Water-Resources Investigations Report 87–4105, 54 p.

Graves, R.P., 1989, Water resources of the Humacao-Naguabo 

area, eastern Puerto Rico: U.S. Geological Survey WaterResources Investigations Report 87–4088, 69 p.

Hartley, J.R., 1989, Subsurface geology of the Tertiary carbonate rocks, northwestern Puerto Rico: New Orleans, University of New Orleans, unpublished M.S. thesis, 214 p.

Kaye, C.A., 1959, Geology of Isla Mona, Puerto Rico, and 

notes on age of Mona Passage: U.S. Geological Survey 

Professional Paper 317– C, 178 p.

Mattson, P.H., 1960, Geology of the Mayagüez area, Puerto 

Rico: Bulletin of the Geological Society of America, v. 71, 

p. 319–362.

McGuinnes, C.L., 1948, Groundwater resources of Puerto 

Rico: Puerto Rico Aqueducts and Sewer Service, 613 p.

Meyerhoff, H.A., 1933, Geology of Puerto Rico: Puerto Rico 

University Monograph Series B, Physical and Biological 

Sciences, no. 1, 306 p.

Molina-Rivera, Wanda, and Gómez-Gómez, Fernando, 2008, 

Estimated water use in Puerto Rico, 2005: U.S. Geological 

Survey Open-File Report 2008–1286, 37 p.

Monroe, W.H., 1976, The karst landforms of Puerto Rico: 

U.S. Geological Survey Professional Paper 899–D, 69 p.

Monroe, W.H., 1980, Geology of the middle Tertiary formations of Puerto Rico: U.S. Geological Survey Professional 

Paper 953, 93 p.

National Oceanographic and Atmospheric Administration, 

1982, Climate of Puerto Rico and Virgin Islands, in Climatography of the United States No. 60, 25 p.

Neumann, Eduardo, 1913 (Reprinted 1987), Verdadera y 

Auténtica Historia de la Ciudad de Ponce: Instituto de 

Cultura Puertorriqueña, 284 p.

Picó, R., 1964, Geografia de Puerto Rico: Parte II Geografia 

Económica: Editorial Universitaria, Universidad de Puerto 

Rico, Río Piedras, 220 p. 

Potential of the Central American-Caribbean Region: CircumPacific Council for Energy and Mineral Resources, Earth 

Science Series, Springer-Verlag, v. 16, p. 369–377. Also 

reprinted: Gómez-Gómez, Fernando, Quiñones-Aponte, 

Vicente, and Johnson, A.I., eds., Regional aquifer systems 

of the United States, aquifers of the Caribbean Islands: 

American Water Resources Association Monograph Series 

no. 15, p. 25–36.

Puerto Rico Environmental Quality Board, 1973, Las islas de 

Mona y Monito B Una evaluación de sus recursos naturales 

e históricos, v. no. 1, Junta de Calidad Ambiental, San Juan, 

Puerto Rico, 47 p.

Puig, J., and Rodriguez, J.M., 1993, Ground-water resources 

of the Caguas-Juncos valley, Puerto Rico: U.S. Geological 

Survey Water-Resources Investigations Report 91–4079, 

52 p. 

Quiñones, Ferdinand, and López, Marisol, 1984, Publications 

of the U.S. Geological Survey, Water Resources Division 

for Puerto Rico and the U.S. Virgin Islands, 1946–1984: 

U.S. Geological Survey Open-File Report 84 –229, 32 p. 

Quiñones-Marquez, Ferdinand, and Fusté, L.A., 1978, 

Limnology of Laguna Tortuguero, Puerto Rico: U.S. 

Geological Survey Water-Resources Investigations 

Report 77–122, 86 p. 
40 Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona

Ramos-Ginés, Orlando, 1999, Estimation of magnitude 

and frequency of floods for streams in Puerto Rico—New 

empirical models: U.S. Geological Survey Water-Resources 

Investigations Report 99 –4142, 41 p.

Renken, R.A., Gómez-Gómez, Fernando, Quiñones-Aponte, 

Vicente, and Dacosta, Rafael, 1995, Structure and 

depositional patterns and their influence on the hydraulic conductivity of fan deltas in southern Puerto Rico, 

in Miller, R.L., Escalante, G., Reinemund, J.A., and 

Bergin, M.J., eds., Energy and Mineral Potential of the 

Central American–Caribbean Regions: Heidelberg, 

Springer-Verlag, p. 369–377.

Renken, R.A., Ward, W.C., Gill, I.P., Gómez-Gómez, Fernando,

Rodríguez-Martínez, Jesús, and others, 2002, Geology and 

hydrogeology of the Caribbean Islands aquifer system of the 

Commonwealth of Puerto Rico and the U.S. Virgin Islands: 

U.S. Geological Survey Professional Paper 1419, 139 p., 

5 pls.

Robison, T.M., and Anders, R.B., 1973, Electrical analog 

model study of the alluvial aquifer in the Yabucoa valley, 

Puerto Rico, Phase 2—The planning, construction and use 

of the model: U.S.Geological Survey Water-Resources 

Investigations Report 73 –1, 22 p.

Santiago-Rivera, Luis, 1992, Low-flow characteristics 

at selected sites on streams in eastern Puerto Rico: 

U.S.Geological Survey Water-Resources Investigations 

Report 92–4063, 46 p.

Santiago-Rivera, Luis, 1996, Low-flow characteristics 

at selected sites on streams in southern and western 

Puerto Rico: U.S.Geological Survey Water-Resources 

Investigations Report 95 –4147, 46 p.

Santiago-Rivera, Luis, 1998, Low-flow characteristics 

at selected sites on streams in northern and central 

Puerto Rico: U.S.Geological Survey Water-Resources 

Investigations Report 98 –4200, 53 p.

Scharlach, R.A., 1990, Depositional history of OligoceneMiocene carbonate rocks, subsurface of northeastern Puerto 

Rico: New Orleans, University of New Orleans, unpublished M.S. thesis, 242 p.

Struckmeiser, W.F., and Margat, Jean, 1995, Hydrogeological 

maps—A guide and a standard legend: International Association of Hydrogeologists, v. 7, 177 p.

Torres-González, Arturo, 1984, Use of surface geophysical 

techniques for ground-water exploration in the CanóvanasRío Grande area, Puerto Rico: U.S. Geological Survey 

Water-Resources Investigations Report 83–4266, 25 p.

Torres-Gónzalez, Sigfredo, 1989, Reconnaissance of groundwater resources of Vieques island, Puerto Rico: U.S. 

Geological Survey Water-Resources Investigations

Report 86 –4100, 37 p.

U.S. Bureau of the Census, 1991, 1990 Census of Population 

and Housing: Puerto Rico, Bureau of Census, CPH-1-53, 

199 p.

U.S. Bureau of the Census, 2012, 2010 Census Summary File 1

[Puerto Rico]/prepared by the U.S. Census Bureau, 2012 

http://www.census.gov/prod/cen2010/doc/sf1.pdf.

U.S. Geological Survey, 2010, Water-resources data for the 

United States, Water Year 2010, at http://wdr.water.usgs.gov/.

Verrjuit, A., 1968. A note on the Ghyben-Herzberg formula: 

Delft, Netherlands, Technological University, Bulletin of 

the International Association of Scientific Hydrology, v. 13, 

no. 4, p. 43– 46. 

Volkman, R.P., 1984, Geologic map of the Puerto Real quadrangle, southwest Puerto Rico: U.S. Geological Survey 

Miscellaneous Investigations Services, 1 pl.

Wilson, H.M., 1899, Water resources of Puerto Rico: U.S. 

Geological Survey Water-Supply Paper 32, 48 p.

Zapp, A.D., Berquist, H.R., and Thomas, C.R., 1948, Tertiary 

geology of the coastal plains of Puerto Rico: U.S. Geological Survey Oil and Gas Investigation Preliminary Map 85, 

scale 1:60,000.
Manuscript approved April 1, 2014

Prepared by the USGS Science Publishing Network

Raleigh Publishing Service Center

Edited by Kay P. Naugle

Illustrations by Jeffrey Corbett

Layout by Caryl J. Wipperfurth

For more information concerning this report, contact:

Director, Caribbean Water Science Center

651 Federal Drive Suite 400-15

Guaynabo, PR 00965

(787) 749-4346

http://pr.water.usgs.gov/ 
Gómez-Gómez and others—Hydrogeology of Puerto Rico and the Outlying Islands of Vieques, Culebra, and Mona—Scientific Investigations Map 3296

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3296