Investigations in groundwater flow toward a spring in the Saphire area, Soufriere, Saint Lucia, West Indies

Abstract

The Cocoa Grove Group is planning a housing development on approximately 5.5 acres in the area of Saphire, Diamond, Saint Lucia. Directly downhill of the property is a Water and Sewage Company (WASCO) spring that supplies drinking water to the town of Soufriere. This potable water is of high purity. Concern was expressed by WASCO as to the advisability of implementing development directly above the emanation of the spring. The obvious concerns were the possible change in flow volumes and chemical and biological contamination if a housing development was completed. F. D. Morgan and the Saint Lucia Water Resources personnel representing the Cocoa Grove Group discussed whether geophysical methods could be used to map the direction of groundwater flow into the spring. The group agreed that geophysical methods could be used in an attempt to delineate the underground flow paths into the spring. It was made clear that investigations could produce results that could be either favorable or unfavorable to the proposed development. Consequently, geophysical surveys were planned and executed in the area of concern to measure resistivity and self potentials. The geophysics did not indicate evidence of substantial fluid flow into the spring. However, we were able to locate the main water supply from the top of Terre Blanche down toward the spring. The flow comes downhill via a significant geologic fracture that is hidden from sight in the dense tree cover. Recommendations were made that it is relatively safe to develop the site as intended with respect to possible water contamination. In conclusion, we also recommended that WASCO take water from another point of a topographic step on Terre Blanche. Doing so would reduce the contamination risk essentially to zero from the planned housing development area.