EXTENDED POTENTIOMETRIC HEAD OF
THE ARTESIAN AQUIFER OF THE CIBAO
FORMATION AND THE LARES LIMESTONE.
OWING TO SEA DEPTH AND
S2000- POSSIBLE LEAKAGE -2000
LW f04NNk RESULTING FROM IL
Z4 + O4 DECREASED HYDRAULIC Z
SoCONDUCTIVITY DOWN DIP.
3000- -\ \ o3v000
SO HYDRAULIC CONDUCTIVITY
0" \ &P i (100) IN CUBIC FEET PER DAY -
__ J t 100)PER SQUARE FOOT -4000
S4000- (FEET PER DAY)
SAN SEBASTIAN FORMATION
AND VOLCANIC -00
7000- 01 -
01 t t ooo
VERTICAL EXAGGERATION X 10
10 5 0 6 10 15 20
DISTANCE FROM COAST. IN MILES
Fig. 3 Schematic Diagram of Possible Patterns of Ground-Water Flow
and Estimated Hydraulic Conductivities in the Major Formations.
obtained from these limestone aquifers.
The existence of the mountain core is very important
for the recharge of the aquifer systems. The mountain core
controls the rain concentrations in the north coast and
north-central parts of island causing the drainage direction
to be predominantly towards the karst terrains.
Recharge for the artesian aquifer (Lares and Montebello
limestones) is produced at the highest point of the karst
terrain. Recharge production occurs through sinkholes and
dolines which are predominant features of the Cibao
formation. This implies that a major form of recharge
occurs in fractures within the limestone. Most of the
drainage in limestone terrain occurs underground rather than
above ground. The recharge zone creates a high head in the
artesian aquifer making the aquifer a very important water
The second aquifer system or water table recharging
zone is located farther north and supplies the Aguada and
Aymamon limestone. Sinkholes, dolines and the blanket sand
also act as recharge areas for the system.
These aquifer systems are used the most as water
supplies for the north coast. PRASA (Puerto Rico Aqueduct
Sewer Authority) has established many pumping wells for
domestic use. Industries like Abbott and Union Carbide
control wells that are pumping water for their own use from
the aquifer. Also some wells have been installed for
agricultural use by the land authority. Private wells also
exist in the areas. These uses help to illustrate the
amount of pumping from the aquifer and to show the
importance of a clean aquifer.
IV. PROBLEMS OF THE AQUIFER
An increasing variety of problems are developing within
the aquifer systems. The increase of pumping in the zone
has produced salt-water encroachment into the fresh-water
aquifer. Groundwater pollution by way of sinkholes is
occurring in industrial, agricultural, and urbanized areas.
Industrial contamination is being directly accessed to the
limestone through the use of deep sinkholes being used for
drainage of waste water. This contamination problem is of
the most concern here because sinkholes access is a major
source of direct contamination to the aquifer.
High bacteria counts and pesticides have been also
found in water samples. This contamination is most likely
due to the increase in agricultural activity. Blanket sand
deposits used for agriculture contribute to the recharging
of the aquifer. Also some blanket sand contains water
reserves defined as surficial aquifers, or perched aquifer,
that are used for water supplies for domestic use.
Trace-organic pollutants have been detected in
Barceloneta and Vega Alta within domestic water samples. A
trace of trichloroethylene in the amount of 670 ppb has been
detected in a well know as the Ponderosa well in Vega Alta.
This is a unsafe amount for human consumption. The source
of this pollutant is from a cleaner used by major
industries, as well as local dry cleaners, and the primary
source of contamination.
The contamination problem has now spread into the karst
zone and the lack of knowledge on water-quality degradation
of the aquifer in the water table (Aguada and Aymamon)
limestone is a very serious problem. This aquifer has the
potential to be permanently lost as a domestic water supply
if pollution continues to increase from the.present rate.
V. REGIONAL STUDY
The karst region of the northerncoast can be divided
into 5 sub-regions (Torres Atall-1984):
1- Aguadilla to Rio Grande de Arecibo
2- Rio Grande de Arecibo to Rio Grande Manati
3- Rio Grande de Manati to Rio Cibuco Area
4- Rio Cibuco to Rio de la Plata Area
5- San Juan Metropolitan Area
The Aguadilla to Rio Grande de Arecibo Area (Fig. 4)
has had limited groundwater data collected from it due to
the lack of understanding of the physical and hydraulic
characteristics of the water table. A good pattern of
groundwater flow has not been produced due to this lack of
information. Rio Camuy and Tamama, however, appear to have
good groundwater drainage based on the presence of many
interconnecting caves and fractures within the karst region.
The artesian aquifer in this region does not appear to be