Resource Evaluation

La Gamba de Golfito, Costa Rica

For:  Isaac LeBourgeois

By:  Paul Collar

Osa Water Works, S.A.

September  19, 2008

View from Site 2 looking south at the mouth of Golfito Bay

Introduction

Osa Water Works was contracted to undertake a resource evaluation of a 179-hectare property located in the highlands between the small community of La Gamba and the port city of Golfito in Costa Rica’s Southern Zone.  The objectives of the field investigation were to identify options for water supply, alternative power generation, and waste management for the development of three home sites on the property and the possible development of a modest eco-lodge at one of the residential sites.  A site survey was undertaken on September 13, 2008.  This report summarizes the findings that were made.

Location and Methods

The property investigated is shown on the property map in Figure 1 and is largely comprised by the top and flanks of a mountain.  Access to the property is by an unimproved clay two-track from the town of La Gamba, passable by all-terrain vehicle.  Extensive road work is required to provide access by four-wheel-drive vehicles.

Field assessment was made by visual inspection and the determination of key elevations of building sites and stream drainages as well as distances separating them.  Elevations were determined using a Casio digital barometric altimeter, and geographic location was determined with a Garmin GPSmap 76Cx global positioning system.  Flow rates of streams were visually estimated.

Seasonality

The field inspection was undertaken during the rainy season.  For this reason the flow rates observed are not reflective of dry season conditions, which represent the base line upon which year-round conditions can be reliably predicated.  However, no rain had fallen on the two days prior to the field survey, and the streams inspected had no turbidity and were clearly constituted by base flow with no rainfall runoff contributing to flow.  All indications are that both of the streams observed are perennial and likely to flow at the locations visited during the dry season.  However, final confirmation of dry season hydrology will be essential for conclusive determination of year-round resource potential and for refinement of system design.

Facility Demands

Three building sites are under consideration for the development of residential homes for seasonal use by the ownership.  The onsite manager reports that the residences may be placed on the vacation rental market and that one site is being considered for the commercial operation of a few bungalows as a small eco-lodge.  Only two of the three sites were visited during the field investigation.  For purposes of this report, the sites are referred to as Sites 1 and 2, which correspond in the parlance of the ownership to Paul’s building site and the Rancho, respectively.  The third building site, the Pineapple lot, was not visited as part of this investigation.

FIGURE 1.  Property map showing the outline of the 180 hectare property that is the subject of this report and the location of Sites 1 and 2 described in detail in the body of this report.

The onsite manager reported that Sites 1 and 2 were in consideration for development, with a number of other possible locations on the property for possible development in the future.  The onsite manager reported that a number of bungalows is being considered for Site 2 for the operation of an eco-lodge.  For purposes of this report, it would appear reasonable to summarize expected demands from both a fully stocked residential development as well as a small eco-lodge.  In this manner the ownership will have some preliminary numbers with which to evaluate a wide variety of potential development plans, since the water and power requirements of one residence can be assumed representative of other houses presuming comparable distributions of appliances and occupancy rates. 

Water

Potable water demands are estimated in the United States on the basis of a daily per capita water demand of 100 gallons.  In practice, this is arguably twice as much as the average resident actually uses in Costa Rica.  For the sake of the analysis to follow, I have assumed a 75 gpd allocation for full time residential needs and a 50 gpd demand for eco-lodging.  This is an allocation to include all possible uses of water with the exception of irrigation of facility grounds.  Irrigation is an intensive water resource demand and must be determined based on the acreage to be irrigated and the type of plants and has not been factored in for this application.

If we assume a full time residential occupancy by four persons at Site 1, this corresponds to a potable water supply requirement of 300 gallons per day, which is equal to a full time flow rate of 0.21 gallons per minute.  This means that with adequate storage capacity, a continuous flow rate of a mere trickle of water (about one fifth of a faucet’s output) will satisfy the water demands of the household.

If we assume a peak lodging capacity of 12 guests in a hypothetical commercial installation at Site 2, this amounts to 600 gallons of daily potable water requirement, which is still less than one half of one gallon per minute, presuming adequate storage capacity.

Power

Table 1 summarizes the anticipated power demands of a well-anointed American style home.  The analysis includes neither air conditioning nor hot water, and all alternatives considered assume the use of 12-volt refrigeration because of its much greater economy than conventional 110V refrigerators.  Table 1.A assumes that all remaining appliances are powered by electricity, including those that involve a heating element, such as the stove, oven, and clothes dryer, all of which require 220V for operation.  This power option is referred to euphemistically as the “electric universe” option.  Table 1.B. assumes that the most power-consumptive appliances, including the stove, oven, and clothes dryer are powered by natural gas for the heating component.  This pattern of appliance deployment is referred to hereinafter as “hybrid household.” 

Table 1.   Estimation of power demands for a typical residential well-anointed home for Building Site 1.  A)  Electric universe includes full electrical power for all appliances except hot water;  B)  Hybrid household assumes that the stove, oven, and dryer are all heated by propane.

1. Electric Universe

2. Hybrid Household

For site 2, it would appear reasonable to presume that all the appliances assumed for Site 1 also apply, except for the water pressurization pump, since Site 2 is amenable to pressurization by gravity.  The power requirements for Site 2 were expanded to account for the increased facility power demands expected to result from commercial operation of a five-bungalow eco-lodge, most notably including the modest bungalow power requirements summarized in Table 2 and additional cooking and laundering needs.  Table 3 summarizes the expanded electrical demand from these considerations, again divided between an electric universe (Table 3.A.) and hybrid commercial (Table 3.B.) model

TABLE 2.  Estimated power demands for each bungalow separately, and all five together.

TABLE 3. Estimation of power demands for a residential, well-anointed home for Building Site 2, with increased cooking and laundry duties to satisfy a support role for a commercial eco-lodge.

A)  Electric universe includes full electrical power for all appliances except hot water.

B)  Hybrid commercial  assumes that the stove, oven, and dryer are all heated by propane.

The analysis reveals that for a hybrid commercial model dependent upon propane for cooking, clothes drying, and hot water, a daily charging source of around 13 kilowatt-hours are required.  For the electric universe residential model, the expected charging source required to fully power the hypothetical home is 39 kw-hours.  If we add the expected power demands at peak occupancy for five bungalows (summarized in Table 2) to the power demand estimated for the residence described above, we derive a required charging source of 24 kw-hours for a hybrid commercial facility and 50 kw-hours for an electric universe model.

Waste Management

Sewage management is most practically undertaken through conventional two-celled septic tanks, sized according to anticipated occupancy rates.  The location of all building sites on elevated portions of the property suggests that there is unlikely to be any hydraulic limitations in the waste assimilative properties of the soils.  Likely decisions that will bear upon the final design relate to Site 2, where the possibility exists that bungalows may be deployed in addition to a main residence.  In most cases it will likely be most reasonable to use small individual systems for each of the cabins, though larger shared septic tanks and leach fields can be used if bungalows are not greatly separated.

Solid waste will be divisible into the following categories:  1)  organic kitchen;  2)  paper/cardboard;  3)  organic lawn and gardening clippings;  3)  plastics;  4)  glass;  5)  aluminum;  and 6)  non-aluminum metals.  The last four of these may be kept in separate bins and periodically carried offsite for recycling.  Paper and cardboard may be periodically burned.  Organic kitchen waste is best distributed for chicken feed, and what is not consumed by the chickens may be composted alongside chicken droppings, lawn clippings, and ash from burned paper, turned periodically for proper aeration, and used upon completion of composting (3-6 month turnover) as fertilizer and soil conditioner for fruit trees and a kitchen garden.  Composting should be undertaken above ground in segmented compost troughs to make sure the material is never saturated with ground water and must be turned regularly to encourage a healthy aerobic bacterial assemblage to degrade the waste.

Field Survey

Figure 2 shows a topographic map of the area, superimposed by the outline of the property boundary as defined on the property map, superimposed by the best fit that I could achieve of the field track of what was undertaken during the field survey.

FIGURE 2.  Site map showing the topographic quadrangle as a base, overlain by the outline of the property boundaries as defined by the property map, overlain by the GPS field track of sites visited during the field investigation.

Sites 1 and 2 are both located on high points of the property, well above naturally occurring water sources (other than rainfall).

As Figure 2 reveals, the stream that is located adjacent to Site 1 is very near the boundary of the property.  This area is a plateau on the shoulder of the mountain, and as the topographic map reveals does not have much relief until beyond the property boundaries.  Even though a flow rate of over 100 gpm was observed at the time of the field survey, it is unlikely that sufficient relief is present within the property boundaries to develop a robust self-standing hydroelectric facility to power the residential Site 1, at least without straying onto the adjacent property.  Not only does the available relief limit what can be done at this location, the amount of water that flows during the dry season remains unknown and may also present a limitation, even if the 75 feet of estimated available head is in fact present within the property boundaries.

The stream located at Site 2, however, has at least twice as much flow as the first stream, and unlike the stream at Site 1, has an estimated 180 meters of vertical relief within the property boundaries.  An estimated flow rate of 250 gpm was observed at the time of the field survey.  Across the entire relief available, this flow rate amounts to a dramatic hydroelectric potential of 13.3 kilowatts, or 318 kilowatt-hours per day, fully 6 times the amount required for even the electric universe model for full electrification of a commercial installation at Site 2.

However, for environmental sustainability, not all the water can be taken, and furthermore, dry season flow rates remain unknown at this time and must be determined in advance of settling on a final penstock diversion flow rate.  Nevertheless, an abundance of seeps and springs located in the stream channel itself makes it possible to divert as much as 75% of actual base flow at any location without any harm to the environment.  Typical recharge of rivers by springs and seeps similar to the stream in question normally creates a doubling of stream flow every 200 meters or so downstream, so that water diverted at one point is nearly always replenished within a short distance by the watershed itself.  All of the water used for hydroelectric power is returned to the stream at the point of power generation anyway, so the water that is used is not removed from the watershed but simply diverted for the length of the penstock.

Because there is in essence an unlimited amount of relief available for the Site 2 hydroelectric development, the design process appropriate for Site 2 is to define what is required by the facility, to confirm the amount of water diversion possible at the driest time of the year, and to calculate the length of pipeline and elevation drop required to achieve the needed power.

Potable Water Supply

Since both building sites are located at an elevation that precludes the possibility of gravity water supply to either, there are five alternatives available for potable water supply to both Sites One and Two, most of which require an energetic investment.  These alternatives are discussed below.

1)     Deep well.  A deep well is out of the question until the road is vastly improved owing to the impossibility of getting a rig up on the mountain.  At a rate of $200 per drilled meter and a minimum likely depth of 50 meters, the capital cost of $10,000 for this alternative is only the beginning of a bad idea.  A submersible pump to raise the water to the surface is expected to be a dramatic power sink.  Nevertheless, this is an alternative nearly certain to provide consistent water year round.   This water would likely not require any treatment to ensure potability but might have high hardness and could possibly contain objectionable quantities of iron and manganese, which cannot be easily removed from water.

2)     Shallow well.  It is likely that a shallow hand-dug well will provide the water supply required, though this cannot be guaranteed and would need to be undertaken to prove it out one way or the other.  Nevertheless it is likely that this would be viable, but similar to the first alternative, this would require a continuous investment in energy to pressurize a home or would require pumping to an elevated storage tank to provide gravity home pressurization.  This water would likely not require any treatment to ensure potability but would be more vulnerable to accidental contamination than a deep well.  It would be unlikely to have high hardness or iron/manganese contamination. 

3)     Spring water capture.  A year-round spring could be easily isolated from the watershed adjacent to both Sites 1 and 2.  Such a water source would not require any treatment to ensure potability, but would require power to pump the water to an elevation where it could provide gravity home pressurization.  The water could possibly have carbonate (calcium and magnesium) and mineral (iron and manganese) hardness issues.

4)     Stream water capture.  A hydraulic pump would be able to provide energy-free delivery of stream water to a water tank positioned high enough to provide gravity flow for residential or commercial purposes, either to a tower-based pressure tank for Site 1 or a land-based tank for Site 2 near the existing gate (Figure 2).  This alternative would absolutely require ultraviolet disinfection to ensure potability.

5)     Rainfall capture.  The most environmentally sustainable alternative, rainfall capture, is unquestionably viable for both residential and commercial usage.  However, since water is captured from roofs and typically stored in buried storage tanks, this alternative requires energy investment for in situ home pressurization or for pumping to a gravity tank on either a tower or a higher land surface.  This alternative also requires a disinfection system, either an ultraviolet home-purification system, or a sodium-hypochlorite based tank-disinfection system.

Of these alternatives, it would appear that the most practical is some combination of ram pump delivery and rainfall capture.

For Site 2, the mountain slope behind the building site offers a nearby land surface with adequate elevation to provide gravity feed water supply to the building site.  Incidentally, since this is the highest portion of the property, a water tank located here is likely to provide water distribution alternatives to other possible building sites on the property as well.  This is not the case at Site 1, where the ownership will need to weigh the alternatives of deploying a tower and water tank to provide low-pressure gravity feed to the house versus a simple buried capture tank that is pressurized using a pressure pump/tank assemblage and powered by alternative energy. 

Rainfall capture, while highly attractive from an environmental perspective, is a capitally intensive alternative.  The key design variable for such a system is the storage capacity of the holding tank, since it must provide water supply during the dry season.  While climate change is causing rains to punctuate the dry season more than ever before and La Gamba is a notoriously rainy area anyway, primary dependence upon rainfall presupposes a tank of at least ten thousand gallons presuming a full-time occupancy of four persons, preferably more for complete security.  The final size of the tank will vary as a function of the following factors:  1)  peak occupancy;  2)  the frequency of rains during the driest time of year;  3)  the ability to depend upon alternative sources of water; and 4)  owner preferences and budget.

Both streams visited would appear capable of easily supplying potable water supply needs using a ram pump.  However, until dry season stream flow distributions are quantified, it is not possible to reach such a conclusion unequivocally.  Figure 3 shows a design layout for a ram pump system for Site 1, which presumes an in situ home pressurization system made possible with a centrifugal pump and pressure tank.  Figure 4 shows the same thing for Site 2, presuming that residential pressurization is achieved by gravity from a pressure tank located uphill from the Site 2 facility.  In both cases a driveline of 15 meters of vertical relief is shown in the diagrams, though this is considerably over-designed and in fact, drivelines could be as little as six meters for both applications, since they both require a lift of around 60 meters.

Power Supply

Wind resources are essentially negligible in most parts of the southern Pacific coastal reaches of Costa Rica.  A sustained wind speed of 12 mph is typically required to provide a reasonable return on investment from wind power capitalization.  During the field survey, no breeze was felt even at the top of the property, and this is somewhat in standing with surprising findings that I have made across the region.  Wind power is rarely practical as an alternative power supply in this region.

Solar power on the other hand is a steady and reliable source of alternative energy.  Because of the region’s location only slightly more than eight degrees north of the Equator, the hours of daylight have little variation during the year.  While there is less sun during the rainy season, there is normally enough sun year round to be able to base designs on an average eight-hour solar day.  Solar power is clearly an alternative for the property in question.

FIGURE 3.  Conceptual design for a ram-pump / pressure pump/tank tank based water supply system for Site 1.

FIGURE 4.  Conceptual design for a ram-pump / gravity pressure tank based water supply system for site 2.

Micro-hydroelectric is a promising alternative energy source for those properties possessing both adequate flow rates in existing perennial streams in combination with adequate relief across the reaches of such streams.  Hydroelectric power generation is clearly an attractive alternative for electrification of portions of the property in question.

Fossil fuel power generation is commonly the least capitally-intensive alternative for supplying power to remote locations.  However, at one gallon of fuel per hour of generator operation, a cursory accounting of anticipated operating costs quickly reveals that the costs of fossil-fuel power generation exceed any other alternative over any but the shortest of time frames.  Additional negatives associated with this alternative include:  1)  the aesthetic negative of the sound of a generator;  2)  the attendant need to continually transport fuel to the property;  and 3)  fossil fuel power generation introduces carbon dioxide into the atmosphere, directly contributing to global warming, making it an environmentally unsustainable practice.

Grid Connection is the first line of facility electrification for most facilities that are not located too far distant from the grid.  Current costs for extending grid power are approximately $15,000 per kilometer plus the roughly $3000 cost of a transformer.  While this alternative is commonly less capital intensive than solar or hydroelectric development—except for remote locations—this represents a more costly alternative on mid-term and certainly long-term time frames owing to monthly power bills and is furthermore compromised as an ideal alternative by frequent power outages, particularly where power lines pass through forests in which falling branches often down lines.  Installation of power lines and connection to the grid requires an access road that can be transited at a minimum by a four-wheel-drive vehicle.

Site 1

It may be possible to provide much of the energetic requirements of Site 1 by hydroelectric power.  However, as discussed earlier, it appears that the most reasonable location for a water intake is too close to the property boundary to achieve the head necessary for robust hydroelectric development.  While it may be possible even in that case to put together a hybrid system, I have compiled a solar system design for Site 1, predicated on the power demands anticipated by Table 1. 

Electric Universe.  Using the contemporary 224-watt solar panels and an average solar day of eight hours, the charging source required for the electric universe model of power supply defined in Table 1 amounts to 14 panels attenuated with two charge controllers.  A battery bank of 750 amp-hour capacity represents the baseline storage requirement, and additional capacity is certainly desirable, given that power during two thirds of every day depends implicitly upon the battery bank as much or arguably more than any other system component.  Anticipated solar power system costs for both electric universe (A) and hybrid household (B) are estimated in the Table 4. 

TABLE 4.  Site 1 solar power supply estimated installation budgets.

(A)  Electric Universe

(B)    Hybrid household

Site 2

It is certain that Site 2 can be powered completely by hydroelectric power.  It will necessarily require a dry season assessment, however, before determining the precise configuration of the system.  Nevertheless, I have assumed a summertime flow rate of one half that observed during the field investigation and assume a diversion of 75% of that flow for the purposes of this discussion.  This amounts to a total hydroelectric flow rate of around 95 gpm.  The water intake for the hydroelectric penstock would most logically be located immediately beneath the location of a hypothetical ram pump in order to capture the 90% water waste rate generated by the ram pump.

If we assume the electric universe model of facility electrification and the appliance distribution described in Table 2, this means that a charging source of 50 kilowatt-hours, or 2.08 kilowatts continuous (i.e. per hour) is required to supply the needed power demands.  Hydroelectric generation potential is defined by equation (1).

P =  Q  x  H  x  0.18  x  e                                     (1)

where P = power in watts, Q = flow rate in gallons per minute, H = vertical relief (or head) measured in feet, 0.18 is a units conversion coefficient, and e is the efficiency of the turbine.  For micro-hydroelectric turbines, an efficiency of 50% can be assumed.  For mini-hydroelectric applications the efficiency is higher, typically around 65%.

By solving Equation (1) backward for head using a continuous power demand of 2080 watts and a flow rate of 95 gpm, we determine that a head of 243 feet is required.  With a land slope of about 1:5 rise to run, this implies a pipeline length of 1215 feet.  A three-inch pipeline with 95 gpm generates head losses of 2.2 feet per 100 feet of pipeline, or 27 feet total friction loss, so the preliminary design would suggest that this additional head be added, increasing the pipeline length by 135 feet to a total projected design length of 1350 feet. 

A 3.5 kilowatt induction hydroelectric generator provides for 480V output that can be transmitted the approximately 1600 feet to Site 2 through number 4 cable with line losses of less than 1 percent.  Final components include four 3.6 kilowatt 24-volt Outback inverters stacked to provide a capacity of 7.2 kilowatts at 220 volts or 14.4 kilowatts at 110 Volts.  This provides for 3.2 kilowatts of supplemental power capacity while the most power-consumptive appliance of all—the clothes dryer—is on.  For this system a minimum of 750 amp-hour battery capacity is required.  I recommend Mastervolt 2-volt cells for this duty, though less expensive 6-volt batteries can also be used to reduce the capital costs though at the sacrifice of a reduced battery-bank life expectancy.   

Table 5 summarizes a cost estimate for such a power supply system.  For a hybrid household system, the same quality of components would carry an estimated cost as summarized in Table 6, though for reduced capacity, the design analysis has been omitted to spare the reader the redundancy.  Less expensive batteries have been included in the Table 6 hybrid estimate to demonstrate the capital savings possible in less expensive but less long-lasting batteries.  There is no room for sacrifice in any of the other components.

Table 5.  Electric universe hydroelectric installation estimate for Site 2

 .

Table 6.  Hybrid household hydroelectric installation estimate for Site 2.

An overall power and water layout and preliminary design for Site 2 is shown in Figure 5.  While it is expected that this will closely approximate what is practical and viable, it will be necessary to confirm flow rates during the dry season to ensure that the system provides for year round reliable performance.  

FIGURE 5.  Proposed layout of water and power system for site 2, based on one half the water flow rate observed at the time of the field survey and “electric universe” power supply for a residential/commercial installation consisting of a well-anointed American-style household and five modest bungalows with only light and fan powering requirements.

For ram pump installations at Sites 1 and 2 and for penstock hydroelectric water supply, this report has repeatedly invoked the use of “infiltration galleries” as water intakes.  These are proprietary Osa Water Works black-magic water intakes that in most cases do not require maintenance for years on end.  They consist of buried installations that are for all practical purposes undetectable to an untrained eye.  I am including schematics in Figure 6 to provide greater insight into how these work.  Osa Water Works has thirty or so of these intakes installed country-wide and providing consistent and ecologically friendly water supply for both potable water applications as well as for hydroelectric water intakes.

Conclusion

Based on the wet season site survey undertaken, it is clear that year round hydroelectric power generation will be possible for Site 2.  It is also apparent that potable water supply can be provided for both Sites 1 and 2 using energy-free hydraulic ram pumps.  It is likely that Site 1 will not be amenable to hydroelectric power generation because the required intake location is very near the property boundary, and it is doubtful that adequate relief and flow rate is contained within the property boundaries to adequately develop hydroelectric resources at this location.

A dry season site survey is required, however, to determine precise flow rates at the driest time of the year in order to confirm the design required for both ram pumping as well as for the hydroelectric system sizing for Site 2.  The system designs presented in this report are nevertheless expected to closely approximate what will be possible, and a dry season visit is expected to resolve details in pipe sizing and precise intake locations but is not expected to dramatically impact the findings presented.

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