Revolutionary groundwater method reveals megawatersheds in Trinidad & Tobago
Successful groundwater development projects in Trinidad & Tobago open up the possibility that other Caribbean countries may discover vast quantities of groundwater resources by using megawatershed technology.
Almost all member states of the Caribbean Community & Common Market (CARICOM) share a common chronic water shortage problem that impedes food production and stifles economic growth and private investment. In desperation, many countries have undertaken expensive, frequently unaffordable and environmentally short-sighted water supply schemes that are highly vulnerable to vagaries of weather and energy prices, and which ultimately exacerbate local economic instability.
Former Trinidad & Tobago President and Mrs. N.R. Robinson toast the commissioning of an historical deep bedrock well in Charlotteville, Tobago with ETI CEO Robert Bisson in the town centre. This high-quality water well solved a 40-year long critical water shortage for the remote coastal town.
The current hurricane season underscored this vulnerability of surface water supply sources when centralised electrical power generators shut down and highly turbid, contaminated surface runoff and seawater sources made treatment difficult or impossible. Following catastrophic events, such as hurricanes, people must filter and boil surface runoff, which is a daunting task for newly homeless people without stoves, electricity or gas. Or massive quantities of drinking water must be imported and distributed via washed-out roads at a high cost, leaving tons of empty plastic containers that add to the waste cleanup challenge.
In contrast, the use of groundwater resources can provide clean, safe water immediately after a hurricane. Fresh groundwater can be pumped for a limited time from shallow limestone and alluvial wells equipped with diesel generators, but only until they exhaust their limited storage capacities and contaminated water enters the formations from local surface runoff, from which they receive recharge.
In 1999, the energy-rich, but drinking-water scarce twin-island republic of Trinidad & Tobago reached a point where they had to decide on a strategy to develop critically needed, additional potable water sources. A major groundwater initiative was considered futile after a 1999 hydrogeological consultant's report concluded that all available groundwater in Tobago was fully utilised, and that significant untapped sources near Trinidad's demand areas were limited to few low-yield alluvial aquifers. Given the failure of decades of previous attempts to discover large water sources and the 1999 report findings, the state-run Water and Sewerage Authority of Trinidad and Tobago (WASA) focused its efforts to develop water sources from surface water schemes, including dams, diversions and seawater desalination.
Historically, the country's high dependence on surface water created severe seasonal restrictions on domestic supplies. River flows dropped low during dry seasons, while rainy seasons increased surface water turbidity to untreatable levels. A massive desalination plant under construction in Trinidad was under construction to provide very expensive, but reliable fresh water only to high-end commercial users near the plant. A proposed new dam and pipeline in Tobago's Richmond River watershed was planned to yield five million imperial gallons per day (imgd), but this long-term, US$ 60-million project would damage Tobago's ancient rainforest and associated eco-tourism industry. In an average rainfall year, Tobago's domestic customers received water supplies for only a few hours a day and for a few days a week. Often during the height of tourist season, hotels with internal storage systems designed to supply their patrons with a 24-hour supply, were forced to limit water access to four hours per day.
In 1999, the water crisis reached a critical point that, if not abated, would have caused unprecedented hardship on the population, discouraged foreign investment and derailed economic growth. The crisis delayed opening of a new five-star, US$ 100-million Hilton luxury hotel for over a year. The developer considered installing its own desalination plant despite the objections of the local Tobago House of Assembly (THA) and environmental scientists concerned about the impact of waste brines on sensitive local coral reefs.
By mid-1999, local proponents of a novel hydrogeological paradigm called "megawatersheds" recommended implementing a pilot project to locate and develop new sources of groundwater from potential megawatersheds on the island of Tobago using state-of-the-art groundwater exploration and drilling technologies. This new approach had been proven effective in many projects carried out in Africa and the USA.
The term "megawatershed" describes groundwater systems that are integrated in terms of recharge, discharge, storage, transmissivity and containment. As mappable groundwater resources spatially delineated by subsurface bedrock fracture structures and stratigraphy, megawatersheds may not coincide with surface topographic divides, and they may receive recharge from parts of several surface watersheds. Similarly, as a structurally contained water resource, wells drilled into multiple aquifers in a single megawatershed may produce water from potentially dissimilar lithologies with common hydraulics related to brittle fracturing and gravity-fed contributions from adjacent and overlying unconsolidated sediments.
Megawatersheds often occupy diverse host environments exhibiting both primary (continuous) and secondary (fracture) porosities with flow systems delineated by fracture systems, faulted or weathered lithologic contacts, igneous intrusions (e.g. dykes), and overlying adjoining weathered rock and porous unconsolidated sediments. The history and nature of regional tectonic stress fields and principal bounding faults, interacting with lithology and climate, play a major role in determining the geometry and extend of megawatershed boundaries. The megawatershed paradigm operates effectively and has scientific validity and economic and management utility at a scale of tens to thousands of square kilometres.
In Trinidad and Tobago, WASA considered the development of megawatersheds to be "high risk," so they decided that contractors should operate under a "success-based" agreement. The parties explored two contract models: build, own, operate and transfer (BOOT): and build, own and transfer (BOT). WASA opted for a BOT contract because the nation's oil and gas economy permitted the authority to pay the contractor in cash for water well production facilities as they were completed. Other CARICOM and most small island developing states (SIDS) might have opted for the BOOT contract concept, especially if the contractor included both new water sourcing and financing and construction of the infrastructure required to deliver new water to local mains.
In Tobago, a bi-national joint venture, comprised of Earthwater Technology International, Inc. (ETI) and Lennox Petroleum Services Ltd. (Lennox) developed nearly five imgd of new potable groundwater sources within one year. In addition, the ETI-Lennox team located and drilled these high-yield (averaging over 500,000 gpd each) deep bedrock wells nearby WASA mains, and discovered an additional 36 imgd of untapped, renewable groundwater sources in Tobago's megawatersheds for future development. ETI's team pioneered the exploration technology that led to discovery of the megawatershed phenomenon in the 1970s and 1980s, while the Caribbean water well drilling company, Lennox Petroleum used innovative drilling technology to penetrate Tobago's hard, fractured volcanic bedrock. Figure 1 shows the water supply-demand situation on the island in 2000, indicating a transition from surface to deep groundwater sources, which saved the island from suffering water crises during the record-setting droughts of 2000 and 2002.
Figure 1 shows the water supply-demand situation on the island in 2000.
WASA applied the same model to Trinidad with even more notable results. The two-year Trinidad megawatersheds project, also carried out by the ETI-Lennox team, produced more than 15 imgd of new fresh water sources from deep bedrock and alluvial wells drilled into previously undetected highly productive aquifers within megawatersheds. The ETI-Lennox wells yielded an average 1 imgd of potable water. The project also identified more than 300 imgd of additional groundwater supply, mostly in Trinidad's Northern Range bedrock.
Overall, WASA developed more than 20 imgd of new, year-round reliable water supply for the two islands for less than US$ 40 million, inclusive of all new water delivery infrastructure, with the contractor carrying 90% of the "high-risk" water source discovery and development. Ongoing operating costs for water delivered to WASA mains from these megawatersheds average less than US$ 0.40 per 1,000 imperial gallons.
The megawatersheds paradigm and associated exploration and drilling technologies demonstrated that both islands have potential for additional groundwater of seven to ten times the original estimates from prior studies and pre-1999 production. The project delivered more than 100% of the contractually required amount of production capacities, and resulted in the discovery of substantial amounts of additional groundwater available on both islands. This success proves that this method provides the most cost-effective and environmentally sound option to improve the quantity and reliability of water supply while encouraging private investment and economic growth, especially in Tobago's tourist-dependent economy.
Since 1999, production wells constructed in Tobago's megawatersheds have continued producing water with no significant reduction in quality or quantity even through two of the worst droughts in Tobago's recorded history. They operate at far lower operating costs than surface water treatment and have not affected local farmers or ecologically sensitive environments.
Similarly, Trinidad's new wells placed in service under the BOT contract have produced water through all seasons of much higher quality and lower cost than surface or desalinated water. These projects provide compelling evidence that new groundwater sources from aquifers hydraulically associated with megawatersheds are superior to surface sources for potable water, in terms of reliability and development costs for many CARICOM countries and other small island developing states (SIDS) possessing appropriate hydrogeological environments and climates.
Mr. Errol Grimes, WASA's current chief executive officer and past president of the Caribbean Water & Wastewater Association (CWWA), described the effect of the ETI-Lennox megawatershed technology on groundwater development and testing in Trinidad and Tobago during a 2000 "CaribScope" television documentary film interview: "This type of groundwater technology is very cost effective, and, in terms of implementation, is very timely; it takes a very short time compared to development of surface water sources and gets relief to customers very quickly. Groundwater traditionally requires less treatment than surface water sources. I think this technology could be used all over the Caribbean."
Authors' Note
Robert A. Bisson is the chief executive officer of Earthwater Technology International, Inc., based in the Washington, DC area. Dr. Utam Maharaj, Ph.D., was the director of the WASA Water Supply Agency during the Tobago megawatersheds development program.
In July 2004, John Wiley & Sons, Inc. published a book co-authored by Robert A. Bisson and former Groundwater editor Dr. Jay H. Lehr, "Modern Groundwater Exploration: Discovering New Water Resources in Consolidated Rocks Using Innovative Hydrogeologic Concepts, Exploration, Drilling, Aquifer Testing and Management Methods." (www.wiley.com)
