General Hydrological Study

Live the Blue Dream of Cabuya Project, Ltd.

Cabuya, Cóbano, Puntarenas

March 2007

Professional responsible for this study:
María Gómez Tristán: Masters of Science: Geology

 Bachelor’s en Geology, University of Costa Rica
Masters of Science in Hydrological and Water Resource Management

University of Costa Rica
CGCR # 286
SETENA CI-03-2004

March 2007

Contents

Summary                                                                                                          ------4
Section 1: Geology                                                                                           - -----5
Section 1.2: Geomorphology                                                                               ------7
Section 2: Hydrology                                                                                         ------9
Conclusions and Recommendations                                                                    -----12
References                                                                                                        -----14

 Summary

This technical geological study includes the sections of basic geology and hydrology in order to give a general description of the hydrology of the farm # P-655229-2000, located near Cabuya, Cóbano in the province of Puntarenas.

The local geology includes the Nicoya Complex, which is comprised of basalts and intrusions, limonites and clear-grey sandstone from the Montezuma formation. Near the beach there are Quaternary Deposits. The farm is found upon the Montezuma formation.

The geomorphology of the zone includes mountain ranges and structural mountains, flood plains outside of the area of the farm and the abrasion platform on the coast. The area of the project is found over mountains and mountainous structures where the topography is undulating with sudden and gentle rock formations.

Hydrologically the farm is located over a sedimentary aquifer, corresponding with the Montezuma formation. This aquifer has very hydrological potential (little water) with approximate water reserves of 4 liters per second.

 General hydrological study
Live the Blue Dream of Cabuya Project, Ltd.
Cabuya, Cóbano, Puntarenas 

Introduction

The project Live the Blue Dream of Cabuya, Ltd. is situated 1.5 kilometers from the beach of Cabuya, on the road that connects Mal País with Cabuya. This property is 29.33 hectares.

The project is located approximately between the coordinate’s 176.0 – 177.1 latitude North and 414.95 – 415.70 longitude east on the attached Cabuya map number 3144.1, scale 1:50,000, Figure 1. The present report was carried out using a bibliographical summary, survey and inspection of the farm.

Section 1: Geology

The area of study is comprised of three geological parts: the Nicoya complex, the Montezuma complex and the Quaternary Deposits, Figure 1.

1.1  Regional Geology

            - Nicoya Complex

The Nicoya Complex protrudes to the surface on the Nicoya, Santa Elena, Osa and Burica peninsulas as well as in Quepos and Herradurra. Dengo (1962a, 1962b) did several studies on the Nicoya Complex and includes various igneous rock types (diabase, diorites, and nodules found in fissures, sills and stocks, and abundant conglomerates of basalts and peridots). Some sedimentary rocks are comprised of lutites, grawacas and silica. The basalt events and intrusions of diabase are interspersed with intervals of conglomerate rocks and that makes certain that the majority of the marine sediment sequences and pillows of basalt are recent. The agglomerates of the upper layer of the Nicoya Complex are massive basalts and become thicker below 300 meters.

 Gursky (1989) did a study of the sediment rocks of the Nicoya Complex which has a thickness of dozens of meters filled with pillow-like lava spaces, xenoliths, intrusive bodies, and tectonics, components of breaches and volcaniclastic sandstone, a product of the erosion of basalt flows. The radiolarites dominate the formation as well with their rhythmic stratification with a high content of hematite, magnesium and an absence of terrigenous detritus, indicating a sedimentary environment of very little energy typical in deep waters.

 Sinot et all (1997) by means of radiometric data were able to prove that the basalts of the Nicoya Complex were formed between 88 and 90 million years ago, which negates the hypothesis about the existence of the Matapalo and Esperanza units mentioned previously by Kuypers (1979).

 Hauff et all (1999) with a database 40AR/39Ar, define the age of a pillow lava as 94.7 million years and a plagiogranite rock with an age of 87.5 million years. They also conclude that the interval of the formation of the igneous bedrock is between 95 and 83 million years ago in contrast with the formation of the radiolarites with an age between 163 and 84 million years.

-Montezuma Formation

The Montezuma Formation is made up of sandstone, limestone and conglomerates with colored variations and granules. Dengo (1962) describes the interior lithography as conglomerates and sandstone that gradually change to limestone and fine colored sandstone of a clear grey-blue color. Some sites appear like sandstone with a green-grey color.

The Montezuma Formation has a thickness of 30 meters near the town of Montezuma and it gets thinner towards Cóbano. Sprechmann (1984) has said that it originated in the Miocene Period. The whole area of the farm is on top of the Montezuma Formation

-Quaternary Deposits

The Quaternary Deposits are made up of blocks, gravels, sands and intercalations of clay, associated with the removal and deposition of material from the Nicoya Complex and the Montezuma Formation. The deposition of the material occurs because of a change in slope that exists in eroded mountains made up of material from the Nicoya Complex and the Montezuma Formation with flat zones.

These deposits are not isolated and are found in low lying areas near the coast.

1.2  Local Geology

As already mentioned, the entire farm is found over the Montezuma Formation. In the talus slopes of the roads you can observe lutites and limonite of a clear gray color, found in pockets with very breakable, thin layers. Generally in the bases of the outcroppings you can find alternating layers of fine sandstone of blue-gray and brown colors. Both the limonite and the sandstone rocks have a tiny layer of dark brown color.

Some outcroppings have fractures with similar directions towards the dips of the layers and in some sites you find these fractures with calcite.

                                    Photograph 1: Limonite located in horizontal pockets.

                                    Photograph 2: Limonite with fractures in various directions.

1.2 Geomorphology

1.2.1        Regional Geomorphology

The geomorphology of the property is made up of three entities that include abrasive marine platforms, structural plains/ folded mountains and flood plains. Figure 2, photograph 3.

Forms of Marine Erosion

The forms of marine erosion include the platforms of marine erosion.

-Platforms of Marine Erosion

The platforms of marine erosion are found in the extreme south of Cabuya Beach, in Punta Mocha. These platforms are associated with the recession of the cliffs and generally 80% of these cliffs are under water during high tide.

The platforms are made up off igneous basalt rocks and intrusions of the Nicoya Complex.

Igneous Formations

Igneous formations include the mountainous areas of the Nicoya Complex.

-Structural Plains and Folded Mountains

These are made of old mountain ranges made from materials of the Nicoya Complex and the Montezuma Formation. The highlands of the mountains are related to the structural plains and the slopes of the mountains or mountain ranges that have sizeable intrusions. The majority of the mountain ranges have smooth surfaces because of the fluvial erosion. The inter-fluvial spaces are smaller than 200 meters and the valley floors are deep.

The zone of the project is found on structural plains and folded mountains of the south of the Nicoya Peninsula. Because of the fine and breakable materials, you can find eroded material from fluvial erosion in the ravines very far from the farm.

Forms of Alluvial Deposition

-Alluvial Plains

The alluvial plains outcrop with low elevations, paralleling the coast in the town of Cabuya. The outcrops are almost non-existent and the topography is practically flat. These plains correspond with systems of colluvial-alluvial deposition. The sediment is a product of the erosion of materials of the Nicoya Complex and the Montezuma Formation.

There are no alluvial plains on the property.

1.4.2 Local Geomorphology

As already mentioned, the property of Live the Blue Dream in Cabuya, Ltd is located over folded mountains associated with the tectonic uplift of the coast. The outcrops are gradual to steep with inclines of 30 to 50 degrees approximately in the mountain ranges of Buenos Aires, Antiliano and Pénjamo. Figure 3 shows 3 defined faults, of which the one on Route s60E has a relatively upward movement in the Southeast Block and a descending movement in the Northeast Block.

The fault on Route N85 crosses the entire peninsula of Mal País until Cabuya.

                                    Photograph 3: Mountains of the Montezuma Formation

The fault on Route N50E ends falling towards the Northeast. All the faults are tertiary, thus the seismic potential associated with them is diminishing.

Section 2: Hydrology

2.1 Hydrological Facts

The farm of the property is found at an elevation between 60 and 110 meters above sea level, comparable to the higher areas of the region.

The average annual precipitations are between 2,500 and 3,000 according to the National Service of Subterranean Waters.

Far from the farm are two seasonal streams and the Cenízaro spring, which is still flowing as of the date of this report. See photographs 4 and 5.

The Cenízaro spring starts within the farm and is from a spring located between 176.160 Latitude North and 414.996 Longitude East (Figure 3) and has an annual flow of .6 liters per second.

According to the National Service of Subterranean Waters (2007 report) there are 6 registered wells in the surrounding area, however none have sourced the Cenízaro spring. (Figure 1)

-Nicoya Complex

The aquifer potential in these igneous rocks is practically non-existent; however, there are flows between .5 liters per second to 3 liters per second. The principal contribution of water in this formation is due primarily to the fractures in every direction at a secondary level because of the strong tectonic activity.

The basalts and gabbros of the Nicoya Complex generally do not contain much water, nor do they transport it very well either. However, in local conditions with a presence of secondary breaks and or local faults, the possibility increases for the permeability and storage of water.

-Sedimentary Aquifer of the Montezuma Formation

The area of the property is found, as already mentioned, over the Montezuma Formation which is considered a sedimentary continental aquifer, with a hydro potential of almost nothing according to the National Service of Subterranean Waters (SENARA) (1992). Under certain conditions you could find flows of up to 4 liters per second.

According to the information obtained from the registered well inventories of the SENARA, National Service of Subterranean Waters, (2007) there are 4 registered perforated wells in this area of the Montezuma Formation (See Figure 3, Box 1) located to the Northeast of the farm. These wells have registered flows of 1 liter per second, with an average depth of 70 meters.

There is no lithological information on any of the 4 registered wells. Only well CY21 has a register at a static level at a depth of 4 meters. This well has a depth of 18 meters.

The porosity and permeability of the wells are low.

The Alluvial Co-Alluvial Aquifer of Cabuya

The wells ILG-73 and ILG-74 are located on the Alluvial Co-Alluvial Aquifer of Cabuya.

There are no lithological or static registry of the wells ILG-73 or ILG-174, however the produce 3.66 and 3.7 liters per day respectively.

The Alluvial Co-Alluvial Aquifer of Cabuya Beach has a medium to high aquifer potential and is made up of unconsolidated and consolidated sediments with medium permeability. The water is potable and in agreement with National Service of Subterranean Waters SENARA (1992) and has flows between 20 liters per second and 45 liters per second. However, it is important to consider that the aquifer is very close to the coast and that the perforated wells of said aquifer should not be very deep so as to avoid a salt water intrusion.

Figure 1: Inventory of the registered wells according to SENARA (2007)

2.2 Proposed sites for perforated wells

Figure 3 shows the proposed location for the wells determined by the surveying team during their initial investigation. Figure 2 has the coordinates and the elevations of the sites.

Figure 2: Proposed sites for wells within the boundaries of the farm. Coordinates and elevations obtained from the field appear in Annex 1.2

Its worth mentioning that the sites are not definite and it is necessary to corroborate retreat zones in agreement with the subdivision plan, the location of buildings and construction sites, protected zones established by the plan supervisor, the direction of urbanization and or the environmental impact study.

2.3 Demand for Water Resources

The calculations of the demand of water resources for the project Live the Blue Dream Cabuya is determined from the preliminary master plan created by Nazca Pacific. The total units correspond with the number of proposed lots and the daily usage per person is a fairly accurate, and establishes an average of 300 liters a day per person for people in hotels and rental homes according to La Gaceta (2004).

In order to satisfy the water needs for human consumption according to the proposed size and dimensions o the project (83 units) they need 2.37 liters per second of water per day, or the equivalent of 4.7 wells with extraction rates of 1 liter per second, assuming 12 hours of water extraction daily. The requirement of 5 liters per square meter for watering open spaces during the dry season, La Gaceta (2004), is not included in the volume of 2.34 liters per day, and obviously depends on the established green areas and/or gardens within the development.

Conclusions an Recommendations

Conclusions

• Geologically speaking the property is located over limonites and fine sandstone of a clear-gray to blue color on the Montezuma Formation.
• Because of the breakable material of the Montezuma Formation, far from the property there are gullies that deepen and erode during the rainy season because of the runoff. This phenomenon should be considered when construction takes place to avoid unstable foundations and long term structural problems when building over natural drainages.  
• Geomorphologicaly speaking, there are folded mountains of the Montezuma Formation associated with the tectonic uplift in the area.
• Hydrologically speaking the property is located over a tiny aquifer with little hydrological potential, with maximum flows under special conditions of 4 liters per second.
• There are no Quaternary Deposits or alluviums within the boundaries of the property.
• Materials from the Nicoya Complex and the Quaternary Deposits outcrop to the east of the property.
• The proposed sites for well drilling are not definite, and will depend on the final design of the development.
• The calculations for water demand of the property were obtained from the information given by the developers.

Recommendations

• It is recommended to take a geo-electric and seismic profile of the land to determine the presence of fractures of the surrounding areas of the proposed well sites. The analysis of these profiles would be a useful tool to determine the well levels and the presence of secondary fractures which could contain water.
• The protective radius of the Cenízaro Spring should be respected. There should be no type of construction or activity around the spring.
• The temporary streams (dry in the dry season) and the Cenízaro Spring possess absolute protected zones, and there should be no wells drilled in this area.
• Wells should be drilled with a small diameter in order to determine the levels of the subterranean water and to establish a range of depth for the perforations for wells. However, it is important to evaluate the real costs of these wells as compared to those costs for wells using a standard well diameter.
• Before carrying out a well drilling, it is important that the access roads to the farm and the well drilling sites are in excellent condition.
• Flow monitoring of the seasonal streams is important in order to establish a hydrological relation between the seasonal stream flows and the subterranean water levels.
• It is estimated that well drilling depths of depths between 60 and 80 meters produce flows of about 1 liter per second.
• Given the hydrological characteristics of the Montezuma Formation, it is not recommended to extract water from the wells for 24 hours straight. The recommended extraction time would be 12 hours straight maximum so that the wells can recuperate their water levels every day.
• The hydrological requirement of the daily human consumption for the development Live the Blue Dream Cabuya is 205,425 liters a day. This amount does not include the hydrological requirement for the watering of gardens and lawns which would be an additional 5 liters per square meter a day.
• The hydrological requirements or the project are satisfied with a daily flow of 2.37 liters per second. Assuming that the wells have an extraction potential of 1 liter per second, it would be necessary to have 4.7 wells with 12 hours of extraction each in order to satisfy the water needs of the development.

References

DENGO,G., 1962a: Estudio geológico de la región de Guanacaste, Costa Rica.- 112 págs. I.G.N., San José, Costa Rica

DENGO,G., 1962b: Tectonic-igneous sequence in Costa Rica.- En: ENGEL,A.E.J., JAMES,H.J. & LEONARD,B:F: (eds): A volume to honor A.F. Budington.-Geol. Soc.Amer.Spec.

Vol.:133-161.

DENYER, P., MONTERO, W. & ALVARADO, G.E., 2003: Atlas tectónico de Costa Rica.- 79 págs Editorial de la Universidad de Costa Rica Atlas 1 ed., San José, Costa Rica.

GURSKYK, H.J., 1989: Presencia y origen de rocas sedimentarias en el basamento

            Ofiolítico de Costa Rica.- Rev. Geol. Amér. Central, 10: 19-66.

HAUFF,F., HOWENLW, K., BOOGARD, v.d.,P., ALVARADO, G:E: & GARBE-SCHÖNDERBERG, D., 2000: Age and geochemistry of basaltic complexes in western Costa Rica: Contributions to the geotectonic evolution of Central America.-Geochem. Geophys. Geosystems [Revista electrónica]

INSTITUTO GEOGRAFICO NACIONAL, 1998: Hoja Cabuya No. 3144 I.-Escala 1: 50 000, I.G.N., San José.

MINISTERIO DE AMBIENTE Y ENERGIA, 2007: Inventario de nacientes, hojas Cerro Azul y

            Puerto Coyote.-San José.

SERVICIO NACIONAL DE AGUAS SUBTERRANEAS, RIEGO Y AVENAMIENTO, 1992: Mapa Hidrogeológico de la península de Nicoya, Costa Rica.- San José

SERVICIO NACIONAL DE AGUAS SUBTERRANEAS, RIEGO Y AVENAMIENTO, 2006: Inventario de pozos, hojas Cerro Azul y Puerto Coyote.- Oficina Central, San José.

SINTON, C:W., DUNCAN, R.A.: & DENYER, P., 1997: Nicoya peninsula: A single suite of Caribbean oceanic plateau magmas.-J. Geophysics. Res. 102 (B7): 15507-15520.

SERVICIO NACIONAL DE AGUAS SUBTERRANEAS, RIEGO Y AVENAMIENTO, 2006: Inventario de pozos, hoja Cabuya No. 3144 I.- Oficina Central, San José.

SPRECHMANN, P, 1984: Manual de Geología de Costa Rica.- Edit. Universidad de Costa Rica,

            San José, Costa Rica.