Ola Ballena Infrastructure
and Cabina Installations
Recommendations and Installations Proposal
For: [--redacted--]
By: Osa Water Works and Osa-Agg
October 12, 2002
1.0 Introduction
A site survey of the property destined for development as Ola Ballena was undertaken on November 10, 2002 by Paul Clift and Paul Collar of Osa Water Works and Osa-Agg, David Rice of Osa Water Works and Sistema Solar Internacional, and Felipe Calderón of Paradoxe. The objective of the survey was to determine the best alternatives for the development of potable water supply, waste management, and for the installation of footers for the planned construction of four beachside bungalows. This document summarizes findings made on site and recommendations for the development and installation of the desired infrastructure.
2.0 Findings
2.1 Drainage and Rainfall Runoff Control
The single largest challenge facing the development of a viable tourism development infrastructure is the marshy nature of the flat portion of the property. The boggy land poses several complications from both a development perspective as well as for tourist comfort once the infrastructure is in place. Relevant issues are enumerated below.
1) Construction. Whereas the existing architectural design that calls for concrete pilings to serve as bungalow footers is certainly viable, this alternative is very expensive and not indispensable for the successful construction of the facilities that have been designed.
2) Waste Management. Conventional septic design is not applicable to water-saturated soils.
3) Access and Development Complications. The existence of the marshy bog complicates the delivery of construction materials and the utility of heavy equipment, specifically the pilings driver and dump trucks.
4) Mosquitoes. Marshy areas are breeding grounds for mosquitoes, which in this latitude are vectors for both malaria and dengue fever.
5) Aesthetics. A marshy yard area for the bungalows under planning may not be the most appropriate for the use intended.
2.2 Water Supply
The abundance of near surface ground water is a strong indication that a well can be constructed that will provide all the water necessary for the tourism project planned. Although well yield cannot be accurately predicted in the absence of additional subsurface and regional hydrologic information, it is almost certain that the ground water that can be pumped from a well will provide all the water necessary for existing plans as well as future expansion.
Water pressure for the facilities can be provided by either a central pressure tank or by locating the tank at a higher elevation. The relief between the highway and the anticipated water service elevation of the cabinas is only about 50 feet, which can provide water delivery pressures in the range of 18-20 psi. This is about half of the standard recommended domestic pressure of 40 psi that is employed in municipal water supplies in industrialized societies. Whereas a pressure of 40 psi can be obtained through the fabrication and installation of a 50-foot water tower on the edge of the highway, the higher pressure is not necessary for full facility functionality and boils down to owner preference. As a point of reference, the water pressure provided in the town of Puerto Jimenez is only 12 psi. For bungalows, even for a restaurant, a pressure of 40 psi is by no means required. A lesser pressure simply means that shower water, garden hoses, etc., will not have the force to which a first-world foreign national might be accustomed.
2.3 Waste Management
Deployment of a septic system is not feasible in the flat portion of the property owing to high ground water levels. However, the sloping upper portion of the property just below the proposed parking area is amenable to the installation of a septic tank and the corresponding leach field. One complication of this configuration is that it cannot be powered by gravity pressure. Therefore, a centralized sump and a sump pump will be necessary for transfer of accumulated waste to the slope-based septic tank and leach field. The alternative waste-management practices of a mounded septic system and constructed wetland are not practical owing to the small size of the property. The alternative of a package treatment facility is unattractive due to the high capital and operating expenses.
2.4 Electricity
Aside from the bogginess of the flatland, the single greatest challenge to the optimal development of the property is the supply of electricity. Both water supply and waste management depend upon the use of pumps. In the absence of grid power supply by the domestic utility company, ICE, the only viable alternative for provision of power is a solar-power system with a backup generator, or a stand-alone generator. Deployment of a robust solar system would represent a substantial capital investment, particularly if grid electricity is extended in the near future to the vicinity of the property, enabling connection to the grid. An appropriately-sized (15 kW) generator would be capable of supplying all the energy required until ICE grid power is provided to the area but would require the construction of a generator storage facility with buried exhaust and intake pipes to minimize noise.
3.0 Recommendations
3.1 Drainage and Fill
The most important development for the long-term success of both the infrastructure development and the commercial attractiveness of the project is the application of drainage and fill to the flat portions of the property.
The drainage ditch that has already been planned is an integral part of the drainage solution for the property. However, additional drainage control mechanisms to optimize drainage efficiency include the development of correct slopes for drainage to the central swale (using a bulldozer) and for the inclusion of subsurface French drains that are deployed in an orientation perpendicular to the central drainage swale as shown in Figure 1. These supplementary drainage ditches can be installed in such a way that they shall remain buried and never visible, with the drainage discharge emptying into the central drainage channel.
Subsequent to the installation of drainage infrastructure and slope-smoothing, we recommend the placement of a thickness of up to 15 inches of compacted coarse sand and gravel to raise the ground level and the addition of 4-6 inches of topsoil above. It is likely that material accumulated during slope grooming can be used for placement atop the sand and gravel fill to minimize the cost of topsoil acquisition.
Figure 1. Existing and proposed drainage of the flatland portion of the Ola Ballena property.
3.2 Footers
The placement of fill in the flat portion of the property enables the deployment of a footer design that does not depend upon pilings. This “floating footer” design is an ancient technology employed by the Incas as a protection against earthquake damage to the structures constructed during that imperial reign. It is a footer design that is used by Osa-Agg for seaside construction in loosely consolidated soils. Our analysis indicates that only the three shaded footers shown in Figure 2 and that the one originally planned for the center is not necessary for support of the structures planned
Figure 2 is a plan view of the footer distribution for each bungalow. The shaded circles represent the areal extent of each floating footer. Osa-Agg proposes the use of 16” I-beams for the horizontal support beams, 40 cm diameter concrete support columns and a circular outer linnel of reinforced concrete, and the bid reflects these recommendations. Figure 3 is a cross-sectional view showing the relevant details of the construction design.
Figure 2. Floating footers (plan view).
Figure 3. Floating Footers (cross-sectional view).
The design is a robust alternative to driven pilings. It provides a buried, footer base comprised of large boulders compacted with a vibrating compactor. Each column rising from the floating footer base is tied into each of the other columns by buried concrete ties. The net design ensures that no single column can be influenced by variability in subsurface consistency. Because of the columnar ties differential subsidence is not possible. Resistance to vertical subsidence is provided by the surface area of the floating footer bases (total of 6.62 square meters per bungalow). Additional resistance to subsidence is achieved by the fact that the floating footer cobbles are all driven into the subsoil using a vibrating compactor.
On the basis of our experience, the proposed footer configuration is more than adequate for the relatively small load posed by the bungalows. A substantial advantage to this alternative is in the cost, which would be less than half the cost of pre-forming and driving concrete pilings.
3.3 Water Supply
It is probable that all portions of the flat part of the property will enable the development of a high-yield well. The only practical consideration for well positioning is that the well be sufficiently distant from the septic system so as to be free of impact by contaminants introduced into the subsurface by the leach field. On the basis of the most reasonable site for a septic leach field (shown in Figure 4), we have proposed the positioning of the well on the opposite side of the property as shown in the same Figure.
Figure 4. Potable water and waste management elements.
In the absence of detailed information concerning the hydrologic characteristics of the property during the dry summer months, it is advisable that this well be dug as deeply as possible. In practical terms, this corresponds to a depth of up to 8 meters or until the depth achieves a well yield of 25 gpm, whichever comes first. On the basis of the hydrologic character of the location proposed for positioning the well, it is likely that this yield rate will be achieved within six meters of the surface.
Upon the completion and development of the well, it is recommended that a water quality sample be collected and submitted for analysis by the Acueductos y Alcantarillados-certified OWW analytical associate firm, Laboratorios Aqylasa, located in San Jose. It may be advisable to transport a portable water purification system to the well site and to collect a second sample that is processed by the filtration system. In this manner, if the well contains detectable fecal coliform bacteria, the second sample will immediately corroborate the water treatment alternative proposed for the system so that permit issuance will not be delayed by the need for follow-up testing of the filtration system, a stipulation of the ICT construction permit. Whereas a comprehensive water quality analysis should be undertaken of the raw water sample, only bacteriological water quality need be analyzed from the treated water quality sample.
Depending on the yield of the well, it is probable that a 1000-gallon water storage tank will provide all the storage needed for routine operation. Only if the well yield is very low will a larger-sized tank be needed. As a point of reference, let us assume a demand based on a maximum occupancy of 24 people and a very liberal daily consumption rate of 100 gallons per person, which corresponds to a 24-hour sustained well yield requirement of 1.6 gallons per minute, or across a 16-hour usage day of 2.5 gpm. We anticipate a well yield in excess of 10 gpm under the driest of conditions. For consideration of peak usage, if we assume that all 24 residents take a shower at the same time and each shower has a duration of 5 minutes, this represents a total consumption of about 600 gallons of water, which at a well yield of 10 gpm would take one hour to replace. This is an exaggerated assumption, but serves to illustrate that storage greater than 1000 gallons is in excess of anticipated requirements for routine usage assuming 12 cabins. If large irrigation demands are required, then additional water storage can be added at that time.
As mentioned in an earlier section of this document, bungalow water pressures of 18-20 psi will be obtained by placing the water tank at ground level on the part of the property near the highway. Additional pressure can be obtained proportional to the height of the tower used as the base for the water storage tank. To obtain the ideal pressure of 40 psi, a steel tower 50 feet in height would be needed. We emphasize that elevation of this water tank to achieve the higher pressure is strictly a user-preference decision, since all routine water utilization activities can be undertaken perfectly well at a delivery pressure of 18 psi, and even lower for that matter.
3.4 Electricity
It is very difficult to depend upon ICE to install power lines according to any anticipated time schedule. Nevertheless, it appears likely that completion of the power lines will be achieved in the relatively near future (3-12 months). Since all power requirements during construction can be provided by generator, it does not appear reasonable to plan for a comprehensive solar power system to provide electricity in the interim on the basis of the relatively large capital outlay that would be required. It appears most reasonable to plan for construction activities to be dependent upon a diesel-powered 15 kW/hour generator. If, upon completion, power lines have still not been installed, then the owners can make a decision about the acquisition and installation of a solar-power system, which requires a generator backup anyway. It is likely that the most economically favorable alternative in this circumstance is the construction of a small generator housing equipped with sound-protection. In this manner, the facility can be powered by generator until ICE completes the power line and transformer installations necessary to close the 10 km gap in electrical power provision along the Costanera highway.
3.5 Waste Management
The location proposed for the septic tank and leach field is shown in Figure 4. A centralized sump is required for the initial collection of raw wastewater, and the location proposed for this mostly subsurface tank is also shown in Figure 4. Transfer to the actual subsurface septic tank will be accomplished with a sump pump. Four-inch diameter PVC pipe will be buried. A conceptual design of the entire waste management system is shown in Figure 4, and the design of the individual structures is shown in Figure 5.
4.0 Time Frame
We recommend that the well and a highway-ground-level 1000-gallon storage tank be installed immediately and that the water-quality testing be undertaken upon well completion to expedite the permit application process. Upon the acquisition of the building permit, the order of work remaining should be undertaken as follows.
1) Drainage ditch and slope grooming (1 week). This will require a bulldozer to cut a swale for property drainage and for the sloping of ground surfaces. A temporary access road will also be cut to allow for access by dump trucks for subsequent fill placement. Also, the parking lot area can be prepared. Removed soil will be stored for subsequent distribution atop property fill.
2) Installation of transverse French drains for drainage of property areas on the sides of the central swale (2 weeks).
3) Installation of septic system, including sump, transfer pipes, septic tank, and leach field. Construction of a temporary outhouse to be located on top of the septic tank (4 weeks)
4) Installation of water and power distribution lines (2 weeks)
5) Gravel the parking lot, access road, and lay, smooth, and compact fill on the flat portion of the property (1 week).
6) Floating footer construction (1 month).
7) Construction of Column, Beams, and Slab (3 months).
