Highway 52

66°32'00" 66°30' 66°28' 66°26'00"

30

35

40

45

50

55

1997 1998 1999 2000 2001 2002

JANUARY

2003 2004 2005

DEPTH TO WATER, IN FEET BELOW 

LAND SURFACE

18°04'00"

18°02'

18°00'00"

Base from U.S. Geological Survey Digital Raster Graphic for the Ponce,

Playa de Ponce, Santa Isabel and Río Descalabrado quadrangles 1989

Geologic information modified from Bawiec, 2001

Lambert conformal conic projection. Datum North American Datum (NAD) of 1927

Geology

EXPLANATION

QUATERNARY ALLUVIAL AND SURFICIAL DEPOSITS

PONCE LIMESTONE

JUANA DÍAZ FORMATION

OTHER TERTIARY NON-VOLCANICLASTIC TERRANES

VOLCANICLASTIC TERRANES

GROUND-WATER LEVEL DATA CONTROL POINT - Number on top 

left quadrant is the measured water level, in feet above mean sea 

level. Number on top right quadrant is specific conductance, in 

microsiemens per centimeter at 25 degrees Celsius. Number on 

bottom left quadrant is instantaneous discharge rate, in gallons per 

minute, and number in bottom right quadrant is average well discharge,

in million gallons per day for June 2005. R, indicates that water level 

was recovering after pumping was discontinued for at least 

30 minutes prior to measurement

U.S. GEOLOGICAL SURVEY OBSERVATION WELL 

AND IDENTIFICATION NUMBER - Number to the left is the 

measured water level, in feet above mean sea level

POTENTIOMETRIC CONTOUR - Shows altitude at which 

water level would have stood in tightly cased well. Hachures 

indicate depression of potentiometric surface. Dashed line 

indicates where approximately located. Contour interval 

variable at 5 and 10 feet. Datum is mean sea level

DIRECTION OF GROUND-WATER FLOW 

JUANA DÍAZ IRRIGATION CANAL AND DIRECTION OF FLOW

STREAM OR IRRIGATION CANAL FLOW MEASUREMENT SITENumber on top is the instantaneous discharge rate, in cubic feet

per second, date of measurement is shown in parentheses. Number

on bottom is specific conductance, in microsiemens per centimeter

at 25 degrees Celsius

NATIONAL WEATHER SERVICE STATION AND 

IDENTIFICATION NUMBER 

21

0.44

842 R

180020066261500

310

30

665020

14.5 (6/30/2005)

524

5

30

20

10

10

20

5

5

30

5

6

24

20

9

13

600

18

33

38

35

75

8

17

24

17

6

50

100

60

3 713

756

756

705

400

390

325

842

1200

170 0.23

310 1230

1360

449

0.24

0.44

300 0.44

0.35

0.22

0.11

0.48

566

709

862

759

816

180

863

220

647

190 0.24

0.26

0.08

0.26

0.2

0.2

0.3

0.14

0.17

420 0.29

794

749

742

0.20 

million gallons per day

from 3 wells

694

0.18 170 130

665

42

70

21

28

29

7

4

122

140 0.18

435

260

160

57

4

10

11

19

-1

R

R

R

R

R

26

36

18

34

20

30

30

24

21

665020

180020066261500

3 (7/1/2005)

935

239

---

0 (7/1/2005)

19.4 (7/1/2005)

245

19.4 (7/1/2005)

245

2.81 (6/30/2005)

672

22.1 (7/1/2005)

---

23.7 (7/1/2005)

---

34.8 (6/30/2005)

Cordillera Central

STUDY AREA

MONA PASSAGE

0.5 1 1.5 2 MILES

0 0.5 1 1.5 2 KILOMETERS

0

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

PUERTO RICO ENVIRONMENTAL QUALITY BOARD

SCIENTIFIC INVESTIGATIONS MAP 2947

Potentiometric Surface of the Alluvial Aquifer and Hydrologic Conditions

in the Juana Díaz area, Puerto Rico, June 29 - July 1, 2005

By José M. Rodríguez and others

POTENTIOMETRIC SURFACE OF THE ALLUVIAL AQUIFER 

AND HYDROLOGIC CONDITIONS IN 

THE JUANA DÍAZ AREA, PUERTO RICO, 

JUNE 29 - JULY 1, 2005

By José M. Rodríguez, Luis Santigo-Rivera, and Fernando Gómez-Gómez

Potentiometric Surface of the Alluvial Aquifer and Hydrologic Conditions 

in the Juana Díaz area, Puerto Rico, June 29 - July 1, 2005

By José M. Rodríguez, Luis Santiago-Rivera, and Fernando Gómez-Gómez

A synoptic survey of the hydrologic conditions in the Juana Díaz area, Puerto Rico, was 

conducted between June 29 and July 1, 2005, to define the spatial distribution of the potentiometric surface of the alluvial aquifer. The study area encompasses 21 square miles of 

the more extensive South Coastal Plain Alluvial Aquifer system and is bounded along the 

north by foothills of the Cordillera Central mountain chain, to the south by the Caribbean 

Sea, the east by the Río Descalabrado and to the west by the Río Inabón. Ground water in 

the Juana Díaz area is in the Quaternary-age alluvial deposits and the middle-Tertiary age 

Ponce Limestone and Juana Díaz Formation (Giusti, 1968). The hydraulic properties of the 

Ponce Limestone in the Juana Díaz area are unknown, and the Juana Díaz Formation is a 

unit of poor permeability due to its high clay content. Consequently, the Ponce Limestone 

and the Juana Díaz Formation are generally considered to be the base of the alluvial aquifer in the Juana Díaz area with ground-water flow occurring primarily within the alluvial 

deposits. 

The potentiometric-surface map of the alluvial aquifer was delineated using ground-water 

level measurements taken at existing wells. The water-level measurements were taken at 

wells that were either not pumping during the survey or were shut down for a brief period. 

In the latter case, a recovery period of 30 minutes was allowed for the drawdown in the 

wellbore to achieve a near static level position representative of the aquifer at the measurement point. Land-surface altitude from U.S. Geological Survey (USGS) 1:20,000 scale 

topographic maps (Playa de Ponce, Ponce, Río Descalabrado, and Santa Isabel) were 

used to refer ground-water levels to mean sea level datum (National Geodetic Vertical 

Datum of 1929). In addition to the ground-water level measurements, the potentiometricsurface contours were delineated using hydrologic features, such as drainage ditches and 

saturated intermittent streams that were considered as aquifer drains and losing streams, 

respectively.

The survey included ground-water level measurements in 38 wells, instantaneous streamdischarge measurements at 8 locations in streams and irrigation canals, and estimates of 

ground-water withdrawal rates at 20 active production wells. Specific conductance was 

measured at the wellhead from water samples collected at pumping wells. The survey was 

conducted after a period of above-average precipitation. Cumulative rainfall between January 1 and May 31, 2005, at the Juana Díaz Camp National Weather Service (NWS) station 

665020 (fig. 1) and Santa Isabel 2ENE NWS station 668940 (not shown on map) located 

about 4 miles southeast of Central Cortada was 22.34 and 12.15 inches, respectively; 

these amounts are about 2 and 1.5 times, respectively, above normal for this period. 

Ground-water levels measured at the USGS Cabrera observation well, 180020066261500, 

located near Río Descalabrado, are presented in figure 2 for the period of record from 1997 

to 2005 and in figure 3 for the period from January to July 2005. Water levels in this observation well increased by 6.87 feet from April 13 to June 30, 2005 (fig. 3).

The general direction of ground-water flow is indicated by flow lines drawn perpendicular 

to the potentiometric-surface contours on the plate. The general direction of ground-water 

flow in the alluvial aquifer is to the south with minor flow components to the southwest and 

southeast. During the synoptic survey, the ground-water levels ranged from 1 foot below to 

122 feet above mean sea level. The potentiometric-surface contours indicate that the 

alluvial aquifer is gaining water from the streams that traverse the coastal plain. In general, 

the potentiometric surface during July 2005 had overall altitudes and contour patterns 

similar to those observed in March 1987 (Rodríguez-del-Río and Gómez-Gómez, 1990). 

The water levels during both synoptic studies were within 4-foot differences in wells located 

to the south of the 10-foot contour shown on the plate. The greatest difference between 

water levels measured in July 2005 and March 1987 was observed in a well located near 

the northern limit of the coastal plain near the Río Descalabrado at Barrio Río Cañas 

Abajo, Juana Díaz, where the water level was 20 feet above mean sea level in this survey 

as compared to 52 feet above mean sea level in March 1987. In this general area, crops 

are irrigated by large capacity wells; however, during the synoptic survey, wells were not in 

use due to recent rainfall.

The specific conductance values of ground water ranged from 450 to 1,360 microsiemens 

per centimeter at 25 degrees Celsius. In the alluvial deposits along the coastal plain, 

specific conductance values ranged from 450 to 860 microsiemens per centimeter at 25 

degrees Celsius. Specific conductance values greater than 1,000 microsiemens per centimeter at 25 degrees Celsius were measured in wells near the outcrops of the Juana Díaz 

Formation. Higher specific conductance values in ground water from wells near the Juana 

Díaz Formation are associated with its marine origin (Giusti, 1968). In general, groundwater withdrawals in the study area are for public-supply water and irrigation purposes. 

Public-supply water withdrawals were estimated to be 4.5 million gallons per day based on 

instantaneous well-discharge meter readings obtained during the survey. Ground-water 

withdrawals for irrigation purposes are unknown, but about 4,000 acres of land were under 

cultivation according to 2004 aerial photos.

Instantaneous surface-water discharge measurements were taken at selected sites along 

the Río Inabón, Río Jacaguas, Río Cañas, Río Descalabrado, and the Canal de Juana 

Díaz (plate) to estimate ground- and surface-water interactions during the synoptic survey. 

The instantaneous stream discharge measurements taken on July 1, 2005, along the Canal 

de Juana Díaz indicated a flow rate of 23.7 cubic feet per second near the town of Juana 

Díaz and 19.4 cubic feet per second near the Río Descalabrado (plate). The difference in 

flow between each set of measurements at the irrigation canals may be caused by infiltration losses and diversion for irrigation. The instantaneous discharge measured near the 

coast in the Río Inabón, Río Jacaguas, and Río Descalabrado were 14.5, 34.8, and 2.8 

cubic feet per second, respectively. The streamflow in the Río Cañas was estimated at 3 

cubic feet per second near the northern boundary of the coastal plain; however, the channel was observed to be dry at about 1.18 miles downstream.

REFERENCES CITED

Bawiec, Walter, 2001, Geology, geochemistry, geophysics, mineral occurrences, and 

mineral resources assessment for the Commonwealth of Puerto Rico: U.S. Geological 

Survey Open-File Report 98-38.

Giusti, E.V., 1968, Water resources of the Juana Díaz area, Puerto Rico - A preliminary 

appraisal, 1966: U.S. Geological Survey Water-Resources Bulletin 8, 43 p.

Rodríguez-del-Río, Félix, and Gómez-Gómez, Fernando, 1990, Potentiometric surface of 

the alluvial aquifer and hydrologic conditions in the Santa Isabel-Juana Díaz area, Puerto 

Rico, March to April,1987: U.S. Geological Survey Water-Resources Investigations 

Report 89-4116, 2 sheets.

0

2

4

6

8

10

12

14

Juana Díaz Camp NWS station (665020) monthly average

(see plate for location)

Juana Díaz Camp NWS station (665020) 2005 monthly total

Santa Isabel 2ENE NWS station (668940) monthly average

Santa Isabel 2ENE station (668940) 2005 monthly total

January February March April May June July

RAINFALL, IN INCHES

Figure 1. Rainfall at Juana Díaz Camp (665020) and Santa Isabel 2ENE (668940) 

 National Weather Service stations.

2005

Figure 2. Ground-water levels at U.S. Geological Survey Cabrera observation well (180020066261500) Juana Díaz, 

 Puerto Rico (see plate for location).

30

32

34

36

38

40

42

44

January February March April May June July August

2005

DEPTH TO WATER, IN FEET BELOW 

LAND SURFACE

Figure 3. Ground-water levels at U.S. Geological Survey Cabrera observation well (180020066261500), 

 Juana Díaz, Puerto Rico, from January to July 2005 (see plate for location).

Río Cañas Abajo