Water, Power, and Waste Planning :  Bosque Verde private reserve

Nosara, Guanacaste, Costa Rica

For:  Julio Batista

By:  Paul Collar

Osa Water Works, S.A.

January 1, 2009

Pacific Ocean view from building site at Bosque Verde.

INTRODUCTION AND SETTING

Bosque Verde is a private residential reserve on 114 hectares of primary and secondary forest in the mountains overlooking the Pacific Ocean near Nosara in the Nicoya Peninsula, Guanacaste, Costa Rica.  The project comprises 75 distinct residential lots, averaging over an acre in size and most having Pacific Ocean views, many of them spectacular.  Approximately 70 hectares of the entire tract has been set aside as a forested wildlife preserve, protected in perpetuity in conservation and accessible only to Bosque Verde homeowners and their guests, a private parkland that includes three waterfalls and a variety of hiking trails. 

The Bosque Verde project infrastructure is comprehensive and well-conceived.  A well-engineered, drained, and built network of well-maintained roads provides access to the lots and two points of access to public roads, the primary entrance where the guardhouse is located, and a locked back entrance to a separate public road, a gate through which only Bosque Verde owners have access.  The entire project is electrified with ICE grid power.  Potable water is provided by a well located at the lowest level of the property and a series of three tanks moving up the mountain step-wise with about 100 meters of relief between each tank.  Water distribution to home sites is undertaken from the uppermost two tanks to provide optimal pressure to lots that vary in elevation along on the sloping land surface.  A calcium hypochlorite tablet chlorination system is deployed to ensure potability.  An array of fire hydrants is strategically located along the main roads for fire protection, and slope stability is enhanced with orderly gabions filled with white limestone quarried in the nearby Santa Cruz vicinity.   At the time of this writing, two houses had been completed, two more were under construction, a fifth was in planning.  The guardhouse and property manager’s house were also under construction. 

OBJECTIVES

Osa Water Works was hired to undertake a resource evaluation of the Bosque Verde gated community with the following specific objectives targeted:

1.         Determine viability of using hydroelectric power to offset maintenance and operational costs.

2.         Evaluation of surface water resources for expansion of potable water supply

3.         Evaluation of water harvesting options for irrigation water during dry season months.

4.         Assessment of waste management alternatives.

5.         Internet and telecommunications alternatives.

6.         Recommendations for the adoption of green engineering, eco-friendly, and environmentally sustainable infrastructural and operational alternatives for continuing development efforts.

METHODS

A field assessment was undertaken on December 10, 2008 in the company of the project owner and the facility manager.  Roads were transited during the site survey, and the water installations and other key elements of the property infrastructure were visited.  A large-scale topographic map of the property was used for estimation of elevations.  A Garmin GPSmap 76C global positioning system was used for determining location while onsite.  During the field survey and also during analysis it became clear that the objectives of this report related every bit as much to individual lot owners as to overall project management and on both different scales and contexts.  So, this report is intended to provide insight into the stated objectives for both the overall project and for individual lot owners as well.  All design calculations and recommendations were undertaken with conservative estimations and safety margins as appropriate.  Best engineering and management design principles were employed in the recommendations and observations made, unless otherwise noted.

FIELD AREA

The location of Bosque Verde is outlined in red on a copy of the Garza quadrangle in Figure 1.

the quadrangle contours.  In Figure 3, the property transit undertaken by car and on foot during the field survey is shown as a transparent overlay on top of the project map.  An index to the waypoints labeled on Figure 3 is given as Appendix 1.

POTABLE WATER SUPPLY

Bosque Verde contains 75 lots, all of which are expected to eventually accommodate luxurious to opulent American-style homes for seasonal and full-time occupancy.  Whereas the seasonal nature of occupancy makes projections tenuous, the double-use of second homes as vacation rentals invites the assumption that upon final project completion, it may be reasonable to expect eventually complete occupancy during the peak months December through April, the driest times of the year.  If we assume six full-time residents per lot and a water allocation of 100 gpd per person, peak occupancy presumes a daily water demand of 45,000 gallons, which is equivalent to a continuous flow rate of 31 gpm. 

A pump test (Aquaambiente, 2002, written report) reported a well yield for the 30-meter well of 3 lps, sustainable for eighteen hours per day.  The pump test report recommended (oddly) that two hours of well recovery be allowed in every eight hour pumping period.  The overall water system engineer doubled the recommended recovery time, specifying that the 3 lps extraction rate not exceed 16 hours in every 24 of routine operations.  There is no explanation of the discrepancy, and the raw data would suggest that the extraction rate is sustainable around the clock, at least in the rainy season, at the time of the pump test (June).  For the purposes of this report, a sixteen-hour per day extraction of 3 lps is assumed to represent the well yield.  And 3 lps is equal to 47.6 gpm.  Across 18 hours, this amounts to 51,428 gallons, which normalized for the 24 hour diurnal cycle suggests that the well’s actual yield is 35.7 gpm, which provides for peak facility occupancy demands with 13% to spare. 

The allocation of 100 gpd per person is a traditional standard for US municipal water supply design and represents potable and residential water use only, to include pool makeup water.  Significantly, this design criterion does not include any provision for irrigation beyond the needs of indoor potted plants.

Having established the adequacy of the water supply for anticipated occupancy patterns, let us now test the adequacy of the storage volume that is already built into the system.  In order to do this, let us invoke a rudimentary water usage model consisting of two states that evenly divide the day, defined as follows:  1)  daytime, during which all water is assumed to be used;  and 2)  nighttime, during which no water is assumed to be used.  Admittedly this is a simplistic assumption but arguably adequate for a preliminary assessment of storage capacity design.

Since Tank 1 is used for re-pumping and does not comprise the operating storage capacity of the system, the effective storage capacity consists of what is provided by tanks 2 and 3, which have volumes 30,000 and 50,000 liters, respectively, for a combined volume of 21,000 gallons. 

According to the two-state usage model proposed above, the 24,000 daily water demand calculated for peak occupancy is consumed during the day, which presumes a continuous water consumption rate of 33 gpm.  Since the well yield exceeds this use requirement, it is apparent that the storage capacity is indeed adequate to provide potable water at the peak facility capacity of 450 onsite residents.  The operational model presumes, implicitly, that the pump sets provide effective delivery of 35 gpm continuously to Tanks 2 and 3.  Even if the effective pump delivery is less, the storage capacity appears adequate.  For instance, at an effective pumping delivery rate of 20 gpm, this means that only 11 gpm would have to be abstracted for storage during the day to satisfy the demand.  This deficit adds up to 7,920 gallons, less than half the storage capacity provided.

While the existing well yield and storage capacity are indeed designed to provide for peak facility occupancy, there is no margin for error.  Continued use of water at peak facility capacity following failure of a single one of the three pumps would cause depletion of water supply in less than 24 hours.  While peak capacity likely remains in the future, the fact that the system is finite and naturally subject to equipment failure interruptions, particularly at peak occupancy, carries implications for both the overall project management as well as at the level of the individual property owner:

1)        Backup pump.  At least one backup pump should be maintained on hand to enable rapid changeover in the event of a pump failure.  Traditional American-style residential systems with redundancy factored in would ideally have two pumps in each tank to divide the duty, rather than a single pump, a practice which extends the life of both pumps and provides uninterrupted service in the event of a failure of one of the pumps in either of the tanks.

2)        Independent home storage.  For homeowners, it is relatively inexpensive to include a water storage tank and secondary pressurization system to provide for emergency water supply or to make it acceptable to exceed water allocation limits corresponding to strictly potable use, at least within bounds.  In fact, for those homeowners electing to include storage tanks to extend their water usage permissions, it may be advisable to boost home systems additionally to provide for rainfall capture to optimize water usage versatility, leaving facility for backup and during hard times. 

3)        Rainfall capture.  Figure 4 is a conceptual diagram illustrating key components of a rainfall-capture system.  In effect the same system can be designed to provide simply supplemental storage, with the only difference being a reduction in the size of the storage tank and a connection to the facility water supply actuated by a float valve. 

IRRIGATION WATER SUPPLY

Lawn and garden irrigation requires much more water than is typically required for even high occupancy domestic needs.  Irrigation criteria used for the Costa Rican dry season to support lawns and ornamentals call for 5 mm of daily application.  For a one-hectare lawn, this amounts to 50,000 liters of water per day, the same as 9.2 gallons per minute of continuous flow.  If we divide the 35 gpm well yield among the 75 lots evenly, this means that each home would be able to irrigate 500 square meters (a little more than one tenth an acre) with none left over for residential water demand. 

Figure 4.  Conceptual design of a rainfall capture domestic water supply system augmented by a municipal water supply line. 

In practice the tolerance of irrigation in residential developments is a self-nourishing loop that can spiral out of control and lead to unwelcome policy changes that are arguably best made and enforced in advance of the eventual water shortfalls if irrigation is not controlled in some way.  While it is reasonable to give an Owner’s Association a series of recommendations for economy in irrigation, the only way to limit its abuse is to charge for the water.  And there is a very simple, environmentally friendly avenue to supply as much irrigation water as residents are willing to purchase.

The Nosara highlands get around 2.500 m of rain per year.  If that were distributed across every day evenly, that would be 6.9 mm of rain per day, 40% in excess of optimal dry season irrigation needs.  Across a single hectare, 6.9 mm is equal to 12.6 gpm, enough drinking water for 180 people.  The cruel irony, of course, is that the water is not distributed evenly, and that there are four months of the year that do not get any rain at all.  To complicate matters, the dry season months are the time period of peak tourism, when the country swells in population.  Not only do these months require more water for irrigation, therefore, but there is also a greater country-wide need for drinking water.  As a final twist, over 80% of the country’s power supply is hydroelectric, so the peak tourism season impacts the water supply further by requiring that greater amounts of water be dedicated to power supply.  With all the designs on scarce dry season water, the surface environment cannot afford to have small streams tapped for irrigation, as the precedent is snow-balling, and what suffers sooner or later is the environment and thirsty animals.

In Guanacaste, the dichotomy between supply and demand is particularly evident, and poor water management practices and unchecked development has spawned widespread water shortages and dramatically compromised small community water supplies.  As more homes are built and more springs and surface water supplies are tapped responsibly and otherwise for varying uses, the amount of remaining surface water is correspondingly reduced, thereby presenting an impact on environmental health of animals and plants.

Irrespective of seasonal imbalances, rainfall patterns reveal that excess water in the rainy season is more than adequate to make up for shortfalls in the dry season.  All we have to do is store water from the winter to apply as irrigation during the summer.  Unfortunately, the large amounts of irrigation water make the required storage structures impractically large.  The only practical alternative, artificial surface impoundment, is undesirable for a whole host of reasons:

1)        Impoundment of surface waters disturbs existing natural ecosystems and both removes the carbon sink of living plants and introduces a carbon source of methane and carbon dioxide from organic decomposition in pond sediments.

2)        The impoundment of water exposes it to intense evaporative pressure that can lead to large losses, as much as one third or more of total water impounded, especially for shallow impoundments.  This has a feedback effect of boosting the water’s mineral content and ironically decreasing its value for irrigation.

3)        Surface impoundment removes potentially useful land and employs it in a service that is less valuable than if it were not flooded.

Much of the rational initiative for diversion of surface water for water supply is that so near the coast, much of the surface water will flow to the sea and never be of environmental relevance anyway, and that therefore its abstraction for beneficial human use is reasonable.  However incomplete this rationalization is in the context of downstream water demands, the same logic is nevertheless arguably more true for ground water, yet at a much larger scale.  The amount of ground water that is discharged to the Pacific Ocean by undersea springs vastly exceeds what drains into the ocean from surface rivers.  Since there are no surface water sources draining into the peninsula, all ground water on the Nicoya Peninsula must necessarily originate as rain water.  While regional static and production water levels remain within seasonal standards, an evaluation that can be made from long-term changes in the dynamic ground water level at the Bosque Verde production well(s), it is reasonable to withdraw as much ground water as residents are willing to pay for. 

The ground water of Costa Rica may still be considered at this point to be an essentially limitless supply, endlessly recharging with vast amounts of water, with local exceptions resulting from over-pumping.  Where access to well water is not limited hydrogeologically nor production from nearby wells, ground water supply is limited by the capital and operating costs of sinking wells and pumping water.  Since ground water is an existing de facto rain water reservoir already in place, and since rainfall patterns on a yearly basis exceed what is required in the dry season for irrigation, the use of ground water for irrigation is therefore sustainable from an environmental perspective, provided that withdrawals follow some regional planning.  The only downside is that ground water is relatively expensive.

Figure 5 shows points of the property that are expected to be planted with ornamentals that will require irrigation in the summer time.  The field notes in Appendix 1 summarize the area estimation for each location.  Whereas drip irrigation and careful stewardship is likely to reduce irrigation water demands beneath the 5 mm daily theoretical application rate, the total desired irrigation area of about one hectare amounts to 9 gpm of continuous flow.  This is nearly two times the estimated flow rate of the creek at Location 12 (Figure 3), and about equal to the estimated flow rate at location 14 (Figure 3).  Even at an optimized irrigation criterion of only 2.5 mm per day, that would still require the entire stream flow rate at Location 12, and the wholesale abstraction via evapo-transpiration of the entire stream flow at this location cannot be dismissed as an environmentally sustainable practice.

Irrigation at Bosque Verde should therefore be considered from five different perspectives to arrive at a balance that is environmentally sustainable, economically practical, and which provides the quality

of life and ornamental beauty that residents are likely to expect and demand.  These factors are summarized below:

1)     Horticulture.  Facility irrigation should be predicated based on careful selection of species that require a minimum of water.

Figure 5.  Points of desired irrigation along project access roads.

2)     Style.  Irrigation methods must be designed that reduce evaporation and runoff losses to a bare minimum to provide maximum irrigation efficiency and still enable ease of use without requiring supplemental maintenance demands.

3)     Irrigation Area.  Areas to be irrigated should be maintained to the lowest area possible that will balance aesthetics and sustainability.

4)     Pay to Play.  It is not practical to enforce technical rules and guidelines upon homeowners as to what they can water and when and by what mechanism.  The only reasonable control on individual homeowner irrigation patterns is to charge them for the water, and to use the profits to maintain secondary wells to provide additional water flow to sustain overall water use patterns. 

5)     Sustainability.  Whereas surface water may suffice to provide facility irrigation of a few keys spots along the road, it makes most sense for the ownership to take the moral lead to irrigate using ground water rather than diverting scarce dry season resources in such an unsustainable manner.

HYDROELECTRIC POTENTIAL

There is a single perennial stream within the Bosque Verde property tract.  It offers the facility the alternative to consider hydroelectric power generation as a supplement to the grid-power supply distributed facility-wide.  There are several factors that provide the framework for its rational consideration, and these are enumerated below:

1)     Economics.  As the ensuing economic analysis will review, small-scale hydroelectric power generation is always economically viable at some finite pay-back period and at a level of return on investment that will vary in traditional economic analysis terms to the value of money at the time.  This is the case irrespective of the future inflation of energy.

2)     Seasonality.  Since stream flow varies dramatically between rainy and dry seasons, the hydroelectric power generation capacity varies commensurately as well.  A hydroelectric plant optimized for rainy season flows would be inoperable during the dry season, and a system optimized for dry season flows would have a capacity trivial in the context of the rainy season runoff.  The seasonality of the hydrology is complicated by residential seasonality as well.  Much greater occupancy and energy demands are expected during the dry season when hydroelectric potential is much lower than during the rainy season.

1)        Competing uses for water.  Whereas the existing water supply demand is satisfied by a single water well, increasing occupancy of Bosque Verde points to increasing water demands from its residents, both potable, pool, and irrigation water supply.  As discussed in an earlier section, the ownership has considered using existing dry season water supply to provide irrigation to some common areas along access roads.  For every gallon of water that is applied to irrigation demand it is one less gallon that can be used for hydroelectric power supply.  And unlike irrigation water, which is abstracted from the surface environment and transferred to the atmosphere and biosphere during evapo-transpiration, hydroelectric water is merely diverted, temporarily, to harvest its energy and then returned unchanged to the stream channel, so the water is removed from the environment from only a portion of its natural pathway.

2)        Regulatory environment.  Costa Rica is in an interesting transition in its regulatory framework.  The country is experiencing a dramatic tightening of its water law and permitting.  At the same time, it has a goal of being the first carbon-neutral nation by the year 2021.  In order to achieve this goal it will be necessary to be more permissive with carbon-free, eco-friendly power sources such as micro- and mini-hydroelectric and solar.  While non-trivial costs in permitting are presently required to obtain government permission to extract water from a stream for personal hydroelectric use, this process is likely to become less costly as the country normalizes its national energy policy.

3)        Marketing added value.  Today’s commercial environment places great value in environmentally friendly residential living.  For an upscale gated community like Bosque Verde, the ability to boast the integration of eco-friendly development practices adds value to the properties being marketed.  This adds a wrinkle to  the economic equation that is difficult to pin down but one that can be ignored at the peril of losing business to developers that focus their appeal to this increasing market segment.

Depending on the maximum amount of water that can be diverted from the target stream during different times of the year, either mini- or micro-hydroelectric power supply could be considered.

Locations 12 (Figure 3) had an estimated flow of 5 gallons per minute at the time of the field survey.  It is located 180 meters above the base of the property.  If we were to assume a sustained dry season flow rate of 5 gpm across 180 meters, this would correspond to a hydroelectric power potential of 266 watts, 6.4 kilowatt-hours per day.  During the rainy season, it is likely that this same location would sustain a hydroelectric diversion adequate to fill a three-inch pipeline.  At a corresponding flow rate of 90 gpm (and neglecting friction losses for the moment), the rainy season hydroelectric potential would be on the order of 4.8 kilowatts continuous, eighteen times more than the dry season estimate.

The ensuing discussion will suggest that this is clearly not the correct location for an intake, but the figures allow the illustration of an important point relating to seasonal differences and the two types of hydroelectric technology.  Mini-hydroelectric power produces AC power that must be used as it is produced, introduced into a power grid for wider distribution, or burned off as heat.  Micro-hydroelectric power generation provides for a battery bank that can store the power produced for use as desired.  Criteria for selection between the two for individual applications involve two discreet factors:  1)  size and constancy of flow rate (large flows are required for meaningful mini-hydroelectric power generation;  and 2)  the ability to continuously consume all the power generated, or tie into an electrical grid.

Costa Rica does not presently permit grid-tie power systems.  Therefore a mini-hydroelectric power generation capacity presupposes that all of its power is used internally.  Returning now to the example of the anticipated rainy season hydroelectric capacity of a three inch penstock originating at Site 12 and terminating at the base of the property, a continuous production of around 5 kilowatts is approximately enough to continuously operate a single 10 horsepower submersible pump, such as the one used to deliver water from the well to Tank One.  However, it is likely to be not quite enough to actually start the pump, since startup requires often a 50% additional surge.  For the sake of argument, let us assume that it would adequately operate the pump.  Water pumping is an intermittent duty; therefore when Tank 1 is filled and the pump is disconnected, a mini-hydroelectric output would need to immediately be used by other power consumptive demands, such as operation of the guard house, the manager’s home, and perhaps other facility applications.  But since the entire amount of power would be required each time the pump started, all systems would necessarily require a grid connection to make sure that there was never a failure of service.   In addition to the electronics required to ensure this capacity, there would be a time (at night) when the full amount of power generated is not used, so some of the energy generated would necessarily have to be wasted as heat, most reasonably diverted through a heating element in a tank of water to provide the guard house or the manager’s home with hot water.

While it is fully within reach to configure a power supply that is able to seamlessly switch between grid- and onsite power as needed, the electronics required to do this, in addition to the cost of the AC-direct turbine, would likely be as great as a micro-hydroelectric configuration in which all energy generated is stored in a battery bank and used as needed.

There is one final argument against mini-hydroelectric technology for this application.  The turbines are rated for a narrow flow range at a specified pressure.  Unlike micro-hydroelectric turbines, which tolerate wide variance in flow rates, a mini-hydroelectric turbine would be non-functional once dry-season flow rates reduced the available water to beneath its rated lower limits.  This means that a mini-hydroelectric system optimized for the rainy season would have to be turned off in the dry season and one optimized for the dry season would under-perform in the rainy season.

Micro-hydroelectric turbines do not present this restriction.  They are designed to accommodate relatively modest flows from 1.5” to 3” pipelines.  They may be deployed in parallel so that at low flow rates a single turbine is operational, whereas at high flow rates as many turbines can operate simultaneously as the water and capital budget allow.  The downside of micro-hydroelectric applications is that they require batteries, inverter(s), and charge controller(s) to use the energy produced, and these ancillary components are typically costly.

A rational hydroelectric design for the Bosque Verde facility requires two separate analyses:

1)     A review of power demands that could be satisfied by the new power supply.  Since this power cannot be transmitted through existing power lines, it is almost certain that the economics will favor using this power only for the Bosque Verde facility installations at the base of the property to include:  the pump, guard house, and manager’s home.

2)     A dry/wet season determination of optimal intake location to provide for full operation of a single turbine in the dry season and as many as three turbines in the rainy season, the total number deployed contingent upon the power demands identified in (1).

Power Demand:

Pump.  While there is no one-to-one conversion between horsepower and wattage, a 10 horsepower pump is expected to require 5000 watts for operation, 7.5 kw or so to start.  At some point, occupancy at Bosque Verde is expected to require full-time pumping, so we may reasonably assume that this pump will eventually operate full time.  So, the pumping demand is expected to eventually be 5 kilowatts just in itself.

Guard Shack.  Power consumption will depend on outfitting, with a large variance related to whether air conditioning is to be used.  Lighting, security cameras, fountain pump, and other power demands are likely to consume 10 kilowatt-hours per day alone, and if AC is used, then this may push demands much higher.  If we assume a peak of 24 kilowatt-hours for this facility, then this represents an additional continuous 1 kilowatt demand.

Manager’s home.  Anointment of the home will determine the power demand it presents.  If it were to be equipped with DC refrigeration, no air conditioner, and basic amenities, including lights, fans, television, basic kitchen appliances, washer, hybrid dryer, we can approximate that the home would be expected to have a power demand not likely to exceed 15 kilowatt-hours, but let us consider a power demand of 18 kilowatt-hours, as a safety margin and to round out the math with its 1.5 kilowatt charging demand equivalent.

Powering the three operations at full capacity is therefore expected to require a continuous power generation capacity of 7.5 kilowatts. 

It will require a dry season visit to determine the amount of summertime flow that can be diverted at what elevation, but if we assume an intake 80 meters beneath the low-flow but perennial Location 12, it would be necessary to divert 250 gpm across the 100 meters available head to produce 7.5 kilowatts continuously.  Figure 6 provides a conceptual system design.

Figure 6.  Hydroelectric conceptual plan drawing.

A flow rate of 250 gpm presupposes a pipe diameter of at least six inches (momentarily neglecting friction losses).  The most reasonable turbine for this application is likely to be an induction turbine rated at a capacity of 3.6 kilowatts.  Two of these units would provide for 7.2 kilowatts, reasonable for the ballpark estimations and assumptions used in the analysis.

Until facility demands push the pumping duty to 24 hours, however, the pump’s power demand is expected to be lower than that projected in the analysis.  It is also not known in the absence of a dry season visit the amount of water diversion that can be reasonably sustained from the stream.  Beyond what may be reasonable from an engineering and environmental perspective, regulatory limitations might vary according to a variety of subjective factors.  Water concessions are commonly limited on paper to 20% of the total flow rate.  To comply with this criterion, should it ever become concrete, would require that for a penstock diversion of 250 gpm, the stream would have to have a flow rate of 1250 gpm.  While this is likely in the rainy season, this is something that would have to be measured in the dry season to determine the extent of the water that could be diverted for hydroelectric power supply.

At pipeline sizes larger than 4”, plastics available in Costa Rica lose competitive advantage over imported plastics and a wide range of options in steel.  Therefore the estimation on installation costs for such a pipeline will require further engineering to determine the following and the corresponding costs:

1)     Final locations of intake and generation points and correspondingly the pipeline length, effective head, and the usable flow rate.

2)     Determination of the pipeline material to be used, which could be one of the following:  PVC, polyethylene pipe (imported), new or used steel pipe (imported).

3)     Intake structure and generator housing design.

4)     Pipeline anchors, collars, flanges, and valving.

5)     Installation work plan.

Other than the pipeline, the remainder of the required system can vary in voltage and capacity and should ultimately be predicated on the facility amenities of the guard house and the manager’s home.  For the moment let us assume that peak power consumption is expected to be in the neighborhood of 12 kilowatts.  Of those 12 kilowatts, five kilowatts are in 240 volt (the pump), the remainder in 110 volt appliances, unless the guard house is to be air conditioned.  Deployment of a stacked set of six 3.5 kilowatt Outback inverters will provide 10.5 kilowatts at 240 volt, 21 kilowatts at 120 volt, or a combination of the two simultaneously. 

Each 3.6 kilowatt induction turbine will require its own charge controller.  The design of the battery bank required for this system should be most reasonably predicated on a balance between the length of backup power capacity desired and capital constraints.  Since power generation is expected to be continuous (24-hour hydroelectric), and since the entire system is expected to be grid-tie and to have the electrical power grid as backup, the proposed system in effect requires no backup power capacity.  Therefore the battery bank may be sized small enough to be serviceable for operations with no intention of providing independent backup capacity beyond an hour or so of full system utilization. 

Forty-eight volt input is the most reasonable voltage for the high-performance power system, and 750 amp-hours of battery capacity are expected to be adequate.  In addition to the facility infrastructure, turbines, inverters, controllers, and batteries, the last component of the system is the two sets of cables that feed the power system from the turbines, and the three sets of cables that distribute power to the three points of use.  The capital costs of the cable and conduit will necessarily depend on the location of the generation house.  If the power inversion system is located in the same building as the hydroelectric turbines, then the two 3.6 kilowatt turbines projected may be replaced with three Harris hydroelectric turbines for a slightly greater output at a capital savings of $10,000.  However, if the distance from the generation house to the point of use is significant the extra costs of thicker cable or the introduction of transformer sets will cut into this savings.  Also, capital costs of building and security may favor the deployment of the power inversion system and battery set at the guard house or at the manager’s home.   Every variance in physical system configuration carries dramatic design and cost consequences.

Figure 7 is a conceptual diagram of a micro-hydroelectric power generation system for powering of the Bosque Verde facilities at the base of the property.  Table 2 is a preliminary estimate of the cost of installation of such a system.  If we assume today’s Costa Rica residential power cost of $0.30 per kilowatt hour, the 7.2 kilowatt capacity of the two–turbine system has a daily power generation capacity of 173 kilowatt-hours for a yearly power generation potential of 63 megawatt-hours, which translates to $18.922 in the value of the power generated.  Discounting permitting costs, this implies a payback period of six years and an annual return on investment thereafter of 16.8%.

This rough analysis does not factor into account the following, several of which are expected to be somewhat self-cancelling:

1)     The inflation in energy costs

2)     Operational and maintenance costs

3)     The value of carbon credits achieved by the zero-emissions capacity.

4)     The perceptual value-added to the facility as a whole and individual properties.

5)     Eventual grid-tie and sale of excess rainy season capacity.

Figure 7.  Conceptual hydroelectric power supply, management, and distribution.

Table 2.  Projected capital cost of hydroelectric and electronics system shown in Figures 6 and 7.

WASTE MANAGEMENT

Sewage

For the widely separated homes on the relatively large lots at Bosque Verde, traditional septic tank disposal of sewage is likely to be not only the most economical but also the most environmentally sustainable means of sewage management.  Barring problems with percolation, which are typically associated with areas of high ground water tables, swampy areas, beach areas, and sporadically in area with impermeable soils, the climate favors rapid aerobic metabolism for the relatively expedient biologic degradation of human sewage.  Septic systems should be designed in accordance with occupancy and percolation patterns determined onsite with a standard percolation test.  Best design practices include a multi-celled digestion tank with leach field sized in concert with soil percolation capacity.  In most cases, well designed and built septic systems will never require pumping, as anaerobic bacteria degrade solids in equilibrium with their accumulation.  Biologic degradation of leach water in the soil horizon usually results in limited migration in the soil horizon of impaction.  The great depth of chemical weathering typically offers very deep soil profiles that are effective in isolating septic tank contamination from deep aquifers. 

The alternative is the collection of sewage using gravity drainage and occasional lift stations and its conveyance to a central area for processing in a package plant using either activated sludge, trickling filter, rotating biological contactor, or some similar mechanism of aerated sewage treatment.  This presumes high capital costs, high operating costs, and a subsequent environmental degradation if the effluent is released to a receiving stream and operational challenges and maintenance costs if discharged into the subsurface.  Batch treatment of sewage is a reasonable alternative in space-limited concentrations of occupants, perhaps in Tamarindo condominiums, but for Bosque Verde, traditional septic systems are it is not even on the radar of being even worthy of consideration.

Grey Water

Unlike sewage, grey water has potential value for re-use as irrigation water and may warrant additional analysis to determine if it is worth segregating from home drainage systems for treatment and re-use.  A rudimentary comparison of capital costs will reveal that facility wide grey water management is certainly not economically competitive with adding wells for irrigation purposes, due to the piping, treatment, pumping, and distribution costs, all of which would have to be justified across a nominal 4-month window of irrigation utility per year.

For individual homeowners it is unlikely that the capital costs and the management complications will make grey water recycling competitive with the purchase of clean irrigation water, even at costly irrigation water rates, considering that irrigation is required only four months out of the year.  Except for residents specifically interested in reducing their resource footprint, grey water re-use is unlikely to be an attractive residential operation.  For homeowners acutely interested in personal environmental responsibility, however, grey water re-use is a perfectly viable means of stretching resources to their maximum utility and reducing personal water consumption footprints.  An individual grey water recycling system would necessarily contain the following components:

1)     Separate drains.  Toilets to drain to the septic tank; sinks, shower drains, laundry, all to pass through a sieve filter and fill a collection tank.

2)     Pressurization system.  A separate pressure tank and pump are required to provide the pressure required to apply this water as irrigation water.

3)     Filtration system.  An automatic backwashing sand filter will be required to remove particulates from the system to reduce clogging of nozzles.

4)     Micro-filtration for surfactants.  If conventional laundry technology is used, then detergents may be partially removed from the irrigation water using micro-filtration.  This is an aesthetic rather than technical or environmental alternative, as the limited amounts of detergents introduced by laundry will not represent an environmental adversity, and nutrients in the detergents are expected to be largely bio-assimilated by plants.  For those homeowners that seek additional operational control over contaminants, a laundry system using ozone and silver catalysis produces detergent free waste water and eliminates the need to use detergents or bleach.

5)     Shortfall.  Residential water consumption is unlikely to produce as much irrigation water as is required, since typical irrigation needs greatly exceed domestic water needs.  So, water-conservative irrigation practices will continue to be required, coupled with augmentation from  ground water.

6)     Seasonality.  Since irrigation is not necessary from May through December, the water re-use system would ideally have dual valving to enable disposal of grey water together with sewage during months in which irrigation is not required.

Solid Waste

Solid waste management is an operational rather than infrastructural challenge and is most effectively undertaken through waste minimization, product substitution, and re-use.  This is achieved at the household level, and may include such practices as the following:

1)     shopping with bags that can be re-used to avoid the accumulation of used plastic bags.

2)     Use of returnable bottles for soda and beer to eliminate the acquisition and elimination of plastic bottles.

3)     Purchase in bulk where possible to reduce the acquisition of packaging materials.

4)     Replacement of traditional washing machine with ozone based machine for elimination of surfactant waste stream.

5)     Segregation of trash for management of separate waste streams as follows:

a.      Paper and cardboard:  burn

b.      Plastic, aluminum, glass, and metal:  recycle

c.      Organic food scraps:  compost along with yard clippings for soil conditioner and fertilizer.

6)     Many people do not segregate trash for recycling.  Since the facility will logically have some form of trash collection or pickup, it may be worthwhile to have a capacity for segregating trash manually offsite to provide home owners an avenue for the assuagement of guilt for not being more personally environmentally pro-active.

Carbon Emissions

in general, the only offsets required for each household are those associated with air travel in arriving, vehicular locomotion while in country, and the propane usage associated with cooking and hot water heating.  For those that are truly interested in carbon-neutral living, propane can be wholly substituted by electrical cookware, including the highly efficient induction stove and cookware technology, and individual homes can be fully powered by solar, with grid-tie to provide for supplemental power as needed and for an eventual market, once Costa Rica begins to trade with local, small-scale power producers. 

Hot water heating can be achieved with passive solar hot water heaters, augmented with heating elements as desired or required by picky homeowners that want their water hot all the time, no matter how rainy the weather.  Natureair is already a carbon neutral airline, so domestic air travel can be restricted to this airline to circumvent the safety and administrative hazards of Sansa and assuage contemporary consumer guilt at the same time.  That leaves only international air travel and gasoline to offset with the green zones.  A fair projection per passenger is 0.1 kg carbon dioxide per km flown, a 1000 kg carbon footprint for annual air travel of 10,000 kilometers.  Assuming 4000 kilograms per hectare uptake from undisturbed tropical forest, a value in line with academic findings, each 10,000 person-miles of air travel is offset by 0.25 hectares, suggesting that the 70 hectare reserve can offset 2.8 million person-air kilometers.  With the carbon sink of the lawns, secondary, and shrubbery, the overall property sink will easily offset the air travel carbon footprint of nearly all its occupants and arguably a portion of its in-country car usage as well.

INTERNET AND TELECOMMUNICATIONS

Internet, telecommunications, and television are no longer luxuries in even remote residential installations but essential features.  Satellite television is available to individual clients for a nominal $100 installation fee and a rate of as little as $30.  Satellite Internet is also available everywhere, no matter how remote, though the equipment and installation is costly, as is the monthly service plan.

However, wireless Internet is now available in the Nosara region for relatively modest equipment / installation (~$750 total) and monthly costs (~$100 per month for 128 kbps down, 64 kbps up).  The low price is due to the fact that the company offering the service, Inasol Inalambrico, S.A., already  has a radio transmitter installed in the town of Nosara.  Since Bosque Verde is within 5 kilometers of this radio transmission hub, the capital costs of an individual installation are modest.  For locations farther away, both equipment and monthly plans are considerably more expensive, more in the range of the cost of satellite Internet.  All of these systems have the capacity to support VOIP and all other Internet transactions and technologies.

Costa Rican land line telephone service varies as a function of infrastructure and is likely to become increasingly accessible in the newly deregulated telecommunications environment.  Until switching boxes and lines are extended throughout the property at the behest of the ownership and in accordance with the infrastructure in place regionally, this will be beyond the ability of individual homeowners or the facility ownership to dramatically effect.  Similarly cell service depends upon cell towers for distribution of service.  Individual homeowners may erect cell antennas to boost reception, but the success of this alternative must be tested on a trial and error basis.  With enough interested subscribers it may be possible to pressure service providers to erect a tower to provide local service.  This may alternately be capitalized internally if the interest is sufficiently great.

Conclusions and Recommendations

1)       Potable Water Supply.  The existing water system is entirely adequate according to standard design practices for potable water supply for the entire project.  The well yield was determined in June (rainy season) and therefore it is unknown if the well yield is maintained in March and April, and this may be worthwhile confirming for planning purposes.  It is recommended that the ownership procure a backup submersible pump to have on hand in case of failure of one of the existing pumps to ensure continued water supply even in the event of equipment failure.  By the same logic, it is recommended that one or more generators be maintained on site in

the event that a protracted power outage makes it necessary to operate the pumps using alternate power supply. 

2)       Water Concession.  It is recommended that the ownership immediately proceed with the application for a water concession for its existing well.

3)       Water Use Fees.  The ownership is strongly encouraged to create a mechanism that provides for sale of water to clients.  This should be predicated on a base amount for a modest price, intended for domestic water supply with greater rates charged in excess of 12.000 gallons of usage per month for instance.  This is recommended in order to discourage rampant irrigation and to provide an operational pool for routine water system maintenance, chlorine tablet costs, energy costs for pumping water, and any capital costs that may be required for new wells to satisfy facility irrigation demands.

4)       Irrigation.  The existing water system is not adequate for irrigation by all the Bosque Verde owners present and future.  The scant surface water resources are also not sufficiently abundant to support even limited irrigation without some degree of environmental impact.  Irrigation capacity is readily achieved, however, with additional water supply derived from the drilling of additional well(s).  While the existing system is likely to support irrigation while only a few houses are in operation or under construction, it is recommended that a policy of charging for this use be instituted immediately to forestall owners’ future dissatisfaction when this liberty is later restricted, taken away, or made more costly.

5)       Chlorination.  If irrigation water supply is to be supplemented for distribution through the existing water supply, it may be reasonable to re-think the chlorination program.  Operational experience and costs will be the ultimate arbiter, but there is questionable value in introducing calcium hypochlorite to water that is not strictly intended for domestic water consumption.  While chlorination is an industry standard for small municipal water systems in the United States, it is not unreasonable to expect individual homes to provide their own disinfection.  This is particularly the case if individual homes employ supplemental onsite storage, in which case they will require an independent disinfection system anyway.

6)       Hydroelectric.  It is entirely reasonable to divert surface water resources to support a micro-hydroelectric power generation capacity to power facilities located at the base of the property, including the well pump, the guard house, and the manager’s home.  Final decisions on pipeline size and hydroelectric capacity should be predicated upon March flow rates.  It is strongly encouraged that the environmental permitting consultant tasked to pursue the water well concession also take exploratory footsteps to determining the most appropriate regulatory approach for permitting the surface water for hydroelectric diversion.

7)       Waste Management.  Conventional septic system management of waste is the most rational and environmentally sustainable manner of managing sewage.  Grey water re-use is an option for forward leaning residents on a home by home basis, but the fact that irrigation is needed only 25% of the year makes it unlikely that a robust grey water recycling system can compete economically with purchasing ground water except on a payback timeframe of many years.  The existence of the forestry preserve and its intrinsic sink for carbon dioxide offers the interesting marketing tool of being able to offset the carbon footprint of 2.8 million person miles, so each of the 75 lots compensates for the carbon emissions of 37.333 kilometers of air travel per year.

8)       Internet.  There is a very modest price wireless Internet service newly inaugurated in Nosara.  Due to the proximity of the project to Nosara, clients may procure the service for very modest installation fees and DSL-speed service for monthly rates as little as twice as much as what comparable bandwidth fees might be in the United States.

APPENDIX 1:  Waypoints and field notes

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