Exploration and Development of Significant New Groundwater Supply for Trinidad
Client: Water and Sewerage Authority (WASA) of Trinidad and Tobago
The field exploration and drilling program schedules were very aggressive, as was the objective of developing 15 imgd of new groundwater supply. The previous, major island-wide assessment of the groundwater supply potential, by a Dutch company in 1999, concluded that the potential was extremely small and that future water needs would need to be met by the construction of multiple new large surface impoundments. However, our joint venture program’s reassessment indicated very large supply potential. The technical program we applied was “cutting edge” and required the integration of multiple current analytical techniques and technologies.Significant challenges to the project included:
- Updating the geologic map of Trinidad based on current stratigraphic and structural mapping.
- Integrating data from the scales of satellite images, to aerial photographs, to outcrops, to well logs.
- Very detailed hydrologic budgets had to be developed to evaluate the groundwater recharge over the entire island.
- Geologic and geophysical mapping required the development of a new classification scheme for the hydrogeologic characteristics and supply potential for the bedrock and some young, poorly consolidated sedimentary deposits.
- Very difficult drilling conditions in the western part of the Northern Basin.
- Right-hand steering in automobiles and poisonous snakes sometimes made the field work tricky!
The Interdisciplinary Approach
We developed maps based on the so-called “megawatershed” paradigm. This involved the delineation of megawatersheds that are not always coincident with the topographic divides that are used to define conventional watersheds. Supply target priorities in the Northern Range frequently focused on metamorphic limestone (carbonate) bedrock that included significant groundwater storage and transmission in dissolved conduits, in addition to fractures. Geological and geophysical mapping focused on priority target areas, followed by test well drilling, well and aquifer testing, and construction of production wells and associated facilities. Part II of the project was implemented on the basis of a Build-Own-Transfer agreement with Water and Sewerage Authority (WASA).
The Sustainable Result
The new hydrogeologic map of Trinidad was the result of perhaps the most comprehensive hydrogeologic reassessment ever conducted in the Caribbean. Technology transfer to WASA included an interactive GIS database with computer hardware and software. The program delivered 15 imgd. Four types of groundwater environments were identified that, collectively, have the potential to provide a sustainable yield of over 330 imgd, most of which is either naturally potable or treatable using readily available technologies at minimal costs.
- International collaborative project team with participants from several U.S. companies and a Trinidad drilling company.
- Project scientists included geologists, hydrogeologists, geophysicists, meteorologists, GIS specialists, drillers, and exploration managers.
- Development of many new geologic maps and digital databases.
- Part I of the associated work scope comprised an island-wide reassessment of the hydrogeology that identified groundwater development potential, and classified the island’s best, economically recoverable groundwater resources according to sustainable withdrawal quantities.
- Part II of this project involved the groundwater development phase, which started in early 2001 with the goal of producing a maximum of 15 Imperial million gallons per day (imgd, equal to 68 million liters/day) from WASA-designated priority target areas. This objective was achieved with new supply wells largely constructed in the Northern Range and the Northern (or Caroni) Basin.
- In total, 280 million Imperial gallons per day imgd of newly discovered fresh groundwater resources were discovered.
- Payment from WASA was based on a “success only” contract.